A new mechanical perspective on a shallow megathrust near-trench slip from the high-resolution fault model of the 2011 Tohoku-Oki earthquake

A new mechanical perspective on a shallow megathrust near-trench slip from the high-resolution fault model of the 2011 Tohoku-Oki earthquake | 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 A new mechanical perspective on a shallow megathrust near-trench slip from the high-resolution fault model of the 2011 Tohoku-Oki earthquake Tatsuya Kubota, Tatsuhiko Saito, Ryota Hino This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1714847/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract The 2011 Tohoku-Oki earthquake generated a surprisingly large near-trench slip, and earth scientists have devoted significant attention to understanding why. Some studies proposed special rupture mechanisms, such as extensive dynamic frictional weakening; others simulated this near-trench slip behavior using standard rupture mechanics. However, we have not reached a decisive conclusion for this question due to limited spatial near-trench slip resolution. Hence, we quantitatively clarified the along-plate mechanical state by significantly improving the spatial resolution of the stress release distribution with the first use of tsunami data recorded just above the large slip area in addition to offshore and onshore geodetic data. A maximum slip of 53 m reaching the trench and an insignificant stress drop (< 3 MPa) at the shallowest portion of the plate were estimated, and our model suggested that dynamic friction at the shallow near-trench portion was low during the coseismic slip. This result provides novel perspectives on the shallow slip behavior along the plate boundary, in which the strain energy accumulation at the deep portion of the fault accounts for the anomalous large shallow slip, but shallow mechanical coupling does not. A large shallow slip has been considered as a result of the release of sufficiently large strain energy in the shallow portion of the plate interface, but we suggest that shallow slips similar to that during the 2011 Tohoku-Oki earthquake may occur in any subduction zones where the energy accumulates only in the deeper portion. The 2011 Tohoku-Oki earthquake Ocean-bottom pressure gauge Tsunami Stress Frictional strength of megathrust Fault mechanics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1 Introduction The devastating tsunami generated by the 2011 Tohoku-Oki earthquake caused severe damage to the coast of Japan. The most surprising feature of this megathrust earthquake was the occurrence of a very large slip (> 50 m) reaching the trench (Kodaira et al., 2012 ; 2020 ; Sun et al., 2017 ). Before this earthquake, it was widely believed that the two plates at the shallow portion, corresponding to a depth range shallower than ~ 10 km from the free surface (i.e. seafloor), were stably sliding (creeping) during the interseismic period, resulting in no stress accumulation and hence no coseismic slip occurrence, while only the deep portion of the plate interface (deeper than ~ 10 km) exhibited unstable stick-slip (i.e. earthquake) behavior (Byrne et al., 1988 ; Scholtz, 1998; Bilek et al., 2002). To better understand shallow slip behavior and tsunami generation in subduction zones, it is important to clarify why this unexpected extremely large slip occurred during the Tohoku-Oki earthquake. To explain this shallow slip behavior, some studies have considered that the frictional strength along the shallow plate was high enough interseismically to accumulate shear stress. It was proposed that when the Tohoku-Oki earthquake occurred the shallow frictional strength dynamically reduced with an increase in the slip rate (dynamic weakening) (Di Toro et al., 2011 ; Noda and Lapusta, 2013 ), leading to a large shallow slip. Another special dynamic frictional weakening mechanism related to frictional heating along the plate interface, called “thermal pressurization”, was also proposed to explain the shallow slip behavior (Hirono et al., 2019 ; Shibazaki et al., 2019 ). These mechanisms related to the extensive reduction in frictional strength require significant shear stress release at the shallow portion of the plate. On the other hand, other studies explained the shallow slip behavior without considering these special mechanisms requiring a shallow, large stress drop and relied on the conventional viewpoint of plate coupling and rupture mechanics (Lay et al., 2012 ). Dynamic rupture simulation studies suggested that surface-reaching slip can occur with moderate or no stress drop at the shallow portion but by strong mechanical plate locking at the deep portion and its interaction with the free surface (Fukuyama and Hok, 2015 ). A seafloor drilling survey (Chester et al., 2013 ) showed the existence of a low-friction material along the fault slip zone (Fulton et al., 2013 ; Ujiie et al., 2013 ). An experimental study of a shallow fault-zone material under a water-dampened condition mimicking a plate boundary suggested that the low-friction material was insensitive to the slip rate (i.e., no dynamic weakening behavior) (Remitti et al., 2015 ). Based on fault mechanics, some recent studies pointed out that theoretically, a large shallow slip could occur because of the ‘pinning’ effect of the deep frictionally locked area which causes slip delay (or slip deficit) in the shallow portion (Herman and Govers, 2020 ; Lindsey et al., 2021 ). It was difficult to identify the shallow stress release process in detail because of the large uncertainty in the near-trench slip, owing to the lack of a dataset with sufficient quality to resolve it. The distributions of the coseismic slip and stress release proposed in the past vary from model to model, particularly at the shallowest portion (Brown et al., 2015 ; Sun et al., 2017 ; Lay, 2018 ). Therefore, the cause of the large shallow slip has been investigated for the past ten years, but no decisive conclusion has been reached. In this study, we attempted to constrain the slip and stress drop distributions with the highest precision possible to reveal the cause of the near-trench large slip during the 2011 Tohoku-Oki earthquake. To achieve this, we used the tsunami data recorded by several ocean-bottom pressure gauges installed directly above the fault area, which have not before been utilized (Fig. 1 ). 2 Data And Methods 2.1 Modeling Strategy To understand the mechanics of the shallow trench-reaching rupture, it is essential to reveal the fault rupture mechanics (more specifically, the coseismic stress drop at the shallow portion) and to precisely estimate the shallow slip with ultra-high resolution. Seafloor geodetic data (Fujiwara et al., 2011 ; Kido et al., 2011 ; Sato et al., 2011 ) have made large contributions towards elucidating this issue (Iinuma et al., 2012 ; Sun et al., 2017 ); however, the spatial resolution of such data is limited, which contains information that is only relevant at the location of the observation point. In addition to these offshore, and onshore, geodetic datasets (Fig. 1 c), the present study utilized tsunami waveform data (Figs. 1 a and 1 b) which contain unique and robust spatial information about the distribution of the fault slip, in particular at the shallow portion near the trench, as the spatial extent of the tsunami source. This is because shallow near-trench slips excite tsunamis more efficiently than the deeper slip. Furthermore, we used data from ocean-bottom pressure gauges installed just above the large slip area (Kubota et al. 2021 ), which have not been used before in any modeling analyses (Fig. 1 b). The advantages of combining the far-field tsunami waveforms and the in-situ ocean-bottom pressure gauge waveforms contribute to a significant improvement of the fault model construction, particularly the estimation with the high-resolution on the fault slip at the shallow portion. In contrast, the onshore datasets, which have been widely used in past studies but obtained far from the focal area had a worse constraint on the shallow slip. The onshore geodetic data, recorded more than 200 km from the trench axis, have difficulty in resolving the slip near the trench (Loveless and Meade, 2015 ). The analyses using the onshore seismograms require the assumption of the rupture propagation velocity across the fault, but this assumption may cause a large uncertainty in estimating the spatial extent of the entire slip region because of a substantial trade-off between the rupture velocity and the spatial extent (Kubota et al., 2018 ). Some conventional fault modeling methods using tsunami data (e.g., Satake et al., 2013 ; Yamazaki et al., 2018 ) have often simplified the fault geometry by assuming planar subfaults, which do not reflect the real three-dimensional fault geometry. This simplification may cause serious problems in inferring the correct fault slip and stress changes on the fault (Wang et al., 2018 ). Thus, we incorporated the non-planar plate geometry model (Koketsu et al., 2012 ) using small triangular subfault elements. Note that the shallowest part of the fault geometry was slightly modified from the plate geometry model, to appropriately simulate trench-breaching rupture (Wang et al., 2018 , see Section 2.3.1 for details). 2.2 Data We used the tsunami data recorded by the ocean-bottom pressure gauges installed around the focal area, obtained by Tohoku University (Kubota et al., 2021 ) (green inverted triangles in Figs. 1 a and 1 b) and the University of Tokyo (Maeda et al., 2011 ) (dark red inverted triangles in Fig. 1 b). The station information is summarized in Table 1 . After removing the signal fluctuation due to the ocean tide, we applied a low-pass filter with a cut-off period of 100 s to these records. Table 1 List of tsunami stations used in this study Station Latitude [°N] Longitude [°E] Depth [m] Inversion time window [s] Agency Sampling rate of original data [s] a TM2 39.2459 142.4526 997 0–1800 ERI 0.1 TM1 39.2283 142.7720 1618 0–1800 ERI 0.1 P06 38.6340 142.5838 1254 0–3600 Tohoku University 1 P02 38.5002 142.5016 1104 0–3600 Tohoku University 1 P03 38.1834 142.3998 1052 0–3600 Tohoku University 1 P07 38.0016 142.4495 1059 0–3600 Tohoku University 1 P08 38.2829 142.8320 1418 0–3600 Tohoku University 1 P09 38.2650 143.0002 1556 0–3600 Tohoku University 1 GJT3 38.2945 143.4814 3293 0–3600 Tohoku University 1 21418 38.7180 148.6980 5500 1200–4200 DART 15 KPG2 42.2365 144.8454 2210 600–3600 JAMSTEC 0.1 KPG1 41.7040 144.4375 2218 600–3600 JAMSTEC 0.1 KCTD 41.6675 144.3409 2540 600–3600 JAMSTEC 10 NMS09 42.3692 145.9167 3316 600–3600 Tohoku University 1 NMS05 42.1667 145.8235 4548 600–3600 Tohoku University 1 BOSO2 34.7550 140.7517 2098 600–4200 JMA 1 BOSO3 34.8050 140.5067 1912 600–4200 JMA 1 HPG1 35.0031 139.2247 1176 1800–5400 JAMSTEC 1 VCM3 35.0712 139.3906 1225 1800–5400 NIED 0.1 VCM1 34.5954 139.9198 2125 1800–5400 NIED 0.1 807 40.1167 142.0667 125 0–3600 NOWPHAS 5 804 39.6272 142.1867 200 0–3600 NOWPHAS 5 802 39.2586 142.0969 204 0–3600 NOWPHAS 5 803 38.8578 141.8944 160 0–3600 NOWPHAS 5 801 38.2325 141.6836 144 0–3600 NOWPHAS 5 806 36.9714 141.1856 137 0–3600 NOWPHAS 5 613 42.9106 144.3972 50.0 1800–5400 NOWPHAS 5 602 42.5439 141.4458 50.7 1800–5400 NOWPHAS 5 202 40.9250 141.4242 43.8 1800–4800 NOWPHAS 5 203 40.5608 141.5683 27.7 Not Used NOWPHAS 5 219 40.2178 141.8600 49.5 Not Used NOWPHAS 5 205 38.2500 141.0661 21.3 Not Used NOWPHAS 5 a All observed records were resampled to 1 s in the inversion analyses. We also used the offshore tsunami data obtained far from the source area (far-field data) from the ocean-bottom pressure gauges of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC, light blue inverted triangles in Fig. 1 a), Japan Meteorological Agency (JMA, red inverted triangles), National Research Institute for Earth Science and Disaster Resilience (NIED, black inverted triangles), and National Oceanic and Atmospheric Administration (NOAA)’s DART (Deep-ocean Assessment and Reporting of Tsunamis) system (a blue inverted triangle). We also used the tsunami waveforms from the GPS buoys (yellow squares in Figs. 1 a and 1 b) and the wave gauges (orange triangles) of NOWPHAS (Nationwide Ocean Wave information network for Ports and HArbourS) of the Port and Airport Research Institute (PARI). The data processing was similar to the pressure data around the focal area, but a bandpass filter with a passband of 100–3600 s was used. We also used onshore GPS data obtained by the Geospatial Information Authority of Japan (GSI), as well as offshore geodetic observation data (Fig. 1 c) (Kido et al., 2011 ; Sato et al., 2011 ). 2.3 Methods 2.3.1 Fault Geometry and Crustal Deformation Calculation As mentioned above, conventional fault modeling using tsunami data has often simplified the fault geometry by using methods such as implementing large-sized planar faults and/or a buried fault whose top does not reach the free surface. However, these simplifications, which do not reflect the real three-dimensional fault geometry, may cause serious problems when inferring fault slip (Wang et al., 2018 ). Serious problems also occur in the calculation of the stress drop distribution. If large-sized subfaults with uniform slip are used, the stress concentration and/or the artificial discontinuity of the stress drop occur at the boundaries of the subfaults. If the fault top does not reach the free surface, the spurious stress increase occurs in the area between the free surface and the buried fault top. Hence, it is essential to appropriately consider the three-dimensional fault geometry to obtain the correct stress drop distribution. In contrast to most of the past tsunami modeling studies using the simple planar fault configuration, we incorporated the nonplanar fault geometry of the Japan Integrated Velocity Structure Model (JIVSM) (Koketsu et al., 2012 ) for the analysis. To derive the fault slip distribution via Green's functions, the plate geometry was divided into small triangular subfault elements, in which the length of one side of the triangle was approximately 10 km, referring to the subfault configuration of a previous study (Iinuma et al., 2016 ) (triangles in Fig. 1 ). Using these triangular subfault elements, we calculated the seafloor displacement using a uniform half-space structure model (Meade, 2007 ). To correctly simulate the trench-extending rupture (Wang et al., 2018 ), we slightly modified the fault configuration as follows: First, the depths of all the triangular vertices were systematically moved vertically towards the surface by 8 km, considering the seawater depth around the trench axis. Then, the depths of the uppermost row of triangular subfaults (i.e. the computational free surface) were set to 0 km so that the shallowest fault surface accorded with the trench axis. 2.3.2 Estimation of Fault Slip Distribution The procedure for the analyses to estimate the slip distributions (Fig. 2 a) was similar to that used in our previous studies (Kubota et al., 2021 ). Considering that the observed data is expressed by the linear superposition of Green's function, we estimated the amount of slip at each of the triangular subfaults by solving the following equation: $$\left(\begin{array}{c}{w}_{\text{t}\text{s}\text{u}\text{n}}{\mathbf{d}}_{\text{t}\text{s}\text{u}\text{n}}\\ {w}_{\text{g}\text{e}\text{o}\text{d}}{\mathbf{d}}_{\text{g}\text{e}\text{o}\text{d}}\\ 0\\ 0\end{array}\right)=\left(\begin{array}{c}{w}_{\text{t}\text{s}\text{u}\text{n}}{\mathbf{G}}_{\text{t}\text{s}\text{u}\text{n}}\\ {w}_{\text{g}\text{e}\text{o}\text{d}}{\mathbf{G}}_{\text{g}\text{e}\text{o}\text{d}}\\ \alpha S\\ \beta E\end{array}\right)\mathbf{m}$$ 1 . The vector d is the data vector, consisting of the observed data, and G is the matrix consisting of Green’s functions (the synthetics by the unit slip of the subfault). The subscripts denote the types of datasets. The scalar value w denotes the weight of each dataset. The weight of the tsunami data is ten times larger than