Submarine paleoseismology in the Japan Trench of northeastern Japan: turbidite stratigraphy and sedimentology using paleomagnetic and rock-magnetic analyses

Submarine paleoseismology in the Japan Trench of northeastern Japan: turbidite stratigraphy and sedimentology using paleomagnetic and rock-magnetic analyses | 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 Research Article Submarine paleoseismology in the Japan Trench of northeastern Japan: turbidite stratigraphy and sedimentology using paleomagnetic and rock-magnetic analyses Toshiya Kanamatsu, Ken Ikehara, Kan-Hsi Hsiung This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2008594/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Mar, 2023 Read the published version in Progress in Earth and Planetary Science → Version 1 posted 9 You are reading this latest preprint version Abstract Previous studies on sediment recovered from the Japan Trench document distinctive turbidite beds induced by huge earthquakes along the Japan Trench and their wide occurrences in area of 37°25’- 38°30’N. We studied two sedimentary cores at 39°N in order to investigate the depositional earthquake record in the further spatio-extened areas of the Japan Trench. We examined specifically the precise stratigraphy of turbidite beds using paleomagnetic secular variation (PSV), and a tephra correlation. Additionally, anisotropy of magnetic susceptibility (AMS) was investigated to understand the depositional conditions of each turbidite bed. The inferred ages of turbidite beds in this study closely approximate their earlier reported, which are correlated to the historical and pre-historical huge earthquakes off Tohoku, northeastern Japan. The paleo current directions during deposition of turbidite are inferred from their grain alignment based on AMS data. The directions of basal part reveal northeastward in the slope-side basin and north-northeast in oceanward basin. The directions of basal and upper thick muddy part of a turbidite bed are not always consistent, which suggests the hydraulic condition in the narrow elongated deep-sea basin. This fact could be essential information to elucidate a unique hydraulic condition during the turbidite deposition in the confined basin in the Japan Trench basin. Historical earthquake Japan Trench Turbidite Paleomagnetic secular variation Paleo current anisotropy of magnetic susceptibility Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1 Introduction Geological data along the Japan Trench are expected to provide spatial and temporal information related to plate boundary megathrust earthquakes as the 2011 Tohoku-oki earthquake. Evidence of historical and pre-historical huge earthquakes have often been found as onshore tsunami deposits (e.g., Sawai 2020 ). Furthermore, deep-sea turbidites in the Japan Trench have been reported as indication of huge earthquakes (Ikehara et al. 2016 , 2017 ; Kioka et al. 2019 a; McHugh et al. 2020 ). The massive thick turbidite in the trench basin were attributed to the remobilization of large amounts of sediment from slopes during the earthquakes. The three distinctive thick turbidite beds were discovered off Miyagi in the Japan Trench at ~ 38° N (Ikehara et al. 2016 ). The uppermost turbidite bed is regarded as having formed during the 2011 Tohoku-oki earthquake. The next two upper turbidite beds have been correlated with the 1454 common era (CE) “Kyotoko”, and the 869 CE “Jogan” earthquakes (Ikehara et al. 2016 ; Bao et al. 2018). Ikehara et al. 2018 show those three turbidites beds were recognized widely in 37°25’- 38°30’N along the Japan Trench. Because at least some of those turbidite beds can be regarded as the consequences of surface sediment remobilization induced by strong ground shaking (McHugh et al. 2020 ; Schwestermann et al. 2021 ), the lateral correlation of turbidite beds along the Japan Trench provide important data to elucidate not only the timing but the affected area by past huge earthquakes. On the contrary, the formation mechanism of turbidites with thick mud in the Japan Trench has been not yet fully understood, but their depositional mechanisms may be similar to that of “homoginite” which is considered to be related to earthquake-event in a confined basin (e.g. Beck et al. 2007). Dating of turbidite beds is essential information for this work. Nevertheless, it is difficult to determine precise depositional ages of turbidite because of a lack of suitable methods to analyze the sediment deposited in super deep basins (over 7000-m water depth), especially for the time range in historical time. Kanamatsu et al. 2017 , 2022 developed the dating method of turbidite beds using paleomagnetic secular variation (PSV) records. Moreover, they found that the derived ages are well correlated to the ages of huge earthquakes in historical documents. They found that excellent PSV records are preserved in Japan Trench sediments because of the high sedimentation rate of the hemipelagic interval. Geophysical and geological distinctive features in the Japan Trench related to the 2011 Tohoku-oki earthquake have been discovered through intensive investigations after the earthquake (e.g. Kodaira et al. 2020 ). Results of some studies suggest that a large displacement occurred around 38°N because of the 2011 Tohoku-oki earthquake (Fujiwara et al. 2011 ; Kodaira et al. 2012; Strasser et al. 2012), but no major bathymetric change was associated with the earthquake north of 39°N (Fujiwara et al. 2017 ). Fujie et al. (2022) interpreted the smectite-rich pelagic clay layer at around 39°N in the subduction sediment as having been disturbed or as having metamorphosed by an interplate “pettispot volcanism” (Hirano et al. 2006 ). They proposed that the smectite-rich pelagic clay layer around 39°N might be a barrier to the northward propagation of large, shallow coseismic slip of the 2011 Tohoku-oki earthquake. Based on that knowledge, 39°N in the Japan Trench should a unique boundary for constraint of rapture width not only for the 2011 Tohoku-oki earthquake but also past huge earthquakes that occurred along the Japan Trench. We, therefore, examined the distribution of turbidite along the Japan Trench as a proxy of past huge earthquake occurrences in order to explore this concept. We studied turbidite records in sediment samples taken at Japan Trench at 39°N, aiming to understand whether the turbidite depositions at 39°N occurred simultaneously with those at south of 38°30’N previously reported, and their depositional mechanism at 39°N. 2 Methods 2.1 Materials The graben and horst structure have been produced on the subducting Pacific plate in the Japan Trench. Isolated and semi-isolated basins develop in the graben and trench floor along the Japan Trench (Kioka et al. 2019 ). Thick sedimentary sequences recognized acoustically in the basins are distributed in basins of narrow-width (Kioka et al. 2019 ). Piston cores KS1416PC06 (39°01. 9’ N, 144°14.8’ E, water depth 7394m) and KS1416 PC07 (39°02.2’ N, 144°12.6’ E, water depth 7282m) were obtained in a graben basin and a trench basin respectively. The location of core KS1416PC07 is on the trench basin near the landward slope, which is 11 km in length and less than 3 km in width. The location of core KS1416PC06 is in a graben basin east of the core KS1416PC07 basin, which is 30 km in length and less than 2 km in width. The both basins are separated by a ridge of few hundred meters’ height (horst) (Fig. 1 b). The north and south extensions of KS1416PC07 basin are topographically closed. However, the core KS1416PC06 basin extends continuously to the north and south. The respective lithologies of cores KS1416PC06 and KS1416PC07 were reported by Ikehara et al. ( 2017 ). Their lithostratigraphy in the upper part of the sediment cores KS1416PC06 and KS1416PC07 (Figs. 2 a and h) reveals that the thick turbidite units show similarities to those reported earlier (Ikehara et al. 2016 ). According to the results of that study, several turbidite beds were recognized in both cores. Thicknesses of turbidite beds range from centimeters to more than one meter. These beds are sometimes composed of a few to several amalgamated subunits. Other than turbidite interval, hemipelagite interval is recognized by presences of bioturbation in the visual description. For this study, the turbidite beds are labeled sequentially as presented in Figs. 2 a and 2 h. Other than turbidite and hemipelagic beds, a tephra layer containing glass shards is found in the interval between 392.2 cm and 394.5 cm in core KS1416PC07. 2.2 Sample analysis Paleomagnetic and rock magnetic samples (2.2-cm square plastic cube) were taken from halved sections of cores KS1416PC06 and KS1416PC07. The remanent magnetizations were measured using a superconducting rock magnetometer (2G Enterprises model 760) at Japan Agency for Marine-Earth Science and Technology (JAMSTEC). All the samples were demagnetized with alternating field demagnetization (AFD) at step-wise levels of 5mT between 0 and 40 mT, and 10 mT between 50 and 80 mT. Natural remanent magnetization (NRM) was measured after each demagnetization treatment. Anhysteretic remanent magnetization (ARM) was imparted in an 80 mT alternating field with a 0.1 mT direct field. The inclinations, declinations, and maximum angular deviation (MAD) values of NRM of all the sample were calculated using software (PuffinPlot; Lurcock and Wilson 2012 ). Aiming at documenting the thick-turbidite textural characteristics using magnetic properties, the magnetic susceptibility (MS) and its anisotropy (AMS) was measured using KLY-4 (Agico Inc.) at JAMSTEC. Directions and magnitudes of three principal susceptibility axes: maximum (Kmax), intermediate (Kint), and minimum (Kmin) are obtained by measurements. The AMS parameters “L” (Kmax/Kint) for characterizing the linearity and “F” (Kint/Kmin) for characterizing the oblateness of samples are calculated from magnitudes of three principal susceptibilities to determine their shape of magnetic fabric (Tarling and Hrouda 1993 ). Another rock magnetic measurements were performed to investigate the sample's magnetic properties. The domain state and coercivity of selected samples from the hemipelagic interval were measured by a vibrating sample magnetometer (VSM, model 2900; Princeton Measurements Corp.). Saturation remanent magnetization (Mr), saturation magnetization (Ms), and coercive force (Hc) were calculated after paramagnetic contributions were removed. We also obtained the coercivity of the remanence (Hcr) of each sample by VSM measurements. Also, the isothermal remanent magnetization (IRM) acquisition experiments were performed on those samples. The S-ratio (Bloemendal et al. 1992 ) was obtained, which is used to estimate magnetic mineralogy. We consider that the magnetic particle size is very informative to recognize turbidite depositional structures such as fining upward. It was investigated using the simple proxy of ferrimagnetic grain size (ARM/MS) (Banerjee et al. 1981 ; King et al. 1982 ), which changes inversely with magnetic particle size increasing in the range of 1–10 µm (e.g. Stoner et al. 1996 ). One tephra bed is involved in the interval between 392.2 and 394.5 cm in core KS1416PC07. The morphology and refractive index of volcanic glass shards and the mineral composition of the bed was assessed by Kyoto Fission Track Ltd., Kyoto, Japan, for correlation with earlier reported tephra deposits in the Japan Trench. The obtained paleomagnetic data were compared to a master curve of secular variation (ARCH3k.1: Korte et al. 2009 ), which was generated through compilation between 0 and 3 ka archeomagnetic data. ARCH3k.1 was also used in the previous studies in the Japan Trench (Kanamatsu 2017, 2022), because they are suitable for paleomagnetic field study in Europe and Asia, and reliable for the Northern hemisphere data (Donadini et al. 2009 ). We used “StratFit” software (Sagnotti and Caricchi 2018) to compare the obtained paleomagnetic data to the master data. The tie points were selected as apparent peaks and troughs in the inclination and declination profiles (Table 1 ). Using “StratFit”, we obtained the age of each core. Table 1 Tie point between cores and ARCHE3k.1 data *: depth after turbidite removing Declination point ARCHE3k.1 Age(year) PC06 depth* (cm) PC07 depth* (cm) B 923 CE 78.0 119.3 C 105 BCE 169.9 D 939 BCE Inclination point ARCHE3k.1 Age(year) PC06 depth* (cm) PC07 depth* (cm) a 1672 CE 25.2 b 1225 CE 61.8 c- 475 CE 86.8 d 238 CE 110.0 3 Results 3.1 Depth variation of magnetic parameters The profiles of magnetic susceptibility (MS), ARM/MS (parameters for magnetic grain size), AMS parameters “L” and “F” with depth are plotted in Fig. 2 . Extremely instant peaks of MS are generally found in silt to very fine sand layers corresponding to bases of turbidite beds in intervals between 0 and 200 cm (P6t1-P6t6) in core KS1416PC06, and between 0 and 400 cm (P7t1-P7t5) in core KS1416PC07 (Figs. 2 b and 2 g). Multiple fining-upward sub-beds are observed in some turbidite beds. For example, MS shows an increase at the base of turbidite at 288 cm of P7t1 (Fig. 2 f). It decreases gradually upward. Then a small MS increase in the silt layer occurs. Prominent MS peaks occur in the silt and coarse silt layer at 58 cm and 80 cm in unit P7t1. Among all the turbidite beds, the highest peaks of MS occur at 198 cm in P6t4 and in at 380 cm P7t2 in respective cores. Analysis by ARM/MS reveals an approximate mirror image with MS above 180 cm in core KS1416PC06 (Fig. 2 c) and above 400 cm in KS1416PC07 (Fig. 2 g). The ARM/MS indicate a large grain size at the base of turbidite beds. For example, a sudden increase of grain size at the base of P7t2 and a gradual decrease upward. The ARM/MS values gradually or rapidly approach that of the overlying hemipelagite. Those features are interpreted as arising from the finning-upward of the turbidite beds. However, below 180 cm (P6t5-P6t9) in core KS1416PC06, and 400 cm (P7t3-P7t6) in core KS1416PC07, a sharp peak of MS does not occur always in the turbidite bases. Also, ARM/MS show no upward decreasing pattern. Moreover, MS of P6t5-P6t9, and P7t3-P7t6 are markedly weaker than those of overlying and underlying hemipelagic intervals. The different variation in MS between the turbidite and the hemipelagite is considered to cause from their different content of magnetic minerals. The magnetic mineral content in hemipelagite would be homogenized by bioturbation, while the MS variation of turbidite interval is not affected by bioturbation but the depositional process. The MS homogenization of hemipelagite is suggested by smoothed variation without spiky change of MS (Fig. 2 ). A change of ARM/MS between turbidite and hemipelagite is interpreted to reflect a different size of magnetic particle. The ARM/MS in turbidite is considered to reflect grain size sorting during turbidite deposition. The muddy interval of turbidite bed is also well sorted in grain size, which could make difference from the homogenized magnetic grain size of hemipelagite. In addition to MS peaks of turbidites, prominent peaks were found in the tephra bed at 398 cm in core KS1416PC07 and at 190 cm in a hemipelagic interval of core KS1416PC06. 