9:15 AM - 9:30 AM
★ [MIS33-02] What long-term seafloor observations told us about the 2011 Tohoku-Oki Earthquake
We continued seismological and geodetic observation after the earthquake to know postseismic activity. The obtained data indicate that the postseismic crustal deformation field show very complex spatial pattern as compared to those observed by the onshore network. The complexity is caused by large viscoelastic relaxation induced by the huge coseismic slip and makes it difficult to identify the elastic deformation associated with the afterslip along the megathrust, although it is the most important information to understand the behavior of the fault. The situation requires us to enhance the abilities of seafloor monitoring to detect the slip activities on the fault. Detecting slow-slip transient slips is one of the solutions and we started an array of arrays observation including broad-band seismographs to detect and locate slow-slip events and low-frequency tremors, which can happen in the transient process regaining interplate coupling. Another observation we started is direct-path acoustic ranging across the trench axis. Slip rate of the shallow fault can be measured by monitoring the change in distance between the benchmarks on the incoming and overrding plates.