the geodetic data. Vector m consists of the slip amount of the triangular subfaults, which is to be estimated. To stabilize the solution, we imposed the smoothing constraint (Maerten et al., 2005 ) expressed by matrix S and the damping constraint using the identity matrix E . Parameters α and β are the weights of each constraint. The procedure to calculate Green’s functions for tsunamis (matrix G tsun in Eq. ( 1 )) is as follows: The initial seafloor vertical displacement distribution from each of the triangular subfaults (Meade, 2007 ) was simulated. The total number of the triangular subfaults used in this study was N sub = 434. The effect of the apparent seafloor vertical movement due to the horizontally moving seafloor was also incorporated (Tanioka and Satake, 1996 ). We then simulated the initial sea-surface height change distribution from the seafloor deformation using a spatial smoothing filter related to the seawater depth (Saito, 2019 ). Finally, we simulated tsunamis using the linear dispersive equation (Saito, 2019 ). The cosine-shaped source time function with the duration of T r = 40 s is assumed for the rupture time history of each subfault, as used in Kubota et al. ( 2021 ). In this simulation, the bathymetry data of GEBCO 2020 were interpolated to 2 km spatial intervals. The time interval for this simulation was 1 s. Green’s functions for the geodetic data ( G geod ) were also calculated similarly from each of the triangular subfaults (Meade, 2007 ). We consider the temporal evolution of the rupture by distributing the Green’s function in the time domain in addition to the space domain. We distributed the Green’s functions in the time domain for each subfault with the temporal interval of Δ t = 20 s (i.e., the slip of the k -th temporal element begins at t = t k beg = ( k − 1) × Δ t and ends at t = t k end = t k beg + T r ). We assumed N t = 9 Green’s functions in the time domain for each subfault. The total number of unknown parameters was N = N sub × N t = 3906. Considering the rupture front propagation, the slips of the k -th temporal element at the i -th subfault were constrained to be zero when the rupture front did not arrive there (i.e., we allowed the slip only when satisfying the condition V r × t k end ≥ a i , a i is the distance between the hypocenter and the center of the i -th subfault and V r = 4 km/s is the rupture velocity). Using Green’s function, Eq. ( 1 ) was solved. The time windows used for this inversion analysis are shown in the blue traces in Fig. 3 a–d. The weights of the spatial smoothing and damping constraints (parameters α and β ) were set based on the previous modeling results (Kubota et al., 2021 ). 2.3.3 Evaluation of Fault Slip We evaluated our fault slip distribution model (Fig. 2 a) based on several approaches. First, the modeling uncertainty of the shallow slip estimation was evaluated by an inversion analysis based on the jack-knife or leave-one-out approach (red shaded area in Fig. 4 a, in the Off-Miyagi region). In this test, we excluded one of the nine near-field pressure gauge stations and used the remaining eight stations to estimate the slip distribution. The inversion setting was identical to the original setting, which used all the data. The possible range of the slip amount was defined by the maximum and minimum slip amounts from all tested models. We also examine the improvement in the slip distribution of our model by conducting tsunami simulations using the previous slip distributions of Satake et al. ( 2013 ), Iinuma et al. ( 2012 ), and Yamazaki et al. ( 2018 ) (Fig. 5 ). For the model of Satake et al. ( 2013 ) and Yamazaki et al. ( 2018 ), the propagation of rupture front was considered as done in these studies. The multiple source functions in the time domain were taken into account in the model of Satake et al. ( 2013 ) and the single source time function with duration of T r = 32 s in the time domain was assumed in the model of Yamazaki et al. ( 2018 ). The temporal evolution was not considered in the static fault model of Iinuma et al. ( 2012 ), but we assumed that the slips of all subfaults begin simultaneously at t = 0 with the rise time of T r = 60 s. The tsunami simulations were conducted using the linear long equation (Saito, 2019 ). We further examined whether the observed near-field pressure waveforms could be explained by the slip profile estimated from the change in the bathymetry near the trench (Sun et al., 2017 ) (Fig. 6 ). We assumed the slip amounts of the i -th triangular subfaults ( \({m}_{i}^{\text{'}}\) ) to emulate the along-dip slip profile in Sun et al. ( 2017 ), based on the following formula: $${m}_{i}^{\text{'}}={m}_{i}+{\Delta }{m}_{i}$$ 3 . Here, \({m}_{i}\) is the slip amount of the present model (Fig. 1 b) and \({\Delta }{m}_{i}\) is the amount of modification. The modification value is defined as: $${\Delta }{m}_{i}=\left\{\begin{array}{c}\begin{array}{cc}{d}_{0}& \left(0\le {r}_{i}<{r}_{1}\right)\end{array}\\ \begin{array}{cc}2{d}_{0}-{d}_{0}\frac{{r}_{i}}{{r}_{2}-{r}_{1}}& \left({r}_{1}\le {r}_{i}<{r}_{2}\right)\end{array}\\ \begin{array}{cc}0& \left({r}_{i}\le {r}_{2}\right)\end{array}\end{array}\right.$$ 4 , where r i is the horizontal distance between the center location of the i -th triangular subfault, x i = ( x i , y i ), and the reference point, x 0 = ( x 0 , y 0 ) = (144.0°E, 38.08°N), defined as: $${r}_{i}=\sqrt{{\left({x}_{i}-{x}_{0}\right)}^{2}+{\left({y}_{i}-{y}_{0}\right)}^{2}}$$ 5 We used the values of r 1 = 50 km, r 2 = 100 km, and d 0 = 12.5 m. The modification value with a function of the horizontal distance from point x 0 is shown by a grey line in Fig. 6 a. 2.3.4 Calculation of Stress Drop Distribution After estimating the slip distribution of the triangular subfaults, we calculated the distribution of the shear stress change along the fault (i.e. stress drop, Fig. 2 b) by computing the shear stress change along the slip direction at the center of each subfault: $${\Delta }{\sigma }_{i}={\sum }_{i}{\Delta }{\sigma }_{ij}^{0}{m}_{j}$$ 2 , where \({\Delta }{\sigma }_{i}\) is the stress drop at the i -th fault, \({\Delta }{\sigma }_{ij}^{0}\) is the stress drop at the center of the i -th triangular subfault by the unit slip at the j -th subfault, and m j is the slip amount at the j -th subfault. 2.3.5 Evaluation of stress drop area To validate the location of the large stress drop area and to examine the stress drop amount at the shallow portion, we conducted additional tsunami simulations (Figs. 7 and 8 ). First, we constructed the fault slip distribution models of the triangular subfaults. In this procedure, we assigned a stress drop of 5 MPa in the shallow, deep, and deeper portions, respectively (Figs. 7 a– 7 c, shown by thick black lines). Then, considering the given stress drop amount as the data (left-hand side of Eq. ( 1 )), the slip amount of the j -th subfault ( \({m}_{j}\) ) was estimated by solving the linear inversion problem, and then tsunamis were calculated (Fig. 7 d). 3 Results 3.1 Fault Slip Distribution A large slip of up to 53 m extending to the trench axis was estimated to occur in the region off Miyagi (Fig. 2 b). The synthetic tsunami (Fig. 3 a– 3 d) and onshore and offshore displacement (Fig. 3 e) from this slip distribution model were in good agreement with the observations. The main slip area, defined as the region where the slip exceeded 10 m, was almost consistent with that reported previously (e.g., Iinuma et al., 2012 ; Satake et al., 2013 ; Yamazaki et al., 2018 ). Based on the inversion test based on the jack-knife approach (see Section 2.3.3 ), the possible range of the shallowest slip was between 49 and 55 m at the Off-Miyagi region (red shaded area in Fig. 4 ). Our model had a peak slip at the trench axis (red line in Fig. 4 a), which was consistent with the study by Sun et al. ( 2017 ) who estimated the near-trench slip profile using the near-trench bathymetry change after the Tohoku-Oki earthquake (blue line in Fig. 4 a). In contrast, other previous models (e.g., Yamazaki et al., 2018 ) located the peak slip a few tens of kilometers from the trench axis (green line in Fig. 4 a). In this study, the spatial gradient of the slip along the dip direction was also consistent with that of Sun et al. ( 2017 ), although the slip amount which they estimated was slightly larger than that in our study by ~ 12 m within ~ 50 km from the trench axis. We show the simulated waveforms using the previous slip distributions of Satake et al. ( 2013 ) (Fig. 5 a), Iinuma et al. ( 2012 ) (Fig. 5 b), and Yamazaki et al. ( 2018 ) (Fig. 5 c) (see Section 2.3.3 ). The models with a sharper slip peak at the trench produced a short-wavelength tsunami component, which was not consistent with the actual observations (stations P03, P07, Fig. 5 d). If we assume a modified fault model which had a slightly larger near-trench slip of ~ 65 m based on the near-trench slip profile of Sun et al. ( 2017 ) estimated from the bathymetry change (blue line in Fig. 6 a, see Section 2.3.3 ), the simulated tsunami waveforms were consistent with the observation, but the peak amplitudes at the stations near the epicenter (P08 and P09) were larger than those observed (Fig. 6 b). This may indicate that the maximum slip near the trench was not as large as 65 m. The use of the brand new near-field tsunami data obtained by the pressure gauges contributed to revealing the detailed shallow slip profile at the trench. 3.2 Stress Drop Using the slip distribution, we calculated the shear stress change along the plate boundary (i.e., the stress drop) (Fig. 2 b, see Section 2.3.4 ). The stress at the deep portion (> 10 km) was largely released (> 5 MPa), where the slip amount was smaller than ~ 40 m, whereas the stress release at the shallowest portion ( > ~ 40 m slip) was insignificantly small (< 3 MPa). Considerable stress drop at the deeper portion suggests a strong mechanical coupling at the deeper portion and an accumulation of the shear stress before the earthquake, while insignificant coseismic stress release at the shallow portion suggests much weaker shallow mechanical coupling than the deep portion before the earthquake (discussed later, in Fig. 9 a). Some past fault models had a significantly large stress drop at the shallowest part, corresponding to a large slip near the trench axis (e.g., Yamazaki et al., 2018 ). To examine the location of the main stress drop area and examine the stress drop amount at the shallow portion, we conducted additional tsunami simulations (Figs. 7 and 8 ; see Section 2.3.5 ). When assuming a large stress drop area at the shallowest portion near the trench (Fig. 7 a), a maximum slip of > 80 m and a large spatial gradient of the slip amount were necessary, which generated very large short-wavelength tsunamis but could not explain the observation (blue traces in Fig. 7 d). The ~ 20 m shallow slip based on the assumption of a deeper stress drop area (Fig. 7 c) did not explain the observation as well (green traces). On the other hand, the near-trench slip up to ~ 50 m was obtained assuming a large stress drop area at the deep portion of the plate boundary (Fig. 7 b), and the features of the observed tsunamis were explained (red traces). Therefore, the large stress drop area should be located around the hypocenter, and the stress drop should be insignificantly small at the shallowest part. To cause a stress drop of 5 MPa at the shallowest portion near the trench, a maximum slip of > 80 m and a large spatial gradient of the slip amount were necessary, which was inconsistent with the observation because it generated very large short-wavelength tsunamis (blue traces in Fig. 7 d). On the other hand, when assuming a large stress drop region at a deeper portion corresponding to the main stress drop region estimated in our analyses, a moderate spatial slip gradient, comparable to that of our model with a maximum slip of ~ 50 m, was obtained (Figs. 7 b and 8 ), explaining the features of the observed tsunamis (red traces in Fig. 7 d). Therefore, we concluded that the main stress drop area should be located at the deeper part, and the stress drop should be much less significant, at the shallowest part. 4 Discussion 4.1 Kinematic and Dynamic Perspectives of the Fault Boundary Based on these results, we propose that the main reason for the large shallow coseismic slip without significant shallow stress drop during the Tohoku-Oki earthquake was a rupture of a deeper locked zone with a large coseismic stress drop. In other words, the Tohoku-Oki earthquake slip occurred to compensate for the interseismic slip deficit, which was provoked by deep mechanical coupling (Fig. 9 ) (Herman and Govers, 2020 ; Lindsey et al., 2021 ). This means that shallow mechanical locking was not necessary to generate a large slip and indicates that the shallow friction was intrinsically small and shear stress did not accumulate during the interseismic period. Our hypothesis is supported by an experimental study using a shallow fault-zone material, which showed that the friction between the two plates was inherently small and insensitive to the slip rate (no dynamic weakening) (Remmiti et al., 2015). This shallow stress accumulation behavior is consistent with that expected before the Tohoku-Oki earthquake (Scholtz, 1988; Bilek and Lay, 2002 ). Most previous studies have conventionally understood the occurrence of large earthquakes based on a kinematic perspective (e.g., Nishikawa et al., 2019 ; Uchida et al., 2021) (Fig. 9 b). As has been seen in other large earthquakes, the main slip of the Tohoku-Oki earthquake was located in the slip deficit area during the interseismic period (Lindsey et al., 2021 ), indicating that the earthquake released the interseismic slip deficit. Seismic waves were radiated mainly at deeper depths, but there was almost no radiation at shallow depths (Ide et al., 2011 ). Afterslips occurred in areas without coseismic slip (Watanabe et al., 2021 ). Other typical kinematic pictures are shown in Fig. 9 b. To explain the extremely large shallow slip which was unusual within this kinematic perspective, some studies considered the possibility of an additional mechanism causing an extensive dynamic reduction of friction, such as thermal pressurization, which results in an extremely large stress drop process at the shallow part (Hirono et al., 2019 ; Shibazaki et al., 2019 ). Here, based on the data analysis focusing on the stress drop distribution, we expanded this kinematic view to a new mechanical picture (Fig. 9 a). From a mechanical point of view, the rupture area of the Tohoku-Oki earthquake can be divided into deep ( > ~ 10 km) and shallow ( < ~ 10 km) portions. We propose that the driving force of the entire slip was the accumulated strain energy at the deep mechanically coupled area. The amount of shallow slip seemed incredibly large, but it can be reasonably interpreted by considering the effect of the deep stress release and its interaction with the free surface (Herman and Govers, 2020 ). In addition, a large seismic wave radiation area (Ide et al., 2011 ) is well correlated with the area of the large stress drop, whereas the shallow weak seismic wave radiation area corresponds to the low stress drop area. Although the kinematic concept of afterslip was simple and complementary to the main shock (Watanabe et al., 2021 ), we propose two different mechanisms of afterslip: the afterslips located just north (~ 39.5°N) and south (~ 37°N) of the rupture area were driven by stress concentration due to the mainshock, while the afterslip which occurred ~ 200 km south (~ 35.5°N) was not directly driven by it. 4.2 Toward Understanding of Megathrust Earthquake Physics The use of the seafloor records of tsunamis and displacement offsets obtained just above the focal area made it possible to obtain the detailed stress change distribution of the Tohoku-Oki earthquake. In addition to the conventional kinematic perspective of the megathrust earthquake, the stress drop distribution provided us with new mechanical information about the megathrust earthquake, including the cause of the driving force that triggered the shallow large slip, the source of seismic wave excitation, and the existence of different types of afterslip generation mechanisms (Fig. 9 ). These observations are consistent with the basic mechanical model of faulting (Kostrov, 1974 ), in which the strain energy stored in the lithosphere between the interseismic period excites the fault slip and seismic wave radiation. Without assuming any special mechanism requiring an extremely large shallow stress drop, the anomalous shallow slip can be explained by a combination of free surface and deep stress release (Herman and Govers, 2020 ). The large shallow slip of the Tohoku-Oki earthquake was mainly due to the effect of the free surface and the deep stress release (Herman and Govers, 2020 ). This indicates that the shallow slip behavior depends largely on where and how much energy is available during the earthquake. More specifically, the earthquake slip behavior relies on the amount of strain energy accumulated around the locking portion. Interplate slip deficits have been geodetically detected in many subductions (e.g., Loveless and Meade, 2015 ; Noda et al., 2018 ; Herman and Govers, 2020 ; Lindsey et al., 2021 ), which are interpreted as a manifestation of the strong interplate mechanical coupling. Our results show that unusually large shallow slips and giant tsunamis such as those occurring due to the Tohoku-Oki earthquake can occur in any subduction zones without a shallow mechanical coupling if enough strain energy is accumulated to generate earthquakes around the deeper locked portion. In the future, it will be important to evaluate the frictional strength of deep coupling and the resultant strain energy to quantitatively investigate the possibility of large shallow slips and giant tsunamis. Our results showed that observational earthquake science is steadily progressing from kinematic modeling toward mechanical modeling to achieve quantitative evaluation. 