3.2 Magnetic fabric Results of AMS measurements are used to investigate the sediment fabric of turbidite beds reflecting depositional mechanisms. Because of the small number of data in the thin beds (P6t2, P6t5, P6t6), we excluded the beds from the evaluation. Actually “L” is generally low: close to 1.0 in both cores of KS1416PC06 and KS1416PC07 (Figs. 2 d and 2 h), except for the interval of 60–300 cm in core KS1416PC07. Some turbidite beds reveal increasing “F” around their bases (P6t3, P6t8, Pt7t1, P7t3, P7t4, P7t5). High “F” are observed at upper interval rather than at basal interval in the turbidite beds (P6t1, P6t4, P6t6, P7t2). For example, P6t1 and P7t1 show high “F” values at the upper depth of the turbidite beds, the lithostratigraphy indicates that these high “F” values occur in the other overlying subunit beds. AMS directions are orientated by the mean of paleomagnetic declination of the cores. AMS directions (Kmax, Kint, and Kmin) of the turbidite beds are plotted on the lower hemisphere equal area projections (Figs. 3 a). Along with the turbidite beds, AMS of all the hemipelagic intervals in each core is shown respectively in Fig. 3 b. Three patterns of AMS directions are recognized based on the directional distributions of Kmax, Kint and Kmin. 1) A girdle formed by the Kmax and Kint axes (e. g. P6t1 in Fig. 3 a, P7t5 in Fig. 3 a). The girdle plane of this type is slightly oblique to the horizontal plane. The directional distributions of Kmax and Kint axes are largely overlapped or weakly clustered with each other. The Kmin axes slightly deviate from the vertical axes. 2) Kmax axis distribution shows strong clustering and Kint and Kmin axes form a girdle around the Kmax axis (e. g. P7t1 in Fig. 3 a). 3) Kmax and Kint axes are scattered in the horizontal plane of equal area projection (e. g. Figure 3 b). Kmin is well clustered, perpendicular to the horizontal plane. 3.3 Remanent magnetization Simple decreasing of horizontal and vertical magnetic components during AFD experiments reveal stable single component in most samples (Figs. 4 a and 4 b). Saturations of IRM around 300 mT and the S-ratio ranging about 0.98 in the selected samples indicate that the magnetization is carried by low coercive force magnetic minerals, such as magnetite. Ratios Mrs/Ms and Hcr/Hc of the hysteresis parameter plotted in Day diagram (Day et al., 1977 ) indicate that the values range in the pseudo-single domain state (Fig. 4 c). Figures 5 a, 5 b, and 5 c are plots of the component-analyzed inclination and declination. The declination is expressed as a relative declination with ΔD 95 and ΔI 95 (95% confidence level converted from MAD; Khokhlov and Hulot 2016 ). The ΔD 95 and ΔI 95 are mostly large at the turbidite intervals, indicating that the obtained magnetic directions are unstable. A large break exists in the declination variation at 65 cm and the scattered in the interval above 65 cm in core KS1416PC06 (Fig. 5 a), which might have been horizontally twisted during piston coring or during handling or the core sample operations before taking the subsamples. The values of ΔD 95 and ΔI 95 are also high in 0–65 cm in core KS1416PC06 (Figs. 5 a and 5 b), indicating that some artificial influence might have affected the magnetization. In accordance with the observations above, the interval was excluded from the paleomagnetic interpretation. 3.4 Tephra The tephra layer at 392.2-394.5 cm (Fig. 2 ) in KS1416PC07 is 2.3 cm thick, coarse silt in grain size, and consisting of fibrous pumice-type glass fragments, which is a glass type of “T” in the definition by Yoshikawa et al. 1976. Green-colored hornblende and orthopyroxene are the major heavy minerals. Opaque minerals and orthopyroxene are present in trace amounts. The refractive indices of the volcanic glass shards range from 1.5047–1.5091 (mode: 1.507). These petrographic features are consistent with the Haruna-Futatsudake-Ikaho (Hr-FP) tephra which was previously reported on land and in marine sediments off Sanriku (Table 2 , and 3 in Ikehara et al., 2018 ), the occurrence of the Hr-FP tephra in marine sediments is restricted strongly to around 39–40°N (Fig. 3 B in Ikehara et al., 2018 ). This distribution is also consistent with the location of KS1416PC07, in which Hr-FP tephra is found. The erupted age of Hr-FP tephra is considered to have in in the 6th century (Soda 1998). Table 2 Ages of Turbidite units based on PSV correlation. Turbidite bed No. CE (year) P6t1 - P6t2 - P6t3 - P6t4 978 P6t5 343 P6t6 -45 P6t7 -301 P6t8 -720 P6t9 <-5948 P7t1 1254 P7t2 829 P7t3 222 P7t4 -12 P7t5 -171 P7t6 <-635 Table 3 Mean Kmin direction (vertical axis to magnetic foliation) of turbidite beds and hemipelagic intervals of cores KS1416PC06 and KS1416PC07. k: Fisherian precision parameter; α95 = radius of cone of 95% confidence Bed No. (subbed) Sample Number declination inclination α95 kappa P6t3 4 114 88 3.6 645.2 P6t3 base 2 157.6 82.1 23.7 113.5 P6t4 25 161.7 87.3 1.9 229.8 P6t4 base 2 168.6 75.5 6.6 724.6 P6t7 39 136 80 3 59.1 P6t7 base 2 166.7 73.7 13.4 174.5 P6t8 15 145.4 81.3 7.2 27.5 P6t8 base 2 167.5 67.5 3.3 2833.5 P6t9 44 97.6 77.7 4.4 25.3 P7t2u1 2 265.8 79 4.7 143.3 P7t2u1 3 107 88.2 6.4 250.6 P7t2 base 2 107.4 78.5 47.5 14.9 P7t3 4 147.1 76.3 5.6 200.9 P7t3base 1 146 78 - - P7t4 4 138 67.7 17.4 21.7 P7t4 base 2 164.9 76.9 34.4 27.4 P7t5u1 6 177.2 78.5 14.8 21.5 P7t5u2 14 162 82.8 3.5 131.5 P7t5u3 17 209.6 73.4 3.4 112.4 P7t5u4 69 170.5 80.4 1.6 109 P7t5base 4 124.3 69.4 20.4 21.3 P7t6 51 181.3 77.5 3.5 34.3 P7 hemipelagite 79 129.9 84.7 3.1 28.2 P6 hemipelagite 245 151.5 79.9 1.6 32.6 4 Discussion 4.1 PSV record Because NRM of turbidite is largely subjected by grain alignment of turbidite deposition (e. g. Tanty et al. 2016 ), NRM direction of turbidite beds does not reflect geomagnetic field directions. Therefore, NRM of turbidite beds must be excluded from the paleomagnetic stratigraphic interpretation (Kanamatsu et al. 2017 , 2022 ). The boundary between turbidite and hemipelagite can be recognized from rock magnetic parameters of MS and ARM/MS (see section 3.1 ). PSV data constructed by removing turbidite intervals are used to estimate the depositional age of the turbidite beds (Fig. 6 a). After removing the turbidite data, we recalculated the depth of the paleomagnetic data assuming no large gaps in deposition (Fig. 5 ). In fact, P6t3 and P6t4 are different turbidite beds which are separated by 2 cm henipelagite. But because thickness is smaller than resolution of sampling (2.2 cm), we regard that the both beds deposition occurred at the same time. The obtained paleomagnetic data of core KS1416PC07 is correlated to ARCH3k.1 with a tephra key bed (Fig. 6 b). Under the assumption that the sedimentation rates of the hemipelagic intervals in KS1416PC07 are similar to that of core KS1416PC06, we compare the paleomagnetic data using “StratFit” (Fig. 6 b). The paleomagnetic tie points (Table 1 ; Fig. 6 b) and the eruption age of Hr-FP found in core KS1416PC07, which is regarded as being of 6th century (Soda 1989 ), are used. The sedimentation rates of the hemipelagic intervals in KS1416PC07 is 81.4 cm/kyr, and that of KS1416PC06 is 71.2 cm/kyr. Because the reference curve is only available for data up to 3,000 years ago, For the older periods, the age is obtained from the extrapolation using the sedimentation rate of that of above interval (The results are available in supplemental data). The calculated ages of the turbidites are shown in Table 2 . Turbidites that can be correlated between cores KS1416PC06 and KS1416PC07 based on age are shown with broken lines in Fig. 6 . 978 CE of P6t3 and P6t4, and 829 CE of P7t2 are close to the turbidite ages previously reported, which are 972 CE (14t3 of core KS1416PC10 in Fig. 7 b) and 881 CE (15t3 of core KS1503PC10 in Fig. 7 c). They were determined to correspond to the 869 CE “Jogan” earthquake (Kanamatsu et al 2022 ). Also, 1254 CE of P7t1 is very close to 1272 CE (14t2 of core KS1416PC10 in Fig. 7 b), and 1265 CE (15t2 of core KS1503PC10 in Fig. 7 c), which were attributed to the 1454 CE “Kyotoku” earthquake (Kanamatsu et al 2022 ). P6t7 (BCE 301) and P7t5 (BCE 171) are close to the ages of turbidite BCE 283 (14t4 of core KS1416PC10 in Fig. 7 b) and BCE 128 (15t5 of core KS1503PC10 in Fig. 7 c), which are regarded having been deposited at 2.3 ka. The other comparable pair of turbidites is P6t8 (BCE 720) and P7t6 (BCE 635) judged from their ages. Figure 7 shows the turbidite bed correlations and their magnetic susceptibility profiles of cores of this study and previous studies in the Japan Trench and the slope basins near the sites of cores KS1416PC06 and KS1416PC07 (Fig. 1 a). Turbidite beds correlated to the “Jogan” earthquake are characterized by their high magnetic susceptibility values (Fig. 7 ). The occurrence of a “Jogan” turbidite bed (P7t2) just above the 6th-century Hr-FP tephra is stratigraphically consistent with the interpretation that P7t2 (Fig. 7 d) is correlated to the “Jogan” earthquake (869 CE), and also profiles of NT1318PC10 and NT1318PC08. Thus, “Jogan” turbidite was found both on the landward slope and on the trench axis around 39°N. “2.3 ka” turbidite beds reported in the previous study (Kanamatsu et al 2022 ) can be correlated to P6t7 and P7t5 in this study, and also to turbidites T5 (about 2.3 ka) in NT1318PC10 and NT1318PC08 (Usami et al. 2018 ). The uppermost part of core KS1416PC07 is thought to have been deposited at about 1900 CE based on the PSV data (Fig. 7 ). The interval of KS1416PC07 between “Kyoutoku” (1454 CE) and 1900 CE involve no distinct thick turbidite bed as it was for the older thick turbidites. Whreas within that time interval, the records of tsunami and tsunami deposits along the coast off Tohoku are well documented of the 1611 CE Keicho and 1896 CE Meiji Sanriku tsunamis (e.g. Sawai et al. 2020). A turbidite corresponding to 1896 CE Meiji Sanriku is also found in the slope sediment off the northern Tohoku (Ikehara et al. submitted). Small magnetic susceptibility peaks and upward fining patterns in ARM/MS observed in core KS1416PC07 may be related to the Meiji Sanriku earthquakes judged from its stratigraphic position (Fig. 2 ). 4.2 Magnetic fabric AMS directions are used to presume local current flow direction during turbidite bed depositions. Axes of the magnetic susceptibility are reorientated by the mean directions of paleomagnetic declination of the cores. Because the paleomagnetic data of P6t1 is not available, AMS direction of P6t1 is without directional reconstruction. Under a hydraulic flow, Kmax axes could be parallel to a flow direction, whereas the Kmax axis could be transverse to the flow direction in a strong flow condition (e.g. Taring and Hrouda 1983). Perpendicular Kmax to the current direction is formed in a strong flow, which roll grains over the surface (e.g. Baas et al. 2007 ). Taira and Scholle (1979) proposed an AMS fabric evolution in a turbidite deposition. They demonstrated the relationship between the shape type and orientation of principle AMS axes, and turbidite depositional environments, which is defined by divisions of the Bouma sequence (Bouma 1962 ). They demonstrated in the basal part of turbidite that “subdivision A” is characterized by perpendicular Kmax distribution to the flow direction and tilting Kmin upstream (imbrication). They revealed that Kmax orientation in the upper part of “division A”, and “divisions B and C”, changes to be parallel to the flow direction. The imbrication angle dipping to upstream is gradually shallow. Consequently, the Kmax direction can be parallel and perpendicular to a flow direction during turbidite deposition. It implies that the flow analysis using only Kmax direction is difficult without understanding the depositional environment of the “subdivision” of turbidite. For this study, we therefore use the Kmin dipping direction to investigate a local current direction as suggested by Taring and Hroud 1983. Shallower of Kmin inclinations are observed around the base of turbidite beds (Figs. 8 and 9 ), and in several cm from the base of turbidite beds. For example, in P6t4 (Figs. 8 ) and P7t5 (Figs. 9 ) respectively. This observation indicating an imbricated fabric around the basal interval is consistent with the magnetic fabric evolution model presented by Taira and Scholle 1979. We divided AMS directions of a turbidite bed into a basal sandy interval and an upper muddy interval, because depositional conditions of the two intervals could be different in confined basins. For the upper interval of homogeneous mud, unique depositional models for explaining a thick muddy bed have been proposed based on natural observations and experiments. A suspension cloud caused by a flow rebound in a confined basin have been considered for forming the thick muddy interval (e.g. Patacci et al 2015 ). Furthermore, “homogenite” deposition related to earthquake-event in a confined basin was proposed (e.g. Beck et al. 2007; McHugh et al 2016; Polonia et al 2017). A massive structureless characteristic of “homogenite” is considered to be induced by seiche effects generated by the earthquakes. The seiche motion increases segregation of the fine-grained fraction and sustains the suspension (Beck et al 2007) or induces fine-grain flows in the suspension (McHugh et al., 2006). Another interpretation is that the thick deposits are attributed to multiple simultaneous turbidite formation induced by an earthquake (e.g., Goldfinger et al., 2012 ). The thick and homogenous muddy intervals in turbidite beds recognized in cores KS1416PC06 and KS1416PC07 were possibly have been formed by the similar mechanisms in the small and narrow basins along Japan Trench. In such a case, the basal sandy interval and upper muddy interval were formed under different hydraulic conditions. Accordingly, the basal sandy interval and upper muddy interval are divided for interpretation. The divided AMS directions of turbidite beds are shown in Fig. 8 . We regard mean Kmin dipping directions as current directions for turbidite beds (Table 3 ). A dominant AMS direction in the basal sandy intervals for core KS1416PC07 (Figs. 9 ) is revealed to southeast, whereas the dominant AMS direction for core KS1416PC06 (Figs. 8 ) is south-southeast (P6t1 is exception due to no paleomagnetic data). By contrast, the directions of the upper muddy intervals are diverse. Some sites show no prevailing flow direction of muddy portion indicated by vertical Kmin. (e.g. P6t4 in Figs. 8 ). It is interpreted as a deposition under still hydraulic conditions. In the most cases of muddy upper intervals, the AMS directions are slightly oblique to their basal directions (e.g. P6t7, P6t8 in Figs. 8 , P7t3, P7t4 in Figs. 9 ). The smaller changes in flow directions are suggested during the upper interval depositions. In the thick upper portion of P7t5 (Figs. 9 ), the intervals are subdivided into several beds based on directions. They are changing frequently, but the major direction seems to be southward. On the other side, AMS directions of upper intervals in two beds (P6t1 in Figs. 8 and P7t2 in Figs. 9 ) show anti-parallel directions to their basal directions, although AMS of P6t1 bed is not reoriented by paleomagnetic directions. AMS of P7t2 indicates that an eastward flow in the initial depositional stage changed to a westward flow in the upper muddy deposition. Those changes might be occurred by deflection and reflection of currents which were controlled by topographical contains (e.g. Patacci et al. 2015 ). The oblique flow directions observed in many cases could be explained by deflection of flows from the initial flow, which is oblique to north-south extending edges of basins (Fig. 1 b). The reversed