2D pre-stack depth migration imaging across the 2011 Tohoku (Mw9.0) coseismic rupture zone off NE Japan

Among the hydrological, and structural factors that potentially affect tsunami earthquakes, the fluid effect on rupture along the shallow plate boundary faults also one among those of the most importance. The relationship of the volume of fluid between the seismic region (fluid-rich) and the aseismic region (fluid-poor) is closely associated with tsunami earthquake generation at subduction zones (Saffer, 2017). Therefore, similar to all the other earthquakes which happened in the Japan Trench, The 2011 Tohoku earthquake (Mw 9.0) might offer an example for role of fluid that can cause the tsunami earthquake. However, the relatively comparison of fluid volume between the seismic region and the aseismic region and fluid-involved mechanism for tsunami earthquakes are poorly understood. For figuring out detailed geologic structure and estimate the fluid volume influencing the accreted structure landward of the Japan Trench, we tried to do 2D pre-stack depth migration (PSDM) imaging using multi-channel seismic (MCS) reflection data in the the 2011 Tohoku coseismic rupture zone off Miyagi, northeast Japan。

The 2D MCS reflection data were acquired along line D13 by R/V Kairei of the JAMSTEC in May 2011 immediately after the Tohoku earthquake. We built initial depth interval velocity model and update it in using horizon-based tomography, and grid-based tomography. Ocean bottom seismograph velocity data (Miura et al., 2005) on a nearby wide-angle seismic line guided the 2D PSDM velocity model building.

We recognize a bright reflector as the topmost oceanic crust (i.e., plate interface) of the Pacific plate subducting beneath the overlying Okhotsk plate, which can be traceable to more than 100 km landward from the Japan Trench axis (Fig. 1). The seaward Pacific plate is characterized by horst and graben structure with normal faults. A strong reflector of Moho discontinuity, which is observed beneath the oceanic crust before subduction, is also observed even after subduction of the Pacific plate, up to more than 100 km landward from the Japan Trench axis. In the upper plate, we identify the Neogene sedimentary layer overlying the Cretaceous erosional unconformity and backstop interface with high amplitude and negative polarity. We observe a reflection of Arc Moho at depth of about 20 km.