[S-CG40] Science of slow-to-fast earthquakes

[SCG40-P15] Seismic reflection imaging in the northern part of the Japan Trench subduction zone

*Yasuyuki Nakamura¹, Tetsuo No¹, Ryo Miura¹, Gou Fujie¹, Seiichi Miura¹, Shuichi Kodaira¹, Jin-Oh Park², Tetsuro Tsuru³ (1.Japan Agency for Marine Earth Science and Technology, 2.Aytmosphere and Ocean Research Institute, University of Tokyo, 3.Tokyo University of Marine Science and Technology)

Keywords:Japan Trench, Seismic reflection imaging, Slow earthquake

The Japan Trench hosted many subduction zone earthquakes. Several M7-8 earthquakes occurred during the last ~100 years in the northern Japan Trench. The 1896 Meiji Sanriku earthquake generated devastating tsunami. On the other hand, the fault slip of the 2011 Tohoku earthquake did not propagate to the northern part of the Japan Trench. Recent seafloor observation network revealed this area hosts slow earthquakes. It has been suggested that the variation of the incoming plate structure is linked to different slip behaviors of the plate boundary faults in the Japan Trench subduction zone, however the detailed structural variation in the subduction zone has not been well investigated in the northern Japan Trench.
We conducted seismic surveys in the northern part of the Japan Trench to reveal the structural characteristics from outer rise to the subduction zone. We obtained 7 seismic reflection profiles using a ~6 km streamer cable and a 10600 inch³ air gun array of R/V Kaimei. Post-stack time migrated sections obtained by the preliminary data analysis show the variations in the structure in the northern Japan Trench subduction zone. The ruptured areas of previous large (M7-8) earthquakes tend to have weak reflection along the plate boundary. The areas with slow earthquakes have reflective zones in the deeper part of the hanging wall plate above the plate boundary. Two profiles indicate high relief of the subducting oceanic crust in the shallow portion of the subduction zone, which may be related to subducting petit-spots. The moho reflection is generally well identified seaward of the trench but is obscured around the petit-spot region. We plan to process the obtained data through pre-stack depth migration, and will discuss the structural features and its relation to plates boundary slip behaviors.