direction of P7t2 could be explained by a reflection of eastward flow against the west facing ridge of the basin. The general consistent directions among basal beds of each core may implicate a primal mechanism controlling the direction during initial deposition. Their local slope topography may be a possible control factor which constrain a flow pathway. The steep slope west side to core KS1416PC07 location could have induced southeastward flows (Fig. 1 b). On the other side, the south-southeast directions in core KS1416PC06 suggest flows along the basin axis (Fig. 1 b). The causes of different direction of muddy upper interval could be caused from many factors originated from flow properties (flow thickness, sastainment of flow, initial flow direction etc.) and basin properties (volume, shape, axis direction etc). The AMS variation of P7t1 is greatly in contrast to the other AMS axis directional patterns (Fig. 9 ). P7t1 is subdivided into subbed based on AMS directions. The AMS direction of the basal part (subbed “P7t1base”) can be interpreted as rolling of the Kmax directions perpendicular to a strong flow, suggesting northeastward or southwestward. However, the Kint axes become well clustered in vertical and the Kmin axes horizontal in subbed “P7t1u3” with the horizontal Kmax direction. The Kint and Kmin directions of the subbed “P7t1u2” are regard as similar to that of subbed “P7t1base”. The subbeds “P7t1base” and “P7t1u2” can be interpreted as having been formed under strong flows from the northeast or southwest. Also subbed “P7t1u1” has Kmax and Kint scattered in a horizontal plane: a direction under still hydraulic condition. However, horizontal Kmin and vertical Kint of subbed “P7t1u3” are enigmatic directions as sedimentary fabric. This type is usually reported as “prolate type” indicting layer parallel sharing or layer parallel shortening (e.g. Pares 2014), although we have no evidence based on data from this study to discuss the possibility of deformation. The AMS directions in all the hemipalegite intervals of core KS1416PC07 (Fig. 3 b) show no preferred orientation in Kmax, suggesting a still hydraulic condition during hemipelagic deposition. By contrast, the AMS direction of hemipelagite in core KS1416PC06 are indicated as southward (Fig. 3 b). The obtained direction of KS1416PC06 may suggests the exist of bottom current during hemipelagite deposition. The extensions of the basin of core KS1416PC06 are not closed topographically, but closed in the basin of core KS1416PC07 (Fig. 1 b). This topographical setting would allow a flow entering from north in the basin of core KS1416PC06, but restrict a flow entering in the basin of core KS1416PC07 site, if a deep current system exists in the trench floor. Although no study of deep-sea bottom current on the floor of Japan Trench over 7,000 m has been reported, several reports have described long-term steady bottom currents in both landward (southward flow) and seaward (northward flow) slopes along the Japan Trench as deep western boundary currents in ~ 6,000 m water depth (Mitsuzawa et al. 1998, Fujio and Yanagimoto 2005). Mitsuzawa et al. 1998 reported the deep western boundary current flows south-southwest in the landward slope of the Japan Trench with mean speed of 3–7 cm/s and maximum speed of 15–20 cm/s. On the other side, a deep bottom current in the abyssal plain in the east of Japan Trench reveals westward (Owens and Warren, 2001 , Fujio and Yanagimoto 2005). AMS study for surface sediments in the abyssal plain east of the Japan Trench (Kawamura et al. 2015 ) revealed the AMS directions as generally parallel to the deep bottom current in the abyssal plain. Because a flow of more than 1cm/s current can form imbricated magnetic fabric (Taring and Hrouda 1993), a few cm/s of bottom current might generate the flow pattern in AMS in the hemipelagite. AMS data of turbidite basal sandy beds in the 39°N, the Japan Trench floor indicate a flow to southeast at core KS1416PC07 location, and south-southeast at core KS1416PC06 location. However, the directions of most thick muddy interval of turbidite beds are not always consistent to those of their basal sandy intervals. These AMS directions indicate no consistent flow direction during thick muddy part of turbidite, and suggest a complex hydraulic condition in the elongated small basin. Although more dense spatial AMS data should be necessary to confirm the flow evolution in the confined basin, we demonstrated the possibility that the AMS method might be able to reconstruct the complex flow patten. Conclusion (1) Turbidites of ages in two cores corresponding to the 1454 CE “Kyoutoku”, 869 CE “Jogan” and “2.3 ka”, were recognized in the Japan Trench floor at 39°N as confirming finding from earlier reported piston core samples obtained at 38°-38°30’N. (2) High magnetic susceptibility was widely observed for the turbidites corresponding to the “Jogan” earthquake. The 39°N “Jogan” turbidite is associated with a distinct MS peak arising from tephra “Hr-FP” just below the turbidite horizon. These clear signatures will be useful for identification of the “Jogan” turbidite. (3) Paleo-flow directions of turbidites based on the magnetic fabric in each core show that the directions from the basal sandy interval and the upper muddy interval in one turbidite bed is not always consistent. The prevailing directions in the basal intervals of turbidites are recognized in each location as southeastward at core KS1416PC07 location in the landward trench-basin, while to south-southeastward at core KS1416PC06 site in the graben-basin. Abbreviations PSV: paleosecular variation, CE: common era, NRM: natural remanent magnetization, ARM: anhysteretic remanent magnetization, AMS: anisotropy of the magnetic susceptibility, MAD: maximum angular deviation, Hr-FP Haruna-Futatsudake-Ikaho tephra Declarations Availability of data and material Obtained data in this study are presented in Tables, and supplemental data. For other data, please contact the corresponding author to request data. Competing interests The authors declare that they have no competing interest. Funding This work was supported by Japan Society for the Promotion of Science (KAKENHI) Grant No. 19H05596 (Representative: Hino R). Authors' contributions TK led conducted magnetic measurements, constructed the age model, and drafted the manuscript. KI conducted the sedimentological analyses and tephra analysis. KH conducted interpretation of magnetic results. All authors have read and approved the final manuscript. Acknowledgements We thank K. Tsuchida for providing excellent technical support throughout this study. References Baas JH, Hailwood EA, McCaffrey WD, Kay M, Jones R (2007) Directional petrological characterisation of deep-marine sandstones using grain fabric and permeability anisotropy: methodologies, theory, application and suggestions for integration. Earth-Science Reviews 82:101–142. doi:10.1016/j.earscirev.2007.02.003 Banerjee SK, King J, Marvin J (1981) A rapid method for magnetic granulometry with applications to environmental studies. Geophys. Res. Lett 8:333–336. doi:10.1029/GL008i004p00333 Bao R, Strasser M, McNichol AP, Haghipour N, McIntyre C, Wefer G, Eglinton TI (2018) Tectonically triggered sediment and carbon export to the Hadal zone. Nat. Commun. 9, 121. https ://doi.org/10.1038/s4146 7-017-02504 -1 Bloemendal J, King JW, Hall FR, Doh SJ (1992) Rock magnetism of late Neogene and Pleistocene deep-sea sediments: Relationship to sediment source, diagenetic processes, and sediment lithology. J Geophys Res 97:4361–4375. Bouma AH (1962) Sedimentology of some flysch deposits: Amsterdam,Elsevier, 168 p. Campos C, Beck C, Crouzet C, Demory F, Van Welden A, Eris K (2013) Deciphering hemipelagites from homogenites through anisotropy of magnetic susceptibility. Paleoseismic implications (Sea of Marmara and Gulf of Corinth). Sediment Geol 292:1–14. doi:10.1016/j.sedgeo.2013.03.015 Day R, Fuller MV, Schmidt A (1977) Hysteresis properties of titanomagnetites: Grain-size and compositional dependence. Phys Earth Planet Inter 13:260–267 doi:10.1016/0031-9201(77)90108-X. Donadini F, Korte M, Constable CG (2009) Geomagnetic field for 0–3 ka: 1. New data sets for global modeling. Geochem Geophys Geosys 10. Q06007. doi: 10.1029/2008GC002295. Fujie G, Kodaira S, Nakamura Y, Morgan J, Dannowski A, Thorwart M, Grevemeyer I, Miura S (2020) Spatial variations of incoming sediments at the northeastern Japan arc and their implications for megathrust earthquakes. Geology 48 (6): 614–619. doi:10.1130/G46757.1 Fujiwara T, Kodaira S, No T, Kaiho Y, Takahashi N, Kaneda Y (2011) The 2011 Tohoku-oki earthquake: displacement reaching the trench axis. Science 334 (6060): 1240. doi:10.1126/science.1211554. Fujiwara T, dos Santos Ferreira C, Bachmann AK, Strasser M, Wefer G, Sun T, Kanamatsu T., and Kodaira S. (2017) Seafloor displacement after the 2011 Tohoku-oki earthquake in the northern Japan Trench examined by repeated bathymetric surveys. Geophys Res Lett 44:11833–11839. doi:10.1002/2017GL075839 Goldfinger C, Hans Nelson C, Morey AE, Johson JE, Patton JR, Karabanov E, Gutierrez-Pator J, Eriksson AT, Gracia E, Dunhill G, Enkin RJ, Dallimore A, Vallier T (2012) Turbidite event history –Methods and implications for Holocene paleoseismicity of the Cascadia subduction zone. In: USGS Professional Paper, 1661- F, p. 184. US Geological Survey. doi:10.3133/pp1661f. Hirano N, Takahashi E, Yamamoto J, Abe N, Ingle SP, Kaneoka I, Kimura J, Hirata T, Ishii T, Ogawa Y, Machida S, Suyehiro K (2006) Volcanism in response to plate flexure. Science 313:1426–1428. Doi:10.1126/science.1128235 Ikehara K, Kanamatsu T, Nagahashi Y, Strasser M, Fink H, Usami K, Irino T, Wefer G (2016) Documenting large earthquakes similar to the 2011 Tohoku-oki earthquake from sediments deposited in the Japan Trench over the past 1500 years. Earth Planet Sci Lett 445:48–56. Ikehara K, Usami K, Kanamatsu T, Arai K, Yamaguchi A, Fukuchi R (2018) Spatial variability in sediment lithology and sedimentary processes along the Japan Trench: use of deep-sea turbidite records to reconstruct past large earthquakes. Geological Society, London Special Publications 456:75-89. doi:10.1144/SP456 .9 Ikehara K, Usami K , Kanamatsu T, Danhara T, Yamashita T (2017) Three important Holocene tephras off the Pacific coast of the Tohoku region, Northeast Japan: Implications for correlating onshore and offshore event deposits. Quaternary international 456:138-153, doi:10.1016/j.quaint.2017.08.022 Kanamatsu T, Usami K, McHugh CMG, Ikehara K (2017) High-resolution chronology of sediment below CCD based on Holocene paleomagnetic secular variations in the Tohoku-oki earthquake rupture zone. Geochem. Geophys. Geosys. 18:2990–3002. doi:10.1002/2017GC006878 Kanamatsu T, Ikehara K, Hsiung KH (2022) Stratigraphy of deep-sea marine sediment using paleomagnetic secular variation: Refined dating of turbidite relating to giant earthquake in Japan Trench, Marine Geology, 443 106669. Doi:10.1016/j.margeo.2021.106669 Kawamura K, Kanamatsu T, Oishi M, Yamano M (2015) Physical and magnetic properties in piston core samples collected from the Japan Trench before the 2011 Tohoku earthquake. JAMSTEC-R, 20, p. 51-60, doi:10.5918/jamstecr.20.51 King J, Banerjee SK, Marvin J, Özdemir Ö (1982) A comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials: some results from lake sediments. Earth Planet Sci Lett 59:404–419. doi:10.1016/0012-821X(82)90142-X Khokhlov A, Hulot G (2016) Principal component analysis of palaeomagnetic directions: converting a maximum angular deviation (MAD) into an α95 angle. Geophys J Int 204:279–291. doi:10.1093/gji/ggv451. Kioka A, Schwestermann T, Moernaut J, Ikehara K, Kanamatsu T, Eglinton TI, Strasser M (2019) Event stratigraphy in a Hadal oceanic trench: the Japan Trench as sedimentary archive recording recurrent giant subduction zone earthquakes and their role in organic carbon export to the deep sea. Front Earth Sci 7:319. doi:10.3389/feart .2019.00319 Kodaira S, Fujiwara T, Fujie G, Nakamura Y, Kanamatsu T (2020) Large Coseismic Slip to the Trench During the 2011 Tohoku-Oki Earthquake, Annual Review of Earth and Planetary Sciences, 48:321-343, https://doi.org/10.1146/annurev-earth-071719-055216 Korte M, Donadini F, Constable CG (2009) Geomagnetic field for 0–3 ka: 2. A new series of time-varying global models. Geochem. Geophys. Geosyst. 10:Q06008. doi:10.1029/2008GC002297. Lurcock PC, Wilson GS, 2012. PuffinPlot: A versatile, user-friendly program for paleomagnetic analysis. Geochem. Geophys. Geosyst. 13:Q06Z45. doi:10.1029/2012GC004098. McHugh CM, Seeber L, Cormier MH, Hornbach M (2014) Submarine paleoseismology along populated transform boundaries: the Enriquillo-Plantain-Garden fault, Canal du Sud, Haiti, and the North Anatolian Fault, Marmara Sea, Turkey. Oceanography 27:118–131. www.jstor.org/stable/24862162. McHugh CM, Seeber L, Rasbury T, Strasser M, Kioka A, Kanamatsu T, Ikehara K, Usami K (2020) Isotopic and sedimentary signature of megathrust ruptures along the Japan subduction margin. Mar. Geol. 428:106283. doi:10.1016/j.margeo.2020.106283. Mitsuzawa K, Holloway G (1998) Characteristics of deep currents along trenches in the northwest Pacific. J Geophys Res 103(13):13085–13,092. Moreno E, Caroir F, Fournier L, Fauquembergue K, Zaragosi S, Joussain R, Colin C, Blanc-Valleron MM, Baudin F, De Garidel-Thoron T, Valet JP, Bassinot F (2020) Magnetic fabric of Bengal fan sediments: Holocene record of sedimentary processes and turbidite activity from the Ganges–Brahmaputra river system. Mar. Geol. 430:106347. doi:10.1016/j.margeo.2020.106347. Owens WB, Warren BA (2001) Deep circulation in the northwest corner of the Pacific Ocean, Deep-Sea Res. I, 48:959–993. Pares JM (2015) Sixty years of anisotropy of magnetic susceptibility in deformed sedimentary rocks. Frontiers in. Earth Science, 3(4):1–13. doi: 10.3389/feart.2015.00004 Patacci M, Haughton P, Mccaffrey W (2015) Flow behavior of ponded turbidity current, Journal of Sedimentary Research, 85:885–902. doi: dx.doi.org/10.2110/jsr.2015.59. Sagnotti L, Macrì P, Lucchi R, Rebesco M, Camerlenghi A (2011) A Holocene paleosecular variation record from the northwestern Barents Sea continental margin. Geochem Geophys Geosyst 12:Q11Z33. doi:10.1029/2011GC003810. Sawai Y (2020) Subduction zone paleoseismology along the Pacific coast of northeast Japan – progress and remaining problems. Earth-Sci Rev 208:103261. doi:10.1016/j.earscirev.2020.103261. Schwestermann T, Eglinton TI, Haghipour N, McNichol AP, Ikehara K, Strasser M (2021) Event-dominated transport, provenance, and burial of organic carbon in the Japan Trench. Earth Planet. Sci. Lett., 563, 116870, doi: 10. 1016/j.epsl.2021.116870 Soda T (1989) Two 6th Century eruptions of Haruna Volcano, central Japan. Quat. Res. (Daiyonki-kenkyu) 27(297):e312 in Japanese with English abstract. Stoner JS, Channell JET, Hillaire-Marcel C (1996) The magnetic signature of rapidly deposited detrital layers from the deep Labrador Sea: Relationship to North Atlantic Heinrich layers. Paleoceanography 11, 309–325. Tanty C, Valet JP, Carlut J, Bassinot F, Zaragosi S (2016) Acquisition of detrital magnetization in four turbidites. Geochem. Geophys. Geosyst. 