A 7500-year paleotsunami record from the coastal sediment of Sri Lanka and Indian Ocean trans-basin tsunami history.

A 7500-year paleotsunami record from the coastal sediment of Sri Lanka and Indian Ocean trans-basin tsunami history. | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article A 7500-year paleotsunami record from the coastal sediment of Sri Lanka and Indian Ocean trans-basin tsunami history. Pradeep Nalaka Ranasinghe, Joseph Ortiz, Andrew Moore, Tharanath Ambillapitiya, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8757939/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Directly facing the Sumatra and Andaman segments of the Sunda subduction zone, Sri Lanka provides an ideal location to study the large trans-basin tsunamis that occur there. Its location close to the southern boundary of the northern cyclone belt, and the directional advantage of the southern and eastern coastlines makes Sri Lanka one of the best places in the eastern Bay of Bengal region for distinguishing tsunami and cyclone deposits. Although several paleotsunami records have been constructed for the region since the 2004 Indian Ocean Tsunami, most extend only to the last 3000 years, and discrepancies exist among records. Therefore, this study was carried out to construct a longer Holocene tsunami record for the western Bay of Bengal region and to develop a more robust record of large trans-basin tsunamis that occurred at the Sumatra and Andaman trenches, to understand the recurrence interval between events. Thirteen back-barrier environments spanning the southern and eastern coastline of Sri Lanka were selected, and 35 sediment cores (1–5 m long – Total over 100 m length) were extracted along landward transects. Also, one pit was excavated to study abrupt sand layers. After initial logging, 19 sediment cores were selected for further analysis due to visually observed abrupt event layers. Particle size was used as the primary proxy to confirm the observed abrupt sand layers. Sediment texture, sedimentary structures, chemical composition, magnetic susceptibility, and micofossils were used to distinguish marine overwash layers having potential tsunami origin. Stratigraphy and age were used to establish intra- and inter-site, as well as regional, correlations among layers to distinguish regional tsunamis. In addition to five 2004 tsunami sand layers, among the 29 identified ancient abrupt layers with marine origin, 20 were distinguished as high potential paleotsunami (T HP ), and 06 were as medium potential (T MP) tsunami layers deposited during nine events that occurred around 1100, 3000, 4000, 4600, 5700, and 7300 yrs BP (T HP ), and 2000, 5100, 6300 yrs BP (T MP ) based on local and regional-correlation analyses. Abrupt layers deposited during another two low-potential tsunami (T LP ) events and other marine overwash events (OM) were also recognized by this study. In addition, published regional records show widely distributed, chronologically correlating evidence for a paleotsunami that occurred around 600 years BP, which was not observed at our study sites in Sri Lanka. Including the 2004 tsunami, when all 11 trans-basin events (excluding T LP ) reported over the last 7500 yrs are considered, tsunami frequency in the Indian Ocean has increased during the last 1000 yrs and during the interval between 4000–5000 yrs BP. Increased seismicity between 500–1500 yrs BP in the Sunda trench correlates with increased tsunami frequency during the last 1000 yrs. Earth and environmental sciences/Climate sciences Earth and environmental sciences/Environmental sciences Earth and environmental sciences/Natural hazards Earth and environmental sciences/Ocean sciences Earth and environmental sciences/Solid earth sciences Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction The Indian Ocean is now recognized as a tsunami hotspot following the devastating 2004 tsunami. Earthquakes along the Sunda-Java trench can generate tsunamis that spread across the Indian Ocean in different directions, depending on the segment where the epicenter is located. Numerous paleotsunami studies were conducted after the 2004 event at various coastal plains in countries such as Indonesia 1,2 , Thailand 3,4,5 , India 6.7 , Sri Lanka 8 , Maldives 9 , East Africa 10 , and the Andaman islands 11 , which are situated east and west of the Bay of Bengal, have produced many records. However, a clear consensus on the linkage between specific paleotsunami events documented by these studies and paleoseismic events recognized by prior investigations 12–16 has yet to emerge. Depending on the direction of faulting at the Sunda subduction zone, tsunami intensity can vary along different coastlines, resulting in differences in paleotsunami records. Local geographic differences at the site of impact can also influence the preservation potential for paleotsunami deposits. Despite the differences due to fault direction, there are discrepancies in the timing and number of records from coastal plains facing the same trench segments 2,8,17–19 . Such incompatibilities and gaps in records prompted us to conduct this study and to produce this comprehensive paleotsunami record from coastal sedimentary archives in Sri Lanka, correlating with regional records. 1.1 Structural setting The Sunda subduction zone (SZ), which is divided into the Andaman, Sumatra, and Java subduction zones, is part of the large convergent boundary extending from the Himalayan front to Sumba Island (Fig. 1 ). This subduction zone accommodates the northward motion of the Indian and Australian plates (formerly the Indo-Australian Plate) and produces the ~ 3,200 km-long Sunda-Java trench. West of Sumba, the dense oceanic lithosphere of the Indo-Australian plate subducts beneath the continental Sunda shelf of the Eurasian plate. To the east, the lighter continental Australian lithosphere thrusts beneath the oceanic lithosphere 20 . Subduction is nearly parallel at the Andaman, oblique along Sumatra, and almost normal southwest of Java 21 . The oblique subduction beneath Sumatra has partitioned the convergent motion. The strike-slip component occurs along the major strike-slip Sumatra and Mentawai Faults 22 . The strike-slip rate of the Sumatra fault varies from ∼6mmyr − 1 near the Sunda Strait 23, 24 to ∼25 mm yr − 1 near the equator 25 . Convergence at the Sumatra SZ is likely 40 to 50 mm yr − 1 . To the north, the convergence rate is much slower. It is < 20 mm yr -1 because of the nearly parallel relative motion at the Andaman-Nicobar section of the subduction zone (Andaman subduction zone) 20 . 1.2 Tsunami potential in Sri Lanka. Sri Lanka is situated in the middle of the Indian Plate and is surrounded by a passive continental margin along its coasts. The Sunda subduction zone, situated about 1200 km to the east, is the most likely source of seismic tsunamis. The 2004 Indian Ocean Tsunami, generated by a magnitude 9.1 earthquake in the northern section of the Sunda subduction zone, is considered a modern analog for paleotsunami events in the region 26 . Three separate waves of this tsunami struck the southern and eastern coasts of Sri Lanka, and the tsunami runup ranged from 5 to 12 m 27 . Inundation distances varied from a few hundred meters to 1–2 km. The 2004 Indian Ocean tsunami event significantly altered regional coastal morphology through extensive erosion. Marine sediment and sand brought by barrier overwash were deposited in back-barrier environments 28 . Historical records also offer tantalizing clues into past coastal flooding events in Sri Lanka and India. According to Arisen Ahubudu, a leading linguist of the Sinhala language, the famous Indian epic, the “Ramayanaya” mentions the submersion of part of Sri Lanka by two separate ocean-flooding events. Although their exact dates are unknown, they must have occurred prior to the 5th century BCE (~ 2449 yrs BP) when the Ramayanaya was composed. South Indian scriptures and literature likewise suggest two possible tsunami events that damaged the eastern coast of South India around 500 AD and 900 AD (or 1450 and 1050 yrs BP 29 . The “Mahawamsa,” the main written historical text of Sri Lanka (written in the 6th century AD or 1450 to 1350 yrs BP), discusses a coastal flooding event on the western coast of Sri Lanka around the 2nd century BC (2149 − 2049 yrs BP). In more recent history, the Krakatau eruption in Indonesia on 27th August 1883 (67 yrs BP) created 1–3 m waves in Sri Lanka 30 . In short, Sri Lanka’s setting is nearly optimally situated to record the history of tsunamis generated by exceptionally large earthquakes along the northern portion of the Indonesian subduction zone. Recently developed records have identified several paleo-tsunami events in Sri Lanka. Jackson et al 8 . identified seven tsunami events, including one between 2417 ± 152 yrs BP and 2925 ± 98 yrs BP, and another six between 4064 ± 128 yrs BP and 6665 ± 110 yrs BP. Two paleo tsunami events around 1682 ± 126 and 4829 ± 362 yrs BP were reported by Abeyratne 31 . Dahanayaka and Kulasena 32 also identified two past tsunami events, but without dates. 1.3 Suitability of Sri Lanka for paleo tsunami studies Identification of sediment layers deposited by tsunamis is not straightforward because other abrupt events can deposit similar sand layers 33 . Both storm surges and coastal flooding events by rivers can deposit abrupt event layers, although the latter has no marine origin. Storm surge deposits are often difficult to distinguish from tsunami layers 34 . Because Sri Lanka is situated close to the southern boundary of the northern cyclone belt, cyclones are rare in the northern portion of the Bay of Bengal 35 . However, landfalls can be expected more frequently than tsunamis, as they occur more often than large seismic events. As a country situated in the Indian monsoon region, the coastline of Sri Lanka can experience coastal flooding from the Indian summer and winter monsoonal precipitation, particularly near river channels. Tropical cyclones and depressions can also produce significant precipitation over a short period, leading to coastal flooding. However, Sri Lanka provides an exceptional opportunity to study tsunamis generated at the Sumatra and Andaman segments of the Sunda subduction zone for several reasons. The greatest advantage for paleo-tsunami investigations in Sri Lanka is that it has coasts facing all compass directions, which exhibit different susceptibilities to tsunamis and storms (Fig. 2 ). Most storms generated in the Bay of Bengal affect Sri Lanka on its eastern coast 35 . Out of 15 cyclones that made landfall on the Sri Lankan coastline during the period from 1900 to 2006, only one approached from the west. ( http://www.meteo.gov.lk/ ). In contrast, large tsunamis generated at the Sunda subduction zone can directly hit both Sri Lanka’s eastern and southern coastlines, creating significantly higher waves there than the background wave climatology (Fig. 2 ). The western coast experiences minimal impact from tsunamis generated by the Sunda subduction zone. In fact, Sri Lanka is primarily vulnerable only to tsunamis generated by large earthquakes in the western sections of the Sunda subduction zone (Fig. 1 ), rather than in its southwestern and southern sections, because tsunamis generated in those sections tend to propagate southwest and have minimal impact due west 36 . In summary, the eastern coastline of Sri Lanka is susceptible to both storms and tsunamis, while the southern coast is susceptible only to tsunamis. Back-barrier environments located in the vicinity of large rivers can contain terrestrial flood deposits on both eastern and southern coasts. 2. Methods 2.1 Field sampling. Back-barrier marshes, lagoons, and swales in beach ridge plains are attractive sites to seek paleo-tsunami and storm surge deposits because such events will form distinctive barrier over-wash sand sheets in these otherwise low-energy, protected clay-rich environments 37, 38 . They also have a low potential for subsequent erosion or reworking, increasing preservation potential 39, 40 . Fourteen back-barrier environments were sampled for this study, representing about 600 km of coastline along the southwestern to northeastern coast of Sri Lanka (Fig. 2 ). Ratgama (RG) and Koggala (KG) are inland lagoons formed during the Holocene highstand and are now separated from the sea by more than 0.5 km of land. Devundara (DV), Tangalle (TG), Kumana (KU), Okanda (OK), Komari (KM), Tirukkovil (TK), and Akkaraipattu (AK) are coastal lagoons separated from the sea by barrier bars. Kirinda (KD) swamp is in the vicinity of a paleo estuary, while Panama (PN) wetland is close to a modern estuary. Sittandi (SD) and Vakarai (VK) are from swales in beach ridge plains, while the Chundikulam (CK) location is in a coastal sinkhole. These sites can potentially capture the above-discussed coastal flooding events (Fig. 2 , Table 1 ). Table 1 – Sampling locations of cores having distinguishable abrupt sand layers. Recovered core length and actual length after removing collapsed sections (if available) and the typoe of potential event layers which could be preserved at each site are given. Location Core no Lat Long Height from msl (cm) Recovered length (cm) Core length (cm) Potential coastal hazards Ratgama RG1 6.1008 80.1348 -3.2 260 258 Tsunami RG2 6.1131 80.1353 -2.4 128 128 Koggala KG1 5.9933 80.3335 -3.3 225 225 Tsunami KG2 6.0028 80.3302 -2.5 186 186 Devundara DV1 5.9332 80.5831 -1.2 155 155 Tsunami Monsoonal waves DV2 5.9349 80.5848 -0.8 144 144 DV3 5.9359 80.5863 -0.6 135 135 Tangalle TG1 6.0380 80.8070 -1.6 150 144 Tsunami Monsoonal waves TG2 (Pit) 6.0364 80.8052 -0.7 N/A N/A Kirinda KD2 6.2058 81.3218 + 1.1 500 348 Tsunami Flood Cyclone (rare) KD3 6.2082 81.3213 + 1.6 430 296 KD4 6.2111 81.3205 + 2.2 500 340 Kumana KU2 6.5442 81.7230 + 0.1 125 125 Tsunami Cyclone KU5 6.5443 81.7160 -0.2 75 65 Panama PN2 6.7703 81.8057 -0.1 500 304 Tsunami Flood Cyclone PN3 6.7675 81.8003 + 0.1 500 274 Okanda OK3 6.6810 81.7629 + 2.1 500 283 Tsunami Cyclone Komari KM1 6.9590 81.8583 -0.4 400 192 Tsunami Cyclone Vakarai V12 8.19503 81.40033 + 0.1 500 314 Tsunami Cyclone V13 8.13044 81.41866 + 0.6 300 203 V31 8.12558 81.40500 + 0.2 200 168 Sampling was conducted using a vibracorer, which connects 7.5 cm diameter core tubes, and a customized slide-hammer soil coring device, which collects sediment cores in 2.5 cm diameter, 1 m long plastic tubes. By re-entering the coring hole with 1 m long extension rods, a maximum coring depth of up to 5 m was achieved using the slide hammer device. The maximum coring depth was determined either by the depth to bedrock, the presence of impenetrable subsurface layers, or the collapse of the hole. At most sites, coring was carried out along transects running from the coastline to the inland boundary of the lagoons (Fig. Supplement 1 and 2). In the ridge and swale topography, coring was done in selected suitable swales across the beach ridge plain (Fig. Supplement 1 and 2). 2.2 Laboratory analysis All the cores were visually logged and photographed after opening. Locations with visually distinguishable layers having abrupt lower contacts were selected for further analysis (Table 1 ). A combination of textural, geochemical, and physical properties helped differentiate the origins of the abrupt event layers 33, 34, 41, 42, 43 . The percentage of the sand-size fraction was measured by sieving in Ratgama and Koggala sediment cores and using laser particle size analyzers in the rest of the cores (Malvern Mastersizer (KD, PM, OK, KM, and VK cores), Beckman Coulter (TG and KU cores), or Microtrac (RG and KG cores). Standard samples were used to determine the accuracy and precision of instruments. Grain size measurements were taken at a resolution of 1–3 cm, depending on the visual homogeneity of the sediment. Samples were treated with H 2 O 2 to remove organics before sieving through a 63µm mesh size to calculate the sand fraction. Particle size was first measured on untreated samples using particle size analyzers. Abrupt event layers, identified visually and based on grain size plots, were then subsampled at 1 cm resolution, treated with H 2 O 2 , and subsequently reanalyzed using the above procedure. If these sand samples had shells, they were treated with HCl before grain size analysis to yield grain size spectra based solely on the siliciclastic sediment component. Unless there was a significant difference, untreated data were used in down-core grain size plots to maintain consistency. Coarser (2000 µm and larger) grains (if available) were separately analyzed with a Retsch-Camsizer video particle size analyzer. Sample spacing for measurements was 1 cm for Magnetic susceptibility (MS) and diffuse spectral reflectance (DSR), and 2 cm for X-ray Fluorescence (XRF), due to differences in sensitivity and the sampling rates at which each instrument could operate. MS was measured using a Bartington MS2 magnetic susceptibility meter. DSR was measured using a Konica-Minolta CM-2600d visible color spectrophotometer. Relative variation of elemental composition was measured by scanning the cores with Innov-X (KD, PM, OK, KM, and VK cores) or Bruker (RG and KG cores) handheld XRF spectrometers, or an Itrax core scanner (TG and KU cores). All cores were allowed to dry for 2 days after opening before MS and XRF measurements were taken. Standard samples, sample blanks, and replicate measurements were used to evaluate the accuracy and precision of each method. (Supplement Table 1 ). Collapsed infill lengths at core tops were determined by comparing the drive length and sediment core length, stratigraphic contacts, and by analysis of sediment properties. Any collapsed or disturbed boundary at the top of each core section was identified by measuring the texture, fabric, and color variability of the sediment at high resolution using a Konica-Minolta CM-2600d visible color spectrophotometer. Ages of the abrupt event layers were determined by the standard AMS radiocarbon technique and the gas accepting ion source method (GAIS) 44 . Intact mollusk microshells, organic matter, and bulk organics in sediment from above or below (when no distinct erosive contacts are present), the abrupt layers were selected for age dating. Selected samples were submitted to the NOSAMS laboratory of Woods Hole Oceanographic Institution, USA, following standard protocols. Radiocarbon Ages were calibrated using the IntCal20 and Marine20 curves in Calib 8.2 software 45 . Unless δ 13 C of mollusks indicates their marine origin (δ 13 C > 0), all other mollusk ages and organic carbon ages were calibrated using the IntCal 20 curve, considering the shallow water environments from which they were retrieved. ΔR value − 28 and uncertainty 69 46 were used for reservoir correction on samples from the south and southeast, while ΔR value 356 and uncertainty 57 46 were used for eastern locations, considering the influence of Indian coastal currents. Ages of event layers were reported as younger or older than the radiocarbon age when no bracketing ages were available. When there were no dates for nearby depths, the age of the top of the event layer was estimated by extrapolating from the nearest age. Radiocarbon results are shown in Supplement Table 1 . Calibrated radiocarbon ages are reported in the text as calibrated years before present (yrs BP), and all other ages, including estimated ages, are given as years before present (yrs BP). 