5 Conclusions To understand the reason for the large near-trench slip during the 2011 Tohoku-Oki earthquake, this study estimated the slip and stress drop distributions with the high spatial resolution using the tsunami data recorded by ocean-bottom pressure gauges installed above the fault area, which had not before been used in the past. The estimated model had a large slip of > 40 m at the shallowest portion ( z < 10 km) in the Off-Miyagi region and the slip peaked at 53 m at the Japan Trench. However, the stress release at the shallowest portion was insignificantly small ( 5 MPa) was located at the deep portion (> 10 km) where the slip amount was smaller than ~ 40 m. The results suggested the deep mechanical plate locking corresponding to the large stress drop provoked the interseismic slip deficit in both shallow and deep regions of the plate boundary. Although a large shallow slip had been considered as a result of the release of large strain energy in the shallow portion of the plate in the past, our analyses provided us with a new mechanical perspective along the plate boundary, in which shallow slips can occur without the shallow energy accumulation but only with the energy accumulation in the deeper portion. Abbreviations DART Deep-ocean Assessment and Reporting of Tsunamis GSI Geospatial Information Authority of Japan JAMSTEC Japan Agency for Marine-Earth Science and Technology JMA Japan Meteorological Agency JPL Jet Propulsion Laboratory NASA National Aeronautics and Space Administration NIED National Research Institute for Earth Science and Disaster Resilience NOAA National Oceanic and Atmospheric Administration NOWPHAS Nationwide Ocean Wave information network for Ports and HArbourS PARI Port and Airport Research Institute Declarations Availability of data and material The ocean-bottom pressure gauge data installed by Tohoku University are available in the supplementary data of Kubota et al. (2021), at https://doi.org/10.5281/zenodo.4420393. DART tsunami data were downloaded from https://www.ngdc.noaa.gov/hazard/dart/2011honshu_dart.html (accessed on 1 June 2022). The tsunami data of JAMSTEC were downloaded from http://www.jamstec.go.jp/scdc/top_e.html (accessed on 1 December 2019). The pressure data of the JMA were available in the Technical Report of the Japan Meteorological Agency Vol. 133 ‘Report on the 2011 Off the Pacific Coast of Tohoku Earthquake’ (https://www.jma.go.jp/jma/kishou/books/gizyutu/133/gizyutu_133.html, accessed on 1 June 2022, available only in Japanese). The NIED pressure gauge data were provided on request. The tsunami data of the nearshore GPS buoy and wave gauges were downloaded from the NOWPAHS webpage (https://nowphas.mlit.go.jp/pastdata/, only available in Japanese, accessed on 1 June 2022). The coseismic displacements at offshore geodetic stations (Kido et al., 2011; Sato et al., 2011) are listed in Iinuma et al. (2012). The coseismic displacement data at the onshore geodetic stations were downloaded from the website of Jet Propulsion Laboratory (JPL), National Aeronautics and Space Administration (NASA) (https://gipsy-oasis.jpl.nasa.gov/index.php?page=pppdata, accessed on 1 June 2022), which were originally acquired by the GSI. The Japan Integrated Velocity Structure Model (Koketsu et al., 2012) was downloaded from https://www.jishin.go.jp/evaluation/seismic_hazard_map/lpshm/12_choshuki_dat/ (accessed on 1 June 2022, available only in Japanese). The GEBCO 2020 bathymetry data was downloaded from https://www.gebco.net/data_and_products/historical_data_sets/#gebco_2020 (accessed on 1 June 2022). We used a triangular dislocation element (tde) program (Meade, 2007, https://github.com/brendanjmeade/tde) to calculate seafloor deformation. The digital data of the slip distribution and stress drop estimated by this study are available in Supplementary Datasets S1 to S6 and the detailed caption of the dataset is shown in Supplementary Material S1. The will also be available on the external data repository after the acceptance of the manuscript. Competing interests The authors declare that they have no competing interest. Funding This work was financially supported by JSPS KAKENHI Grant Numbers JP19H02409 (TK, TS), JP19H05596 (RH), JP19K04021 (TS), JP19K14818 (TK), and JP22K22K14126 (TK). Authors' contributions TK conducted the analyses and numerical experiments described in this paper. TS and RH interpreted the results. All authors drafted the manuscript. All authors read and approved the final manuscript. Acknowledgements The figures in this manuscript were prepared using Generic Mapping Tools (GMT) version 6 (Wessel et al., 2019). We also thank Editage for the English language review. References Bilek SL, Lay T (2002) Tsunami earthquakes possibly widespread manifestations of frictional conditional stability. Geophys Res Lett 29:1673. doi: 10.1029/2002GL015215 Brown L, Wang K, Sun T (2015) Static stress drop in the Mw 9 Tohoku-oki earthquake: heterogeneous distribution and low average value. 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List of tsunami stations used in this study Station Latitude [°N] Longitude [°E] Depth [m] Inversion time window [s] Agency Sampling rate of original data [s] a TM2 39.2459 142.4526 997 0 – 1800 ERI 0.1 TM1 39.2283 142.7720 1618 0 – 1800 ERI 0.1 P06 38.6340 142.5838 1254 0 – 3600 Tohoku University 1 P02 38.5002 142.5016 1104 0 – 3600 Tohoku University 1 P03 38.1834 142.3998 1052 0 – 3600 Tohoku University 1 P07 38.0016 142.4495 1059 0 – 3600 Tohoku University 1 P08 38.2829 142.8320 1418 0 – 3600 Tohoku University 1 P09 38.2650 143.0002 1556 0 – 3600 Tohoku University 1 GJT3 38.2945 143.4814 3293 0 – 3600 Tohoku University 1 21418 38.7180 148.6980 5500 1200 – 4200 DART 15 KPG2 42.2365 144.8454 2210 600 – 3600 JAMSTEC 0.1 KPG1 41.7040 144.4375 2218 600 – 3600 JAMSTEC 0.1 KCTD 41.6675 144.3409 2540 600 – 3600 JAMSTEC 10 NMS09 42.3692 145.9167 3316 600 – 3600 Tohoku University 1 NMS05 42.1667 145.8235 4548 600 – 3600 Tohoku University 1 BOSO2 34.7550 140.7517 2098 600 – 4200 JMA 1 BOSO3 34.8050 140.5067 1912 600 – 4200 JMA 1 HPG1 35.0031 139.2247 1176 1800 – 5400 JAMSTEC 1 VCM3 35.0712 139.3906 1225 1800 – 5400 NIED 0.1 VCM1 34.5954 139.9198 2125 1800 – 5400 NIED 0.1 807 40.1167 142.0667 125 0 – 3600 NOWPHAS 5 804 39.6272 142.1867 200 0 – 3600 NOWPHAS 5 802 39.2586 142.0969 204 0 – 3600 NOWPHAS 5 803 38.8578 141.8944 160 0 – 3600 NOWPHAS 5 801 38.2325 141.6836 144 0 – 3600 NOWPHAS 5 806 36.9714 141.1856 137 0 – 3600 NOWPHAS 5 613 42.9106 144.3972 50.0 1800 – 5400 NOWPHAS 5 602 42.5439 141.4458 50.7 1800 – 5400 NOWPHAS 5 202 40.9250 141.4242 43.8 1800 – 4800 NOWPHAS 5 203 40.5608 141.5683 27.7 Not Used NOWPHAS 5 219 40.2178 141.8600 49.5 Not Used NOWPHAS 5 205 38.2500 141.0661 21.3 Not Used NOWPHAS 5 a All observed records were resampled to 1 s in the inversion analyses. Supplementary Files GraphicalAbst.png DatasetS1.csv DatasetS2.csv DatasetS3.txt DatasetS4.grd DatasetS5.txt DatasetS6.grd SupplementaryMaterial.pdf Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 10 Jun, 2022 Reviewers invited by journal 10 Jun, 2022 Editor assigned by journal 07 Jun, 2022 First submitted to journal 01 Jun, 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-1714847","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":112550285,"identity":"194f6da1-54ad-458e-93a1-a79b7b16094b","order_by":0,"name":"Tatsuya Kubota","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6ElEQVRIie3QvQrCMBDA8RNBl+h8pdC+wkmguDn6GkrXVgQXB5GCUBdxrm/hIyRLXequdFGcFSdxELFFN6Efm0j+UwL5weUAVKofDIF9TvXF+55GuUSkb1hUmqBTcDAtcOXpOnl0aH+Wx/ukDWbXg9Ewg+g4sEmE1F/HA5uzEKEVCeBBBjHQsVDUqEexY+lQS0jQA85yyZOSwSJLuz8LED0l0qfKescsbPgIJuYQbXGxabvk/VWU/KWxREZMepl/wY0rD+Ob0WlutsnGblPDnM9CnrWxrxiJis/LCADTg+qpHFGpVKo/7wVGSkh5lCJwygAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-4766-4771","institution":"National Research Institute for Earth Science and Disaster Resilience","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Tatsuya","middleName":"","lastName":"Kubota","suffix":""},{"id":112550286,"identity":"394b8f0e-d2ae-4e19-8393-0df080a21ad8","order_by":1,"name":"Tatsuhiko Saito","email":"","orcid":"","institution":"National Research Institute for Earth Science and Disaster Resilience","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Tatsuhiko","middleName":"","lastName":"Saito","suffix":""},{"id":112550287,"identity":"3021b77d-3be7-45f4-ad04-d8ac0fa60403","order_by":2,"name":"Ryota Hino","email":"","orcid":"","institution":"Tohoku University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ryota","middleName":"","lastName":"Hino","suffix":""}],"badges":[],"createdAt":"2022-06-01 08:20:52","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1714847/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1714847/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":22733933,"identity":"03a31920-ab81-42e2-8b8d-9888c4ef94cc","added_by":"auto","created_at":"2022-06-16 15:42:11","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":238905,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Station locations for the tsunami observation. Inverted triangles, squares, and triangles are the ocean-bottom pressure gauges, the offshore GPS buoys, and near-shore seafloor wave gauges, respectively. The colors of the symbols indicate agencies owning each dataset. (b) Close-up around the Off-Tohoku region. The white star denotes the epicenter of the Tohoku-Oki earthquake (Suzuki et al., 2012). (c) The location of the onshore and offshore geodetic stations used in the present study. Black and red squares denote inland GPS and seafloor geodetic observatories, respectively. Small triangles represent the configuration of the triangular subfaults used for the analysis.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/3cfd9de84e749bb9a3a175f7.png"},{"id":22734789,"identity":"d98277ee-9a10-4f6a-9a98-e2eaceef7018","added_by":"auto","created_at":"2022-06-16 15:47:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":224856,"visible":true,"origin":"","legend":"\u003cp\u003eSlip and stress distributions of the 2011 Tohoku-Oki earthquake. (a) Slip distribution obtained in the present study. (b) Stress drop distribution calculated from the slip distribution. Green dashed lines denote the iso-depth contour of the plate interface at 10 km intervals.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/be13ff15c0ead43a4c190ab6.png"},{"id":22734786,"identity":"b949b52f-a2d0-478d-b1cb-a960d26791de","added_by":"auto","created_at":"2022-06-16 15:47:11","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":135496,"visible":true,"origin":"","legend":"\u003cp\u003eComparison between the observed and synthesized data. (a–d) Comparisons of the seafloor pressure gauge waveforms above the focal area, the far-field seafloor pressure gauge waveforms, the offshore GPS buoy waveforms, and the nearshore wave gauge waveforms near the coast. Grey and red waveforms are the observed and synthesized waveforms, respectively. Blue lines indicate the time window used for the analysis. Locations of each station are shown in Figure 1. (e) A comparison of the observed and synthesized data of the geodetic dataset. Black and grey bars and arrows denote the observed movement of the offshore and onshore geodetic stations. Light and dark red bars and arrows are the synthesized ones. Note that the length of the bars and arrows differs between the onshore and offshore stations. The distribution of the seafloor vertical displacement calculated from the fault model was also shown.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/61256d884de140982d24bdf4.png"},{"id":22733930,"identity":"ac49e374-ded6-42ca-a83d-c01c4af9d339","added_by":"auto","created_at":"2022-06-16 15:42:11","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":164062,"visible":true,"origin":"","legend":"\u003cp\u003eCross-sectional view of the fault slip and stress drop of the Tohoku-Oki earthquake. (a) Comparison of the fault slip distributions between the present study (red) and the ones in the previous studies (Iinuma et al., 2012; Satake et al., 2013; Sun et al., 2017; Yamazaki et al., 2018) along the line normal to the trench axis shown in the inset map. The error range of the present study’s model is shown by the red shaded area. The blue shaded area denotes the error range of Sun et al. (2017). The small triangles denote the location of the ocean-bottom pressure gauges. The region of the differential bathymetry survey conducted in Sun et al. (2017) is shown by the cyan line. (b) Comparison of the stress drop distributions.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/a282c4ea0ed4dc9588af5359.png"},{"id":22734788,"identity":"cf76a8cf-f747-4cc2-9954-a0fcab676456","added_by":"auto","created_at":"2022-06-16 15:47:11","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":204620,"visible":true,"origin":"","legend":"\u003cp\u003eTsunami simulation results of previous fault models of the Tohoku earthquake. (a–c) Slip distribution and initial sea-surface height distribution assumed from the fault model proposed by Satake et al. (2013), Iinuma et al. (2012), and Yamazaki et al. (2018), respectively. (d) Comparison between the observed (grey) and simulated waveforms (colored) at representative stations.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/5ab9bce73292e61b60778d2c.png"},{"id":22733934,"identity":"22557f3c-3692-4209-8949-a9c00ea5c30d","added_by":"auto","created_at":"2022-06-16 15:42:11","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":118125,"visible":true,"origin":"","legend":"\u003cp\u003eTsunami simulation using a previous slip model from Sun et al. (2017). (a) Comparison of the along-dip slip profile of the present model (red), the model in which the slip amount is modified (dark blue), and the slip profile estimated by Sun et al. (2017) (blue). The amount of modification of the slip is indicated by the grey line. The colors, shading, triangles, and bathymetry description are the same as in the legend of Figure 4a. (b) Comparison between the observed (grey) and simulated waveforms (colored) at representative stations.