17, 3207–3223. doi:10.1002/2016GC006378. Tarling D, Hrouda F (1993) The Magnetic Anisotropy of Rocks, 217 pp., Chapman and Hall, London, U.K. Usami K, Ikehara K, Kanamatsu T, McHugh CM (2018) Supercycle in great earthquake recurrence along the Japan Trench over the last 4000 years. Geosci. Lett. 5, 11. https ://doi.org/10.1186/s4056 2-018-0110-2 Yoshikawa S (1976) The volcanic ash layers of the Osaka Group. J. Geol. Soc. Jpn. 82, 497e515 in Japanese with English abstract Supplementary Files Supplementarydata.docx Cite Share Download PDF Status: Published Journal Publication published 28 Mar, 2023 Read the published version in Progress in Earth and Planetary Science → Version 1 posted Editorial decision: Major revision 31 Oct, 2022 Reviewer # 2 agreed at journal 17 Sep, 2022 Reviewers agreed at journal 31 Aug, 2022 Reviewers invited by journal 31 Aug, 2022 Reviewer # 1 agreed at journal 30 Aug, 2022 Editor assigned by journal 30 Aug, 2022 Submission checks completed at journal 29 Aug, 2022 Editor invited by journal 29 Aug, 2022 First submitted to journal 28 Aug, 2022 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-2008594","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":133021502,"identity":"6713c2c3-e588-4a5f-aca3-a99ed7a9fea6","order_by":0,"name":"Toshiya Kanamatsu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAklEQVRIie2RMUsDMRTHXxGuSyDry9SvkOMgIhz1q7xSqItzFwdvyi2Cq3s/QRdxfCXgLcHZcosi3u4iJwh6rRw45ToK5gcZEv4//rwXgEjkb5IAAWgJ/OsNA3nRK6rYKXSo0qH1voQC0Z7Tcdk8Pdtplm3c6/qjzScgVwwnd4EW4Y/1zM6N4XtTC1qkBTYEygcUPE9wZo9yw2xqIEeAXoOyIeWs6ZTLPCuq921LX4coZDrFGQ3ePApiAnk1oHhvkB6qDNkva7GYpxYT4tAs47JsVLu8SK9vqtttm08nUrrNiwpsbM9o9zXIP5cECZwqBhT47I7sU5Jh9DaoRCKRyD/iG/2OU35faZsAAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-7108-4534","institution":"Japan Marine Science and Technology Center: Kaiyo Kenkyu Kaihatsu Kiko","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Toshiya","middleName":"","lastName":"Kanamatsu","suffix":""},{"id":133021503,"identity":"bf373d21-2631-4300-9e57-aa2063b9d58a","order_by":1,"name":"Ken Ikehara","email":"","orcid":"","institution":"National Institute of Advanced Industrial Science and Technology Geological Survey of Japan: Sangyo Gijutsu Sogo Kenkyujo Chishitsu Chosa Sogo Center","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ken","middleName":"","lastName":"Ikehara","suffix":""},{"id":133021504,"identity":"504666f5-ba37-4f9d-8ac1-a106f4e5b4cf","order_by":2,"name":"Kan-Hsi Hsiung","email":"","orcid":"","institution":"Japan Marine Science and Technology Center: Kaiyo Kenkyu Kaihatsu Kiko","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Kan-Hsi","middleName":"","lastName":"Hsiung","suffix":""}],"badges":[],"createdAt":"2022-08-29 07:00:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2008594/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2008594/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s40645-023-00545-3","type":"published","date":"2023-03-28T20:13:35+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":25995003,"identity":"71560f5b-e203-4973-bc51-b623d754b549","added_by":"auto","created_at":"2022-09-02 16:25:09","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":5982816,"visible":true,"origin":"","legend":"\u003cp\u003ea) Legend map of the study area: red filled diamond show the location of piston cores in this study and the core location in the earlier studies (Kanamatsu et al. 2017, Usami et al. 2018, Kanamatsu et al. 2022); red line box shows the area of Figure 1b. b) Detailed bathymetric map and piston core locations of cores KS1416PC06 and KS1416PC07.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/a93a1364c5904e0047b2bc8c.jpg"},{"id":25994051,"identity":"ba807c04-e45e-4383-9475-3a95c317643b","added_by":"auto","created_at":"2022-09-02 16:20:09","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2898379,"visible":true,"origin":"","legend":"\u003cp\u003eLithology and magnetic properties of cores KS1416PC06 and KS1416PC07: a) and e) lithology; b) and f) magnetic susceptibility (MS); c) and g) ARM/MS ratio; d) and h) “L” magnetic lineation (red line), “F” magnetic foliation (blue line),respectively for cores KS1416PC06 and KS1416PC07. Their definitions are presented in the text. Lithology columns are based on Ikehara et al. (2017). Legend for lithological columns: white, bioturbated diatomaceous clay-silty clay; gray, homogeneous diatomaceous clay-silty clay; blue, homogeneous nannofossil-bearing diatomaceous mud; red, volcanic ash; black thick line, sand layer; dark gray, coarse silt layer.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/9a6158ea79980d66a52243fe.jpg"},{"id":25994052,"identity":"8a500080-d8e4-4e08-a376-78989981e539","added_by":"auto","created_at":"2022-09-02 16:20:09","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2408143,"visible":true,"origin":"","legend":"\u003cp\u003eAMS principal magnetic susceptibility directions projected on the lower hemisphere in an equal-area projection: Kmax (black open box), and Kmin (red open circle) of a) turbidite beds in cores KS1416PC06 and KS1416PC07, and b) AMS directions of hemipelagic intervals in cores KS1416PC06 and KS1416PC07.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/bad6d771d747c5e920e4bccf.jpg"},{"id":25994057,"identity":"038733b7-776c-4a43-aef1-dd944a3ea2bd","added_by":"auto","created_at":"2022-09-02 16:20:09","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1579907,"visible":true,"origin":"","legend":"\u003cp\u003eOrthogonal projections of AFD experiment. a) sample KS1416PC06S4-11 and b) sample KS1416PC07S5-22: s. c) “Day plot” (Day et al. 1977) for hemipelagic samples. SD, PSD, and MD respectively denote single domain, pseudo-single domain, and multidomain fields.\u0026nbsp;d) Stepwise IRM acquisition experiment.\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/a67fe7cbfc1869ca0f060965.jpg"},{"id":25995004,"identity":"49cf759e-58f7-41d1-99fd-2bac83fa4e33","added_by":"auto","created_at":"2022-09-02 16:25:09","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":2601458,"visible":true,"origin":"","legend":"\u003cp\u003ea) and e) declination data with 0° (grey broken line) for cores KS1416PC06 and KS1416PC07, and b) and d) inclination data with GAD inclination (grey broken line) for cores KS1416PC06 and KS1416PC07, respectively. ΔD\u003csub\u003e95\u003c/sub\u003e and ΔI\u003csub\u003e95\u003c/sub\u003e (Khokhlov and Hulot 2016) shown with declinations and inclinations. Gray hatched intervals indicate turbidite beds.\u003c/p\u003e","description":"","filename":"Figure5a.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/42602bece805283a76cddd6c.jpg"},{"id":25994054,"identity":"227336ee-0124-4de5-a7b1-a7a37c21f84e","added_by":"auto","created_at":"2022-09-02 16:20:09","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":3394717,"visible":true,"origin":"","legend":"\u003cp\u003eDeclination and inclination data after removal of turbidite intervals: a) declination of KS1416PC06, b) declination of KS1416PC07, c) declination of Archeo3k.1 d) inclination of KS1416PC06, e) inclination of KS1416PC07, f) inclination n of Archeo3k.1, respectively. ΔD\u003csub\u003e95\u003c/sub\u003e and ΔI\u003csub\u003e95\u003c/sub\u003e are also shown for declinations and inclinations. Broken lines indicate the horizon of turbidite beds. A-D, a-e are tie points used in correlation between core data and Arche3k.1. g) Fitteing KS1416PC06 declination data (red line) to that of Arche3k.1(gray line), h) KS1416PC06 inclination data (red line) to that of Arche3k.1(gray line), i) KS1416PC07 declination data (red line) to that of Arche3k.1(gray line), j) KS1416PC07 inclination data (red line) to that of Arche3k.1(gray line)\u003c/p\u003e","description":"","filename":"Figure6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/f2b2c9927baf4b97efe816b9.jpg"},{"id":25994055,"identity":"008df8dc-3b98-4364-bdb3-598b8acdac2d","added_by":"auto","created_at":"2022-09-02 16:20:09","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2837932,"visible":true,"origin":"","legend":"\u003cp\u003eContemporaneous turbidite beds and magnetic susceptibility profiles in the Japan trench basins and the slope basins: cores KS1416PC10 and KS153PC10 (Kanamatsu et al. 2022); cores KS1319PC10 and KS1319PC8 (redrawn from Kanamatsu et al. 2017). Red arrows indicate high magnetic susceptibility peaks. Orange line show bases of turbidites of “Kyotoku”, “Jogan”, and “2.3ka”. Black broken lines show the correlations of other turbidite beds in the studied cores. Note scales of horizontal axes are expressed by log scale.\u003c/p\u003e","description":"","filename":"Figure7a.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/96e3c75260dd72b2c467bb32.jpg"},{"id":25994060,"identity":"e4338b17-cbb7-4e62-a6dd-de89cb9319b4","added_by":"auto","created_at":"2022-09-02 16:20:09","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":2846204,"visible":true,"origin":"","legend":"\u003cp\u003eAMS data of core KS1416PC06. Magnetic susceptibility (MS), “L” and “F” and Kmin inclinations of each turbidite beds and stereo plots of with inferred paleo flow. Blue filed arrows, basal sandy interval; white arrow, upper muddy interval; Orange arrows, possible shearing, shorting, or rolling directions. Great circle perpendicular to the Kmin is drawn in red lines.\u003c/p\u003e\u003cp\u003ea)\u0026nbsp;core KS1416PC06, b) core KS1416PC07.\u003c/p\u003e","description":"","filename":"Figure8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/6570fe672cc8959e3d3b29cd.jpg"},{"id":25995005,"identity":"e68c3ef8-f2b9-4a00-b837-e872beb2fa2c","added_by":"auto","created_at":"2022-09-02 16:25:09","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":4011022,"visible":true,"origin":"","legend":"\u003cp\u003eAMS data of core KS1416PC07. Magnetic susceptibility (MS), “L” and “F” and Kmin inclinations of each turbidite beds and stereo plots of with inferred paleo flow. Blue filed arrows, basal sandy interval; white arrow, upper muddy interval; Orange arrows, possible shearing, shorting, or rolling directions. Great circle perpendicular to the Kmin is drawn in red lines.\u003c/p\u003e","description":"","filename":"Figure9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/f13cbf8920115033aaf527c4.jpg"},{"id":44723704,"identity":"bed8936d-665d-4489-986d-8dab5306e41f","added_by":"auto","created_at":"2023-10-16 20:18:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1480423,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/c0fa2b85-89d3-4fe7-adad-30f9378f1fcb.pdf"},{"id":25995725,"identity":"36732fd0-0077-48ed-aeb4-bbee645f77a5","added_by":"auto","created_at":"2022-09-02 16:30:09","extension":"docx","order_by":18,"title":"","display":"","copyAsset":false,"role":"supplement","size":39369,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarydata.docx","url":"https://assets-eu.researchsquare.com/files/rs-2008594/v1/9e7724298ea5d4bcbd99419d.docx"}],"financialInterests":"","formattedTitle":"Submarine paleoseismology in the Japan Trench of northeastern Japan: turbidite stratigraphy and sedimentology using paleomagnetic and rock-magnetic analyses","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eGeological data along the Japan Trench are expected to provide spatial and temporal information related to plate boundary megathrust earthquakes as the 2011 Tohoku-oki earthquake. Evidence of historical and pre-historical huge earthquakes have often been found as onshore tsunami deposits (e.g., Sawai \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Furthermore, deep-sea turbidites in the Japan Trench have been reported as indication of huge earthquakes (Ikehara et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Kioka et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003ea; McHugh et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The massive thick turbidite in the trench basin were attributed to the remobilization of large amounts of sediment from slopes during the earthquakes. The three distinctive thick turbidite beds were discovered off Miyagi in the Japan Trench at ~\u0026thinsp;38\u0026deg; N (Ikehara et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The uppermost turbidite bed is regarded as having formed during the 2011 Tohoku-oki earthquake. The next two upper turbidite beds have been correlated with the 1454 common era (CE) \u0026ldquo;Kyotoko\u0026rdquo;, and the 869 CE \u0026ldquo;Jogan\u0026rdquo; earthquakes (Ikehara et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Bao et al. 2018). Ikehara et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2018\u003c/span\u003e show those three turbidites beds were recognized widely in 37\u0026deg;25\u0026rsquo;- 38\u0026deg;30\u0026rsquo;N along the Japan Trench. Because at least some of those turbidite beds can be regarded as the consequences of surface sediment remobilization induced by strong ground shaking (McHugh et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Schwestermann et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), the lateral correlation of turbidite beds along the Japan Trench provide important data to elucidate not only the timing but the affected area by past huge earthquakes.\u003c/p\u003e \u003cp\u003eOn the contrary, the formation mechanism of turbidites with thick mud in the Japan Trench has been not yet fully understood, but their depositional mechanisms may be similar to that of \u0026ldquo;homoginite\u0026rdquo; which is considered to be related to earthquake-event in a confined basin (e.g. Beck et al. 2007).\u003c/p\u003e \u003cp\u003eDating of turbidite beds is essential information for this work. Nevertheless, it is difficult to determine precise depositional ages of turbidite because of a lack of suitable methods to analyze the sediment deposited in super deep basins (over 7000-m water depth), especially for the time range in historical time. Kanamatsu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2017\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2022\u003c/span\u003e developed the dating method of turbidite beds using paleomagnetic secular variation (PSV) records. Moreover, they found that the derived ages are well correlated to the ages of huge earthquakes in historical documents. They found that excellent PSV records are preserved in Japan Trench sediments because of the high sedimentation rate of the hemipelagic interval.\u003c/p\u003e \u003cp\u003eGeophysical and geological distinctive features in the Japan Trench related to the 2011 Tohoku-oki earthquake have been discovered through intensive investigations after the earthquake (e.g. Kodaira et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Results of some studies suggest that a large displacement occurred around 38\u0026deg;N because of the 2011 Tohoku-oki earthquake (Fujiwara et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Kodaira et al. 2012; Strasser et al. 2012), but no major bathymetric change was associated with the earthquake north of 39\u0026deg;N (Fujiwara et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Fujie et al. (2022) interpreted the smectite-rich pelagic clay layer at around 39\u0026deg;N in the subduction sediment as having been disturbed or as having metamorphosed by an interplate \u0026ldquo;pettispot volcanism\u0026rdquo; (Hirano et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). They proposed that the smectite-rich pelagic clay layer around 39\u0026deg;N might be a barrier to the northward propagation of large, shallow coseismic slip of the 2011 Tohoku-oki earthquake. Based on that knowledge, 39\u0026deg;N in the Japan Trench should a unique boundary for constraint of rapture width not only for the 2011 Tohoku-oki earthquake but also past huge earthquakes that occurred along the Japan Trench.