2.3 Distinguishing tsunami layers The terrestrial vs marine origin of the abrupt event layers identified visually and using grain size spectra was determined from chemical composition and magnetic susceptibility. Varimax-rotated principal component analysis of XRF data was used to identify the provenance of sediment 47, 48 . We refer to these as PCs here for simplicity. Ca, Sr, Br, and Cl indicate marine origin, while Ti and Zr, which are rich in Ilmenite, Rutile, and Zircon accumulations on the beach, indicate overwash sediment. Fe, Zn, and Ba indicate terrigenous sediment, while the Sr/Ba ratio indicates a marine influence 49, 50, 51 . Overwash sediment is typically associated with high MS because of the presence of magnetic minerals, such as magnetite and hematite, in beach sand. Abrupt peaks with values exceeding background in grain size, XRF-PC, Sr/Ba, and MS down-core plots were used to identify event layers. If the abrupt sand layers appeared to have a marine origin based on the above proxies, they were further confirmed using marine microfossils. For that, subsamples from the abrupt sand layers were wet-sieved with a 63 µm sieve, and foraminifera and ostracod identification was done under an optical microscope at 25X magnification for initial picking and using scanning electron microscopic (SEM) images for final identification. Marine abrupt layers were correlated within cores at the same site using age and stratigraphic correlation, and between sites using age. They were first categorized as higher-potential as tsunami events (HPT), lower-potential tsunamis (LPT), or other marine events (OME) following STEP 1 of the criterion shown in Fig. 3 . Secondly (STEP 2), the age correlation of events identified by this study with regional events and paleoseismic events at the Sunda trench was used to confidently categorize them into Tsunami High Potential (T HP ), Tsunami Moderate Potential (T MP ), Tsunami Low Potential (T LP ), or Other Marine events (OM) (Fig. 3 ). 3. Results and Discussion Among the 14 sites selected for coring, 31 abrupt sand layers were discovered at 10 sites. Several cores at five locations recorded sand layers laid by the 2004 tsunami. Their sedimentary and geochemical characteristics provide modern analogues to paleotsunamis. Out of the 31 abrupt layers, 29 (96%) overwash sand layers were recognized as having marine origin (Table 2 and Fig. Supplement 3), while two (6%) had abrupt sand layers of non-marine origin. Based on correlation within the site and among the study sites (STEP 1 Fig. 3 ), 23 layers (74%) were recognized as having a higher potential for tsunami origin (HPT), two (06%) were lower potential for tsunami (LPT), and four (12%) were other marine events (OME). Table 2 – Abrupt marine overwash events recorded during this study from different back barrier environments in southern and eastern Sri Lanka. Interpretations of the events as Higher Potential as Tsunami (HPT), Lower Potential as Tsunami (LPT), and Other Marine Events (OMT) are based on the stratigraphic and age correlation within the site and the age correlation among the locations following STEP 1 of Fig. 2 . Western Coast Southern Coast Eastern Coast Interpretation Ratgama Koggala Devundara Tangalle Kirinda Kumana Okanda Panama Komari Vakarai 2004 RG2 (1 core) 2004 KG1,2 (2 cores) 2004 DV1,2 (2 cores) 2004 KU2, 5 (2cores) 2004 KM1 (1 core) 2004 Tsunami KG1 ~ 1000 (2 cores) VK1 > 996 ± 57 < 1253 ± 48 (2 cores) HPT 1000–1200 yrs BP DV1 ~ 2100 (2 cores) KU1 ~ 2000 (1 core) LPT 2000–2100 yrs BP KG2 < 3170 ± 319 (2 cores) DV2 2832 ± 202 3656 ± 325 (2 cores) OME RG1 > 3801 ± 351 (2 cores) KG4 ~ 4100 (2 cores) DV3 (2 cores) < 4069 ± 371 TG 3954 ± 122 (pit) KD1 2510–4210 (3 core) OK1 4123 ± 125 (2 cores) HPT 3800–4200 yrs BP DV4 > 4552 ± 331 (2 cores) KD2 4954 ± 85 5125 ± 160 < 5255 ± 196 (1 core) KM1 5597 ± 314 (2 cores) TG1 < 5948 ± 47 (1 core) PN3 ~ 5750 (2 cores) HPT 5600–5900 yrs BP TG2 6249 ± 50 6200–6400 yrs BP KD4 > 7229 ± 55 (1 core) VK2 7321 ± 78 (1 core) OME 3.1 2004 tsunami sand layers. Ratgama, Koggala, Devundara, Kumana, and Komari sediment cores preserve sand layers near the core top (Fig. Supplement 3). Since no other tsunami event with a high enough run-up to lay over wash sand layers has been recorded in the last 500 years, the above sand layers were considered to be the 2004 event layers. Their textural, mineralogical, chemical, physical, and micropaleontological characteristics can serve as modern analogues to help identify the past tsunami events. The 2004 sand layer in the Ratgama RG2 sediment core has high scores for XRF PC3 (Ca, Sr), indicating a marine event. The 2004 event layer in the RG 2 sediment core contains broken shell fragments, indicating that it originated from a high-energy coastal environment and/or was transported by the high-energy tsunami flow (Figure supplement 4-A). At Koggala, the 2004 sand layer in both the KG1 and KG2 cores has high scores for XRF PC4 (Ti, Zr), indicating beach overwashing. In Devundara, both DV1 and DV2 cores exhibit two peaks in grain size plots, indicating that deposition associated with the two major waves of the 2004 tsunami reached the area. These sand layers show high scores for XRF PC1 (Ca, Sr, Zr). In both Kumana KU2 and KU5 sediment cores, the 2004 sand layer has high scores for XRF PC1 (Ti, Zr) and XRF PC3 (Ca, Sr), evidencing a marine overwash event. In the Komari KM1 core, this abrupt sand layer has high MS. 3.2 Paleotsunami events from Sri Lanka. The 29 abrupt sand layers of marine origin belong to seven HPT, one LPT, and four OME events, based on intra- and inter-study site correlations. A. Events with higher potential for a tsunami (HPT) i. ~ 1100 yrs BP (Between 1000–1200 yrs BP) Koggala (2 cores) and Vakarai (2 cores) have evidence for a ~ 1000 yrs BP tsunami event, recorded on both the eastern 1, 52 and western sides 19,53 of the Bay of Bengal (Tables 2 and 3 , Fig. 4 ). In the Koggala KG-1 layer, the higher XRF PC4 (Ti, Zr) provides evidence for its origin from beach/barrier overwash. Abundant microfossils, well-rounded quartz grains, and numerous ilmenite, garnet, and rutile grains also support the marine overwash origin of the event (Fig. Supplement 3B). In Vakarai, the VK-1 abrupt sand layer has high Ca and Ti, indicating an overwash event of marine origin (Fig. Supplement 3J). Both Koggala and Vakarai cores show multiple peaks in the event layers (KG-1 and VK-1), evidencing the deposition from multiple waves (Fig. Supplement 3B and 3J). Since these event layers are found in both the south and east, it is unlikely to be any marine event other than a tsunami (T HP) . The event age was estimated from the sedimentation rate of the KG2 sediment core and the bracketing age of the VK1 layer in the V13 core. They show that this event occurred between 996 ± 57 and 1253 ± 48 yrs BP (~ 1000–1200 yrs BP) (Fig. Supplement 3J). Table 3 – Chronological correlation of HPT events of this study (Table 2 ) with local and regional tsunami events recorded by previous studies. The approximate date used to identify the event in the text is in bold letters. Final designation for the event is given following the criteria given in STEP 2 of Fig. 3 Age of the HPT Correlating peleotsunami events from previous studies in Sri Lanka (yrs BP) Correlating peleotsunami events from the western Bay of Bengal (yrs BP) Correlating peleotsunami events from the eastern Bay of Bengal (yrs BP) Final Designation ~ 1100 yrs BP. 1000–1200 yrs BP N/A ~ 1000 10, 17,53 1225 ± 35 9 950 ± 50 65 1045 ± 135 67 < 1065 ± 105 1 ~1000 5 1220 ± 70 60 1265 ± 85 59 1200 ± 210 52 T HP ~ 3000 yrs BP. 2800–3100 yrs BP 2700 ± 321 8 3170 ± 320 54 2900 ± 480 17 2865 ± 50 2 3018 ± 123 11 T HP ~ 4000 yrs BP. 3800–4200 yrs BP 4200 ± 257 8 4110 ± 220 7 4450 ± 500 63 4350 ± 620 63 T HP ~ 4600 yrs BP. 4500–4700 yrs BP 4500 ± 279 8 4829 ± 362 15 N/A 4450 ± 500 63 4350 ± 620 63 4712 ± 126 11 T HP ~ 5100 yrs BP . 4900–5200 yrs BP 5000 ± 330 8 4829 ± 362 15 N/A N/A T MP ~ 5700 yrs BP. 5600–5900 yrs BP N/A 5620 ± 140 17 5719 ± 141 2 5625 ± 145 2 5607 ± 216 11 T HP ~ 7300 yrs BP. 7200–7300 yrs BP N/A N/A 7429 ± 100 2 T HP ii. ~ 3000 yrs BP event (Between 2800–3100 yrs BP) Abrupt sand layers belonging to this event are found in multiple sediment cores at Koggala (2 cores) and Devundara (2 cores) (Table 2 ). In Koggala KG-2, an abrupt sand layer has higher scores for XRF PC4 (Ti, Zr), while DV-1 layer in Devundara has higher scores for XRF PC 1 (Ca, Sr, Zr), indicating an overwash event of a marine origin (Fig. Supplement 3B and 3C). Presence of broken shell fragments and marine foraminifera tests and abundant garnet, ilmenite, and rutile grains confirms the marine overwash origin of the layer. Two peaks in some cores indicate deposition from two strong waves. The distribution of these event layers across a 50 km area along the southern beach suggests three possible origins: i. A rare storm travels along the south coastline, ii. Monsoon overwash events, or iii. a tsunami. Age dating shows that this event occurred immediately after > 3170 ± 319 yrs BP (KG-2), < 3077 ± 308 yrs BP (DV-1), or between 2832 ± 202 and 3061 ± 150yrs BP (KU-2), depending on the age constraints from three cores (Table 2 ). Therefore, this event can be considered to have occurred between ~ 2800–3100 yrs BP. Jackson et al. 8 (2417 ± 152–2925 ± 98 yrs BP) and Premasiri et al. 54 , (3170 ± 320 yrs BP) have reported tsunami events from Hambantota Sri Lanka, which is about 30 km from Koggala, correlating to this event within age uncertainties, while Rubin et al. 2 (2815–2916 yrs BP) and Sanwal et al. 11 (2899–3145 yrs BP) have identified age correlating tsunami events from Aceh Indonesia, and the Andaman islands respectively (Table 3 , Fig. 4 ). Therefore, this event is considered a T HP . iii. ~ 4000 yrs BP event (Between 3800–4200 yrs BP) A chronologically correlated event is recorded in multiple locations along the southern and eastern coasts, dating to between 3800 and 4300 yrs BP. The Ratgama (2 cores), Koggala (2 cores), Tangalle (1 pit), Kirinda (3 cores), Okanda (1 core), and Panama (2 cores) have evidence for an abrupt sedimentation event. Ratgama, RG-1 layer has high scores for XRF PC3 (Ca, Sr) and XRF PC4 (Ti, Zr), while Koggala KG-1 layer has high scores for XRF PC4 (Ti, Zr) (Fig. Supplement 3A and 3B). Kirinda, KD-1 layer, is a yellow-colored sand layer with an erosive basal contact and has higher MS, Sr/Ba, and XRF PC1 (Sr, Zr, Ca) (Fig. Supplement 3E). However, this powerful erosive event might have eroded the hinterland and added yellowish terrestrial sand to the layer. Okanda OK 1 layer has higher scores for XRF PC1 (Ca, Sr, and K), and Panama PN 1 layer has higher XRF PC2 (Ca and Sr) and Sr/Ba (Fig. Supplement 3G and 3H). Therefore, chemical properties and MS indicate that this event is an overwash event having a marine origin. The RG-1 layer has broken shell fragments, indicating transport by high-energy flow (Figure supplement 4-B). RG-1 and PN-1 layers show two peaks in some cores, indicating the deposition by two separate waves. The erosive basal contacts of the layers provide evidence of a powerful tsunami event. Radiocarbon ages above and below this layer show that this event occurred between 3801 ± 351 and 4290 ± 118 yrs BP (Table 2 ). Correlating paleotsunami events have been reported from Sri Lanka 8 , the Maldives 9 , and Thailand 55 (Table 3 , Fig. 4 ). Therefore, this event can be considered as a powerful T HP that occurred around 4000 yrs ago. iv. ~ 4600 yrs BP event (Between 4500–4700 yrs BP) Another chronologically correlated event is recorded in Devundara (2 cores), Kirinda (2 cores), and Panama (1 core) sediment cores between 4500 and 4700 yrs BP. Both Devundara DV-2 and Kirinda KD-2 layers have higher scores for PCs correlating with Ca and Sr, indicating a marine origin (Fig. Supplement 3C and 3E). The Panama PN-2 layer is rich in broken shells, indicating deposition by a high-energy event. DV-2 layer in Devundara (DV2 core) and PN-2 layer in Panama PN2 and PN3 cores show doublet peaks, indicating deposition by two separate waves (Fig. Supplement 3C and 3H). This event chronologically correlates with the tsunami events (4331 ± 126–4583 ± 196 yrs BP) reported by Jackson et al. 8 from Hambantota, Sri Lanka (Table 3 , Fig. 4 ) and Malik et al. 63 (4450 ± 500, 4350 ± 620 yrs BP) and Sanwal et al. 11 (4837 ± 126 yrs BP) from the Andaman Islands. Therefore, this event can be considered a T HP . v. ~ 5100 yrs BP event (Between 5000–5300 yrs BP) The Kirinda (3 cores), Okanda (1 core), and Komari (1 core) sites provide evidence for a tsunami event that occurred around 5100 yrs ago. Higher Sr/Ba ratio and scores for XRF PC2 (Sr, Zr, Ca) in Kirinda core, higher Sr/Ba and scores for XRF PC 1 (Ca, Sr, K) in Okanda OK-2, and higher MS in KM-1 layer in Komari provide evidence for an overwash event of a marine origin (Fig. Supplement 3E, 3G and 3I). In the Kirinda KD3 sediment core, KD-3 layer contains coarse mica flakes, indicating deposition of material from the eroded hinterland. In KD2 core KD-3 layer contains benthic foraminiferal tests of Triloculina spp and Pseudotriloculina subgranulata and shallow marine diatom Calistocythere sp. (Fig Supplement 4 C). These layers have been deposited between 4954 ± 85 and 5255 ± 196 yrs BP (Table 2 ). The occurrence of these chronologically correlating marine overwash sand layers in both the east and south is strong evidence for their tsunamigenic origin. Correlating tsunami events has been recorded between 4764 ± 140 and 5152 ± 178 yrs BP from Hambantota 8 , and 4829 ± 362 yrs BP from Kirinda 31 (Table 3 , Fig. 4 ). However, because no corresponding event has been recorded outside Sri Lanka, this event is classified as a T MP . ~ 5700 yrs BP event. (Between 5600–5900 yrs BP) The Devundara (2 cores), Tangalle (1 core), and Panama (2 cores) sites carry evidence for another abrupt depositional event. The Devundara DV-3 layer exhibits higher scores for XRF PC1 (Ca, Sr, Zr), whereas the TG-2 layer of the Tangalle core displays higher scores for XRF PC2 (Ca, Sr, K) (Fig. Supplements 3C and 3D). This indicates a marine origin of these sand layers. The Panama PN3 layer also exhibits higher Sr/Ba ratios and scores for XRF PC2 (Ca, Sr), indicating a marine origin (Fig. Supplement 3H). Broken shells and coarse mica flakes in the PN-2 layer in the PN2 and PN3 cores are strong evidence for a high-energy erosive event. Radiocarbon dates show that this event occurred around 5700 yrs BP (5597 ± 314–5948 ± 47 yrs BP) (Table 2 ). Rubin et al. 2 and Sanwal et al. 11 reported correlating tsunami events between 5578 and 5866 yrs BP from Aceh, Indonesia, and the Andaman Islands, respectively (Table 3 , Fig. 4 ). Therefore, this abrupt marine flooding event is considered a tsunami (T HP) . vi. ~ 7300 yrs BP event (Between 7200–7300 yrs BP) Both Kirinda and Vakarai have evidence for an abrupt event layer deposited around 7300 yrs BP. At site Kirinda, the KD-4 layer has a high Sr/Ba ratio, while the VK–2 layer of Kirinda cores has high Sr/Ba as well as XRF PC1 (Ca, Ti), indicating a marine origin (Fig. Supplement 3E and 3J). V12-3 layer also has benthic foraminifera tests of Triloculina and Quinqueloculina species, confirming the marine origin of the event (Fig. Supplement 4-D). Radiocarbon dates indicate that this event occurred between 7229 ± 55 and 7321 ± 78 yrs BP (Table 2 ). Rubin et al 2 also reported a tsunami event that occurred between 7324–7529 yrs BP in Aceh, Indonesia (Table 3 , Fig. 4 ). Given the occurrence of this abrupt marine layer at widely separated locations in southern