[S-CG45] Ocean Floor Geoscience

[SCG45-P06] Deformation of the upper plate within the Tohoku Region Pacific Coast analyzed by the top surface structure

*Hiroaki Koge¹, Ayanori Misawa¹, Toshiya Fujiwara², Yoshiaki Suzuki¹, Yusuke Sato³, Ryosuke Komatsu⁵, Chiori Tamura⁴, Katsura Kameo⁴ (1.AIST, 2.JAMSTEC, 3.Tokai Univ., 4.AORI. UTokyo, 5.MOL Marine Co., Ltd)

Keywords:japan trench, subduction zone, sub-bottom profiler, bahtymetry

Large earthquakes and tsunamis have repeatedly occurred along the Japan Trench. In the 2011 Tohoku-Oki earthquake (Mw 9.0), the fault rupture extended to the shallow portion of the Japan Trench. These large slips on shallow decollement resulted in the huge tsunami that devastated much of the east coast of Japan. Therefore, it is key to understand the deformation of forearc for disaster prevention. Geodetic observations have provided insights into the deformation in the landward plate after the 2011earthquake. However, there are few kinds of research that throughout the direct observation of bathymetry or the shallow structure below the seafloor. Therefore, to discuss the following two purposes, we have conducted the shipboard geophysical observation in the KH-20-10 cruise; a multi-narrow beam echo sounder (MBES); proton precession magnetometer (PPM), shipboard three-component magnetometers (STCM), shipboard gravimeter, and sub-bottom profiler (SBP). 1)Subsidence in the forearc slope from the surface structure of the hollow-shaped sedimentary basin. To consider the development of normal faults on the sedimentary basin, we obtained the SBP cross-sections in sedimentary basins scattered in the forearc slope. 2) Revisit postseismic deformation in the forearc slope, The survey lines obtained from the seafloor topography cross-section of Fujiwara et al. (2011) were re-obtained in this cruise. We compare the three seafloor topography data before the 2011 earthquake, immediately after the 2011 earthquake, and approximately 10 years after the earthquake, and examine the presence or absence of postseismic deformation.
We were able to carry out all the planned observations on the KH-20-10 voyage, because of the good conditions of the sea and the equipment. In this presentation, we will introduce the preliminary results while the KH-20-10 voyage. In particular, our presentation will focus on the results related to the topic 2).