\u003c/p\u003e \u003cp\u003eWe, therefore, examined the distribution of turbidite along the Japan Trench as a proxy of past huge earthquake occurrences in order to explore this concept. We studied turbidite records in sediment samples taken at Japan Trench at 39\u0026deg;N, aiming to understand whether the turbidite depositions at 39\u0026deg;N occurred simultaneously with those at south of 38\u0026deg;30\u0026rsquo;N previously reported, and their depositional mechanism at 39\u0026deg;N.\u003c/p\u003e"},{"header":"2 Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1 Materials\u003c/h2\u003e\n\u003cp\u003eThe graben and horst structure have been produced on the subducting Pacific plate in the Japan Trench. Isolated and semi-isolated basins develop in the graben and trench floor along the Japan Trench (Kioka et al. \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e). Thick sedimentary sequences recognized acoustically in the basins are distributed in basins of narrow-width (Kioka et al. \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e). Piston cores KS1416PC06 (39\u0026deg;01. 9\u0026rsquo; N, 144\u0026deg;14.8\u0026rsquo; E, water depth 7394m) and KS1416 PC07 (39\u0026deg;02.2\u0026rsquo; N, 144\u0026deg;12.6\u0026rsquo; E, water depth 7282m) were obtained in a graben basin and a trench basin respectively. The location of core KS1416PC07 is on the trench basin near the landward slope, which is 11 km in length and less than 3 km in width. The location of core KS1416PC06 is in a graben basin east of the core KS1416PC07 basin, which is 30 km in length and less than 2 km in width. The both basins are separated by a ridge of few hundred meters\u0026rsquo; height (horst) (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb). The north and south extensions of KS1416PC07 basin are topographically closed. However, the core KS1416PC06 basin extends continuously to the north and south.\u003c/p\u003e\n\u003cp\u003eThe respective lithologies of cores KS1416PC06 and KS1416PC07 were reported by Ikehara et al. (\u003cspan class=\"CitationRef\"\u003e2017\u003c/span\u003e). Their lithostratigraphy in the upper part of the sediment cores KS1416PC06 and KS1416PC07 (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and h) reveals that the thick turbidite units show similarities to those reported earlier (Ikehara et al. \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e). According to the results of that study, several turbidite beds were recognized in both cores. Thicknesses of turbidite beds range from centimeters to more than one meter. These beds are sometimes composed of a few to several amalgamated subunits. Other than turbidite interval, hemipelagite interval is recognized by presences of bioturbation in the visual description. For this study, the turbidite beds are labeled sequentially as presented in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eh.\u003c/p\u003e\n\u003cp\u003eOther than turbidite and hemipelagic beds, a tephra layer containing glass shards is found in the interval between 392.2 cm and 394.5 cm in core KS1416PC07.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2 Sample analysis\u003c/h2\u003e\n\u003cp\u003ePaleomagnetic and rock magnetic samples (2.2-cm square plastic cube) were taken from halved sections of cores KS1416PC06 and KS1416PC07. The remanent magnetizations were measured using a superconducting rock magnetometer (2G Enterprises model 760) at Japan Agency for Marine-Earth Science and Technology (JAMSTEC). All the samples were demagnetized with alternating field demagnetization (AFD) at step-wise levels of 5mT between 0 and 40 mT, and 10 mT between 50 and 80 mT. Natural remanent magnetization (NRM) was measured after each demagnetization treatment. Anhysteretic remanent magnetization (ARM) was imparted in an 80 mT alternating field with a 0.1 mT direct field. The inclinations, declinations, and maximum angular deviation (MAD) values of NRM of all the sample were calculated using software (PuffinPlot; Lurcock and Wilson \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eAiming at documenting the thick-turbidite textural characteristics using magnetic properties, the magnetic susceptibility (MS) and its anisotropy (AMS) was measured using KLY-4 (Agico Inc.) at JAMSTEC. Directions and magnitudes of three principal susceptibility axes: maximum (Kmax), intermediate (Kint), and minimum (Kmin) are obtained by measurements. The AMS parameters \u0026ldquo;L\u0026rdquo; (Kmax/Kint) for characterizing the linearity and \u0026ldquo;F\u0026rdquo; (Kint/Kmin) for characterizing the oblateness of samples are calculated from magnitudes of three principal susceptibilities to determine their shape of magnetic fabric (Tarling and Hrouda \u003cspan class=\"CitationRef\"\u003e1993\u003c/span\u003e). Another rock magnetic measurements were performed to investigate the sample's magnetic properties. The domain state and coercivity of selected samples from the hemipelagic interval were measured by a vibrating sample magnetometer (VSM, model 2900; Princeton Measurements Corp.). Saturation remanent magnetization (Mr), saturation magnetization (Ms), and coercive force (Hc) were calculated after paramagnetic contributions were removed. We also obtained the coercivity of the remanence (Hcr) of each sample by VSM measurements.\u003c/p\u003e\n\u003cp\u003eAlso, the isothermal remanent magnetization (IRM) acquisition experiments were performed on those samples. The S-ratio (Bloemendal et al. \u003cspan class=\"CitationRef\"\u003e1992\u003c/span\u003e) was obtained, which is used to estimate magnetic mineralogy. We consider that the magnetic particle size is very informative to recognize turbidite depositional structures such as fining upward. It was investigated using the simple proxy of ferrimagnetic grain size (ARM/MS) (Banerjee et al. \u003cspan class=\"CitationRef\"\u003e1981\u003c/span\u003e; King et al. \u003cspan class=\"CitationRef\"\u003e1982\u003c/span\u003e), which changes inversely with magnetic particle size increasing in the range of 1\u0026ndash;10 \u0026micro;m (e.g. Stoner et al. \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eOne tephra bed is involved in the interval between 392.2 and 394.5 cm in core KS1416PC07. The morphology and refractive index of volcanic glass shards and the mineral composition of the bed was assessed by Kyoto Fission Track Ltd., Kyoto, Japan, for correlation with earlier reported tephra deposits in the Japan Trench.\u003c/p\u003e\n\u003cp\u003eThe obtained paleomagnetic data were compared to a master curve of secular variation (ARCH3k.1: Korte et al. \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e), which was generated through compilation between 0 and 3 ka archeomagnetic data. ARCH3k.1 was also used in the previous studies in the Japan Trench (Kanamatsu 2017, 2022), because they are suitable for paleomagnetic field study in Europe and Asia, and reliable for the Northern hemisphere data (Donadini et al. \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e). We used \u0026ldquo;StratFit\u0026rdquo; software (Sagnotti and Caricchi 2018) to compare the obtained paleomagnetic data to the master data. The tie points were selected as apparent peaks and troughs in the inclination and declination profiles (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). Using \u0026ldquo;StratFit\u0026rdquo;, we obtained the age of each core.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eTie point between cores and ARCHE3k.1 data *: depth after turbidite removing\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDeclination point\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eARCHE3k.1\u003c/p\u003e\n\u003cp\u003eAge(year)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ePC06\u003c/p\u003e\n\u003cp\u003edepth* (cm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ePC07\u003c/p\u003e\n\u003cp\u003edepth* (cm)\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\u003eB\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e923 CE\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e78.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e119.3\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eC\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e105 BCE\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e169.9\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eD\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e939 BCE\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eInclination point\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eARCHE3k.1\u003c/p\u003e\n\u003cp\u003eAge(year)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003ePC06\u003c/p\u003e\n\u003cp\u003edepth* (cm)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003ePC07\u003c/p\u003e\n\u003cp\u003edepth* (cm)\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1672 CE\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e25.2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1225 CE\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e61.8\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003ec-\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e475 CE\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e86.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003ed\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e238 CE\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e110.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"3 Results","content":"\u003cdiv class=\"Section2\" id=\"Sec6\"\u003e\n \u003ch2\u003e3.1 Depth variation of magnetic parameters\u003c/h2\u003e\n \u003cp\u003eThe profiles of magnetic susceptibility (MS), ARM/MS (parameters for magnetic grain size), AMS parameters \u0026ldquo;L\u0026rdquo; and \u0026ldquo;F\u0026rdquo; with depth are plotted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. Extremely instant peaks of MS are generally found in silt to very fine sand layers corresponding to bases of turbidite beds in intervals between 0 and 200 cm (P6t1-P6t6) in core KS1416PC06, and between 0 and 400 cm (P7t1-P7t5) in core KS1416PC07 (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb and \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eg). Multiple fining-upward sub-beds are observed in some turbidite beds. For example, MS shows an increase at the base of turbidite at 288 cm of P7t1 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ef). It decreases gradually upward. Then a small MS increase in the silt layer occurs. Prominent MS peaks occur in the silt and coarse silt layer at 58 cm and 80 cm in unit P7t1.\u003c/p\u003e\n \u003cp\u003eAmong all the turbidite beds, the highest peaks of MS occur at 198 cm in P6t4 and in at 380 cm P7t2 in respective cores.\u003c/p\u003e\n \u003cp\u003eAnalysis by ARM/MS reveals an approximate mirror image with MS above 180 cm in core KS1416PC06 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec) and above 400 cm in KS1416PC07 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eg). The ARM/MS indicate a large grain size at the base of turbidite beds. For example, a sudden increase of grain size at the base of P7t2 and a gradual decrease upward. The ARM/MS values gradually or rapidly approach that of the overlying hemipelagite. Those features are interpreted as arising from the finning-upward of the turbidite beds.\u003c/p\u003e\n \u003cp\u003eHowever, below 180 cm (P6t5-P6t9) in core KS1416PC06, and 400 cm (P7t3-P7t6) in core KS1416PC07, a sharp peak of MS does not occur always in the turbidite bases. Also, ARM/MS show no upward decreasing pattern. Moreover, MS of P6t5-P6t9, and P7t3-P7t6 are markedly weaker than those of overlying and underlying hemipelagic intervals.\u003c/p\u003e\n \u003cp\u003eThe different variation in MS between the turbidite and the hemipelagite is considered to cause from their different content of magnetic minerals. The magnetic mineral content in hemipelagite would be homogenized by bioturbation, while the MS variation of turbidite interval is not affected by bioturbation but the depositional process. The MS homogenization of hemipelagite is suggested by smoothed variation without spiky change of MS (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). A change of ARM/MS between turbidite and hemipelagite is interpreted to reflect a different size of magnetic particle. The ARM/MS in turbidite is considered to reflect grain size sorting during turbidite deposition. The muddy interval of turbidite bed is also well sorted in grain size, which could make difference from the homogenized magnetic grain size of hemipelagite.\u003c/p\u003e\n \u003cp\u003eIn addition to MS peaks of turbidites, prominent peaks were found in the tephra bed at 398 cm in core KS1416PC07 and at 190 cm in a hemipelagic interval of core KS1416PC06.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec7\"\u003e\n \u003ch2\u003e3.2 Magnetic fabric\u003c/h2\u003e\n \u003cp\u003eResults of AMS measurements are used to investigate the sediment fabric of turbidite beds reflecting depositional mechanisms. Because of the small number of data in the thin beds (P6t2, P6t5, P6t6), we excluded the beds from the evaluation.\u003c/p\u003e\n \u003cp\u003eActually \u0026ldquo;L\u0026rdquo; is generally low: close to 1.0 in both cores of KS1416PC06 and KS1416PC07 (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed and \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eh), except for the interval of 60\u0026ndash;300 cm in core KS1416PC07.\u003c/p\u003e\n \u003cp\u003eSome turbidite beds reveal increasing \u0026ldquo;F\u0026rdquo; around their bases (P6t3, P6t8, Pt7t1, P7t3, P7t4, P7t5). High \u0026ldquo;F\u0026rdquo; are observed at upper interval rather than at basal interval in the turbidite beds (P6t1, P6t4, P6t6, P7t2). For example, P6t1 and P7t1 show high \u0026ldquo;F\u0026rdquo; values at the upper depth of the turbidite beds, the lithostratigraphy indicates that these high \u0026ldquo;F\u0026rdquo; values occur in the other overlying subunit beds.\u003c/p\u003e\n \u003cp\u003eAMS directions are orientated by the mean of paleomagnetic declination of the cores. AMS directions (Kmax, Kint, and Kmin) of the turbidite beds are plotted on the lower hemisphere equal area projections (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea). Along with the turbidite beds, AMS of all the hemipelagic intervals in each core is shown respectively in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb.\u003c/p\u003e\n \u003cp\u003eThree patterns of AMS directions are recognized based on the directional distributions of Kmax, Kint and Kmin.\u003c/p\u003e\n \u003cp\u003e1) A girdle formed by the Kmax and Kint axes (e. g. P6t1 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea, P7t5 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea). The girdle plane of this type is slightly oblique to the horizontal plane. The directional distributions of Kmax and Kint axes are largely overlapped or weakly clustered with each other. The Kmin axes slightly deviate from the vertical axes.\u003c/p\u003e\n \u003cp\u003e2) Kmax axis distribution shows strong clustering and Kint and Kmin axes form a girdle around the Kmax axis (e. g. P7t1 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea).\u003c/p\u003e\n \u003cp\u003e3) Kmax and Kint axes are scattered in the horizontal plane of equal area projection (e. g. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb). Kmin is well clustered, perpendicular to the horizontal plane.