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| | Abstract | | Faults related to the 2011 Tohoku earthquake (Mw 9.0) were investigated by using seismic reflection data acquired in 1999 and submersible seafloor observations before the earthquake (in 2008) and after the earthquake (in 2011). Because the surveyed area includes the region where the largest vertical displacement is predicted to have occurred, the shallow faults here are likely to be directly related to the tsunami characteristics. On the seismic profile off Miyagi, we identified three predominant faults branching from the plate interface. Normal faults are further observed within the continental crust. The normal fault may be generated by tensile stress due to large displacement along the plate boundary fault near the trench. The seafloor deformation revealed by position of Ocean Bottom Seismometer (OBS) demonstrated that dynamic horizontal seafloor displacement across the branch normal fault is much changed, suggesting that the normal fault could be ruptured associated with the earthquake. We further reveal dynamic change of seafloor geometry and environment associated with the 2011 Tohoku earthquake by comparing the seafloor fault traces before and after the earthquake. The observation after the earthquake demonstrates that several fissures are developed along the reverse fault which could not be observed before the earthquake. |
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