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/80d8bcdc015f4669b2983a86.png"},{"id":22733936,"identity":"8ebd79c0-4bcb-4c08-9724-f4bfeeeff98c","added_by":"auto","created_at":"2022-06-16 15:42:12","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":239531,"visible":true,"origin":"","legend":"\u003cp\u003eNumerical evaluation of plate coupling area location. (a–c) Slip distribution assuming coupling at the shallowest, middle, and deeper portions of the plate boundary, respectively. Polygons drawn with thick black lines denote the regions where the stress drop was assigned. (d) Comparison between the observed (grey) and simulated waveforms (colored) at representative stations\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/eeb4d43a7636ebdfde3ddf24.png"},{"id":22736266,"identity":"0c030907-a90c-4e1d-861c-ab76b14bdec5","added_by":"auto","created_at":"2022-06-16 15:57:12","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":85773,"visible":true,"origin":"","legend":"\u003cp\u003eCross-sectional view of fault slip for the numerical evaluation test. The slip distribution profiles assuming coupling at the shallowest (blue), middle (red), and deeper (green) portions of the plate boundary, respectively, are shown. The colors, shading, triangles, and bathymetry description are the same as in the legend of Figure 4a.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/bd720c9eca41447cae21789c.png"},{"id":22733943,"identity":"deacd01c-3cbf-447a-8f37-b986777c98d3","added_by":"auto","created_at":"2022-06-16 15:42:12","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":111410,"visible":true,"origin":"","legend":"\u003cp\u003eInterpretation of the mechanical and kinematic properties along the Tohoku plate boundary. (a) Mechanical perspective associated with the megathrust Tohoku-Oki earthquake. The regions where the plate boundary is mechanically locked are shown in red, and the regions where the mechanical coupling is weak are shown in blue. The regions surrounded by dashed lines are less certain than those with the solid lines. The regions where the mechanical property is unclear are shown in grey. (b) Kinematic perspective of the seismic activities along the plate boundary. The spatial relationship of the coseismic (magenta) and postseismic (cyan) slips are shown. Aftershock areas are also shown in grey and tremor areas are shown in green.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/ee1fa6e4b5f11ee4f5123d63.png"},{"id":22736269,"identity":"6b163158-45b3-4620-ab2f-0871af2d3ed9","added_by":"auto","created_at":"2022-06-16 15:57:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1828417,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/d0db74da-a8d2-489f-99dd-0514ed6b5054.pdf"},{"id":22734792,"identity":"ee92d11c-b798-48a0-95a6-03e6a3a9c71b","added_by":"auto","created_at":"2022-06-16 15:47:12","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":510410,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbst.png","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/9595001d876b7fefe46cacaa.png"},{"id":22735706,"identity":"94eb34cf-9ac6-47a1-951d-1017d41f9071","added_by":"auto","created_at":"2022-06-16 15:52:11","extension":"csv","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1984,"visible":true,"origin":"","legend":"","description":"","filename":"DatasetS1.csv","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/9d59c0ac0d3d9ce7ccd48fdd.csv"},{"id":22733932,"identity":"c9d272b5-a8a5-4605-910e-d1626673c647","added_by":"auto","created_at":"2022-06-16 15:42:11","extension":"csv","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":13015,"visible":true,"origin":"","legend":"","description":"","filename":"DatasetS2.csv","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/ee0863f370752f5ac78fe610.csv"},{"id":22734793,"identity":"574e02e0-31ff-45d7-bd95-02bd444e6ff5","added_by":"auto","created_at":"2022-06-16 15:47:12","extension":"txt","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":63638,"visible":true,"origin":"","legend":"","description":"","filename":"DatasetS3.txt","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/5ccc433bccd0aabd55067381.txt"},{"id":22735707,"identity":"9b302e1e-f811-461a-b1c1-2ee748523388","added_by":"auto","created_at":"2022-06-16 15:52:12","extension":"grd","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":76015,"visible":true,"origin":"","legend":"","description":"","filename":"DatasetS4.grd","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/63caf5c348171de3cdb943fb.grd"},{"id":22733947,"identity":"126a63ff-8b3f-48dd-aabb-e95f66cb9cd2","added_by":"auto","created_at":"2022-06-16 15:42:12","extension":"txt","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":91585,"visible":true,"origin":"","legend":"","description":"","filename":"DatasetS5.txt","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/5711b88a5a9d1c9f2064d173.txt"},{"id":22733948,"identity":"f872f7a7-0ef3-4534-ba3e-aaa331807e6b","added_by":"auto","created_at":"2022-06-16 15:42:12","extension":"grd","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":160362,"visible":true,"origin":"","legend":"","description":"","filename":"DatasetS6.grd","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/4ca7c0d92fa2df3b26ec7b5a.grd"},{"id":22735709,"identity":"1c4c8f26-0dc7-40f3-878d-9a782a1aacaf","added_by":"auto","created_at":"2022-06-16 15:52:12","extension":"pdf","order_by":8,"title":"","display":"","copyAsset":false,"role":"supplement","size":93711,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterial.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1714847/v1/9210e6ea1733eda8a6a6a1d5.pdf"}],"financialInterests":"","formattedTitle":"A new mechanical perspective on a shallow megathrust near-trench slip from the high-resolution fault model of the 2011 Tohoku-Oki earthquake","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe devastating tsunami generated by the 2011 Tohoku-Oki earthquake caused severe damage to the coast of Japan. The most surprising feature of this megathrust earthquake was the occurrence of a very large slip (\u0026gt;\u0026thinsp;50 m) reaching the trench (Kodaira et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Sun et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Before this earthquake, it was widely believed that the two plates at the shallow portion, corresponding to a depth range shallower than ~\u0026thinsp;10 km from the free surface (i.e. seafloor), were stably sliding (creeping) during the interseismic period, resulting in no stress accumulation and hence no coseismic slip occurrence, while only the deep portion of the plate interface (deeper than ~\u0026thinsp;10 km) exhibited unstable stick-slip (i.e. earthquake) behavior (Byrne et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Scholtz, 1998; Bilek et al., 2002). To better understand shallow slip behavior and tsunami generation in subduction zones, it is important to clarify why this unexpected extremely large slip occurred during the Tohoku-Oki earthquake.\u003c/p\u003e \u003cp\u003eTo explain this shallow slip behavior, some studies have considered that the frictional strength along the shallow plate was high enough interseismically to accumulate shear stress. It was proposed that when the Tohoku-Oki earthquake occurred the shallow frictional strength dynamically reduced with an increase in the slip rate (dynamic weakening) (Di Toro et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Noda and Lapusta, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), leading to a large shallow slip. Another special dynamic frictional weakening mechanism related to frictional heating along the plate interface, called \u0026ldquo;thermal pressurization\u0026rdquo;, was also proposed to explain the shallow slip behavior (Hirono et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Shibazaki et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). These mechanisms related to the extensive reduction in frictional strength require significant shear stress release at the shallow portion of the plate.\u003c/p\u003e \u003cp\u003eOn the other hand, other studies explained the shallow slip behavior without considering these special mechanisms requiring a shallow, large stress drop and relied on the conventional viewpoint of plate coupling and rupture mechanics (Lay et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Dynamic rupture simulation studies suggested that surface-reaching slip can occur with moderate or no stress drop at the shallow portion but by strong mechanical plate locking at the deep portion and its interaction with the free surface (Fukuyama and Hok, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). A seafloor drilling survey (Chester et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) showed the existence of a low-friction material along the fault slip zone (Fulton et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Ujiie et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). An experimental study of a shallow fault-zone material under a water-dampened condition mimicking a plate boundary suggested that the low-friction material was insensitive to the slip rate (i.e., no dynamic weakening behavior) (Remitti et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Based on fault mechanics, some recent studies pointed out that theoretically, a large shallow slip could occur because of the \u0026lsquo;pinning\u0026rsquo; effect of the deep frictionally locked area which causes slip delay (or slip deficit) in the shallow portion (Herman and Govers, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Lindsey et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIt was difficult to identify the shallow stress release process in detail because of the large uncertainty in the near-trench slip, owing to the lack of a dataset with sufficient quality to resolve it. The distributions of the coseismic slip and stress release proposed in the past vary from model to model, particularly at the shallowest portion (Brown et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Sun et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Lay, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Therefore, the cause of the large shallow slip has been investigated for the past ten years, but no decisive conclusion has been reached. In this study, we attempted to constrain the slip and stress drop distributions with the highest precision possible to reveal the cause of the near-trench large slip during the 2011 Tohoku-Oki earthquake. To achieve this, we used the tsunami data recorded by several ocean-bottom pressure gauges installed directly above the fault area, which have not before been utilized (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2 Data And Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Modeling Strategy\u003c/h2\u003e \u003cp\u003eTo understand the mechanics of the shallow trench-reaching rupture, it is essential to reveal the fault rupture mechanics (more specifically, the coseismic stress drop at the shallow portion) and to precisely estimate the shallow slip with ultra-high resolution. Seafloor geodetic data (Fujiwara et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Kido et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Sato et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) have made large contributions towards elucidating this issue (Iinuma et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Sun et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2017\u003c/span\u003e); however, the spatial resolution of such data is limited, which contains information that is only relevant at the location of the observation point. In addition to these offshore, and onshore, geodetic datasets (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec), the present study utilized tsunami waveform data (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) which contain unique and robust spatial information about the distribution of the fault slip, in particular at the shallow portion near the trench, as the spatial extent of the tsunami source. This is because shallow near-trench slips excite tsunamis more efficiently than the deeper slip. Furthermore, we used data from ocean-bottom pressure gauges installed just above the large slip area (Kubota et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which have not been used before in any modeling analyses (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The advantages of combining the far-field tsunami waveforms and the in-situ ocean-bottom pressure gauge waveforms contribute to a significant improvement of the fault model construction, particularly the estimation with the high-resolution on the fault slip at the shallow portion. In contrast, the onshore datasets, which have been widely used in past studies but obtained far from the focal area had a worse constraint on the shallow slip. The onshore geodetic data, recorded more than 200 km from the trench axis, have difficulty in resolving the slip near the trench (Loveless and Meade, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The analyses using the onshore seismograms require the assumption of the rupture propagation velocity across the fault, but this assumption may cause a large uncertainty in estimating the spatial extent of the entire slip region because of a substantial trade-off between the rupture velocity and the spatial extent (Kubota et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSome conventional fault modeling methods using tsunami data (e.g., Satake et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Yamazaki et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) have often simplified the fault geometry by assuming planar subfaults, which do not reflect the real three-dimensional fault geometry. This simplification may cause serious problems in inferring the correct fault slip and stress changes on the fault (Wang et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Thus, we incorporated the non-planar plate geometry model (Koketsu et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) using small triangular subfault elements. Note that the shallowest part of the fault geometry was slightly modified from the plate geometry model, to appropriately simulate trench-breaching rupture (Wang et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e, see Section \u003cspan refid=\"Sec6\" class=\"InternalRef\"\u003e2.3.1\u003c/span\u003e for details).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Data\u003c/h2\u003e \u003cp\u003eWe used the tsunami data recorded by the ocean-bottom pressure gauges installed around the focal area, obtained by Tohoku University (Kubota et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) (green inverted triangles in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) and the University of Tokyo (Maeda et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) (dark red inverted triangles in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The station information is summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. After removing the signal fluctuation due to the ocean tide, we applied a low-pass filter with a cut-off period of 100 s to these records.