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec8\"\u003e\n \u003ch2\u003e3.3 Remanent magnetization\u003c/h2\u003e\n \u003cp\u003eSimple decreasing of horizontal and vertical magnetic components during AFD experiments reveal stable single component in most samples (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb). Saturations of IRM around 300 mT and the S-ratio ranging about 0.98 in the selected samples indicate that the magnetization is carried by low coercive force magnetic minerals, such as magnetite. Ratios Mrs/Ms and Hcr/Hc of the hysteresis parameter plotted in Day diagram (Day et al., \u003cspan class=\"CitationRef\"\u003e1977\u003c/span\u003e) indicate that the values range in the pseudo-single domain state (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec).\u003c/p\u003e\n \u003cp\u003eFigures \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea, \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb, and \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec are plots of the component-analyzed inclination and declination. The declination is expressed as a relative declination with \u0026Delta;D\u003csub\u003e95\u003c/sub\u003e and \u0026Delta;I\u003csub\u003e95\u003c/sub\u003e (95% confidence level converted from MAD; Khokhlov and Hulot \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e). The \u0026Delta;D\u003csub\u003e95\u003c/sub\u003e and \u0026Delta;I\u003csub\u003e95\u003c/sub\u003e are mostly large at the turbidite intervals, indicating that the obtained magnetic directions are unstable. A large break exists in the declination variation at 65 cm and the scattered in the interval above 65 cm in core KS1416PC06 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea), which might have been horizontally twisted during piston coring or during handling or the core sample operations before taking the subsamples. The values of \u0026Delta;D\u003csub\u003e95\u003c/sub\u003e and \u0026Delta;I\u003csub\u003e95\u003c/sub\u003e are also high in 0\u0026ndash;65 cm in core KS1416PC06 (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb), indicating that some artificial influence might have affected the magnetization. In accordance with the observations above, the interval was excluded from the paleomagnetic interpretation.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec9\"\u003e\n \u003ch2\u003e3.4 Tephra\u003c/h2\u003e\n \u003cp\u003eThe tephra layer at 392.2-394.5 cm (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) in KS1416PC07 is 2.3 cm thick, coarse silt in grain size, and consisting of fibrous pumice-type glass fragments, which is a glass type of \u0026ldquo;T\u0026rdquo; in the definition by Yoshikawa et al. 1976. Green-colored hornblende and orthopyroxene are the major heavy minerals. Opaque minerals and orthopyroxene are present in trace amounts. The refractive indices of the volcanic glass shards range from 1.5047\u0026ndash;1.5091 (mode: 1.507). These petrographic features are consistent with the Haruna-Futatsudake-Ikaho (Hr-FP) tephra which was previously reported on land and in marine sediments off Sanriku (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e in Ikehara et al., \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e), the occurrence of the Hr-FP tephra in marine sediments is restricted strongly to around 39\u0026ndash;40\u0026deg;N (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eB in Ikehara et al., \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e). This distribution is also consistent with the location of KS1416PC07, in which Hr-FP tephra is found. The erupted age of Hr-FP tephra is considered to have in in the 6th century (Soda 1998).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable border=\"1\" id=\"Tab2\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAges of Turbidite units based on PSV correlation.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTurbidite bed No.\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCE (year)\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\u003eP6t1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e978\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e343\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-45\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-301\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-720\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;-5948\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1254\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e829\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e222\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-171\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;-635\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable border=\"1\" id=\"Tab3\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMean Kmin direction (vertical axis to magnetic foliation) of turbidite beds and hemipelagic intervals of cores KS1416PC06 and KS1416PC07. k: Fisherian precision parameter; \u0026alpha;95\u0026thinsp;=\u0026thinsp;radius of cone of 95% confidence\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eBed No.\u003c/p\u003e\n \u003cp\u003e(subbed)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample Number\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003edeclination\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003einclination\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026alpha;95\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ekappa\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\u003eP6t3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e114\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e645.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t3 base\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e157.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e82.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e113.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e161.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e87.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e229.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t4 base\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e168.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e75.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e724.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e136\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e59.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t7 base\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e166.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e73.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e174.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e145.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e81.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t8 base\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e167.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e67.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2833.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6t9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e97.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e77.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t2u1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e265.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e143.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t2u1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e107\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e88.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e250.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t2 base\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e107.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e78.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e47.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e147.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e76.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e200.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t3base\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e146\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e138\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e67.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t4 base\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e164.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e76.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t5u1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e177.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e78.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t5u2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e162\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e82.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e131.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t5u3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e209.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e73.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e112.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t5u4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e170.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e109\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t5base\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e124.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e69.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7t6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e181.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e77.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7 hemipelagite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e129.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e84.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e28.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6 hemipelagite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e245\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e151.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e79.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"4 Discussion","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n\u003ch2\u003e4.1 PSV record\u003c/h2\u003e\n\u003cp\u003eBecause NRM of turbidite is largely subjected by grain alignment of turbidite deposition (e. g. Tanty et al. \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e), NRM direction of turbidite beds does not reflect geomagnetic field directions. Therefore, NRM of turbidite beds must be excluded from the paleomagnetic stratigraphic interpretation (Kanamatsu et al. \u003cspan class=\"CitationRef\"\u003e2017\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). The boundary between turbidite and hemipelagite can be recognized from rock magnetic parameters of MS and ARM/MS (see section \u003cspan class=\"InternalRef\"\u003e3.1\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003ePSV data constructed by removing turbidite intervals are used to estimate the depositional age of the turbidite beds (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea). After removing the turbidite data, we recalculated the depth of the paleomagnetic data assuming no large gaps in deposition (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). In fact, P6t3 and P6t4 are different turbidite beds which are separated by 2 cm henipelagite. But because thickness is smaller than resolution of sampling (2.2 cm), we regard that the both beds deposition occurred at the same time.\u003c/p\u003e\n\u003cp\u003eThe obtained paleomagnetic data of core KS1416PC07 is correlated to ARCH3k.1 with a tephra key bed (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb). Under the assumption that the sedimentation rates of the hemipelagic intervals in KS1416PC07 are similar to that of core KS1416PC06, we compare the paleomagnetic data using \u0026ldquo;StratFit\u0026rdquo; (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb). The paleomagnetic tie points (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e; Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb) and the eruption age of Hr-FP found in core KS1416PC07, which is regarded as being of 6th century (Soda \u003cspan class=\"CitationRef\"\u003e1989\u003c/span\u003e), are used. The sedimentation rates of the hemipelagic intervals in KS1416PC07 is 81.4 cm/kyr, and that of KS1416PC06 is 71.2 cm/kyr. Because the reference curve is only available for data up to 3,000 years ago, For the older periods, the age is obtained from the extrapolation using the sedimentation rate of that of above interval (The results are available in supplemental data).\u003c/p\u003e\n\u003cp\u003eThe calculated ages of the turbidites are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. Turbidites that can be correlated between cores KS1416PC06 and KS1416PC07 based on age are shown with broken lines in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. 978 CE of P6t3 and P6t4, and 829 CE of P7t2 are close to the turbidite ages previously reported, which are 972 CE (14t3 of core KS1416PC10 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb) and 881 CE (15t3 of core KS1503PC10 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ec). They were determined to correspond to the 869 CE \u0026ldquo;Jogan\u0026rdquo; earthquake (Kanamatsu et al \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). Also, 1254 CE of P7t1 is very close to 1272 CE (14t2 of core KS1416PC10 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb), and 1265 CE (15t2 of core KS1503PC10 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ec), which were attributed to the 1454 CE \u0026ldquo;Kyotoku\u0026rdquo; earthquake (Kanamatsu et al \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). P6t7 (BCE 301) and P7t5 (BCE 171) are close to the ages of turbidite BCE 283 (14t4 of core KS1416PC10 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb) and BCE 128 (15t5 of core KS1503PC10 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ec), which are regarded having been deposited at 2.3 ka. The other comparable pair of turbidites is P6t8 (BCE 720) and P7t6 (BCE 635) judged from their ages.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e shows the turbidite bed correlations and their magnetic susceptibility profiles of cores of this study and previous studies in the Japan Trench and the slope basins near the sites of cores KS1416PC06 and KS1416PC07 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea). Turbidite beds correlated to the \u0026ldquo;Jogan\u0026rdquo; earthquake are characterized by their high magnetic susceptibility values (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e). The occurrence of a \u0026ldquo;Jogan\u0026rdquo; turbidite bed (P7t2) just above the 6th-century Hr-FP tephra is stratigraphically consistent with the interpretation that P7t2 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ed) is correlated to the \u0026ldquo;Jogan\u0026rdquo; earthquake (869 CE), and also profiles of NT1318PC10 and NT1318PC08. Thus, \u0026ldquo;Jogan\u0026rdquo; turbidite was found both on the landward slope and on the trench axis around 39\u0026deg;N. \u0026ldquo;2.3 ka\u0026rdquo; turbidite beds reported in the previous study (Kanamatsu et al \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e) can be correlated to P6t7 and P7t5 in this study, and also to turbidites T5 (about 2.3 ka) in NT1318PC10 and NT1318PC08 (Usami et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eThe uppermost part of core KS1416PC07 is thought to have been deposited at about 1900 CE based on the PSV data (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e). The interval of KS1416PC07 between \u0026ldquo;Kyoutoku\u0026rdquo; (1454 CE) and 1900 CE involve no distinct thick turbidite bed as it was for the older thick turbidites. Whreas within that time interval, the records of tsunami and tsunami deposits along the coast off Tohoku are well documented of the 1611 CE Keicho and 1896 CE Meiji Sanriku tsunamis (e.g. Sawai et al. 2020). A turbidite corresponding to 1896 CE Meiji Sanriku is also found in the slope sediment off the northern Tohoku (Ikehara et al. submitted).