Correlation of frontal prism structures and slope failures near the trench axis with shallow megathrust slip at the Japan Trench

Abstract

prism sediment, SU2 as incoming hemipelagic and pelagic soft sediment, SU3 as chert, and SU4 as igneous basement. We additionally interpreted a stratified unit TF, which shows a clear onlap relationship with SU2 at the trench axis, corresponding to the trench fill sediments (Fig. 2a,f). Three of the seismic profiles in Fig. 2c-e were acquired in the area with the huge shallow slip during the 2011 Tohoku earthquake around 38°-38°30′N. Seismic profiles HDMY069 and HD65B (Fig. 2c,d), where differential bathymetry suggested a large horizontal displacement 8,9 , show deformation of the sediment units by thrust faults in the vicinity of the trench axis. Seismic profile HD34B (Fig. 2e), located very close to the JFAST drill site C0019, where the coseismic slip was suggested to reach near the trench axis 13-15 , shows similar deformation 12. Three other seismic profiles (Fig. 2a,b,f), located outside of the area with very large shallow slip, display a chaotic acoustic character and no clear thrust faults in the vicinity of the trench axis. The differential bathymetry indicated little or no trench-normal horizontal displacement along these profiles 10,11 .

Connection between high pore-fluid pressure and frictional instability at tsunamigenic plate boundary fault of 2011 Tohoku-Oki earthquake

“…An effective coefficient of basal friction of 0.09 represents a compressively critical state 27 of the plate boundary fault beneath the low-velocity wedge. This is consistent with the fold-and-thrust structures imaged within the sediments 30 and the reverse faults interpreted on the RTM section (Fig. 4 c).…”

“…1 ) to calculate the physical properties of the sediments. The spatial location of this line coincides with 2D seismic line MY101, which was acquired in 1999, and several studies 6 , 15 – 17 , 30 have been conducted to estimate the coseismic slip of 2011 Tohoku-Oki earthquake around this line. Previously, we used line D13 in a different study 42 to apply seismic full waveform inversion on the shallow sedimentary strata in the forearc upper slope.…”

Seafloor Geodesy From Repeated Multibeam Bathymetric Surveys: Application to Seafloor Displacement Caused by the 2011 Tohoku-Oki Earthquake

“…However, deep-sea multibeam bathymetric surveys are generally supposed to map hundreds meter-scale seafloor morphological features for the purposes of marine geology and geophysics, therefore, very high accuracy measurements have rarely been required yet. The magnitudes of seafloor displacements become smaller in areas far away from the 2011 Tohoku-oki earthquake epicentral area (Fujiwara et al, 2017;Kodaira et al, 2020;Nakamura et al, 2020). In the case of the surveys to detect small seafloor displacements, the uncertainties in the bathymetric surveys are not negligible.…”

A Decade of Lessons Learned from the 2011 Tohoku‐Oki Earthquake

“…However, slip models constrained by other data and aftershocks (Nakamura et al., 2016), differential seafloor bathymetry (Kodaira et al., 2020), and near‐trench turbidities (Ikehara et al., 2016) (Figure 11) suggest that the main coseismic slip is limited to the south of 39.2°N. The higher‐frequency tsunami waves (Tappin et al., 2014) and seismic profiles of shallow structure (Nakamura et al., 2020) showed that gravitational slope failures of the trench inner wall may have substantially contributed to the proposed tsunami source around 39–40°N. Given the inherent uncertainties involved in the different types of observations, the northern reach of the rupture remains uncertain.…”