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eList of tsunami stations used in this study\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLatitude [\u0026deg;N]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLongitude [\u0026deg;E]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDepth [m]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eInversion time window [s]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAgency\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSampling rate of original data [s]\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTM2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e39.2459\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e142.4526\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e997\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;1800\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eERI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTM1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e39.2283\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e142.7720\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1618\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;1800\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eERI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.6340\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e142.5838\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1254\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTohoku University\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.5002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e142.5016\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1104\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTohoku University\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.1834\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e142.3998\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1052\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTohoku University\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.0016\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e142.4495\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1059\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTohoku University\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.2829\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e142.8320\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1418\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTohoku University\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.2650\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e143.0002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1556\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTohoku University\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGJT3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.2945\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e143.4814\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3293\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTohoku University\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e21418\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.7180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e148.6980\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1200\u0026ndash;4200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDART\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKPG2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e42.2365\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e144.8454\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2210\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e600\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eJAMSTEC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKPG1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.7040\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e144.4375\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2218\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e600\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eJAMSTEC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKCTD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.6675\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e144.3409\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2540\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e600\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eJAMSTEC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNMS09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e42.3692\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e145.9167\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3316\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e600\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTohoku University\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNMS05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e42.1667\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e145.8235\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4548\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e600\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTohoku University\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBOSO2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e34.7550\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e140.7517\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2098\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e600\u0026ndash;4200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eJMA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBOSO3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e34.8050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e140.5067\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1912\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e600\u0026ndash;4200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eJMA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHPG1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e35.0031\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e139.2247\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1176\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1800\u0026ndash;5400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eJAMSTEC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVCM3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e35.0712\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e139.3906\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1225\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1800\u0026ndash;5400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNIED\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVCM1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e34.5954\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e139.9198\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2125\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1800\u0026ndash;5400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNIED\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e807\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e40.1167\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e142.0667\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e125\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e804\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e39.6272\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e142.1867\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e802\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e39.2586\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e142.0969\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e204\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e803\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.8578\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e141.8944\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e160\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e801\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.2325\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e141.6836\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e806\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e36.9714\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e141.1856\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e137\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u0026ndash;3600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e613\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e42.9106\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e144.3972\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e50.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1800\u0026ndash;5400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e602\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e42.5439\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e141.4458\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e50.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1800\u0026ndash;5400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e202\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e40.9250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e141.4242\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e43.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1800\u0026ndash;4800\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e203\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e40.5608\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e141.5683\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e27.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNot Used\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e219\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e40.2178\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e141.8600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e49.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNot Used\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e205\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.2500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e141.0661\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e21.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNot Used\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNOWPHAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003e\u003csup\u003ea\u003c/sup\u003eAll observed records were resampled to 1 s in the inversion analyses.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eWe also used the offshore tsunami data obtained far from the source area (far-field data) from the ocean-bottom pressure gauges of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC, light blue inverted triangles in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea), Japan Meteorological Agency (JMA, red inverted triangles), National Research Institute for Earth Science and Disaster Resilience (NIED, black inverted triangles), and National Oceanic and Atmospheric Administration (NOAA)\u0026rsquo;s DART (Deep-ocean Assessment and Reporting of Tsunamis) system (a blue inverted triangle). We also used the tsunami waveforms from the GPS buoys (yellow squares in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) and the wave gauges (orange triangles) of NOWPHAS (Nationwide Ocean Wave information network for Ports and HArbourS) of the Port and Airport Research Institute (PARI). The data processing was similar to the pressure data around the focal area, but a bandpass filter with a passband of 100\u0026ndash;3600 s was used. We also used onshore GPS data obtained by the Geospatial Information Authority of Japan (GSI), as well as offshore geodetic observation data (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) (Kido et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Sato et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Methods\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1 Fault Geometry and Crustal Deformation Calculation\u003c/h2\u003e \u003cp\u003eAs mentioned above, conventional fault modeling using tsunami data has often simplified the fault geometry by using methods such as implementing large-sized planar faults and/or a buried fault whose top does not reach the free surface. However, these simplifications, which do not reflect the real three-dimensional fault geometry, may cause serious problems when inferring fault slip (Wang et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Serious problems also occur in the calculation of the stress drop distribution. If large-sized subfaults with uniform slip are used, the stress concentration and/or the artificial discontinuity of the stress drop occur at the boundaries of the subfaults. If the fault top does not reach the free surface, the spurious stress increase occurs in the area between the free surface and the buried fault top. Hence, it is essential to appropriately consider the three-dimensional fault geometry to obtain the correct stress drop distribution.\u003c/p\u003e \u003cp\u003eIn contrast to most of the past tsunami modeling studies using the simple planar fault configuration, we incorporated the nonplanar fault geometry of the Japan Integrated Velocity Structure Model (JIVSM) (Koketsu et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) for the analysis. To derive the fault slip distribution via Green's functions, the plate geometry was divided into small triangular subfault elements, in which the length of one side of the triangle was approximately 10 km, referring to the subfault configuration of a previous study (Iinuma et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) (triangles in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Using these triangular subfault elements, we calculated the seafloor displacement using a uniform half-space structure model (Meade, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). To correctly simulate the trench-extending rupture (Wang et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), we slightly modified the fault configuration as follows: First, the depths of all the triangular vertices were systematically moved vertically towards the surface by 8 km, considering the seawater depth around the trench axis. Then, the depths of the uppermost row of triangular subfaults (i.e. the computational free surface) were set to 0 km so that the shallowest fault surface accorded with the trench axis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2 Estimation of Fault Slip Distribution\u003c/h2\u003e \u003cp\u003eThe procedure for the analyses to estimate the slip distributions (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) was similar to that used in our previous studies (Kubota et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Considering that the observed data is expressed by the linear superposition of Green's function, we estimated the amount of slip at each of the triangular subfaults by solving the following equation:\u003c/p\u003e \u003cp\u003e \u003cdiv id=\"Equ1\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\left(\\begin{array}{c}{w}_{\\text{t}\\text{s}\\text{u}\\text{n}}{\\mathbf{d}}_{\\text{t}\\text{s}\\text{u}\\text{n}}\\\\ {w}_{\\text{g}\\text{e}\\text{o}\\text{d}}{\\mathbf{d}}_{\\text{g}\\text{e}\\text{o}\\text{d}}\\\\ 0\\\\ 0\\end{array}\\right)=\\left(\\begin{array}{c}{w}_{\\text{t}\\text{s}\\text{u}\\text{n}}{\\mathbf{G}}_{\\text{t}\\text{s}\\text{u}\\text{n}}\\\\ {w}_{\\text{g}\\text{e}\\text{o}\\text{d}}{\\mathbf{G}}_{\\text{g}\\text{e}\\text{o}\\text{d}}\\\\ \\alpha S\\\\ \\beta E\\end{array}\\right)\\mathbf{m}$$\u003c/div\u003e \u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e.\u003c/p\u003e \u003cp\u003eThe vector \u003cb\u003ed\u003c/b\u003e is the data vector, consisting of the observed data, and \u003cb\u003eG\u003c/b\u003e is the matrix consisting of Green\u0026rsquo;s functions (the synthetics by the unit slip of the subfault). The subscripts denote the types of datasets. The scalar value \u003cem\u003ew\u003c/em\u003e denotes the weight of each dataset. The weight of the tsunami data is ten times larger than the geodetic data. Vector \u003cb\u003em\u003c/b\u003e consists of the slip amount of the triangular subfaults, which is to be estimated. To stabilize the solution, we imposed the smoothing constraint (Maerten et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) expressed by matrix \u003cb\u003eS\u003c/b\u003e and the damping constraint using the identity matrix \u003cb\u003eE\u003c/b\u003e. Parameters \u003cem\u003eα\u003c/em\u003e and \u003cem\u003eβ\u003c/em\u003e are the weights of each constraint.