and eastern Sri Lanka, and its age correlation with the Indonesian tsunami event, it is reasonably identified as a tsunamigenic layer (T HP ). B. Events with lower potential for a tsunami (LPT) i. ~ 2100 yrs BP event A marine over-wash event was recorded around ~ 2100 yrs BP (Devundara – 2 cores and Kumana 1-core). It correlates with the ~ 2000 yrs BP 56 tsunami sand layer recorded from eastern Sri Lanka, the ~ 2190 ± 150 9 tsunami event reported from the Maldives, and the 2100 ± 260 52 ~2200 59 tsunami events recorded from Thailand, within age uncertainties (Table 4 , Fig. 4 ). Although this event's age correlates with other local and regional tsunami events reported in previous studies, it is classified as a tsunami with moderate potential (TMP) because the abrupt layers recorded in this study have only estimated ages at both locations. Table 4 – Chronological correlation of LPT events of this study (Table 2 ) with local and regional tsunami events recorded by previous studies. The approximate date used to identify the event in the text is in bold letters. The final designation for the event is given following the criteria given in STEP 2 of Fig. 3 Age of the LPT Location Correlating peleotsunami events from previous studies in Sri Lanka (yrs BP) Correlating peleotsunami events from the western Bay of Bengal (yrs BP) Correlating peleotsunami events from the eastern Bay of Bengal (yrs BP) Final Designation ~ 2100 yrs BP. 2000–2100 yrs BP Devundara, Kumana 2100 ± 260 8 2000 56 ~ 2190 ± 150 17 2200 7 2312 ± 302 11 T MP C. Other marine events (OME) Three other marine overwash events were recorded at ~ 3600 yrs BP (Koggala- 2 cores), 7321 ± 78 (Vakarai – 1 core) (Tables 2 and 4 ). The ~ 3600 yrs BP event correlates with 3710 ± 20 yrs BP potential tsunami event in India 53 and 3591 ± 128 yrs BP tsunami recorded in the Andaman Islands 68 (Table 5 , Fig. 4 ). Based on our criteria for recognizing tsunami layers (STEP 2, Fig. 3 ), this event was designated as a T LP co due to its limited occurrence and lack of bracketing 14 C ages. Table 5 – Chronological correlation of Other Marine Events (OME) of this study (Table 2 ) with local and regional tsunami events recorded by previous studies. The approximate date used to identify the event in the text is in bold letters. The final designation for the event is given following the criteria given in the STEP 2 of Fig. 3 Age of the OME Location Correlating peleotsunami events from previous studies in Sri Lanka (yrs BP) Correlating peleotsunami events from the western Bay of Bengal (yrs BP) Correlating peleotsunami events from the eastern Bay of Bengal (yrs BP) Final Designation > 3656 yrs BP. Koggala N/A ~ 3700 53 3591 ± 128 11 T LP < 6249 ± 50 yrs BP. Tangalle ~ 6200 ± 117 8 N/A 6497 ± 417 2 6268 ± 411 2 6357 ± 116 11 T LP ~6300 yrs BP. 6200–6400 yrs BP Tangalle ~ 6400 ± 173 8 7320 yrs BP. Vakarai N/A N/A N/A OM Both 6200–6400 yrs BP and < 6250 yrs BP events chronologically correlated with ~ 6200 and 6400 yrs BP layers recorded from Hambantota, Sri Lanka 8 , 6357 ± 116 tsunami event at the Andaman Islands 11 , as well as the 6080–6915 yrs BP or 5857–6680 yrs BP old event layers from Aceh, Indonesia 2 (Table 5 , Fig. 4 ). The 6200–6400 yrs BP event also correlates with the < 6480 ± 60 yrs BP potential tsunami in Rameswaram, India 67 . Since the 6200–6400 yrs BP event has bracketing ages and it correlates with events reported from both eastern and western BB, it was designated as T MP . The event < 6250 yrs BP was designated as T LP because it lacks bracketing ages eventhough it correlates with above same events as 6200–6400 yrs BP. It does not rule out the possibility of having two events withing about 200 yrs interval. The event > 7321 ± 78 was designated OM, such as a storm surge, because there are no correlating events and bracketing ages. As discussed above, the abrupt marine event layers of different tsunami potential (HPT − 7, LPT − 1, and OME − 4) are designated as T HP (6), T MP (3), T LP (2), and OM (1) based on the chronological correlation with the tsunami events reported from both western and eastern BB by the 24 previous studies as described in the STEP 2 Fig. 3 (Fig. 4 ). 3.3 Regional tsunami record and tsunami frequency. When analyzing regional paleotsunami records from western and eastern Bay of Bengal (BB) sites facing Andaman and Sumatra (SZ), where the 2004 tsunami occurred, we can identify 9 events older than the 2004 event that occurred during the last 7500 years and were reported at multiple locations across the bay (Fig. 5 ). Most studies have been conducted on the eastern side of the bay, and most records date back 3000 years. So, younger events are reported at multiple locations across the BB, whereas older events are reported at only a few locations (Fig. 4 ). It is obvious that not all the tsunamis reported in the eastern BB are recorded at western BB sites because many events are not powerful enough to cross the BB (Fig. 4 ). So, those recorded on both sides of the BB are likely large, 2004-type trans-basin events. The above results show that four T HP and T MP tsunami events (~ 3000, ~ 2100, ~1000 yrs BP, and the 2004 event) have been recorded since 4000 yrs BP. All these event layers were recorded from coring sites situated below sea level and from the beach ridge plain at Vakarai, which developed within the last 2000 yrs. At the end of the mid-Holocene highstand (MHH), sea level began to stabilize around 4000 yrs BP 57 . Coastal accommodation space was subsequently filled, initiating erosion of the coastal plain. Therefore, none of the cores extracted above sea level contain younger tsunami layers, including the 2004 event, possibly due to erosion. Providing further evidence of coastal plain erosion, Moore et al. 26 observed that the 2004 event layer was absent at many sites along the southeastern coast of Sri Lanka, just three years after the tsunami. Ages older than 4000 years, close to the core tops of the onshore Kirinda, Okanda, and Kumana cores, also provide evidence for erosion due to a lack of accommodation space. Sediment ages in Vakarai cores show that the Vakarai beach ridge plain developed after sea level stabilization. Therefore, the preservation of only three marine overwash sand layers may be mainly due to limited accommodation space. The youngest trans-basin potential tsunami event reported across multiple locations in eastern and western BB is around 600 years BP. However, it is not recorded in any study except one in Sri Lanka 56 (Fig. 4 ). Around 1000 yrs BP, a tsunami event is reported across multiple sites (11) in both the eastern and western BB, including this study. The T MP ~2100 years BP event has been reported at three sites in the western BB, including the Maldives. The chronologically correlating sand layer reported at the Devundara and Kumana sites in Sri Lanka may represent this event. The historical chronicle, the “Mahavamsa”, reports a marine flooding event in Sri Lanka between 2155–2111 yrs BP (205 BC − 161 BC). This could refer to the potential 2100 yrs BP tsunami. The ~ 3000 yrs BP tsunami event reported in this study is coeval with events recorded in the Maldives (2420–3380 yrs BP) 9 and Sri Lanka (3170 ± 320 yrs BP) 54 on the western BB and theAndaman Islands (3018 − 2899 yrs BP) and Aceh, Indonesia (3270 and 3353 yrs BP) on the eastern BB within age uncertainties (Fig. 4 ). Correlating paleotsunami events for 4000 and 4600 yrs BP events, were reported only from the Andaman Islands and western BB locations. A gap in tsunami events is reported between 5500 − 3400 yrs BP in Aceh, Indonesia 2 , and a gap in seismic events along the 2004 region of the Sumatra-Andaman subduction zone 16 . This may indicate that 4000 and 4600 yrs BP events might have originated at the Andaman-Nicobar section of the subduction zone. However, due to the lack of any record longer than 2000 years BP in both Sumatra and Thailand, a firm conclusion regarding the origin of these events is not possible. The 5100 yrs BP T MP recorded only in Sri Lanka may have originated in the southern part of the Sumatra SZ. Hydrodynamic simulations in the major seismic zones around the Indian Ocean basin by Okal and Synolakis 58 show that significant tsunamis generated by ruptures on the south Sumatra segment of the Sumatra SZ can also reach Sri Lanka. Time intervals between reported regionally correlated tsunami events were calculated using the midpoint of each event. It shows that three events have occurred over the last 1000 years, with an average interval of 500–700 years between events. Similarly, four events have occurred between 4000 and 6000 yrs BP, making the interval between 500 and 700 yrs. During 1000–4000 yrs BP and 6000–7500 yrs BP, the interval between events is generally 900 − 100 yrs (Fig. 5 ). Using the paleoseismic record reconstructed for the 2004 earthquake region by Patton et al. 16 , based on seismogenic turbidites, a seismic event that correlates within its age uncertainties with each of the above tsunami events can be identified. This paleoseismic record shows increased seismic activity during the period 600–2500 and 4500–5200 (Fig. 5 ). So, the higher tsunami frequency period overlaps with the higher earthquake frequency period. Increased tsunami frequency in the western BB is a rcould result from increased seismicity in the northern Sunda SZ. However, increased activity in the Andaman-Nicobar sections and the southern Sumatra segment may also have contributed to the higher number of tsunamis in some periods. Conclusion This study fulfills the long-standing need for a robust trans-basin paleo-tsunami record for the Indian Ocean, combining a 7000-year record constructed for Sri Lanka by studying 13 back-barrier environments together with other regional records from both the eastern and western Bay of Bengal. This study identified six abrupt marine coastal flooding events that are stratigraphically and/or chronologically correlated between sites within the same back-barrier environments. They chronologically correlate with multiple distal locations across south and eastern Sri Lanka, as well as with other regional records from the western and eastern Bay of Bengal. Due to their regional occurrence, they are identified as trans-basin tsunamis with high potential (T HP ). In addition, abrupt sand layers indicative of three tsunami events with medium potential (T MP ) and two events with low potential (T LP ) were recorded. Paleoseismic events reported at the 2004 rupture area of the Sunda SZ correlate with all the reported tsunami events except the 4000 and 4600 T HP events discussed in this study. When considering the 2004 events and ~ 600 yrs BP event reported in both western and eastern BB, except Sri Lanka, the age interval between events is 500–700 yrs during the last 1000 yrs, and 4000–6000 yrs BP. During other periods, the age interval between events ranges from 900 to 1000 years. Increased seismicity in the northern and southern Sumatra SZ or the southern Andaman SZ could have contributed to the increased frequency observed during the above periods. Declarations Author Contribution P.N.R, J.D.O, J.P.D, T.U.T.W , A.L.M- Manuscript Preparation and editingP.N.R, L.H.M.T.M.B.T , R.P.S.K.R, K.K, D.T.W - Field workP.N.R, L.H.M.T.M.B.T , R.P.S.K.R, K.K, D.T.W , T.U.T.W. - Lab workP.N.R, J.D.O, A.L.M. J.P.D. - Supervision and funding Acknowledgement The authors extend their sincere gratitude to the Woods Hole Oceanographic Institution, the Geological Society of America, the International Association of Sedimentologists, and the National Science Foundation for providing funding. The geological Survey and Mines Bureau of Sri Lanka provides logistic support for field work. Data Availability Age data are included in the Table supplement file. All the generated raw data is available upon request. References Monecke, K. et al. A 1,000-year sediment record of tsunami recurrence in northern Sumatra. Nature 455 , 1232–1234 (2008). Rubin, C. M. et al. Highly variable recurrence of tsunamis in the 7,400 years before the 2004 Indian Ocean tsunami. 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Potential predecessors of the 2004 Indian Ocean tsunami—sedimentary evidence of extreme wave events at Ban Bang Sak, SW Thailand. Sediment. Geol. 239 , 146–161 (2011). Johnson, F. C., Malik, J. N., Kathal, P. K. & Khan, A. Foraminiferal assemblages of inferred onshore paleotsunami deposits in southwestern Andaman Islands, India. J. Geol. Soc. India 97 , 579–595 (2021). Bhat, G. R., Balaji, S., Yousuf, M. & Bali, B. S. Primary on-fault paleoseismic evidence from trench investigation along the Bathubasti fault, South Andaman, India. J. Seismol. 24 , 1159–1173 (2020). Sieh, K., Daly, P., Edwards McKinnon, E., Pilarczyk, J.E., Chiang, H.W., Horton, B., Rubin, C.M., Shen, C.C., Ismail, N., Vane, C.H. and Feener, R.M., Penultimate predecessors of the 2004 Indian Ocean tsunami in Aceh, Sumatra: Stratigraphic, archeological, and historical evidence. Journal of Geophysical Research: Solid Earth , 120 (1), pp.308–325 (2015). Malik, J.N., Johnson, F.C., Khan, A., Sahoo, S., Irshad, R., Paul, D., Arora, S., Baghel, P.K., and Chopra, S.,. Tsunami records of the last 8000 years in the Andaman Islands, India, from mega and large earthquakes: Insights on recurrence interval. Scientific Reports , 9 (1), p.18463 (2019). Chaturvedi, S. K. & Loveson, V. J. Inferences on paleo-tsunami from the shoreline of Poompuhar, central Tamil Nadu coast, India through sedimentological and micropaleontological signatures. Quat. Int. 642 , 73–83 (2022). Rajendran, C. P., Rajendran, K., Anu, R., Earnest, A., Machado, T., Mohan, P. M. & Freymueller, J. Crustal deformation and seismic history associated with the 2004 Indian Ocean earthquake: a perspective from the Andaman–Nicobar Islands. Bull. Seismol. Soc. Am. 97 , S174–S191 (2007). Rajendran, K., Rajendran, C. P., Earnest, A., Prasad, G. R., Dutta, K., Ray, D. K. & Anu, R. Age estimates of coastal terraces in the Andaman and Nicobar Islands and their tectonic implications. Tectonophysics 455 , 53–60 (2008). Rajendran, C. P., Rajendran, K., Andrade, V. & Srinivasalu, S. Ages and relative sizes of pre-2004 tsunamis in the Bay of Bengal inferred from geologic evidence in the Andaman and Nicobar Islands. J. Geophys. Res. Solid Earth 118 , 1345–1362 (2013). Udayaganesan, P., et al. High-Energy Deposits in the Shadow Zone of Rameswaram Island, Southeast Coast of India." Coastal Environments of India: A Comprehensive Approach . Cham: Springer Nature Switzerland, 93–120 ( 2025). Additional Declarations No competing interests reported. Supplementary Files Figuresaccessory.docx Tablesupplement.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8757939","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":589360072,"identity":"7437e723-2cc8-4352-8ee5-59e29985fe45","order_by":0,"name":"Pradeep Nalaka Ranasinghe","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+UlEQVRIiWNgGAWjYPACCTBiYKiwgPB5iNdyRoJoLRBdDIxtRGgxlz787MGPPxZ58tHNj198nCdhLz8jgfHB2zbcWiz70swNe9skig3vHDOznLlNInHDjQRmw7l4tBicYTCT4G2QSNw4I8HMmHebRIKBRAKbNC9eLezfJP/8AWlJ/2b8dw7YYey/8WvhMZPmYZNInC+RY/yYsUGCseFGAhszPi2WPTxl0rJtQC9I5JQx9hwDMs48bJaccw63FnMe9m2Sb/7UJc6fkb75w48aG3v59uSDH96U4XEYnHGAgQ0aKYwNuNUja5FvYGD+gFfpKBgFo2AUjFgAAL2aT9qx8Qb8AAAAAElFTkSuQmCC","orcid":"","institution":"Lake Superior State University","correspondingAuthor":true,"prefix":"","firstName":"Pradeep","middleName":"Nalaka","lastName":"Ranasinghe","suffix":""},{"id":589360077,"identity":"b91515ce-f4e7-417b-9012-428d193724e6","order_by":1,"name":"Joseph Ortiz","email":"","orcid":"","institution":"Kent State University","correspondingAuthor":false,"prefix":"","firstName":"Joseph","middleName":"","lastName":"Ortiz","suffix":""},{"id":589360078,"identity":"35e43987-8c16-4c07-b58f-c96103fb55e3","order_by":2,"name":"Andrew Moore","email":"","orcid":"","institution":"Earlham College","correspondingAuthor":false,"prefix":"","firstName":"Andrew","middleName":"","lastName":"Moore","suffix":""},{"id":589360080,"identity":"067d1a5b-b4cc-4912-b3f7-4b43305b51c4","order_by":3,"name":"Tharanath Ambillapitiya","email":"","orcid":"","institution":"National Aquatic Resources Research and Development Agency","correspondingAuthor":false,"prefix":"","firstName":"Tharanath","middleName":"","lastName":"Ambillapitiya","suffix":""},{"id":589360081,"identity":"892671c4-aa72-4df7-b5ff-7d5eed1a82cb","order_by":4,"name":"Kumari Rajapaksha","email":"","orcid":"","institution":"Western Sydney University","correspondingAuthor":false,"prefix":"","firstName":"Kumari","middleName":"","lastName":"Rajapaksha","suffix":""},{"id":589360082,"identity":"a7ce16e2-b894-49f5-8acb-1b52d21d48df","order_by":5,"name":"Thilini Wijewardhana","email":"","orcid":"","institution":"Kent State University","correspondingAuthor":false,"prefix":"","firstName":"Thilini","middleName":"","lastName":"Wijewardhana","suffix":""},{"id":589360083,"identity":"0e4505a8-4d73-4edd-a03c-5fe2881aac59","order_by":6,"name":"Kopalakrishnan Kovintharajan","email":"","orcid":"","institution":"University of Windsor","correspondingAuthor":false,"prefix":"","firstName":"Kopalakrishnan","middleName":"","lastName":"Kovintharajan","suffix":""},{"id":589360085,"identity":"1fa43130-d772-4c5e-9ddd-67bf68ef5b33","order_by":7,"name":"Jeffrey Donnelly","email":"","orcid":"","institution":"Woods Hole Oceanographic Institution","correspondingAuthor":false,"prefix":"","firstName":"Jeffrey","middleName":"","lastName":"Donnelly","suffix":""},{"id":589360086,"identity":"f5053f7a-ed52-40d3-a9ad-54202cb86d84","order_by":8,"name":"Dharani Wijesundara","email":"","orcid":"","institution":"Geological Survey and Mines Bureau","correspondingAuthor":false,"prefix":"","firstName":"Dharani","middleName":"","lastName":"Wijesundara","suffix":""}],"badges":[],"createdAt":"2026-02-01 17:23:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8757939/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8757939/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102518026,"identity":"fcd2293a-27ba-4561-b929-0cc8c708d6af","added_by":"auto","created_at":"2026-02-12 14:05:52","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":306355,"visible":true,"origin":"","legend":"\u003cp\u003eTectonic boundaries in the Indian Ocean. The movement of India is shown in arrows. Convergence at the Sumatra SZ is likely 40 to 50 mm yr−1. To the north, the convergence rate is \u0026lt;20 mm yr-1 because of the nearly parallel relative motion at the Andaman-Nicobar section of the subduction zone. 2. The triangle shows the 2004 earthquake epicenter.