\u003c/p\u003e\n\u003cp\u003eSmall magnetic susceptibility peaks and upward fining patterns in ARM/MS observed in core KS1416PC07 may be related to the Meiji Sanriku earthquakes judged from its stratigraphic position (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n\u003ch2\u003e4.2 Magnetic fabric\u003c/h2\u003e\n\u003cp\u003eAMS directions are used to presume local current flow direction during turbidite bed depositions. Axes of the magnetic susceptibility are reorientated by the mean directions of paleomagnetic declination of the cores. Because the paleomagnetic data of P6t1 is not available, AMS direction of P6t1 is without directional reconstruction.\u003c/p\u003e\n\u003cp\u003eUnder a hydraulic flow, Kmax axes could be parallel to a flow direction, whereas the Kmax axis could be transverse to the flow direction in a strong flow condition (e.g. Taring and Hrouda 1983). Perpendicular Kmax to the current direction is formed in a strong flow, which roll grains over the surface (e.g. Baas et al. \u003cspan class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eTaira and Scholle (1979) proposed an AMS fabric evolution in a turbidite deposition. They demonstrated the relationship between the shape type and orientation of principle AMS axes, and turbidite depositional environments, which is defined by divisions of the Bouma sequence (Bouma \u003cspan class=\"CitationRef\"\u003e1962\u003c/span\u003e). They demonstrated in the basal part of turbidite that \u0026ldquo;subdivision A\u0026rdquo; is characterized by perpendicular Kmax distribution to the flow direction and tilting Kmin upstream (imbrication). They revealed that Kmax orientation in the upper part of \u0026ldquo;division A\u0026rdquo;, and \u0026ldquo;divisions B and C\u0026rdquo;, changes to be parallel to the flow direction. The imbrication angle dipping to upstream is gradually shallow. Consequently, the Kmax direction can be parallel and perpendicular to a flow direction during turbidite deposition. It implies that the flow analysis using only Kmax direction is difficult without understanding the depositional environment of the \u0026ldquo;subdivision\u0026rdquo; of turbidite. For this study, we therefore use the Kmin dipping direction to investigate a local current direction as suggested by Taring and Hroud 1983.\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eShallower of Kmin inclinations are observed around the base of turbidite beds (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e), and in several cm from the base of turbidite beds. For example, in P6t4 (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e) and P7t5 (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e) respectively. This observation indicating an imbricated fabric around the basal interval is consistent with the magnetic fabric evolution model presented by Taira and Scholle 1979.\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eWe divided AMS directions of a turbidite bed into a basal sandy interval and an upper muddy interval, because depositional conditions of the two intervals could be different in confined basins. For the upper interval of homogeneous mud, unique depositional models for explaining a thick muddy bed have been proposed based on natural observations and experiments. A suspension cloud caused by a flow rebound in a confined basin have been considered for forming the thick muddy interval (e.g. Patacci et al \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e). Furthermore, \u0026ldquo;homogenite\u0026rdquo; deposition related to earthquake-event in a confined basin was proposed (e.g. Beck et al. 2007; McHugh et al 2016; Polonia et al 2017). A massive structureless characteristic of \u0026ldquo;homogenite\u0026rdquo; is considered to be induced by seiche effects generated by the earthquakes. The seiche motion increases segregation of the fine-grained fraction and sustains the suspension (Beck et al 2007) or induces fine-grain flows in the suspension (McHugh et al., 2006). Another interpretation is that the thick deposits are attributed to multiple simultaneous turbidite formation induced by an earthquake (e.g., Goldfinger et al., \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eThe thick and homogenous muddy intervals in turbidite beds recognized in cores KS1416PC06 and KS1416PC07 were possibly have been formed by the similar mechanisms in the small and narrow basins along Japan Trench. In such a case, the basal sandy interval and upper muddy interval were formed under different hydraulic conditions. Accordingly, the basal sandy interval and upper muddy interval are divided for interpretation.\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eThe divided AMS directions of turbidite beds are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e. We regard mean Kmin dipping directions as current directions for turbidite beds (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eA dominant AMS direction in the basal sandy intervals for core KS1416PC07 (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e) is revealed to southeast, whereas the dominant AMS direction for core KS1416PC06 (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e) is south-southeast (P6t1 is exception due to no paleomagnetic data). By contrast, the directions of the upper muddy intervals are diverse. Some sites show no prevailing flow direction of muddy portion indicated by vertical Kmin. (e.g. P6t4 in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e). It is interpreted as a deposition under still hydraulic conditions.\u003c/p\u003e\n\u003cp\u003eIn the most cases of muddy upper intervals, the AMS directions are slightly oblique to their basal directions (e.g. P6t7, P6t8 in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e, P7t3, P7t4 in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e). The smaller changes in flow directions are suggested during the upper interval depositions. In the thick upper portion of P7t5 (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e), the intervals are subdivided into several beds based on directions. They are changing frequently, but the major direction seems to be southward.\u003c/p\u003e\n\u003cp\u003eOn the other side, AMS directions of upper intervals in two beds (P6t1 in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e and P7t2 in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e) show anti-parallel directions to their basal directions, although AMS of P6t1 bed is not reoriented by paleomagnetic directions. AMS of P7t2 indicates that an eastward flow in the initial depositional stage changed to a westward flow in the upper muddy deposition. Those changes might be occurred by deflection and reflection of currents which were controlled by topographical contains (e.g. Patacci et al. \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e). The oblique flow directions observed in many cases could be explained by deflection of flows from the initial flow, which is oblique to north-south extending edges of basins (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb). The reversed direction of P7t2 could be explained by a reflection of eastward flow against the west facing ridge of the basin.\u003c/p\u003e\n\u003cp\u003eThe general consistent directions among basal beds of each core may implicate a primal mechanism controlling the direction during initial deposition. Their local slope topography may be a possible control factor which constrain a flow pathway. The steep slope west side to core KS1416PC07 location could have induced southeastward flows (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb). On the other side, the south-southeast directions in core KS1416PC06 suggest flows along the basin axis (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb). The causes of different direction of muddy upper interval could be caused from many factors originated from flow properties (flow thickness, sastainment of flow, initial flow direction etc.) and basin properties (volume, shape, axis direction etc).\u003c/p\u003e\n\u003cp\u003eThe AMS variation of P7t1 is greatly in contrast to the other AMS axis directional patterns (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e). P7t1 is subdivided into subbed based on AMS directions. The AMS direction of the basal part (subbed \u0026ldquo;P7t1base\u0026rdquo;) can be interpreted as rolling of the Kmax directions perpendicular to a strong flow, suggesting northeastward or southwestward. However, the Kint axes become well clustered in vertical and the Kmin axes horizontal in subbed \u0026ldquo;P7t1u3\u0026rdquo; with the horizontal Kmax direction. The Kint and Kmin directions of the subbed \u0026ldquo;P7t1u2\u0026rdquo; are regard as similar to that of subbed \u0026ldquo;P7t1base\u0026rdquo;. The subbeds \u0026ldquo;P7t1base\u0026rdquo; and \u0026ldquo;P7t1u2\u0026rdquo; can be interpreted as having been formed under strong flows from the northeast or southwest. Also subbed \u0026ldquo;P7t1u1\u0026rdquo; has Kmax and Kint scattered in a horizontal plane: a direction under still hydraulic condition. However, horizontal Kmin and vertical Kint of subbed \u0026ldquo;P7t1u3\u0026rdquo; are enigmatic directions as sedimentary fabric. This type is usually reported as \u0026ldquo;prolate type\u0026rdquo; indicting layer parallel sharing or layer parallel shortening (e.g. Pares 2014), although we have no evidence based on data from this study to discuss the possibility of deformation.\u003c/p\u003e\n\u003cp\u003eThe AMS directions in all the hemipalegite intervals of core KS1416PC07 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb) show no preferred orientation in Kmax, suggesting a still hydraulic condition during hemipelagic deposition. By contrast, the AMS direction of hemipelagite in core KS1416PC06 are indicated as southward (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb). The obtained direction of KS1416PC06 may suggests the exist of bottom current during hemipelagite deposition. The extensions of the basin of core KS1416PC06 are not closed topographically, but closed in the basin of core KS1416PC07 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb). This topographical setting would allow a flow entering from north in the basin of core KS1416PC06, but restrict a flow entering in the basin of core KS1416PC07 site, if a deep current system exists in the trench floor. Although no study of deep-sea bottom current on the floor of Japan Trench over 7,000 m has been reported, several reports have described long-term steady bottom currents in both landward (southward flow) and seaward (northward flow) slopes along the Japan Trench as deep western boundary currents in ~\u0026thinsp;6,000 m water depth (Mitsuzawa et al. 1998, Fujio and Yanagimoto 2005). Mitsuzawa et al. 1998 reported the deep western boundary current flows south-southwest in the landward slope of the Japan Trench with mean speed of 3\u0026ndash;7 cm/s and maximum speed of 15\u0026ndash;20 cm/s. On the other side, a deep bottom current in the abyssal plain in the east of Japan Trench reveals westward (Owens and Warren, \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e, Fujio and Yanagimoto 2005). AMS study for surface sediments in the abyssal plain east of the Japan Trench (Kawamura et al. \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e) revealed the AMS directions as generally parallel to the deep bottom current in the abyssal plain. Because a flow of more than 1cm/s current can form imbricated magnetic fabric (Taring and Hrouda 1993), a few cm/s of bottom current might generate the flow pattern in AMS in the hemipelagite.\u003c/p\u003e\n\u003cp\u003eAMS data of turbidite basal sandy beds in the 39\u0026deg;N, the Japan Trench floor indicate a flow to southeast at core KS1416PC07 location, and south-southeast at core KS1416PC06 location. However, the directions of most thick muddy interval of turbidite beds are not always consistent to those of their basal sandy intervals. These AMS directions indicate no consistent flow direction during thick muddy part of turbidite, and suggest a complex hydraulic condition in the elongated small basin. Although more dense spatial AMS data should be necessary to confirm the flow evolution in the confined basin, we demonstrated the possibility that the AMS method might be able to reconstruct the complex flow patten.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003e(1) Turbidites of ages in two cores corresponding to the 1454 CE \u0026ldquo;Kyoutoku\u0026rdquo;, 869 CE \u0026ldquo;Jogan\u0026rdquo; and \u0026ldquo;2.3 ka\u0026rdquo;, were recognized in the Japan Trench floor at 39\u0026deg;N as confirming finding from earlier reported piston core samples obtained at 38\u0026deg;-38\u0026deg;30\u0026rsquo;N.\u003c/p\u003e\n\u003cp\u003e(2) High magnetic susceptibility was widely observed for the turbidites corresponding to the \u0026ldquo;Jogan\u0026rdquo; earthquake. The 39\u0026deg;N \u0026ldquo;Jogan\u0026rdquo; turbidite is associated with a distinct MS peak arising from tephra \u0026ldquo;Hr-FP\u0026rdquo; just below the turbidite horizon. These clear signatures will be useful for identification of the \u0026ldquo;Jogan\u0026rdquo; turbidite.\u003c/p\u003e\n\u003cp\u003e(3) Paleo-flow directions of turbidites based on the magnetic fabric in each core show that the directions from the basal sandy interval and the upper muddy interval in one turbidite bed is not always consistent. The prevailing directions in the basal intervals of turbidites are recognized in each location as southeastward at core KS1416PC07 location in the landward trench-basin, while to south-southeastward at core KS1416PC06 site in the graben-basin.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003ePSV: paleosecular variation, CE: common era, NRM: natural remanent magnetization, ARM: anhysteretic remanent magnetization, AMS: anisotropy of the magnetic susceptibility, MAD: maximum angular deviation, Hr-FP Haruna-Futatsudake-Ikaho tephra\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch3\u003eAvailability of data and material\u003c/h3\u003e\n\u003cp\u003eObtained data in this study are presented in Tables, and supplemental data. For other data, please contact the corresponding author to request data.\u003c/p\u003e\n\u003ch3\u003eCompeting interests\u003c/h3\u003e\n\u003cp\u003eThe authors declare that they have no competing interest.\u003c/p\u003e\n\u003ch3\u003eFunding\u003c/h3\u003e\n\u003cp\u003eThis work was supported by Japan Society for the Promotion of Science (KAKENHI) Grant No. 19H05596 (Representative: Hino R).\u003c/p\u003e\n\u003ch3\u003eAuthors\u0026apos; contributions\u003c/h3\u003e\n\u003cp\u003eTK led conducted magnetic measurements, constructed the age model, and drafted the manuscript. KI conducted the sedimentological analyses and tephra analysis. KH conducted interpretation of magnetic results. All authors have read and approved the final manuscript.