\u003c/p\u003e \u003cp\u003eThe procedure to calculate Green\u0026rsquo;s functions for tsunamis (matrix \u003cb\u003eG\u003c/b\u003e\u003csub\u003etsun\u003c/sub\u003e in Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)) is as follows: The initial seafloor vertical displacement distribution from each of the triangular subfaults (Meade, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) was simulated. The total number of the triangular subfaults used in this study was \u003cem\u003eN\u003c/em\u003e\u003csub\u003esub\u003c/sub\u003e = 434. The effect of the apparent seafloor vertical movement due to the horizontally moving seafloor was also incorporated (Tanioka and Satake, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). We then simulated the initial sea-surface height change distribution from the seafloor deformation using a spatial smoothing filter related to the seawater depth (Saito, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Finally, we simulated tsunamis using the linear dispersive equation (Saito, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The cosine-shaped source time function with the duration of \u003cem\u003eT\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e = 40 s is assumed for the rupture time history of each subfault, as used in Kubota et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In this simulation, the bathymetry data of GEBCO 2020 were interpolated to 2 km spatial intervals. The time interval for this simulation was 1 s. Green\u0026rsquo;s functions for the geodetic data (\u003cb\u003eG\u003c/b\u003e\u003csub\u003egeod\u003c/sub\u003e) were also calculated similarly from each of the triangular subfaults (Meade, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWe consider the temporal evolution of the rupture by distributing the Green\u0026rsquo;s function in the time domain in addition to the space domain. We distributed the Green\u0026rsquo;s functions in the time domain for each subfault with the temporal interval of Δ\u003cem\u003et\u003c/em\u003e\u0026thinsp;=\u0026thinsp;20 s (i.e., the slip of the \u003cem\u003ek\u003c/em\u003e-th temporal element begins at \u003cem\u003et\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003ek\u003c/em\u003e\u003c/sub\u003e\u003csup\u003ebeg\u003c/sup\u003e = (\u003cem\u003ek\u003c/em\u003e\u0026thinsp;\u0026minus;\u0026thinsp;1) \u0026times; Δ\u003cem\u003et\u003c/em\u003e and ends at \u003cem\u003et\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003ek\u003c/em\u003e\u003c/sub\u003e\u003csup\u003eend\u003c/sup\u003e = \u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003ek\u003c/em\u003e\u003c/sub\u003e\u003csup\u003ebeg\u003c/sup\u003e\u003cem\u003e+ T\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e). We assumed \u003cem\u003eN\u003c/em\u003e\u003csub\u003et\u003c/sub\u003e = 9 Green\u0026rsquo;s functions in the time domain for each subfault. The total number of unknown parameters was \u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eN\u003c/em\u003e\u003csub\u003esub\u003c/sub\u003e \u0026times; \u003cem\u003eN\u003c/em\u003e\u003csub\u003et\u003c/sub\u003e = 3906. Considering the rupture front propagation, the slips of the \u003cem\u003ek\u003c/em\u003e-th temporal element at the \u003cem\u003ei\u003c/em\u003e-th subfault were constrained to be zero when the rupture front did not arrive there (i.e., we allowed the slip only when satisfying the condition \u003cem\u003eV\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e \u0026times; \u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003ek\u003c/em\u003e\u003c/sub\u003e\u003csup\u003eend\u003c/sup\u003e \u0026ge; \u003cem\u003ea\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003ea\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e is the distance between the hypocenter and the center of the \u003cem\u003ei\u003c/em\u003e-th subfault and \u003cem\u003eV\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e = 4 km/s is the rupture velocity).\u003c/p\u003e \u003cp\u003eUsing Green\u0026rsquo;s function, Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) was solved. The time windows used for this inversion analysis are shown in the blue traces in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea\u0026ndash;d. The weights of the spatial smoothing and damping constraints (parameters \u003cem\u003eα\u003c/em\u003e and \u003cem\u003eβ\u003c/em\u003e) were set based on the previous modeling results (Kubota et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.3.3 Evaluation of Fault Slip\u003c/h2\u003e \u003cp\u003eWe evaluated our fault slip distribution model (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) based on several approaches. First, the modeling uncertainty of the shallow slip estimation was evaluated by an inversion analysis based on the jack-knife or leave-one-out approach (red shaded area in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, in the Off-Miyagi region). In this test, we excluded one of the nine near-field pressure gauge stations and used the remaining eight stations to estimate the slip distribution. The inversion setting was identical to the original setting, which used all the data. The possible range of the slip amount was defined by the maximum and minimum slip amounts from all tested models.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWe also examine the improvement in the slip distribution of our model by conducting tsunami simulations using the previous slip distributions of Satake et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), Iinuma et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), and Yamazaki et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). For the model of Satake et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) and Yamazaki et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), the propagation of rupture front was considered as done in these studies. The multiple source functions in the time domain were taken into account in the model of Satake et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) and the single source time function with duration of \u003cem\u003eT\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e = 32 s in the time domain was assumed in the model of Yamazaki et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The temporal evolution was not considered in the static fault model of Iinuma et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), but we assumed that the slips of all subfaults begin simultaneously at \u003cem\u003et\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0 with the rise time of \u003cem\u003eT\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e = 60 s. The tsunami simulations were conducted using the linear long equation (Saito, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWe further examined whether the observed near-field pressure waveforms could be explained by the slip profile estimated from the change in the bathymetry near the trench (Sun et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). We assumed the slip amounts of the \u003cem\u003ei\u003c/em\u003e-th triangular subfaults (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({m}_{i}^{\\text{\u0026#039;}}\\)\u003c/span\u003e\u003c/span\u003e) to emulate the along-dip slip profile in Sun et al. (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), based on the following formula:\u003c/p\u003e \u003cp\u003e \u003cdiv id=\"Equ2\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${m}_{i}^{\\text{\u0026#039;}}={m}_{i}+{\\Delta }{m}_{i}$$\u003c/div\u003e \u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e.\u003c/p\u003e \u003cp\u003eHere, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({m}_{i}\\)\u003c/span\u003e\u003c/span\u003e is the slip amount of the present model (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\Delta }{m}_{i}\\)\u003c/span\u003e\u003c/span\u003e is the amount of modification. The modification value is defined as:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${\\Delta }{m}_{i}=\\left\\{\\begin{array}{c}\\begin{array}{cc}{d}_{0}\u0026amp; \\left(0\\le {r}_{i}\u0026lt;{r}_{1}\\right)\\end{array}\\\\ \\begin{array}{cc}2{d}_{0}-{d}_{0}\\frac{{r}_{i}}{{r}_{2}-{r}_{1}}\u0026amp; \\left({r}_{1}\\le {r}_{i}\u0026lt;{r}_{2}\\right)\\end{array}\\\\ \\begin{array}{cc}0\u0026amp; \\left({r}_{i}\\le {r}_{2}\\right)\\end{array}\\end{array}\\right.$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e,\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003er\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e is the horizontal distance between the center location of the \u003cem\u003ei\u003c/em\u003e-th triangular subfault, \u003cb\u003ex\u003c/b\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e = (\u003cem\u003ex\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003ey\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e), and the reference point, \u003cb\u003ex\u003c/b\u003e\u003csub\u003e0\u003c/sub\u003e = (\u003cem\u003ex\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e, \u003cem\u003ey\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e) = (144.0\u0026deg;E, 38.08\u0026deg;N), defined as:\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$${r}_{i}=\\sqrt{{\\left({x}_{i}-{x}_{0}\\right)}^{2}+{\\left({y}_{i}-{y}_{0}\\right)}^{2}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWe used the values of \u003cem\u003er\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;50 km, \u003cem\u003er\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;100 km, and \u003cem\u003ed\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;12.5 m. The modification value with a function of the horizontal distance from point x\u003csub\u003e0\u003c/sub\u003e is shown by a grey line in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.3.4 Calculation of Stress Drop Distribution\u003c/h2\u003e \u003cp\u003eAfter estimating the slip distribution of the triangular subfaults, we calculated the distribution of the shear stress change along the fault (i.e. stress drop, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) by computing the shear stress change along the slip direction at the center of each subfault:\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$${\\Delta }{\\sigma }_{i}={\\sum }_{i}{\\Delta }{\\sigma }_{ij}^{0}{m}_{j}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e,\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\Delta }{\\sigma }_{i}\\)\u003c/span\u003e\u003c/span\u003e is the stress drop at the \u003cem\u003ei\u003c/em\u003e-th fault, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\Delta }{\\sigma }_{ij}^{0}\\)\u003c/span\u003e\u003c/span\u003e is the stress drop at the center of the \u003cem\u003ei\u003c/em\u003e-th triangular subfault by the unit slip at the \u003cem\u003ej\u003c/em\u003e-th subfault, and \u003cem\u003em\u003c/em\u003e\u003csub\u003e\u003cem\u003ej\u003c/em\u003e\u003c/sub\u003e is the slip amount at the \u003cem\u003ej\u003c/em\u003e-th subfault.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.3.5 Evaluation of stress drop area\u003c/h2\u003e \u003cp\u003eTo validate the location of the large stress drop area and to examine the stress drop amount at the shallow portion, we conducted additional tsunami simulations (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). First, we constructed the fault slip distribution models of the triangular subfaults. In this procedure, we assigned a stress drop of 5 MPa in the shallow, deep, and deeper portions, respectively (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea\u0026ndash;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec, shown by thick black lines). Then, considering the given stress drop amount as the data (left-hand side of Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)), the slip amount of the \u003cem\u003ej\u003c/em\u003e-th subfault (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({m}_{j}\\)\u003c/span\u003e\u003c/span\u003e) was estimated by solving the linear inversion problem, and then tsunamis were calculated (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3 Results","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Fault Slip Distribution\u003c/h2\u003e \u003cp\u003eA large slip of up to 53 m extending to the trench axis was estimated to occur in the region off Miyagi (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). The synthetic tsunami (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea\u0026ndash;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed) and onshore and offshore displacement (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee) from this slip distribution model were in good agreement with the observations. The main slip area, defined as the region where the slip exceeded 10 m, was almost consistent with that reported previously (e.g., Iinuma et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Satake et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Yamazaki et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Based on the inversion test based on the jack-knife approach (see Section \u003cspan refid=\"Sec8\" class=\"InternalRef\"\u003e2.3.3\u003c/span\u003e), the possible range of the shallowest slip was between 49 and 55 m at the Off-Miyagi region (red shaded area in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOur model had a peak slip at the trench axis (red line in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea), which was consistent with the study by Sun et al. (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) who estimated the near-trench slip profile using the near-trench bathymetry change after the Tohoku-Oki earthquake (blue line in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). In contrast, other previous models (e.g., Yamazaki et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) located the peak slip a few tens of kilometers from the trench axis (green line in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). In this study, the spatial gradient of the slip along the dip direction was also consistent with that of Sun et al. (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), although the slip amount which they estimated was slightly larger than that in our study by ~\u0026thinsp;12 m within ~\u0026thinsp;50 km from the trench axis.\u003c/p\u003e \u003cp\u003eWe show the simulated waveforms using the previous slip distributions of Satake et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), Iinuma et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb), and Yamazaki et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec) (see Section \u003cspan refid=\"Sec8\" class=\"InternalRef\"\u003e2.3.3\u003c/span\u003e). The models with a sharper slip peak at the trench produced a short-wavelength tsunami component, which was not consistent with the actual observations (stations P03, P07, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). If we assume a modified fault model which had a slightly larger near-trench slip of ~\u0026thinsp;65 m based on the near-trench slip profile of Sun et al. (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) estimated from the bathymetry change (blue line in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, see Section \u003cspan refid=\"Sec8\" class=\"InternalRef\"\u003e2.3.3\u003c/span\u003e), the simulated tsunami waveforms were consistent with the observation, but the peak amplitudes at the stations near the epicenter (P08 and P09) were larger than those observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). This may indicate that the maximum slip near the trench was not as large as 65 m. The use of the brand new near-field tsunami data obtained by the pressure gauges contributed to revealing the detailed shallow slip profile at the trench.