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8757939/v1/373278c814717cd044f4a941.png"},{"id":102518033,"identity":"5729f24a-dbd0-4b32-83f3-43775e6e34fb","added_by":"auto","created_at":"2026-02-12 14:05:54","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":238142,"visible":true,"origin":"","legend":"\u003cp\u003eSediment sampling locations of this study. Symbols show the susceptibility of different coastal segments to different coastal hazards.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8757939/v1/dbc7b05e61724dca1e02a0d2.png"},{"id":102518027,"identity":"7c62fb52-76ea-4de1-89cf-b835b2d8e844","added_by":"auto","created_at":"2026-02-12 14:05:52","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":240047,"visible":true,"origin":"","legend":"\u003cp\u003eCriterion to categorize tsunami potential in abrupt event layers recorded in this study.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8757939/v1/9e411365311cbb098b0bf0d9.png"},{"id":102518030,"identity":"d91e8517-c1b7-4fae-acea-f1f1347bc469","added_by":"auto","created_at":"2026-02-12 14:05:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":892324,"visible":true,"origin":"","legend":"\u003cp\u003eAge correlation of tsunami events recorded in eastern and western (green shaded) Bay of Bengal. Basin-wide T\u003csub\u003eHP\u003c/sub\u003e s recorded by this study are shaded in pink. T\u003csub\u003eMP \u003c/sub\u003es \u0026nbsp;identified from previous studies but not convincingly documented by this study, are shaded in yellow. Age uncertainties of the different records are shown. Record number, author, and reference number (superscript) are given in the legend.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8757939/v1/f3577b40bb6be0a7bbcc0646.png"},{"id":102518028,"identity":"cde8a126-60ed-4b21-b808-94b9c31fac91","added_by":"auto","created_at":"2026-02-12 14:05:52","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":47499,"visible":true,"origin":"","legend":"\u003cp\u003eTime offset between tsunami events calculated based on all the reported tsunamis. Paleoseismic events, reported in 2004-rupture segment\u003csup\u003e16\u003c/sup\u003e and Mentawai segment\u003csup\u003e12\u003c/sup\u003e of the Sumatra subduction zone, and basin-wide tsunamis identified from previous studies and recorded by this study, and time intervals are shown in the graph. Shaded areas indicate the increased tsunami frequency.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8757939/v1/9b5d3146e6b223cb4d3eaf24.png"},{"id":106401862,"identity":"9484a9d3-53e0-4419-b14c-26584153a538","added_by":"auto","created_at":"2026-04-08 09:10:05","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3384528,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8757939/v1/98dd99ea-fa91-4a7f-8ef7-5a47fee37554.pdf"},{"id":102518032,"identity":"d48dbc86-7735-42bd-8fd4-f1a95031aff0","added_by":"auto","created_at":"2026-02-12 14:05:54","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":52207081,"visible":true,"origin":"","legend":"","description":"","filename":"Figuresaccessory.docx","url":"https://assets-eu.researchsquare.com/files/rs-8757939/v1/803bad626e5a6f579092b834.docx"},{"id":102746795,"identity":"289b94fb-8272-41c0-aaf2-ad8dba7b0f5d","added_by":"auto","created_at":"2026-02-16 09:01:22","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":21815,"visible":true,"origin":"","legend":"","description":"","filename":"Tablesupplement.docx","url":"https://assets-eu.researchsquare.com/files/rs-8757939/v1/62e97b8cf096f99f089ac9b3.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"A 7500-year paleotsunami record from the coastal sediment of Sri Lanka and Indian Ocean trans-basin tsunami history.","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe Indian Ocean is now recognized as a tsunami hotspot following the devastating 2004 tsunami. Earthquakes along the Sunda-Java trench can generate tsunamis that spread across the Indian Ocean in different directions, depending on the segment where the epicenter is located. Numerous paleotsunami studies were conducted after the 2004 event at various coastal plains in countries such as Indonesia\u003csup\u003e1,2\u003c/sup\u003e, Thailand\u003csup\u003e3,4,5\u003c/sup\u003e, India\u003csup\u003e6.7\u003c/sup\u003e, Sri Lanka\u003csup\u003e8\u003c/sup\u003e, Maldives\u003csup\u003e9\u003c/sup\u003e, East Africa\u003csup\u003e10\u003c/sup\u003e, and the Andaman islands\u003csup\u003e11\u003c/sup\u003e, which are situated east and west of the Bay of Bengal, have produced many records. However, a clear consensus on the linkage between specific paleotsunami events documented by these studies and paleoseismic events recognized by prior investigations \u003csup\u003e12\u0026ndash;16\u003c/sup\u003e has yet to emerge.\u003c/p\u003e \u003cp\u003eDepending on the direction of faulting at the Sunda subduction zone, tsunami intensity can vary along different coastlines, resulting in differences in paleotsunami records. Local geographic differences at the site of impact can also influence the preservation potential for paleotsunami deposits. Despite the differences due to fault direction, there are discrepancies in the timing and number of records from coastal plains facing the same trench segments\u003csup\u003e2,8,17\u0026ndash;19\u003c/sup\u003e. Such incompatibilities and gaps in records prompted us to conduct this study and to produce this comprehensive paleotsunami record from coastal sedimentary archives in Sri Lanka, correlating with regional records.\u003c/p\u003e \u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003e1.1 Structural setting\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe Sunda subduction zone (SZ), which is divided into the Andaman, Sumatra, and Java subduction zones, is part of the large convergent boundary extending from the Himalayan front to Sumba Island (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This subduction zone accommodates the northward motion of the Indian and Australian plates (formerly the Indo-Australian Plate) and produces the ~\u0026thinsp;3,200 km-long Sunda-Java trench.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWest of Sumba, the dense oceanic lithosphere of the Indo-Australian plate subducts beneath the continental Sunda shelf of the Eurasian plate. To the east, the lighter continental Australian lithosphere thrusts beneath the oceanic lithosphere\u003csup\u003e20\u003c/sup\u003e. Subduction is nearly parallel at the Andaman, oblique along Sumatra, and almost normal southwest of Java\u003csup\u003e21\u003c/sup\u003e. The oblique subduction beneath Sumatra has partitioned the convergent motion. The strike-slip component occurs along the major strike-slip Sumatra and Mentawai Faults\u003csup\u003e22\u003c/sup\u003e. The strike-slip rate of the Sumatra fault varies from \u0026sim;6mmyr\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e near the Sunda Strait\u003csup\u003e23, 24\u003c/sup\u003e to \u0026sim;25 mm yr\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e near the equator\u003csup\u003e25\u003c/sup\u003e. Convergence at the Sumatra SZ is likely 40 to 50 mm yr\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. To the north, the convergence rate is much slower. It is \u0026lt;\u0026thinsp;20 mm yr\u003csup\u003e-1\u003c/sup\u003e because of the nearly parallel relative motion at the Andaman-Nicobar section of the subduction zone (Andaman subduction zone)\u003csup\u003e20\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e1.2 Tsunami potential in Sri Lanka.\u003c/h2\u003e \u003cp\u003eSri Lanka is situated in the middle of the Indian Plate and is surrounded by a passive continental margin along its coasts. The Sunda subduction zone, situated about 1200 km to the east, is the most likely source of seismic tsunamis. The 2004 Indian Ocean Tsunami, generated by a magnitude 9.1 earthquake in the northern section of the Sunda subduction zone, is considered a modern analog for paleotsunami events in the region\u003csup\u003e26\u003c/sup\u003e. Three separate waves of this tsunami struck the southern and eastern coasts of Sri Lanka, and the tsunami runup ranged from 5 to 12 m\u003csup\u003e27\u003c/sup\u003e. Inundation distances varied from a few hundred meters to 1\u0026ndash;2 km. The 2004 Indian Ocean tsunami event significantly altered regional coastal morphology through extensive erosion. Marine sediment and sand brought by barrier overwash were deposited in back-barrier environments\u003csup\u003e28\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eHistorical records also offer tantalizing clues into past coastal flooding events in Sri Lanka and India. According to Arisen Ahubudu, a leading linguist of the Sinhala language, the famous Indian epic, the \u0026ldquo;Ramayanaya\u0026rdquo; mentions the submersion of part of Sri Lanka by two separate ocean-flooding events. Although their exact dates are unknown, they must have occurred prior to the 5th century BCE (~\u0026thinsp;2449 yrs BP) when the Ramayanaya was composed. South Indian scriptures and literature likewise suggest two possible tsunami events that damaged the eastern coast of South India around 500 AD and 900 AD (or 1450 and 1050 yrs BP\u003csup\u003e29\u003c/sup\u003e. The \u0026ldquo;Mahawamsa,\u0026rdquo; the main written historical text of Sri Lanka (written in the 6th century AD or 1450 to 1350 yrs BP), discusses a coastal flooding event on the western coast of Sri Lanka around the 2nd century BC (2149\u0026thinsp;\u0026minus;\u0026thinsp;2049 yrs BP). In more recent history, the Krakatau eruption in Indonesia on 27th August 1883 (67 yrs BP) created 1\u0026ndash;3 m waves in Sri Lanka\u003csup\u003e30\u003c/sup\u003e. In short, Sri Lanka\u0026rsquo;s setting is nearly optimally situated to record the history of tsunamis generated by exceptionally large earthquakes along the northern portion of the Indonesian subduction zone.\u003c/p\u003e \u003cp\u003eRecently developed records have identified several paleo-tsunami events in Sri Lanka. Jackson et al\u003csup\u003e8\u003c/sup\u003e. identified seven tsunami events, including one between 2417\u0026thinsp;\u0026plusmn;\u0026thinsp;152 yrs BP and 2925\u0026thinsp;\u0026plusmn;\u0026thinsp;98 yrs BP, and another six between 4064\u0026thinsp;\u0026plusmn;\u0026thinsp;128 yrs BP and 6665\u0026thinsp;\u0026plusmn;\u0026thinsp;110 yrs BP. Two paleo tsunami events around 1682\u0026thinsp;\u0026plusmn;\u0026thinsp;126 and 4829\u0026thinsp;\u0026plusmn;\u0026thinsp;362 yrs BP were reported by Abeyratne\u003csup\u003e31\u003c/sup\u003e. Dahanayaka and Kulasena\u003csup\u003e32\u003c/sup\u003e also identified two past tsunami events, but without dates.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e1.3 Suitability of Sri Lanka for paleo tsunami studies\u003c/h2\u003e \u003cp\u003eIdentification of sediment layers deposited by tsunamis is not straightforward because other abrupt events can deposit similar sand layers\u003csup\u003e33\u003c/sup\u003e. Both storm surges and coastal flooding events by rivers can deposit abrupt event layers, although the latter has no marine origin. Storm surge deposits are often difficult to distinguish from tsunami layers\u003csup\u003e34\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eBecause Sri Lanka is situated close to the southern boundary of the northern cyclone belt, cyclones are rare in the northern portion of the Bay of Bengal\u003csup\u003e35\u003c/sup\u003e. However, landfalls can be expected more frequently than tsunamis, as they occur more often than large seismic events. As a country situated in the Indian monsoon region, the coastline of Sri Lanka can experience coastal flooding from the Indian summer and winter monsoonal precipitation, particularly near river channels. Tropical cyclones and depressions can also produce significant precipitation over a short period, leading to coastal flooding.\u003c/p\u003e \u003cp\u003eHowever, Sri Lanka provides an exceptional opportunity to study tsunamis generated at the Sumatra and Andaman segments of the Sunda subduction zone for several reasons. The greatest advantage for paleo-tsunami investigations in Sri Lanka is that it has coasts facing all compass directions, which exhibit different susceptibilities to tsunamis and storms (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Most storms generated in the Bay of Bengal affect Sri Lanka on its eastern coast\u003csup\u003e35\u003c/sup\u003e. Out of 15 cyclones that made landfall on the Sri Lankan coastline during the period from 1900 to 2006, only one approached from the west. (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://www.meteo.gov.lk/\u003c/span\u003e\u003cspan address=\"http://www.meteo.gov.lk/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). In contrast, large tsunamis generated at the Sunda subduction zone can directly hit both Sri Lanka\u0026rsquo;s eastern and southern coastlines, creating significantly higher waves there than the background wave climatology (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The western coast experiences minimal impact from tsunamis generated by the Sunda subduction zone. In fact, Sri Lanka is primarily vulnerable only to tsunamis generated by large earthquakes in the western sections of the Sunda subduction zone (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), rather than in its southwestern and southern sections, because tsunamis generated in those sections tend to propagate southwest and have minimal impact due west\u003csup\u003e36\u003c/sup\u003e. In summary, the eastern coastline of Sri Lanka is susceptible to both storms and tsunamis, while the southern coast is susceptible only to tsunamis. Back-barrier environments located in the vicinity of large rivers can contain terrestrial flood deposits on both eastern and southern coasts.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"2. Methods","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Field sampling.\u003c/h2\u003e \u003cp\u003eBack-barrier marshes, lagoons, and swales in beach ridge plains are attractive sites to seek paleo-tsunami and storm surge deposits because such events will form distinctive barrier over-wash sand sheets in these otherwise low-energy, protected clay-rich environments\u003csup\u003e37, 38\u003c/sup\u003e. They also have a low potential for subsequent erosion or reworking, increasing preservation potential\u003csup\u003e39, 40\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eFourteen back-barrier environments were sampled for this study, representing about 600 km of coastline along the southwestern to northeastern coast of Sri Lanka (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Ratgama (RG) and Koggala (KG) are inland lagoons formed during the Holocene highstand and are now separated from the sea by more than 0.5 km of land. Devundara (DV), Tangalle (TG), Kumana (KU), Okanda (OK), Komari (KM), Tirukkovil (TK), and Akkaraipattu (AK) are coastal lagoons separated from the sea by barrier bars. Kirinda (KD) swamp is in the vicinity of a paleo estuary, while Panama (PN) wetland is close to a modern estuary. Sittandi (SD) and Vakarai (VK) are from swales in beach ridge plains, while the Chundikulam (CK) location is in a coastal sinkhole. These sites can potentially capture the above-discussed coastal flooding events (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e\u0026ndash; Sampling locations of cores having distinguishable abrupt sand layers. Recovered core length and actual length after removing collapsed sections (if available) and the typoe of potential event layers which could be preserved at each site are given.