\u003c/p\u003e\n\u003ch3\u003eAcknowledgements\u003c/h3\u003e\n\u003cp\u003eWe thank K. Tsuchida for providing excellent technical support throughout this study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBaas JH, Hailwood EA, McCaffrey WD, Kay M, Jones R (2007) Directional petrological characterisation of deep-marine sandstones using grain fabric and permeability anisotropy: methodologies, theory, application and suggestions for integration. Earth-Science Reviews 82:101\u0026ndash;142. doi:10.1016/j.earscirev.2007.02.003\u003c/li\u003e\n\u003cli\u003eBanerjee SK, King J, Marvin J (1981) A rapid method for magnetic granulometry with applications to environmental studies. Geophys. Res. Lett 8:333\u0026ndash;336. doi:10.1029/GL008i004p00333\u003c/li\u003e\n\u003cli\u003eBao R, Strasser M, McNichol AP, Haghipour N, McIntyre C, Wefer G, Eglinton TI (2018) Tectonically triggered sediment and carbon export to the Hadal zone. Nat. Commun. 9, 121. https ://doi.org/10.1038/s4146 7-017-02504 -1\u003c/li\u003e\n\u003cli\u003eBloemendal J, King JW, Hall FR, Doh SJ (1992) Rock magnetism of late Neogene and Pleistocene deep-sea sediments: Relationship to sediment source, diagenetic processes, and sediment lithology. J Geophys Res 97:4361\u0026ndash;4375.\u003c/li\u003e\n\u003cli\u003eBouma AH (1962) Sedimentology of some flysch deposits: Amsterdam,Elsevier, 168 p.\u003c/li\u003e\n\u003cli\u003eCampos C, Beck C, Crouzet C, Demory F, Van Welden A, Eris K (2013) Deciphering hemipelagites from homogenites through anisotropy of magnetic susceptibility. Paleoseismic implications (Sea of Marmara and Gulf of Corinth). Sediment Geol 292:1\u0026ndash;14. doi:10.1016/j.sedgeo.2013.03.015\u003c/li\u003e\n\u003cli\u003eDay R, Fuller MV, Schmidt A (1977) Hysteresis properties of titanomagnetites: Grain-size and compositional dependence. Phys Earth Planet Inter 13:260\u0026ndash;267 doi:10.1016/0031-9201(77)90108-X.\u003c/li\u003e\n\u003cli\u003eDonadini F, Korte M, Constable CG (2009) Geomagnetic field for 0\u0026ndash;3 ka: 1. New data sets for global modeling. Geochem Geophys Geosys 10. Q06007. doi: 10.1029/2008GC002295.\u003c/li\u003e\n\u003cli\u003eFujie G, Kodaira S, Nakamura Y, Morgan J, Dannowski A, Thorwart M, Grevemeyer I, Miura S (2020) Spatial variations of incoming sediments at the northeastern Japan arc and their implications for megathrust earthquakes. Geology 48 (6): 614\u0026ndash;619. doi:10.1130/G46757.1\u003c/li\u003e\n\u003cli\u003eFujiwara T, Kodaira S, No T, Kaiho Y, Takahashi N, Kaneda Y (2011) The 2011 Tohoku-oki earthquake: displacement reaching the trench axis. Science 334 (6060): 1240. doi:10.1126/science.1211554.\u003c/li\u003e\n\u003cli\u003eFujiwara T, dos Santos Ferreira C, Bachmann AK, Strasser M, Wefer G, Sun T, Kanamatsu T., and Kodaira S. (2017) Seafloor displacement after the 2011 Tohoku-oki earthquake in the northern Japan Trench examined by repeated bathymetric surveys. Geophys Res Lett 44:11833\u0026ndash;11839. doi:10.1002/2017GL075839\u003c/li\u003e\n\u003cli\u003eGoldfinger C, Hans Nelson C, Morey AE, Johson JE, Patton JR, Karabanov E, Gutierrez-Pator J, Eriksson AT, Gracia E, Dunhill G, Enkin RJ, Dallimore A, Vallier T (2012) Turbidite event history \u0026ndash;Methods and implications for Holocene paleoseismicity of the Cascadia subduction zone. In: USGS Professional Paper, 1661- F, p. 184. US Geological Survey. doi:10.3133/pp1661f.\u003c/li\u003e\n\u003cli\u003eHirano N, Takahashi E, Yamamoto J, Abe N, Ingle SP, Kaneoka I, Kimura J, Hirata T, Ishii T, Ogawa Y, Machida S, Suyehiro K (2006) Volcanism in response to plate flexure. Science 313:1426\u0026ndash;1428. Doi:10.1126/science.1128235\u003c/li\u003e\n\u003cli\u003eIkehara K, Kanamatsu T, Nagahashi Y, Strasser M, Fink H, Usami K, Irino T, Wefer G (2016) Documenting large earthquakes similar to the 2011 Tohoku-oki earthquake from sediments deposited in the Japan Trench over the past 1500 years. Earth Planet Sci Lett 445:48\u0026ndash;56.\u003c/li\u003e\n\u003cli\u003eIkehara K, Usami K, Kanamatsu T, Arai K, Yamaguchi A, Fukuchi R (2018) Spatial variability in sediment lithology and sedimentary processes along the Japan Trench: use of deep-sea turbidite records to reconstruct past large earthquakes. Geological Society, London Special Publications 456:75-89. doi:10.1144/SP456 .9\u003c/li\u003e\n\u003cli\u003eIkehara K, \u003cstrong\u003eUsami K\u003c/strong\u003e, Kanamatsu T, Danhara T, Yamashita T (2017) Three important Holocene tephras off the Pacific coast of the Tohoku region, Northeast Japan: Implications for correlating onshore and offshore event deposits. Quaternary international 456:138-153, doi:10.1016/j.quaint.2017.08.022\u003c/li\u003e\n\u003cli\u003eKanamatsu T, Usami K, McHugh CMG, Ikehara K (2017) High-resolution chronology of sediment below CCD based on Holocene paleomagnetic secular variations in the Tohoku-oki earthquake rupture zone. Geochem. Geophys. Geosys. 18:2990\u0026ndash;3002. doi:10.1002/2017GC006878\u003c/li\u003e\n\u003cli\u003eKanamatsu T, Ikehara K, Hsiung KH (2022) Stratigraphy of deep-sea marine sediment using paleomagnetic secular variation: Refined dating of turbidite relating to giant earthquake in Japan Trench, Marine Geology, 443 106669. Doi:10.1016/j.margeo.2021.106669\u003c/li\u003e\n\u003cli\u003eKawamura K, Kanamatsu T, Oishi M, Yamano M (2015) Physical and magnetic properties in piston core samples collected from the Japan Trench before the 2011 Tohoku earthquake. JAMSTEC-R, 20, p. 51-60, doi:10.5918/jamstecr.20.51\u003c/li\u003e\n\u003cli\u003eKing J, Banerjee SK, Marvin J, \u0026Ouml;zdemir \u0026Ouml; (1982) A comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials: some results from lake sediments. Earth Planet Sci Lett 59:404\u0026ndash;419. doi:10.1016/0012-821X(82)90142-X\u003c/li\u003e\n\u003cli\u003eKhokhlov A, Hulot G (2016) Principal component analysis of palaeomagnetic directions: converting a maximum angular deviation (MAD) into an \u0026alpha;95 angle. Geophys J Int 204:279\u0026ndash;291. doi:10.1093/gji/ggv451.\u003c/li\u003e\n\u003cli\u003eKioka A, Schwestermann T, Moernaut J, Ikehara K, Kanamatsu T, Eglinton TI, Strasser M (2019) Event stratigraphy in a Hadal oceanic trench: the Japan Trench as sedimentary archive recording recurrent giant subduction zone earthquakes and their role in organic carbon export to the deep sea. Front Earth Sci 7:319. doi:10.3389/feart .2019.00319\u003c/li\u003e\n\u003cli\u003eKodaira S, Fujiwara T, Fujie G, Nakamura Y, Kanamatsu T (2020) Large Coseismic Slip to the Trench During the 2011 Tohoku-Oki Earthquake, \u003cstrong\u003eAnnual Review of Earth and Planetary Sciences, \u003c/strong\u003e48:321-343, https://doi.org/10.1146/annurev-earth-071719-055216\u003c/li\u003e\n\u003cli\u003eKorte M, Donadini F, Constable CG (2009) Geomagnetic field for 0\u0026ndash;3 ka: 2. A new series of time-varying global models. Geochem. Geophys. Geosyst. 10:Q06008. doi:10.1029/2008GC002297.\u003c/li\u003e\n\u003cli\u003eLurcock PC, Wilson GS, 2012. PuffinPlot: A versatile, user-friendly program for paleomagnetic analysis. Geochem. Geophys. Geosyst. 13:Q06Z45. doi:10.1029/2012GC004098.\u003c/li\u003e\n\u003cli\u003eMcHugh CM, Seeber L, Cormier MH, Hornbach M (2014) Submarine paleoseismology along populated transform boundaries: the Enriquillo-Plantain-Garden fault, Canal du Sud, Haiti, and the North Anatolian Fault, Marmara Sea, Turkey. Oceanography 27:118\u0026ndash;131. www.jstor.org/stable/24862162.\u003c/li\u003e\n\u003cli\u003eMcHugh CM, Seeber L, Rasbury T, Strasser M, Kioka A, Kanamatsu T, Ikehara K, Usami K (2020) Isotopic and sedimentary signature of megathrust ruptures along the Japan subduction margin. Mar. Geol. 428:106283. doi:10.1016/j.margeo.2020.106283.\u003c/li\u003e\n\u003cli\u003eMitsuzawa K, Holloway G (1998) Characteristics of deep currents along trenches in the northwest Pacific. J Geophys Res 103(13):13085\u0026ndash;13,092.\u003c/li\u003e\n\u003cli\u003eMoreno E, Caroir F, Fournier L, Fauquembergue K, Zaragosi S, Joussain R, Colin C, Blanc-Valleron MM, Baudin F, De Garidel-Thoron T, Valet JP, Bassinot F (2020) Magnetic fabric of Bengal fan sediments: Holocene record of sedimentary processes and turbidite activity from the Ganges\u0026ndash;Brahmaputra river system. Mar. Geol. 430:106347. doi:10.1016/j.margeo.2020.106347.\u003c/li\u003e\n\u003cli\u003eOwens WB, Warren BA (2001) Deep circulation in the northwest corner of the Pacific Ocean, Deep-Sea Res. I, 48:959\u0026ndash;993.\u003c/li\u003e\n\u003cli\u003ePares JM (2015) Sixty years of anisotropy of magnetic susceptibility in deformed sedimentary rocks. Frontiers in. Earth Science, 3(4):1\u0026ndash;13. doi: 10.3389/feart.2015.00004\u003c/li\u003e\n\u003cli\u003ePatacci M, Haughton P, Mccaffrey W (2015) Flow behavior of ponded turbidity current, Journal of Sedimentary Research, 85:885\u0026ndash;902. doi: dx.doi.org/10.2110/jsr.2015.59.\u003c/li\u003e\n\u003cli\u003eSagnotti L, Macr\u0026igrave; P, Lucchi R, Rebesco M, Camerlenghi A (2011) A Holocene paleosecular variation record from the northwestern Barents Sea continental margin. Geochem Geophys Geosyst 12:Q11Z33. doi:10.1029/2011GC003810.\u003c/li\u003e\n\u003cli\u003eSawai Y (2020) Subduction zone paleoseismology along the Pacific coast of northeast Japan \u0026ndash; progress and remaining problems. Earth-Sci Rev 208:103261. doi:10.1016/j.earscirev.2020.103261.\u003c/li\u003e\n\u003cli\u003eSchwestermann T, Eglinton TI, Haghipour N, McNichol AP, Ikehara K, Strasser M (2021) Event-dominated transport, provenance, and burial of organic carbon in the Japan Trench. Earth Planet. Sci. Lett., 563, 116870, doi: 10. 1016/j.epsl.2021.116870\u003c/li\u003e\n\u003cli\u003eSoda T (1989) Two 6th Century eruptions of Haruna Volcano, central Japan. Quat. Res. (Daiyonki-kenkyu) 27(297):e312 in Japanese with English abstract.\u003c/li\u003e\n\u003cli\u003eStoner JS, Channell JET, Hillaire-Marcel C (1996) The magnetic signature of rapidly deposited detrital layers from the deep Labrador Sea: Relationship to North Atlantic Heinrich layers. Paleoceanography 11, 309\u0026ndash;325.\u003c/li\u003e\n\u003cli\u003eTanty C, Valet JP, Carlut J, Bassinot F, Zaragosi S (2016) Acquisition of detrital magnetization in four turbidites. Geochem. Geophys. Geosyst. 17, 3207\u0026ndash;3223. doi:10.1002/2016GC006378.\u003c/li\u003e\n\u003cli\u003eTarling D, Hrouda F (1993) The Magnetic Anisotropy of Rocks, 217 pp., Chapman and Hall, London, U.K.\u003c/li\u003e\n\u003cli\u003eUsami K, Ikehara K, Kanamatsu T, McHugh CM (2018) Supercycle in great earthquake recurrence along the Japan Trench over the last 4000 years. Geosci. Lett. 5, 11. https ://doi.org/10.1186/s4056 2-018-0110-2\u003c/li\u003e\n\u003cli\u003eYoshikawa S (1976) The volcanic ash layers of the Osaka Group. J. Geol. Soc. Jpn. 82, 497e515 in Japanese with English abstract\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"progress-in-earth-and-planetary-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"peps","sideBox":"Learn more about [Progress in Earth and Planetary Science](http://progearthplanetsci.springeropen.com)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/peps/default.aspx","title":"Progress in Earth and Planetary Science","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Historical earthquake, Japan Trench, Turbidite, Paleomagnetic secular variation, Paleo current, anisotropy of magnetic susceptibility","lastPublishedDoi":"10.21203/rs.3.rs-2008594/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2008594/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePrevious studies on sediment recovered from the Japan Trench document distinctive turbidite beds induced by huge earthquakes along the Japan Trench and their wide occurrences in area of 37\u0026deg;25\u0026rsquo;- 38\u0026deg;30\u0026rsquo;N. We studied two sedimentary cores at 39\u0026deg;N in order to investigate the depositional earthquake record in the further spatio-extened areas of the Japan Trench. We examined specifically the precise stratigraphy of turbidite beds using paleomagnetic secular variation (PSV), and a tephra correlation. Additionally, anisotropy of magnetic susceptibility (AMS) was investigated to understand the depositional conditions of each turbidite bed. The inferred ages of turbidite beds in this study closely approximate their earlier reported, which are correlated to the historical and pre-historical huge earthquakes off Tohoku, northeastern Japan.\u003c/p\u003e \u003cp\u003eThe paleo current directions during deposition of turbidite are inferred from their grain alignment based on AMS data. The directions of basal part reveal northeastward in the slope-side basin and north-northeast in oceanward basin. The directions of basal and upper thick muddy part of a turbidite bed are not always consistent, which suggests the hydraulic condition in the narrow elongated deep-sea basin. This fact could be essential information to elucidate a unique hydraulic condition during the turbidite deposition in the confined basin in the Japan Trench basin.\u003c/p\u003e","manuscriptTitle":"Submarine paleoseismology in the Japan Trench of northeastern Japan: turbidite stratigraphy and sedimentology using paleomagnetic and rock-magnetic analyses","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-09-02 16:20:07","doi":"10.21203/rs.3.rs-2008594/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2022-10-31T06:19:44+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2022-09-18T00:00:00+00:00","index":2,"fulltext":""},{"type":"reviewerAgreed","content":"","date":"2022-08-31T12:15:19+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-08-31T07:30:01+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2022-08-31T00:00:00+00:00","index":1,"fulltext":""},{"type":"editorAssigned","content":"","date":"2022-08-30T04:34:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2022-08-29T23:00:00+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2022-08-29T23:00:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"Progress in Earth and Planetary Science","date":"2022-08-29T02:58:42+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"progress-in-earth-and-planetary-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"peps","sideBox":"Learn more about [Progress in Earth and Planetary Science](http://progearthplanetsci.springeropen.com)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/peps/default.aspx","title":"Progress in Earth and Planetary Science","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e8127f13-a1c4-477f-932a-6ac7577ac890","owner":[],"postedDate":"September 2nd, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-16T20:17:12+00:00","versionOfRecord":{"articleIdentity":"rs-2008594","link":"https://doi.org/10.1186/s40645-023-00545-3","journal":{"identity":"progress-in-earth-and-planetary-science","isVorOnly":false,"title":"Progress in Earth and Planetary Science"},"publishedOn":"2023-03-28 20:13:35","publishedOnDateReadable":"March 28th, 2023"},"versionCreatedAt":"2022-09-02 16:20:07","video":"","vorDoi":"10.1186/s40645-023-00545-3","vorDoiUrl":"https://doi.org/10.1186/s40645-023-00545-3","workflowStages":[]},"version":"v1","identity":"rs-2008594","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2008594","identity":"rs-2008594","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}