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Stress Drop\u003c/h2\u003e \u003cp\u003eUsing the slip distribution, we calculated the shear stress change along the plate boundary (i.e., the stress drop) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, see Section \u003cspan refid=\"Sec9\" class=\"InternalRef\"\u003e2.3.4\u003c/span\u003e). The stress at the deep portion (\u0026gt;\u0026thinsp;10 km) was largely released (\u0026gt;\u0026thinsp;5 MPa), where the slip amount was smaller than ~\u0026thinsp;40 m, whereas the stress release at the shallowest portion (\u0026thinsp;\u0026gt;\u0026thinsp;~\u0026thinsp;40 m slip) was insignificantly small (\u0026lt;\u0026thinsp;3 MPa). Considerable stress drop at the deeper portion suggests a strong mechanical coupling at the deeper portion and an accumulation of the shear stress before the earthquake, while insignificant coseismic stress release at the shallow portion suggests much weaker shallow mechanical coupling than the deep portion before the earthquake (discussed later, in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSome past fault models had a significantly large stress drop at the shallowest part, corresponding to a large slip near the trench axis (e.g., Yamazaki et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). To examine the location of the main stress drop area and examine the stress drop amount at the shallow portion, we conducted additional tsunami simulations (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e; see Section \u003cspan refid=\"Sec10\" class=\"InternalRef\"\u003e2.3.5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWhen assuming a large stress drop area at the shallowest portion near the trench (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea), a maximum slip of \u0026gt;\u0026thinsp;80 m and a large spatial gradient of the slip amount were necessary, which generated very large short-wavelength tsunamis but could not explain the observation (blue traces in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed). The ~\u0026thinsp;20 m shallow slip based on the assumption of a deeper stress drop area (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec) did not explain the observation as well (green traces). On the other hand, the near-trench slip up to ~\u0026thinsp;50 m was obtained assuming a large stress drop area at the deep portion of the plate boundary (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb), and the features of the observed tsunamis were explained (red traces). Therefore, the large stress drop area should be located around the hypocenter, and the stress drop should be insignificantly small at the shallowest part.\u003c/p\u003e \u003cp\u003eTo cause a stress drop of 5 MPa at the shallowest portion near the trench, a maximum slip of \u0026gt;\u0026thinsp;80 m and a large spatial gradient of the slip amount were necessary, which was inconsistent with the observation because it generated very large short-wavelength tsunamis (blue traces in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed). On the other hand, when assuming a large stress drop region at a deeper portion corresponding to the main stress drop region estimated in our analyses, a moderate spatial slip gradient, comparable to that of our model with a maximum slip of ~\u0026thinsp;50 m, was obtained (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb and \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e), explaining the features of the observed tsunamis (red traces in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed). Therefore, we concluded that the main stress drop area should be located at the deeper part, and the stress drop should be much less significant, at the shallowest part.\u003c/p\u003e \u003c/div\u003e"},{"header":"4 Discussion","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Kinematic and Dynamic Perspectives of the Fault Boundary\u003c/h2\u003e \u003cp\u003eBased on these results, we propose that the main reason for the large shallow coseismic slip without significant shallow stress drop during the Tohoku-Oki earthquake was a rupture of a deeper locked zone with a large coseismic stress drop. In other words, the Tohoku-Oki earthquake slip occurred to compensate for the interseismic slip deficit, which was provoked by deep mechanical coupling (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e) (Herman and Govers, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Lindsey et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This means that shallow mechanical locking was not necessary to generate a large slip and indicates that the shallow friction was intrinsically small and shear stress did not accumulate during the interseismic period. Our hypothesis is supported by an experimental study using a shallow fault-zone material, which showed that the friction between the two plates was inherently small and insensitive to the slip rate (no dynamic weakening) (Remmiti et al., 2015). This shallow stress accumulation behavior is consistent with that expected before the Tohoku-Oki earthquake (Scholtz, 1988; Bilek and Lay, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2002\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMost previous studies have conventionally understood the occurrence of large earthquakes based on a kinematic perspective (e.g., Nishikawa et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Uchida et al., 2021) (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb). As has been seen in other large earthquakes, the main slip of the Tohoku-Oki earthquake was located in the slip deficit area during the interseismic period (Lindsey et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), indicating that the earthquake released the interseismic slip deficit. Seismic waves were radiated mainly at deeper depths, but there was almost no radiation at shallow depths (Ide et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Afterslips occurred in areas without coseismic slip (Watanabe et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Other typical kinematic pictures are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb. To explain the extremely large shallow slip which was unusual within this kinematic perspective, some studies considered the possibility of an additional mechanism causing an extensive dynamic reduction of friction, such as thermal pressurization, which results in an extremely large stress drop process at the shallow part (Hirono et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Shibazaki et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHere, based on the data analysis focusing on the stress drop distribution, we expanded this kinematic view to a new mechanical picture (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea). From a mechanical point of view, the rupture area of the Tohoku-Oki earthquake can be divided into deep (\u0026thinsp;\u0026gt;\u0026thinsp;~\u0026thinsp;10 km) and shallow (\u0026thinsp;\u0026lt;\u0026thinsp;~\u0026thinsp;10 km) portions. We propose that the driving force of the entire slip was the accumulated strain energy at the deep mechanically coupled area. The amount of shallow slip seemed incredibly large, but it can be reasonably interpreted by considering the effect of the deep stress release and its interaction with the free surface (Herman and Govers, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In addition, a large seismic wave radiation area (Ide et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) is well correlated with the area of the large stress drop, whereas the shallow weak seismic wave radiation area corresponds to the low stress drop area. Although the kinematic concept of afterslip was simple and complementary to the main shock (Watanabe et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), we propose two different mechanisms of afterslip: the afterslips located just north (~\u0026thinsp;39.5\u0026deg;N) and south (~\u0026thinsp;37\u0026deg;N) of the rupture area were driven by stress concentration due to the mainshock, while the afterslip which occurred\u0026thinsp;~\u0026thinsp;200 km south (~\u0026thinsp;35.5\u0026deg;N) was not directly driven by it.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Toward Understanding of Megathrust Earthquake Physics\u003c/h2\u003e \u003cp\u003eThe use of the seafloor records of tsunamis and displacement offsets obtained just above the focal area made it possible to obtain the detailed stress change distribution of the Tohoku-Oki earthquake. In addition to the conventional kinematic perspective of the megathrust earthquake, the stress drop distribution provided us with new mechanical information about the megathrust earthquake, including the cause of the driving force that triggered the shallow large slip, the source of seismic wave excitation, and the existence of different types of afterslip generation mechanisms (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). These observations are consistent with the basic mechanical model of faulting (Kostrov, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1974\u003c/span\u003e), in which the strain energy stored in the lithosphere between the interseismic period excites the fault slip and seismic wave radiation. Without assuming any special mechanism requiring an extremely large shallow stress drop, the anomalous shallow slip can be explained by a combination of free surface and deep stress release (Herman and Govers, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe large shallow slip of the Tohoku-Oki earthquake was mainly due to the effect of the free surface and the deep stress release (Herman and Govers, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This indicates that the shallow slip behavior depends largely on where and how much energy is available during the earthquake. More specifically, the earthquake slip behavior relies on the amount of strain energy accumulated around the locking portion. Interplate slip deficits have been geodetically detected in many subductions (e.g., Loveless and Meade, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Noda et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Herman and Govers, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Lindsey et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which are interpreted as a manifestation of the strong interplate mechanical coupling. Our results show that unusually large shallow slips and giant tsunamis such as those occurring due to the Tohoku-Oki earthquake can occur in any subduction zones without a shallow mechanical coupling if enough strain energy is accumulated to generate earthquakes around the deeper locked portion. In the future, it will be important to evaluate the frictional strength of deep coupling and the resultant strain energy to quantitatively investigate the possibility of large shallow slips and giant tsunamis. Our results showed that observational earthquake science is steadily progressing from kinematic modeling toward mechanical modeling to achieve quantitative evaluation.\u003c/p\u003e \u003c/div\u003e"},{"header":"5 Conclusions","content":"\u003cp\u003eTo understand the reason for the large near-trench slip during the 2011 Tohoku-Oki earthquake, this study estimated the slip and stress drop distributions with the high spatial resolution using the tsunami data recorded by ocean-bottom pressure gauges installed above the fault area, which had not before been used in the past. The estimated model had a large slip of \u0026gt;\u0026thinsp;40 m at the shallowest portion (\u003cem\u003ez\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;10 km) in the Off-Miyagi region and the slip peaked at 53 m at the Japan Trench. However, the stress release at the shallowest portion was insignificantly small (\u0026lt;\u0026thinsp;3 MPa). The main stress drop region (\u0026gt;\u0026thinsp;5 MPa) was located at the deep portion (\u0026gt;\u0026thinsp;10 km) where the slip amount was smaller than ~\u0026thinsp;40 m. The results suggested the deep mechanical plate locking corresponding to the large stress drop provoked the interseismic slip deficit in both shallow and deep regions of the plate boundary. Although a large shallow slip had been considered as a result of the release of large strain energy in the shallow portion of the plate in the past, our analyses provided us with a new mechanical perspective along the plate boundary, in which shallow slips can occur without the shallow energy accumulation but only with the energy accumulation in the deeper portion.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eDART\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eDeep-ocean Assessment and Reporting of Tsunamis\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eGSI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eGeospatial Information Authority of Japan\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eJAMSTEC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eJapan Agency for Marine-Earth Science and Technology\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eJMA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eJapan Meteorological Agency\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eJPL\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eJet Propulsion Laboratory\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eNASA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNational Aeronautics and Space Administration\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eNIED\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNational Research Institute for Earth Science and Disaster Resilience\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eNOAA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNational Oceanic and Atmospheric Administration\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eNOWPHAS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNationwide Ocean Wave information network for Ports and HArbourS\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePARI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ePort and Airport Research Institute\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAvailability of data and material\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe ocean-bottom pressure gauge data installed by Tohoku University are available in the supplementary data of Kubota et al.\u003csup\u003e\u0026nbsp;\u003c/sup\u003e(2021), at https://doi.org/10.5281/zenodo.4420393. DART tsunami data were downloaded from https://www.ngdc.noaa.gov/hazard/dart/2011honshu_dart.html (accessed on 1 June 2022). The tsunami data of JAMSTEC were downloaded from http://www.jamstec.go.jp/scdc/top_e.html (accessed on 1 December 2019). The pressure data of\u0026nbsp;the JMA were available in\u0026nbsp;the Technical Report of the Japan Meteorological Agency Vol. 133 \u0026lsquo;Report on the 2011 Off the Pacific Coast of Tohoku Earthquake\u0026rsquo; (https://www.jma.go.jp/jma/kishou/books/gizyutu/133/gizyutu_133.html, accessed on 1 June 2022, available only in Japanese).\u0026nbsp;The NIED pressure gauge data were provided on request. The tsunami data of the nearshore GPS buoy and wave gauges were downloaded from the NOWPAHS webpage (https://nowphas.mlit.go.jp/pastdata/, only available in Japanese, accessed on 1 June 2022).\u003c/p\u003e\n\u003cp\u003eThe coseismic displacements at offshore geodetic stations (Kido et al., 2011; Sato et al., 2011) are listed in Iinuma et al. (2012). The coseismic displacement data at the onshore geodetic stations were downloaded from the website of Jet Propulsion Laboratory (JPL), National Aeronautics and Space Administration (NASA) (https://gipsy-oasis.jpl.nasa.gov/index.php?page=pppdata, accessed on 1 June 2022), which were originally acquired by the GSI.\u003c/p\u003e\n\u003cp\u003eThe Japan Integrated Velocity Structure Model (Koketsu et al., 2012) was downloaded from https://www.jishin.go.jp/evaluation/seismic_hazard_map/lpshm/12_choshuki_dat/ (accessed on 1 June 2022, available only in Japanese). The GEBCO 2020 bathymetry data was downloaded from https://www.gebco.net/data_and_products/historical_data_sets/#gebco_2020 (accessed on 1 June 2022).