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCore no\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLat\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLong\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHeight from msl (cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRecovered length (cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eCore length (cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003ePotential coastal hazards\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eRatgama\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRG1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.1008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e80.1348\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e260\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e258\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTsunami\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRG2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.1131\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e80.1353\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e128\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e128\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eKoggala\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKG1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.9933\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e80.3335\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e225\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e225\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTsunami\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKG2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.0028\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e80.3302\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e186\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e186\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eDevundara\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDV1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.9332\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e80.5831\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e155\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e155\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eTsunami Monsoonal waves\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDV2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.9349\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e80.5848\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e144\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDV3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.9359\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e80.5863\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e135\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e135\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTangalle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTG1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.0380\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e80.8070\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTsunami Monsoonal waves\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTG2 (Pit)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.0364\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e80.8052\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eKirinda\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKD2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.2058\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.3218\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e348\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eTsunami\u003c/p\u003e \u003cp\u003eFlood\u003c/p\u003e \u003cp\u003eCyclone (rare)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKD3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.2082\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.3213\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e430\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e296\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKD4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.2111\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.3205\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e340\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eKumana\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKU2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.5442\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.7230\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e125\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e125\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTsunami\u003c/p\u003e \u003cp\u003eCyclone\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKU5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.5443\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.7160\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e65\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePanama\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePN2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.7703\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.8057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e304\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTsunami\u003c/p\u003e \u003cp\u003eFlood\u003c/p\u003e \u003cp\u003eCyclone\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePN3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.7675\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.8003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e274\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOkanda\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOK3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.6810\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.7629\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e283\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eTsunami\u003c/p\u003e \u003cp\u003eCyclone\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKomari\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKM1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.9590\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.8583\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e192\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eTsunami\u003c/p\u003e \u003cp\u003eCyclone\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eVakarai\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.19503\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.40033\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e314\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eTsunami\u003c/p\u003e \u003cp\u003eCyclone\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.13044\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.41866\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e203\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.12558\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.40500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e+\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e168\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSampling was conducted using a vibracorer, which connects 7.5 cm diameter core tubes, and a customized slide-hammer soil coring device, which collects sediment cores in 2.5 cm diameter, 1 m long plastic tubes. By re-entering the coring hole with 1 m long extension rods, a maximum coring depth of up to 5 m was achieved using the slide hammer device. The maximum coring depth was determined either by the depth to bedrock, the presence of impenetrable subsurface layers, or the collapse of the hole. At most sites, coring was carried out along transects running from the coastline to the inland boundary of the lagoons (Fig. Supplement 1 and 2). In the ridge and swale topography, coring was done in selected suitable swales across the beach ridge plain (Fig. Supplement 1 and 2).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Laboratory analysis\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eAll the cores were visually logged and photographed after opening. Locations with visually distinguishable layers having abrupt lower contacts were selected for further analysis (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). A combination of textural, geochemical, and physical properties helped differentiate the origins of the abrupt event layers \u003csup\u003e33, 34, 41, 42, 43\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe percentage of the sand-size fraction was measured by sieving in Ratgama and Koggala sediment cores and using laser particle size analyzers in the rest of the cores (Malvern Mastersizer (KD, PM, OK, KM, and VK cores), Beckman Coulter (TG and KU cores), or Microtrac (RG and KG cores). Standard samples were used to determine the accuracy and precision of instruments. Grain size measurements were taken at a resolution of 1\u0026ndash;3 cm, depending on the visual homogeneity of the sediment. Samples were treated with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to remove organics before sieving through a 63\u0026micro;m mesh size to calculate the sand fraction. Particle size was first measured on untreated samples using particle size analyzers. Abrupt event layers, identified visually and based on grain size plots, were then subsampled at 1 cm resolution, treated with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, and subsequently reanalyzed using the above procedure. If these sand samples had shells, they were treated with HCl before grain size analysis to yield grain size spectra based solely on the siliciclastic sediment component. Unless there was a significant difference, untreated data were used in down-core grain size plots to maintain consistency. Coarser (2000 \u0026micro;m and larger) grains (if available) were separately analyzed with a Retsch-Camsizer video particle size analyzer.\u003c/p\u003e \u003cp\u003eSample spacing for measurements was 1 cm for Magnetic susceptibility (MS) and diffuse spectral reflectance (DSR), and 2 cm for X-ray Fluorescence (XRF), due to differences in sensitivity and the sampling rates at which each instrument could operate. MS was measured using a Bartington MS2 magnetic susceptibility meter. DSR was measured using a Konica-Minolta CM-2600d visible color spectrophotometer. Relative variation of elemental composition was measured by scanning the cores with Innov-X (KD, PM, OK, KM, and VK cores) or Bruker (RG and KG cores) handheld XRF spectrometers, or an Itrax core scanner (TG and KU cores). All cores were allowed to dry for 2 days after opening before MS and XRF measurements were taken. Standard samples, sample blanks, and replicate measurements were used to evaluate the accuracy and precision of each method. (Supplement Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003eCollapsed infill lengths at core tops were determined by comparing the drive length and sediment core length, stratigraphic contacts, and by analysis of sediment properties. Any collapsed or disturbed boundary at the top of each core section was identified by measuring the texture, fabric, and color variability of the sediment at high resolution using a Konica-Minolta CM-2600d visible color spectrophotometer.\u003c/p\u003e \u003cp\u003eAges of the abrupt event layers were determined by the standard AMS radiocarbon technique and the gas accepting ion source method (GAIS)\u003csup\u003e44\u003c/sup\u003e. Intact mollusk microshells, organic matter, and bulk organics in sediment from above or below (when no distinct erosive contacts are present), the abrupt layers were selected for age dating. Selected samples were submitted to the NOSAMS laboratory of Woods Hole Oceanographic Institution, USA, following standard protocols. Radiocarbon Ages were calibrated using the IntCal20 and Marine20 curves in Calib 8.2 software\u003csup\u003e45\u003c/sup\u003e. Unless δ\u003csup\u003e13\u003c/sup\u003eC of mollusks indicates their marine origin (δ\u003csup\u003e13\u003c/sup\u003eC\u0026thinsp;\u0026gt;\u0026thinsp;0), all other mollusk ages and organic carbon ages were calibrated using the IntCal 20 curve, considering the shallow water environments from which they were retrieved. ΔR value\u0026thinsp;\u0026minus;\u0026thinsp;28 and uncertainty 69\u003csup\u003e46\u003c/sup\u003e were used for reservoir correction on samples from the south and southeast, while ΔR value 356 and uncertainty 57 \u003csup\u003e46\u003c/sup\u003e were used for eastern locations, considering the influence of Indian coastal currents. Ages of event layers were reported as younger or older than the radiocarbon age when no bracketing ages were available. When there were no dates for nearby depths, the age of the top of the event layer was estimated by extrapolating from the nearest age. Radiocarbon results are shown in Supplement Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Calibrated radiocarbon ages are reported in the text as calibrated years before present (yrs BP), and all other ages, including estimated ages, are given as years before present (yrs BP).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Distinguishing tsunami layers\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe terrestrial vs marine origin of the abrupt event layers identified visually and using grain size spectra was determined from chemical composition and magnetic susceptibility. Varimax-rotated principal component analysis of XRF data was used to identify the provenance of sediment \u003csup\u003e47, 48\u003c/sup\u003e. We refer to these as PCs here for simplicity. Ca, Sr, Br, and Cl indicate marine origin, while Ti and Zr, which are rich in Ilmenite, Rutile, and Zircon accumulations on the beach, indicate overwash sediment. Fe, Zn, and Ba indicate terrigenous sediment, while the Sr/Ba ratio indicates a marine influence\u003csup\u003e49, 50, 51\u003c/sup\u003e. Overwash sediment is typically associated with high MS because of the presence of magnetic minerals, such as magnetite and hematite, in beach sand. Abrupt peaks with values exceeding background in grain size, XRF-PC, Sr/Ba, and MS down-core plots were used to identify event layers.\u003c/p\u003e \u003cp\u003eIf the abrupt sand layers appeared to have a marine origin based on the above proxies, they were further confirmed using marine microfossils. For that, subsamples from the abrupt sand layers were wet-sieved with a 63 \u0026micro;m sieve, and foraminifera and ostracod identification was done under an optical microscope at 25X magnification for initial picking and using scanning electron microscopic (SEM) images for final identification.\u003c/p\u003e \u003cp\u003eMarine abrupt layers were correlated within cores at the same site using age and stratigraphic correlation, and between sites using age. They were first categorized as higher-potential as tsunami events (HPT), lower-potential tsunamis (LPT), or other marine events (OME) following STEP 1 of the criterion shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Secondly (STEP 2), the age correlation of events identified by this study with regional events and paleoseismic events at the Sunda trench was used to confidently categorize them into Tsunami High Potential (T\u003csub\u003eHP\u003c/sub\u003e), Tsunami Moderate Potential (T\u003csub\u003eMP\u003c/sub\u003e), Tsunami Low Potential (T\u003csub\u003eLP\u003c/sub\u003e), or Other Marine events (OM) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eAmong the 14 sites selected for coring, 31 abrupt sand layers were discovered at 10 sites. Several cores at five locations recorded sand layers laid by the 2004 tsunami. Their sedimentary and geochemical characteristics provide modern analogues to paleotsunamis. Out of the 31 abrupt layers, 29 (96%) overwash sand layers were recognized as having marine origin (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig. Supplement 3), while two (6%) had abrupt sand layers of non-marine origin. Based on correlation within the site and among the study sites (STEP 1 Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e), 23 layers (74%) were recognized as having a higher potential for tsunami origin (HPT), two (06%) were lower potential for tsunami (LPT), and four (12%) were other marine events (OME).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab2\" style=\"width: 891px;\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003e\u0026ndash; Abrupt marine overwash events recorded during this study from different back barrier environments in southern and eastern Sri Lanka. Interpretations of the events as Higher Potential as Tsunami (HPT), Lower Potential as Tsunami (LPT), and Other Marine Events (OMT) are based on the stratigraphic and age correlation within the site and the age correlation among the locations following STEP 1 of Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth style=\"width: 146px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eWestern Coast\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 212px;\" colspan=\"3\" align=\"left\"\u003e\n\u003cp\u003eSouthern Coast\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 358px;\" colspan=\"5\" align=\"left\"\u003e\n\u003cp\u003eEastern Coast\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 112px;\" rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eInterpretation\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eRatgama\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKoggala\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 10px;\" align=\"left\"\u003e\n\u003cp\u003eDevundara\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 129px;\" align=\"left\"\u003e\n\u003cp\u003eTangalle\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKirinda\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKumana\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eOkanda\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003ePanama\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKomari\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 66px;\" align=\"left\"\u003e\n\u003cp\u003eVakarai\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e2004\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRG2\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e(1 core)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e2004\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eKG1,2\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e(2 cores)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e2004\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDV1,2\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e(2 cores)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e2004\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eKU2, 5\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e(2cores)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e2004\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eKM1\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e(1 core)\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003e2004 Tsunami\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKG1\u003c/p\u003e\n\u003cp\u003e~\u0026thinsp;1000\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\n\u003cp\u003eVK1\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;996\u0026thinsp;\u0026plusmn;\u0026thinsp;57\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;1253\u0026thinsp;\u0026plusmn;\u0026thinsp;48\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eHPT\u003c/p\u003e\n\u003cp\u003e1000\u0026ndash;1200 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\n\u003cp\u003eDV1\u003c/p\u003e\n\u003cp\u003e~\u0026thinsp;2100\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKU1\u003c/p\u003e\n\u003cp\u003e~\u0026thinsp;2000\u003c/p\u003e\n\u003cp\u003e(1 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eLPT\u003c/p\u003e\n\u003cp\u003e2000\u0026ndash;2100 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKG2\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;3170\u0026thinsp;\u0026plusmn;\u0026thinsp;319\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\n\u003cp\u003eDV2\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;3077\u0026thinsp;\u0026plusmn;\u0026thinsp;308\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKU2\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;2832\u0026thinsp;\u0026plusmn;\u0026thinsp;202\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;3061\u0026thinsp;\u0026plusmn;\u0026thinsp;150\u003c/p\u003e\n\u003cp\u003e(2 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eHPT\u003c/p\u003e\n\u003cp\u003e2800\u0026ndash;3100 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKG3\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;3656\u0026thinsp;\u0026plusmn;\u0026thinsp;325\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eOME\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eRG1\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;3801\u0026thinsp;\u0026plusmn;\u0026thinsp;351\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKG4\u003c/p\u003e\n\u003cp\u003e~\u0026thinsp;4100\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\n\u003cp\u003eDV3\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;4069\u0026thinsp;\u0026plusmn;\u0026thinsp;371\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\n\u003cp\u003eTG\u003c/p\u003e\n\u003cp\u003e3954\u0026thinsp;\u0026plusmn;\u0026thinsp;122\u003c/p\u003e\n\u003cp\u003e(pit)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKD1\u003c/p\u003e\n\u003cp\u003e2510\u0026ndash;4210\u003c/p\u003e\n\u003cp\u003e(3 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eOK1\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;4290\u0026thinsp;\u0026plusmn;\u0026thinsp;118\u003c/p\u003e\n\u003cp\u003e(1 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003ePN1\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;4123\u0026thinsp;\u0026plusmn;\u0026thinsp;125\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eHPT\u003c/p\u003e\n\u003cp\u003e3800\u0026ndash;4200 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\n\u003cp\u003eDV4\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;4552\u0026thinsp;\u0026plusmn;\u0026thinsp;331\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKD2\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;4720\u0026thinsp;\u0026plusmn;\u0026thinsp;116\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003ePN2\u003c/p\u003e\n\u003cp\u003e~\u0026thinsp;4750\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eHPT\u003c/p\u003e\n\u003cp\u003e4500\u0026ndash;4700 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKD3\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;4954\u0026thinsp;\u0026plusmn;\u0026thinsp;85\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;5076\u0026thinsp;\u0026plusmn;\u0026thinsp;200\u003c/p\u003e\n\u003cp\u003e(3 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eOK2\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;5125\u0026thinsp;\u0026plusmn;\u0026thinsp;160\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;5255\u0026thinsp;\u0026plusmn;\u0026thinsp;196\u003c/p\u003e\n\u003cp\u003e(1 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKM1\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;5255\u0026thinsp;\u0026plusmn;\u0026thinsp;196\u003c/p\u003e\n\u003cp\u003e(1 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eHPT\u003c/p\u003e\n\u003cp\u003e4900\u0026ndash;5200 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e~\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\n\u003cp\u003eDV5\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;5597\u0026thinsp;\u0026plusmn;\u0026thinsp;314\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\n\u003cp\u003eTG1\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;5948\u0026thinsp;\u0026plusmn;\u0026thinsp;47\u003c/p\u003e\n\u003cp\u003e(1 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003ePN3\u003c/p\u003e\n\u003cp\u003e~\u0026thinsp;5750\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eHPT\u003c/p\u003e\n\u003cp\u003e5600\u0026ndash;5900 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\n\u003cp\u003eTG2\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;6249\u0026thinsp;\u0026plusmn;\u0026thinsp;50\u003c/p\u003e\n\u003cp\u003e(1 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eOME.\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;6249\u0026thinsp;\u0026plusmn;\u0026thinsp;50\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;6403\u0026thinsp;\u0026plusmn;\u0026thinsp;85\u003c/p\u003e\n\u003cp\u003e(1 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eOME\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;6200\u0026ndash;6400 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eKD4\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;7229\u0026thinsp;\u0026plusmn;\u0026thinsp;55\u003c/p\u003e\n\u003cp\u003e(1 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\n\u003cp\u003eVK2\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;7321\u0026thinsp;\u0026plusmn;\u0026thinsp;78\u003c/p\u003e\n\u003cp\u003e(2 cores)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eHPT\u003c/p\u003e\n\u003cp\u003e7200\u0026ndash;7300 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 10px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 129px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd style=\"width: 66px;\" align=\"left\"\u003e\n\u003cp\u003eVK3\u003c/p\u003e\n\u003cp\u003e\u0026gt;\u0026thinsp;7321\u0026thinsp;\u0026plusmn;\u0026thinsp;78\u003c/p\u003e\n\u003cp\u003e(1 core)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 112px;\" align=\"left\"\u003e\n\u003cp\u003eOME\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n\u003ch2\u003e3.1 2004 tsunami sand layers.\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eRatgama, Koggala, Devundara, Kumana, and Komari sediment cores preserve sand layers near the core top (Fig. Supplement 3). Since no other tsunami event with a high enough run-up to lay over wash sand layers has been recorded in the last 500 years, the above sand layers were considered to be the 2004 event layers. Their textural, mineralogical, chemical, physical, and micropaleontological characteristics can serve as modern analogues to help identify the past tsunami events. The 2004 sand layer in the Ratgama RG2 sediment core has high scores for XRF PC3 (Ca, Sr), indicating a marine event. The 2004 event layer in the RG 2 sediment core contains broken shell fragments, indicating that it originated from a high-energy coastal environment and/or was transported by the high-energy tsunami flow (Figure supplement 4-A). At Koggala, the 2004 sand layer in both the KG1 and KG2 cores has high scores for XRF PC4 (Ti, Zr), indicating beach overwashing. In Devundara, both DV1 and DV2 cores exhibit two peaks in grain size plots, indicating that deposition associated with the two major waves of the 2004 tsunami reached the area. These sand layers show high scores for XRF PC1 (Ca, Sr, Zr). In both Kumana KU2 and KU5 sediment cores, the 2004 sand layer has high scores for XRF PC1 (Ti, Zr) and XRF PC3 (Ca, Sr), evidencing a marine overwash event. In the Komari KM1 core, this abrupt sand layer has high MS.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2 Paleotsunami events from Sri Lanka.\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eThe 29 abrupt sand layers of marine origin belong to seven HPT, one LPT, and four OME events, based on intra- and inter-study site correlations.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eA. Events with higher potential for a tsunami (HPT)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ei. ~\u0026thinsp;1100 yrs BP (Between 1000\u0026ndash;1200 yrs BP)\u003c/em\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eKoggala (2 cores) and Vakarai (2 cores) have evidence for a\u0026thinsp;~\u0026thinsp;1000 yrs BP tsunami event, recorded on both the eastern\u003csup\u003e1, 52\u003c/sup\u003e and western sides\u003csup\u003e19,53\u003c/sup\u003e of the Bay of Bengal (Tables\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). In the Koggala KG-1 layer, the higher XRF PC4 (Ti, Zr) provides evidence for its origin from beach/barrier overwash. Abundant microfossils, well-rounded quartz grains, and numerous ilmenite, garnet, and rutile grains also support the marine overwash origin of the event (Fig. Supplement 3B). In Vakarai, the VK-1 abrupt sand layer has high Ca and Ti, indicating an overwash event of marine origin (Fig. Supplement 3J). Both Koggala and Vakarai cores show multiple peaks in the event layers (KG-1 and VK-1), evidencing the deposition from multiple waves (Fig. Supplement 3B and 3J). Since these event layers are found in both the south and east, it is unlikely to be any marine event other than a tsunami (T\u003csub\u003eHP)\u003c/sub\u003e. The event age was estimated from the sedimentation rate of the KG2 sediment core and the bracketing age of the VK1 layer in the V13 core. They show that this event occurred between 996\u0026thinsp;\u0026plusmn;\u0026thinsp;57 and 1253\u0026thinsp;\u0026plusmn;\u0026thinsp;48 yrs BP (~\u0026thinsp;1000\u0026ndash;1200 yrs BP) (Fig. Supplement 3J).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003e\u0026ndash; Chronological correlation of HPT events of this study (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) with local and regional tsunami events recorded by previous studies. The approximate date used to identify the event in the text is in bold letters. Final designation for the event is given following the criteria given in STEP 2 of Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eAge of the HPT\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCorrelating peleotsunami events from previous studies in Sri Lanka\u003c/p\u003e\n\u003cp\u003e(yrs BP)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCorrelating peleotsunami events from the western Bay of Bengal\u003c/p\u003e\n\u003cp\u003e(yrs BP)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCorrelating peleotsunami events from the eastern Bay of Bengal\u003c/p\u003e\n\u003cp\u003e(yrs BP)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eFinal Designation\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e~\u0026thinsp;\u003cstrong\u003e1100 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e1000\u0026ndash;1200 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e~\u0026thinsp;1000\u003csup\u003e10, 17,53\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e1225\u0026thinsp;\u0026plusmn;\u0026thinsp;35 \u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e950\u0026thinsp;\u0026plusmn;\u0026thinsp;50\u003csup\u003e65\u003c/sup\u003e 1045\u0026thinsp;\u0026plusmn;\u0026thinsp;135\u003csup\u003e67\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;1065\u0026thinsp;\u0026plusmn;\u0026thinsp;105\u003csup\u003e1\u003c/sup\u003e ~1000\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e1220\u0026thinsp;\u0026plusmn;\u0026thinsp;70\u003csup\u003e60\u003c/sup\u003e 1265\u0026thinsp;\u0026plusmn;\u0026thinsp;85\u003csup\u003e59\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e1200\u0026thinsp;\u0026plusmn;\u0026thinsp;210\u003csup\u003e52\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eHP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e~\u0026thinsp;3000 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e2800\u0026ndash;3100 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2700\u0026thinsp;\u0026plusmn;\u0026thinsp;321\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e3170\u0026thinsp;\u0026plusmn;\u0026thinsp;320\u003csup\u003e54\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2900\u0026thinsp;\u0026plusmn;\u0026thinsp;480\u003csup\u003e17\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2865\u0026thinsp;\u0026plusmn;\u0026thinsp;50\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e3018\u0026thinsp;\u0026plusmn;\u0026thinsp;123\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eHP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e~\u0026thinsp;4000 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e3800\u0026ndash;4200 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4200\u0026thinsp;\u0026plusmn;\u0026thinsp;257\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4110\u0026thinsp;\u0026plusmn;\u0026thinsp;220\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4450\u0026thinsp;\u0026plusmn;\u0026thinsp;500\u003csup\u003e63\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e4350\u0026thinsp;\u0026plusmn;\u0026thinsp;620\u003csup\u003e63\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eHP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e~\u0026thinsp;4600 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e4500\u0026ndash;4700 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4500\u0026thinsp;\u0026plusmn;\u0026thinsp;279\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e4829\u0026thinsp;\u0026plusmn;\u0026thinsp;362\u003csup\u003e15\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4450\u0026thinsp;\u0026plusmn;\u0026thinsp;500\u003csup\u003e63\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e4350\u0026thinsp;\u0026plusmn;\u0026thinsp;620\u003csup\u003e63\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e4712\u0026thinsp;\u0026plusmn;\u0026thinsp;126\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eHP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e~\u0026thinsp;5100 yrs BP\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003e4900\u0026ndash;5200 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5000\u0026thinsp;\u0026plusmn;\u0026thinsp;330\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e4829\u0026thinsp;\u0026plusmn;\u0026thinsp;362\u003csup\u003e15\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eMP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e~\u0026thinsp;5700 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e5600\u0026ndash;5900 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5620\u0026thinsp;\u0026plusmn;\u0026thinsp;140\u003csup\u003e17\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5719\u0026thinsp;\u0026plusmn;\u0026thinsp;141\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e5625\u0026thinsp;\u0026plusmn;\u0026thinsp;145\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e5607\u0026thinsp;\u0026plusmn;\u0026thinsp;216\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eHP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e~\u0026thinsp;7300 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e7200\u0026ndash;7300 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7429\u0026thinsp;\u0026plusmn;\u0026thinsp;100\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eHP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eii. ~\u0026thinsp;3000 yrs BP event (Between 2800\u0026ndash;3100 yrs BP)\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAbrupt sand layers belonging to this event are found in multiple sediment cores at Koggala (2 cores) and Devundara (2 cores) (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). In Koggala KG-2, an abrupt sand layer has higher scores for XRF PC4 (Ti, Zr), while DV-1 layer in Devundara has higher scores for XRF PC 1 (Ca, Sr, Zr), indicating an overwash event of a marine origin (Fig. Supplement 3B and 3C). Presence of broken shell fragments and marine foraminifera tests and abundant garnet, ilmenite, and rutile grains confirms the marine overwash origin of the layer. Two peaks in some cores indicate deposition from two strong waves. The distribution of these event layers across a 50 km area along the southern beach suggests three possible origins: i. A rare storm travels along the south coastline, ii. Monsoon overwash events, or iii. a tsunami. Age dating shows that this event occurred immediately after \u0026gt;\u0026thinsp;3170\u0026thinsp;\u0026plusmn;\u0026thinsp;319 yrs BP (KG-2), \u0026lt;\u0026thinsp;3077\u0026thinsp;\u0026plusmn;\u0026thinsp;308 yrs BP (DV-1), or between 2832\u0026thinsp;\u0026plusmn;\u0026thinsp;202\u003c/p\u003e\n\u003cp\u003eand 3061\u0026thinsp;\u0026plusmn;\u0026thinsp;150yrs BP (KU-2), depending on the age constraints from three cores (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Therefore, this event can be considered to have occurred between ~\u0026thinsp;2800\u0026ndash;3100 yrs BP. Jackson et al.