\u003c/p\u003e\n\u003cp\u003eWe used a triangular dislocation element (tde) program (Meade, 2007, https://github.com/brendanjmeade/tde) to calculate seafloor deformation.\u003c/p\u003e\n\u003cp\u003eThe digital data of the slip distribution and stress drop estimated by this study are available in Supplementary Datasets S1 to S6 and the detailed caption of the dataset is shown in Supplementary Material S1. The will also be available on the external data repository after the acceptance of the manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interest.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by JSPS KAKENHI Grant Numbers JP19H02409 (TK, TS), JP19H05596 (RH), JP19K04021 (TS), JP19K14818 (TK), and JP22K22K14126 (TK).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTK conducted the analyses and numerical experiments described in this paper. TS and RH interpreted the results. All authors drafted the manuscript. All authors read and approved the final manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe figures in this manuscript were prepared using Generic Mapping Tools (GMT) version 6\u003csup\u003e\u0026nbsp;\u003c/sup\u003e(Wessel et al., 2019). We also thank Editage for the English language review.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBilek SL, Lay T (2002) Tsunami earthquakes possibly widespread manifestations of frictional conditional stability. 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J Geophys Res: Solid Earth 123:1435\u0026ndash;1458. doi:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/2017JB014749\u003c/span\u003e\u003cspan address=\"10.1002/2017JB014749\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1. List of tsunami stations used in this study\u003c/p\u003e\n \u003ctable border=\"0\" cellpadding=\"0\" cellspacing=\"0\" width=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eStation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003eLatitude [\u0026deg;N]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eLongitude [\u0026deg;E]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003eDepth [m]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003eInversion time window [s]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eAgency\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003eSampling rate of original data [s]\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eTM2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e39.2459\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e142.4526\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e997\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 1800\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eERI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eTM1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e39.2283\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e142.7720\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e1618\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 1800\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eERI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eP06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.6340\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e142.5838\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e1254\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eTohoku University\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eP02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.5002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e142.5016\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e1104\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eTohoku University\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eP03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.1834\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e142.3998\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e1052\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eTohoku University\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eP07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.0016\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e142.4495\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e1059\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eTohoku University\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eP08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.2829\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e142.8320\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e1418\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eTohoku University\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eP09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.2650\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e143.0002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e1556\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eTohoku University\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eGJT3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.2945\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e143.4814\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e3293\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eTohoku University\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e21418\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.7180\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e148.6980\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e5500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e1200 \u0026ndash; 4200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eDART\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eKPG2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e42.2365\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e144.8454\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e2210\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e600 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eJAMSTEC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eKPG1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e41.7040\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e144.4375\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e2218\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e600 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eJAMSTEC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eKCTD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e41.6675\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e144.3409\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e2540\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e600 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eJAMSTEC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eNMS09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e42.3692\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e145.9167\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e3316\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e600 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eTohoku University\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eNMS05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e42.1667\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e145.8235\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e4548\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e600 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eTohoku University\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eBOSO2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e34.7550\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e140.7517\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e2098\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e600 \u0026ndash; 4200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eJMA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eBOSO3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e34.8050\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e140.5067\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e1912\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e600 \u0026ndash; 4200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eJMA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eHPG1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e35.0031\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e139.2247\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e1176\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e1800 \u0026ndash; 5400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eJAMSTEC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eVCM3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e35.0712\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e139.3906\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e1225\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e1800 \u0026ndash; 5400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNIED\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003eVCM1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e34.5954\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e139.9198\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e2125\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e1800 \u0026ndash; 5400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNIED\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e807\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e40.1167\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e142.0667\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e125\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e804\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e39.6272\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e142.1867\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e802\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e39.2586\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e142.0969\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e204\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e803\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.8578\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e141.8944\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e160\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e801\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.2325\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e141.6836\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e144\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e806\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e36.9714\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e141.1856\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e137\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e0 \u0026ndash; 3600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e613\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e42.9106\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e144.3972\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e50.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e1800 \u0026ndash; 5400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e602\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e42.5439\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e141.4458\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e50.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e1800 \u0026ndash; 5400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e202\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e40.9250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e141.4242\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e43.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003e1800 \u0026ndash; 4800\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e203\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e40.5608\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e141.5683\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e27.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003eNot Used\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e219\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e40.2178\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e141.8600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e49.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003eNot Used\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e205\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.554112554112555%\"\u003e\n \u003cp\u003e38.2500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.3997113997114%\"\u003e\n \u003cp\u003e141.0661\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.225108225108226%\"\u003e\n \u003cp\u003e21.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.305916305916305%\"\u003e\n \u003cp\u003eNot Used\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.78932178932179%\"\u003e\n \u003cp\u003eNOWPHAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.326118326118326%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003eAll observed records were resampled to 1 s in the inversion analyses.\u003c/p\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":"The 2011 Tohoku-Oki earthquake, Ocean-bottom pressure gauge, Tsunami, Stress, Frictional strength of megathrust, Fault mechanics","lastPublishedDoi":"10.21203/rs.3.rs-1714847/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1714847/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe 2011 Tohoku-Oki earthquake generated a surprisingly large near-trench slip, and earth scientists have devoted significant attention to understanding why. Some studies proposed special rupture mechanisms, such as extensive dynamic frictional weakening; others simulated this near-trench slip behavior using standard rupture mechanics. However, we have not reached a decisive conclusion for this question due to limited spatial near-trench slip resolution. Hence, we quantitatively clarified the along-plate mechanical state by significantly improving the spatial resolution of the stress release distribution with the first use of tsunami data recorded just above the large slip area in addition to offshore and onshore geodetic data. A maximum slip of 53 m reaching the trench and an insignificant stress drop (\u0026lt;\u0026thinsp;3 MPa) at the shallowest portion of the plate were estimated, and our model suggested that dynamic friction at the shallow near-trench portion was low during the coseismic slip. This result provides novel perspectives on the shallow slip behavior along the plate boundary, in which the strain energy accumulation at the deep portion of the fault accounts for the anomalous large shallow slip, but shallow mechanical coupling does not. A large shallow slip has been considered as a result of the release of sufficiently large strain energy in the shallow portion of the plate interface, but we suggest that shallow slips similar to that during the 2011 Tohoku-Oki earthquake may occur in any subduction zones where the energy accumulates only in the deeper portion.\u003c/p\u003e","manuscriptTitle":"A new mechanical perspective on a shallow megathrust near-trench slip from the high-resolution fault model of the 2011 Tohoku-Oki earthquake","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-06-16 15:42:09","doi":"10.21203/rs.3.rs-1714847/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2022-06-10T19:11:31+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-06-10T07:43:33+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-06-07T06:10:28+00:00","index":"","fulltext":""},{"type":"submitted","content":"Progress in Earth and Planetary Science","date":"2022-06-01T04:19:20+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":"30ad2091-633a-43ba-a060-cf7bcec10f1d","owner":[],"postedDate":"June 16th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2022-11-21T03:37:54+00:00","versionOfRecord":[],"versionCreatedAt":"2022-06-16 15:42:09","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-1714847","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1714847","identity":"rs-1714847","version":["v1"]},"buildId":"ehx78VzkSd0WSzXnipQa-","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}