\u003csup\u003e8\u003c/sup\u003e (2417\u0026thinsp;\u0026plusmn;\u0026thinsp;152\u0026ndash;2925\u0026thinsp;\u0026plusmn;\u0026thinsp;98 yrs BP) and Premasiri et al.\u003csup\u003e54\u003c/sup\u003e, (3170\u0026thinsp;\u0026plusmn;\u0026thinsp;320 yrs BP) have reported tsunami events from Hambantota Sri Lanka, which is about 30 km from Koggala, correlating to this event within age uncertainties, while Rubin et al.\u003csup\u003e2\u003c/sup\u003e (2815\u0026ndash;2916 yrs BP) and Sanwal et al.\u003csup\u003e11\u003c/sup\u003e (2899\u0026ndash;3145 yrs BP) have identified age correlating tsunami events from Aceh Indonesia, and the Andaman islands respectively (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Therefore, this event is considered a T\u003csub\u003eHP\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eiii. ~\u0026thinsp;4000 yrs BP event (Between 3800\u0026ndash;4200 yrs BP)\u003c/em\u003e\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eA chronologically correlated event is recorded in multiple locations along the southern and eastern coasts, dating to between 3800 and 4300 yrs BP. The Ratgama (2 cores), Koggala (2 cores), Tangalle (1 pit), Kirinda (3 cores), Okanda (1 core), and Panama (2 cores) have evidence for an abrupt sedimentation event. Ratgama, RG-1 layer has high scores for XRF PC3 (Ca, Sr) and XRF PC4 (Ti, Zr), while Koggala KG-1 layer has high scores for XRF PC4 (Ti, Zr) (Fig. Supplement 3A and 3B). Kirinda, KD-1 layer, is a yellow-colored sand layer with an erosive basal contact and has higher MS, Sr/Ba, and XRF PC1 (Sr, Zr, Ca) (Fig. Supplement 3E). However, this powerful erosive event might have eroded the hinterland and added yellowish terrestrial sand to the layer. Okanda OK 1 layer has higher scores for XRF PC1 (Ca, Sr, and K), and Panama PN 1 layer has higher XRF PC2 (Ca and Sr) and Sr/Ba (Fig. Supplement 3G and 3H). Therefore, chemical properties and MS indicate that this event is an overwash event having a marine origin. The RG-1 layer has broken shell fragments, indicating transport by high-energy flow (Figure supplement 4-B). RG-1 and PN-1 layers show two peaks in some cores, indicating the deposition by two separate waves. The erosive basal contacts of the layers provide evidence of a powerful tsunami event. Radiocarbon ages above and below this layer show that this event occurred between 3801\u0026thinsp;\u0026plusmn;\u0026thinsp;351 and 4290\u0026thinsp;\u0026plusmn;\u0026thinsp;118 yrs BP (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Correlating paleotsunami events have been reported from Sri Lanka\u003csup\u003e8\u003c/sup\u003e, the Maldives\u003csup\u003e9\u003c/sup\u003e, and Thailand\u003csup\u003e55\u003c/sup\u003e (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Therefore, this event can be considered as a powerful T\u003csub\u003eHP\u003c/sub\u003e that occurred around 4000 yrs ago.\u003c/p\u003e\n\u003cp\u003eiv. ~\u0026thinsp;\u003cem\u003e4600 yrs BP event (Between 4500\u0026ndash;4700 yrs BP)\u003c/em\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eAnother chronologically correlated event is recorded in Devundara (2 cores), Kirinda (2 cores), and Panama (1 core) sediment cores between 4500 and 4700 yrs BP. Both Devundara DV-2 and Kirinda KD-2 layers have higher scores for PCs correlating with Ca and Sr, indicating a marine origin (Fig. Supplement 3C and 3E). The Panama PN-2 layer is rich in broken shells, indicating deposition by a high-energy event. DV-2 layer in Devundara (DV2 core) and PN-2 layer in Panama PN2 and PN3 cores show doublet peaks, indicating deposition by two separate waves (Fig. Supplement 3C and 3H). This event chronologically correlates with the tsunami events (4331\u0026thinsp;\u0026plusmn;\u0026thinsp;126\u0026ndash;4583\u0026thinsp;\u0026plusmn;\u0026thinsp;196 yrs BP) reported by Jackson et al.\u003csup\u003e8\u003c/sup\u003e from Hambantota, Sri Lanka (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) and Malik et al. \u003csup\u003e63\u003c/sup\u003e (4450\u0026thinsp;\u0026plusmn;\u0026thinsp;500, 4350\u0026thinsp;\u0026plusmn;\u0026thinsp;620 yrs BP) and Sanwal et al.\u003csup\u003e11\u003c/sup\u003e(4837\u0026thinsp;\u0026plusmn;\u0026thinsp;126 yrs BP) from the Andaman Islands. Therefore, this event can be considered a T\u003csub\u003eHP\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ev. ~\u0026thinsp;5100 yrs BP event (Between 5000\u0026ndash;5300 yrs BP)\u003c/em\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eThe Kirinda (3 cores), Okanda (1 core), and Komari (1 core) sites provide evidence for a tsunami event that occurred around 5100 yrs ago. Higher Sr/Ba ratio and scores for XRF PC2 (Sr, Zr, Ca) in Kirinda core, higher Sr/Ba and scores for XRF PC 1 (Ca, Sr, K) in Okanda OK-2, and higher MS in KM-1 layer in Komari provide evidence for an overwash event of a marine origin (Fig. Supplement 3E, 3G and 3I). In the Kirinda KD3 sediment core, KD-3 layer contains coarse mica flakes, indicating deposition of material from the eroded hinterland. In KD2 core KD-3 layer contains benthic foraminiferal tests of \u003cem\u003eTriloculina\u003c/em\u003e spp and \u003cem\u003ePseudotriloculina subgranulata\u003c/em\u003e and shallow marine diatom \u003cem\u003eCalistocythere sp.\u003c/em\u003e (Fig Supplement 4 C). These layers have been deposited between 4954\u0026thinsp;\u0026plusmn;\u0026thinsp;85 and 5255\u0026thinsp;\u0026plusmn;\u0026thinsp;196 yrs BP (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). The occurrence of these chronologically correlating marine overwash sand layers in both the east and south is strong evidence for their tsunamigenic origin. Correlating tsunami events has been recorded between 4764\u0026thinsp;\u0026plusmn;\u0026thinsp;140 and 5152\u0026thinsp;\u0026plusmn;\u0026thinsp;178 yrs BP from Hambantota\u003csup\u003e8\u003c/sup\u003e, and 4829\u0026thinsp;\u0026plusmn;\u0026thinsp;362 yrs BP from Kirinda\u003csup\u003e31\u003c/sup\u003e (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). However, because no corresponding event has been recorded outside Sri Lanka, this event is classified as a T\u003csub\u003eMP\u003c/sub\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cem\u003e~\u0026thinsp;5700 yrs BP event. (Between 5600\u0026ndash;5900 yrs BP)\u003c/em\u003e\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ol\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eThe Devundara (2 cores), Tangalle (1 core), and Panama (2 cores) sites carry evidence for another abrupt depositional event. The Devundara DV-3 layer exhibits higher scores for XRF PC1 (Ca, Sr, Zr), whereas the TG-2 layer of the Tangalle core displays higher scores for XRF PC2 (Ca, Sr, K) (Fig. Supplements 3C and 3D). This indicates a marine origin of these sand layers. The Panama PN3 layer also exhibits higher Sr/Ba ratios and scores for XRF PC2 (Ca, Sr), indicating a marine origin (Fig. Supplement 3H). Broken shells and coarse mica flakes in the PN-2 layer in the PN2 and PN3 cores are strong evidence for a high-energy erosive event. Radiocarbon dates show that this event occurred around 5700 yrs BP (5597\u0026thinsp;\u0026plusmn;\u0026thinsp;314\u0026ndash;5948\u0026thinsp;\u0026plusmn;\u0026thinsp;47 yrs BP) (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Rubin et al.\u003csup\u003e2\u003c/sup\u003e and Sanwal et al.\u003csup\u003e11\u003c/sup\u003e reported correlating tsunami events between 5578 and 5866 yrs BP from Aceh, Indonesia, and the Andaman Islands, respectively (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Therefore, this abrupt marine flooding event is considered a tsunami (T\u003csub\u003eHP)\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003evi. ~\u0026thinsp;7300 yrs BP event (Between 7200\u0026ndash;7300 yrs BP)\u003c/em\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eBoth Kirinda and Vakarai have evidence for an abrupt event layer deposited around 7300 yrs BP. At site Kirinda, the KD-4 layer has a high Sr/Ba ratio, while the VK\u0026ndash;2 layer of Kirinda cores has high Sr/Ba as well as XRF PC1 (Ca, Ti), indicating a marine origin (Fig. Supplement 3E and 3J). V12-3 layer also has benthic foraminifera tests of \u003cem\u003eTriloculina\u003c/em\u003e and \u003cem\u003eQuinqueloculina\u003c/em\u003e species, confirming the marine origin of the event (Fig. Supplement 4-D). Radiocarbon dates indicate that this event occurred between 7229\u0026thinsp;\u0026plusmn;\u0026thinsp;55 and 7321\u0026thinsp;\u0026plusmn;\u0026thinsp;78 yrs BP (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Rubin et al\u003csup\u003e2\u003c/sup\u003e also reported a tsunami event that occurred between 7324\u0026ndash;7529 yrs BP in Aceh, Indonesia (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Given the occurrence of this abrupt marine layer at widely separated locations in southern and eastern Sri Lanka, and its age correlation with the Indonesian tsunami event, it is reasonably identified as a tsunamigenic layer (T\u003csub\u003eHP\u003c/sub\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eB. Events with lower potential for a tsunami (LPT)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ei. ~\u0026thinsp;2100 yrs BP event\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eA marine over-wash event was recorded around ~\u0026thinsp;2100 yrs BP (Devundara \u0026ndash; 2 cores and Kumana 1-core). It correlates with the ~\u0026thinsp;2000 yrs BP\u003csup\u003e56\u003c/sup\u003e tsunami sand layer recorded from eastern Sri Lanka, the ~\u0026thinsp;2190\u0026thinsp;\u0026plusmn;\u0026thinsp;150\u003csup\u003e9\u003c/sup\u003e tsunami event reported from the Maldives, and the 2100\u0026thinsp;\u0026plusmn;\u0026thinsp;260\u003csup\u003e52\u003c/sup\u003e ~2200\u003csup\u003e59\u003c/sup\u003e tsunami events recorded from Thailand, within age uncertainties (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Although this event's age correlates with other local and regional tsunami events reported in previous studies, it is classified as a tsunami with moderate potential (TMP) because the abrupt layers recorded in this study have only estimated ages at both locations.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab4\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003e\u0026ndash; Chronological correlation of LPT events of this study (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) with local and regional tsunami events recorded by previous studies. The approximate date used to identify the event in the text is in bold letters. The final designation for the event is given following the criteria given in STEP 2 of Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eAge of the LPT\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eLocation\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCorrelating peleotsunami events from previous studies in Sri Lanka\u003c/p\u003e\n\u003cp\u003e(yrs BP)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCorrelating peleotsunami events from the western Bay of Bengal\u003c/p\u003e\n\u003cp\u003e(yrs BP)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCorrelating peleotsunami events from the eastern Bay of Bengal\u003c/p\u003e\n\u003cp\u003e(yrs BP)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eFinal Designation\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e~\u0026thinsp;\u003cstrong\u003e2100 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e2000\u0026ndash;2100 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eDevundara, Kumana\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2100\u0026thinsp;\u0026plusmn;\u0026thinsp;260\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e2000\u003csup\u003e56\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e~\u0026thinsp;2190\u0026thinsp;\u0026plusmn;\u0026thinsp;150\u003csup\u003e17\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2200\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e2312\u0026thinsp;\u0026plusmn;\u0026thinsp;302\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eMP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\u003cstrong\u003eC. Other marine events (OME)\u003c/strong\u003e\u003c/div\u003e\n\u003cp\u003eThree other marine overwash events were recorded at ~\u0026thinsp;3600 yrs BP (Koggala- 2 cores), \u0026lt;\u0026thinsp;6250 yrs BP (Tangalle \u0026ndash; 1 core), 6200\u0026ndash;6400 yrs BP (Tangalle \u0026ndash; 1 core), and \u0026gt;\u0026thinsp;7321\u0026thinsp;\u0026plusmn;\u0026thinsp;78 (Vakarai \u0026ndash; 1 core) (Tables\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eThe ~\u0026thinsp;3600 yrs BP event correlates with 3710\u0026thinsp;\u0026plusmn;\u0026thinsp;20 yrs BP potential tsunami event in India\u003csup\u003e53\u003c/sup\u003e and 3591\u0026thinsp;\u0026plusmn;\u0026thinsp;128 yrs BP tsunami recorded in the Andaman Islands\u003csup\u003e68\u003c/sup\u003e (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Based on our criteria for recognizing tsunami layers (STEP 2, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e), this event was designated as a T\u003csub\u003eLP\u003c/sub\u003e co due to its limited occurrence and lack of bracketing \u003csup\u003e14\u003c/sup\u003eC ages.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab5\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003e\u0026ndash; Chronological correlation of Other Marine Events (OME) of this study (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) with local and regional tsunami events recorded by previous studies. The approximate date used to identify the event in the text is in bold letters. The final designation for the event is given following the criteria given in the STEP 2 of Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eAge of the OME\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eLocation\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCorrelating peleotsunami events from previous studies in Sri Lanka\u003c/p\u003e\n\u003cp\u003e(yrs BP)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCorrelating peleotsunami events from the western Bay of Bengal\u003c/p\u003e\n\u003cp\u003e(yrs BP)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCorrelating peleotsunami events from the eastern Bay of Bengal\u003c/p\u003e\n\u003cp\u003e(yrs BP)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eFinal Designation\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026gt;\u0026thinsp;3656 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eKoggala\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e~\u0026thinsp;3700\u003csup\u003e53\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3591\u0026thinsp;\u0026plusmn;\u0026thinsp;128\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eLP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026lt;\u0026thinsp;6249\u0026thinsp;\u0026plusmn;\u0026thinsp;50 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTangalle\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e~\u0026thinsp;6200\u0026thinsp;\u0026plusmn;\u0026thinsp;117\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6497\u0026thinsp;\u0026plusmn;\u0026thinsp;417\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e6268\u0026thinsp;\u0026plusmn;\u0026thinsp;411\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e6357\u0026thinsp;\u0026plusmn;\u0026thinsp;116\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eLP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e~6300 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e6200\u0026ndash;6400 yrs BP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTangalle\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e~\u0026thinsp;6400\u0026thinsp;\u0026plusmn;\u0026thinsp;173\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;6480\u0026thinsp;\u0026plusmn;\u0026thinsp;60\u003csup\u003e68\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6497\u0026thinsp;\u0026plusmn;\u0026thinsp;417\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e6268\u0026thinsp;\u0026plusmn;\u0026thinsp;411\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e6357\u0026thinsp;\u0026plusmn;\u0026thinsp;116\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003eMP\u003c/sub\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026gt;\u0026thinsp;7320 yrs BP.\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eVakarai\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eN/A\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eOM\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eBoth 6200\u0026ndash;6400 yrs BP and \u0026lt;\u0026thinsp;6250 yrs BP events chronologically correlated with ~\u0026thinsp;6200 and 6400 yrs BP layers recorded from Hambantota, Sri Lanka\u003csup\u003e8\u003c/sup\u003e, 6357\u0026thinsp;\u0026plusmn;\u0026thinsp;116 tsunami event at the Andaman Islands\u003csup\u003e11\u003c/sup\u003e, as well as the 6080\u0026ndash;6915 yrs BP or 5857\u0026ndash;6680 yrs BP old event layers from Aceh, Indonesia\u003csup\u003e2\u003c/sup\u003e (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). The 6200\u0026ndash;6400 yrs BP event also correlates with the \u0026lt;\u0026thinsp;6480\u0026thinsp;\u0026plusmn;\u0026thinsp;60 yrs BP potential tsunami in Rameswaram, India\u003csup\u003e67\u003c/sup\u003e. Since the 6200\u0026ndash;6400 yrs BP event has bracketing ages and it correlates with events reported from both eastern and western BB, it was designated as T\u003csub\u003eMP\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eThe event\u0026thinsp;\u0026lt;\u0026thinsp;6250 yrs BP was designated as T\u003csub\u003eLP\u003c/sub\u003e because it lacks bracketing ages eventhough it correlates with above same events as 6200\u0026ndash;6400 yrs BP. It does not rule out the possibility of having two events withing about 200 yrs interval.\u003c/p\u003e\n\u003cp\u003eThe event\u0026thinsp;\u0026gt;\u0026thinsp;7321\u0026thinsp;\u0026plusmn;\u0026thinsp;78 was designated OM, such as a storm surge, because there are no correlating events and bracketing ages.\u003c/p\u003e\n\u003cp\u003eAs discussed above, the abrupt marine event layers of different tsunami potential (HPT\u0026thinsp;\u0026minus;\u0026thinsp;7, LPT\u0026thinsp;\u0026minus;\u0026thinsp;1, and OME\u0026thinsp;\u0026minus;\u0026thinsp;4) are designated as T\u003csub\u003eHP\u003c/sub\u003e (6), T\u003csub\u003eMP\u003c/sub\u003e (3), T\u003csub\u003eLP\u003c/sub\u003e (2), and OM (1) based on the chronological correlation with the tsunami events reported from both western and eastern BB by the 24 previous studies as described in the STEP 2 Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n\u003ch2\u003e3.3 Regional tsunami record and tsunami frequency.\u003c/h2\u003e\n\u003cp\u003eWhen analyzing regional paleotsunami records from western and eastern Bay of Bengal (BB) sites facing Andaman and Sumatra (SZ), where the 2004 tsunami occurred, we can identify 9 events older than the 2004 event that occurred during the last 7500 years and were reported at multiple locations across the bay (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). Most studies have been conducted on the eastern side of the bay, and most records date back 3000 years. So, younger events are reported at multiple locations across the BB, whereas older events are reported at only a few locations (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). It is obvious that not all the tsunamis reported in the eastern BB are recorded at western BB sites because many events are not powerful enough to cross the BB (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). So, those recorded on both sides of the BB are likely large, 2004-type trans-basin events.\u003c/p\u003e\n\u003cp\u003eThe above results show that four T\u003csub\u003eHP\u003c/sub\u003e and T\u003csub\u003eMP\u003c/sub\u003e tsunami events (~\u0026thinsp;3000, ~\u0026thinsp;2100, ~1000 yrs BP, and the 2004 event) have been recorded since 4000 yrs BP. All these event layers were recorded from coring sites situated below sea level and from the beach ridge plain at Vakarai, which developed within the last 2000 yrs. At the end of the mid-Holocene highstand (MHH), sea level began to stabilize around 4000 yrs BP\u003csup\u003e57\u003c/sup\u003e. Coastal accommodation space was subsequently filled, initiating erosion of the coastal plain. Therefore, none of the cores extracted above sea level contain younger tsunami layers, including the 2004 event, possibly due to erosion. Providing further evidence of coastal plain erosion, Moore et al.\u003csup\u003e26\u003c/sup\u003e observed that the 2004 event layer was absent at many sites along the southeastern coast of Sri Lanka, just three years after the tsunami. Ages older than 4000 years, close to the core tops of the onshore Kirinda, Okanda, and Kumana cores, also provide evidence for erosion due to a lack of accommodation space. Sediment ages in Vakarai cores show that the Vakarai beach ridge plain developed after sea level stabilization. Therefore, the preservation of only three marine overwash sand layers may be mainly due to limited accommodation space.\u003c/p\u003e\n\u003cp\u003eThe youngest trans-basin potential tsunami event reported across multiple locations in eastern and western BB is around 600 years BP. However, it is not recorded in any study except one in Sri Lanka\u003csup\u003e56\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Around 1000 yrs BP, a tsunami event is reported across multiple sites (11) in both the eastern and western BB, including this study. The T\u003csub\u003eMP\u003c/sub\u003e ~2100 years BP event has been reported at three sites in the western BB, including the Maldives. The chronologically correlating sand layer reported at the Devundara and Kumana sites in Sri Lanka may represent this event. The historical chronicle, the \u0026ldquo;Mahavamsa\u0026rdquo;, reports a marine flooding event in Sri Lanka between 2155\u0026ndash;2111 yrs BP (205 BC\u0026thinsp;\u0026minus;\u0026thinsp;161 BC). This could refer to the potential 2100 yrs BP tsunami. The ~\u0026thinsp;3000 yrs BP tsunami event reported in this study is coeval with events recorded in the Maldives (2420\u0026ndash;3380 yrs BP) \u003csup\u003e9\u003c/sup\u003e and Sri Lanka (3170\u0026thinsp;\u0026plusmn;\u0026thinsp;320 yrs BP)\u003csup\u003e54\u003c/sup\u003e on the western BB and theAndaman Islands (3018\u0026thinsp;\u0026minus;\u0026thinsp;2899 yrs BP) and Aceh, Indonesia (3270 and 3353 yrs BP) on the eastern BB within age uncertainties (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Correlating paleotsunami events for 4000 and 4600 yrs BP events, were reported only from the Andaman Islands and western BB locations. A gap in tsunami events is reported between 5500\u0026thinsp;\u0026minus;\u0026thinsp;3400 yrs BP in Aceh, Indonesia\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e and a gap in seismic events along the 2004 region of the Sumatra-Andaman subduction zone\u003csup\u003e16\u003c/sup\u003e. This may indicate that 4000 and 4600 yrs BP events might have originated at the Andaman-Nicobar section of the subduction zone. However, due to the lack of any record longer than 2000 years BP in both Sumatra and Thailand, a firm conclusion regarding the origin of these events is not possible. The 5100 yrs BP T\u003csub\u003eMP\u003c/sub\u003e recorded only in Sri Lanka may have originated in the southern part of the Sumatra SZ. Hydrodynamic simulations in the major seismic zones around the Indian Ocean basin by Okal and Synolakis\u003csup\u003e58\u003c/sup\u003e show that significant tsunamis generated by ruptures on the south Sumatra segment of the Sumatra SZ can also reach Sri Lanka.\u003c/p\u003e\n\u003cp\u003eTime intervals between reported regionally correlated tsunami events were calculated using the midpoint of each event. It shows that three events have occurred over the last 1000 years, with an average interval of 500\u0026ndash;700 years between events. Similarly, four events have occurred between 4000 and 6000 yrs BP, making the interval between 500 and 700 yrs. During 1000\u0026ndash;4000 yrs BP and 6000\u0026ndash;7500 yrs BP, the interval between events is generally 900\u0026thinsp;\u0026minus;\u0026thinsp;100 yrs (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). Using the paleoseismic record reconstructed for the 2004 earthquake region by Patton et al.\u003csup\u003e16\u003c/sup\u003e, based on seismogenic turbidites, a seismic event that correlates within its age uncertainties with each of the above tsunami events can be identified. This paleoseismic record shows increased seismic activity during the period 600\u0026ndash;2500 and 4500\u0026ndash;5200 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). So, the higher tsunami frequency period overlaps with the higher earthquake frequency period. Increased tsunami frequency in the western BB is a rcould result from increased seismicity in the northern Sunda SZ.\u003c/p\u003e\n\u003cp\u003eHowever, increased activity in the Andaman-Nicobar sections and the southern Sumatra segment may also have contributed to the higher number of tsunamis in some periods.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study fulfills the long-standing need for a robust trans-basin paleo-tsunami record for the Indian Ocean, combining a 7000-year record constructed for Sri Lanka by studying 13 back-barrier environments together with other regional records from both the eastern and western Bay of Bengal. This study identified six abrupt marine coastal flooding events that are stratigraphically and/or chronologically correlated between sites within the same back-barrier environments. They chronologically correlate with multiple distal locations across south and eastern Sri Lanka, as well as with other regional records from the western and eastern Bay of Bengal. Due to their regional occurrence, they are identified as trans-basin tsunamis with high potential (T\u003csub\u003eHP\u003c/sub\u003e). In addition, abrupt sand layers indicative of three tsunami events with medium potential (T\u003csub\u003eMP\u003c/sub\u003e) and two events with low potential (T\u003csub\u003eLP\u003c/sub\u003e) were recorded. Paleoseismic events reported at the 2004 rupture area of the Sunda SZ correlate with all the reported tsunami events except the 4000 and 4600 T\u003csub\u003eHP\u003c/sub\u003e events discussed in this study.\u003c/p\u003e \u003cp\u003eWhen considering the 2004 events and ~\u0026thinsp;600 yrs BP event reported in both western and eastern BB, except Sri Lanka, the age interval between events is 500\u0026ndash;700 yrs during the last 1000 yrs, and 4000\u0026ndash;6000 yrs BP. During other periods, the age interval between events ranges from 900 to 1000 years. Increased seismicity in the northern and southern Sumatra SZ or the southern Andaman SZ could have contributed to the increased frequency observed during the above periods.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eP.N.R, J.D.O, J.P.D, T.U.T.W , A.L.M- Manuscript Preparation and editingP.N.R, L.H.M.T.M.B.T , R.P.S.K.R, K.K, D.T.W - Field workP.N.R, L.H.M.T.M.B.T , R.P.S.K.R, K.K, D.T.W , T.U.T.W. - Lab workP.N.R, J.D.O, A.L.M. J.P.D. - Supervision and funding\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors extend their sincere gratitude to the Woods Hole Oceanographic Institution, the Geological Society of America, the International Association of Sedimentologists, and the National Science Foundation for providing funding. The geological Survey and Mines Bureau of Sri Lanka provides logistic support for field work.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAge data are included in the Table supplement file. All the generated raw data is available upon request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMonecke, K. \u003cem\u003eet al.\u003c/em\u003e A 1,000-year sediment record of tsunami recurrence in northern Sumatra. Nature \u003cstrong\u003e455\u003c/strong\u003e, 1232\u0026ndash;1234 (2008).\u003c/li\u003e\n\u003cli\u003eRubin, C. M. \u003cem\u003eet al.\u003c/em\u003e Highly variable recurrence of tsunamis in the 7,400 years before the 2004 Indian Ocean tsunami. Nat. Commun. \u003cstrong\u003e8\u003c/strong\u003e, 16019 (2017).\u003c/li\u003e\n\u003cli\u003eFujino, S. Stratigraphic evidence for pre-2004 tsunamis in southwestern Thailand. Mar. 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Potential predecessors of the 2004 Indian Ocean tsunami\u0026mdash;sedimentary evidence of extreme wave events at Ban Bang Sak, SW Thailand. \u003cem\u003eSediment. Geol.\u003c/em\u003e\u003cstrong\u003e239\u003c/strong\u003e, 146\u0026ndash;161 (2011).\u003c/li\u003e\n\u003cli\u003eJohnson, F. C., Malik, J. N., Kathal, P. K. \u0026amp; Khan, A. Foraminiferal assemblages of inferred onshore paleotsunami deposits in southwestern Andaman Islands, India. \u003cem\u003eJ. Geol. Soc. India\u003c/em\u003e\u003cstrong\u003e97\u003c/strong\u003e, 579\u0026ndash;595 (2021).\u003c/li\u003e\n\u003cli\u003eBhat, G. R., Balaji, S., Yousuf, M. \u0026amp; Bali, B. S. Primary on-fault paleoseismic evidence from trench investigation along the Bathubasti fault, South Andaman, India. \u003cem\u003eJ. 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Age estimates of coastal terraces in the Andaman and Nicobar Islands and their tectonic implications. \u003cem\u003eTectonophysics\u003c/em\u003e\u003cstrong\u003e455\u003c/strong\u003e, 53\u0026ndash;60 (2008).\u003c/li\u003e\n\u003cli\u003eRajendran, C. P., Rajendran, K., Andrade, V. \u0026amp; Srinivasalu, S. Ages and relative sizes of pre-2004 tsunamis in the Bay of Bengal inferred from geologic evidence in the Andaman and Nicobar Islands. \u003cem\u003eJ. Geophys. Res. Solid Earth\u003c/em\u003e\u003cstrong\u003e118\u003c/strong\u003e, 1345\u0026ndash;1362 (2013).\u003c/li\u003e\n\u003cli\u003eUdayaganesan, P., et al. High-Energy Deposits in the Shadow Zone of Rameswaram Island, Southeast Coast of India.\" \u003cem\u003eCoastal Environments of India: A Comprehensive Approach\u003c/em\u003e. Cham: Springer Nature Switzerland, 93\u0026ndash;120 ( 2025).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-8757939/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8757939/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDirectly facing the Sumatra and Andaman segments of the Sunda subduction zone, Sri Lanka provides an ideal location to study the large trans-basin tsunamis that occur there. Its location close to the southern boundary of the northern cyclone belt, and the directional advantage of the southern and eastern coastlines makes Sri Lanka one of the best places in the eastern Bay of Bengal region for distinguishing tsunami and cyclone deposits. Although several paleotsunami records have been constructed for the region since the 2004 Indian Ocean Tsunami, most extend only to the last 3000 years, and discrepancies exist among records. Therefore, this study was carried out to construct a longer Holocene tsunami record for the western Bay of Bengal region and to develop a more robust record of large trans-basin tsunamis that occurred at the Sumatra and Andaman trenches, to understand the recurrence interval between events.\u003c/p\u003e \u003cp\u003eThirteen back-barrier environments spanning the southern and eastern coastline of Sri Lanka were selected, and 35 sediment cores (1\u0026ndash;5 m long \u0026ndash; Total over 100 m length) were extracted along landward transects. Also, one pit was excavated to study abrupt sand layers. After initial logging, 19 sediment cores were selected for further analysis due to visually observed abrupt event layers. Particle size was used as the primary proxy to confirm the observed abrupt sand layers. Sediment texture, sedimentary structures, chemical composition, magnetic susceptibility, and micofossils were used to distinguish marine overwash layers having potential tsunami origin. Stratigraphy and age were used to establish intra- and inter-site, as well as regional, correlations among layers to distinguish regional tsunamis.\u003c/p\u003e \u003cp\u003eIn addition to five 2004 tsunami sand layers, among the 29 identified ancient abrupt layers with marine origin, 20 were distinguished as high potential paleotsunami (T\u003csub\u003eHP\u003c/sub\u003e), and 06 were as medium potential (T\u003csub\u003eMP)\u003c/sub\u003e tsunami layers deposited during nine events that occurred around 1100, 3000, 4000, 4600, 5700, and 7300 yrs BP (T\u003csub\u003eHP\u003c/sub\u003e), and 2000, 5100, 6300 yrs BP (T\u003csub\u003eMP\u003c/sub\u003e) based on local and regional-correlation analyses. Abrupt layers deposited during another two low-potential tsunami (T\u003csub\u003eLP\u003c/sub\u003e) events and other marine overwash events (OM) were also recognized by this study.\u003c/p\u003e \u003cp\u003eIn addition, published regional records show widely distributed, chronologically correlating evidence for a paleotsunami that occurred around 600 years BP, which was not observed at our study sites in Sri Lanka. Including the 2004 tsunami, when all 11 trans-basin events (excluding T\u003csub\u003eLP\u003c/sub\u003e) reported over the last 7500 yrs are considered, tsunami frequency in the Indian Ocean has increased during the last 1000 yrs and during the interval between 4000\u0026ndash;5000 yrs BP. Increased seismicity between 500\u0026ndash;1500 yrs BP in the Sunda trench correlates with increased tsunami frequency during the last 1000 yrs.\u003c/p\u003e","manuscriptTitle":"A 7500-year paleotsunami record from the coastal sediment of Sri Lanka and Indian Ocean trans-basin tsunami history.","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-12 14:05:47","doi":"10.21203/rs.3.rs-8757939/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c5e59064-f794-422c-8a9c-405c8c42654f","owner":[],"postedDate":"February 12th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":62706548,"name":"Earth and environmental sciences/Climate sciences"},{"id":62706549,"name":"Earth and environmental sciences/Environmental sciences"},{"id":62706550,"name":"Earth and environmental sciences/Natural hazards"},{"id":62706551,"name":"Earth and environmental sciences/Ocean sciences"},{"id":62706552,"name":"Earth and environmental sciences/Solid earth sciences"}],"tags":[],"updatedAt":"2026-04-01T17:10:16+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-12 14:05:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8757939","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8757939","identity":"rs-8757939","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}