Crustal structure, fault segmentation, and activity of the Median Tectonic Line in Shikoku, Japan |
| |
| Authors: | Michiharu Ikeda Dapeng Zhao Yuki Ohno |
| |
| Institution: | aDepartment of Civil Engineering, Shikoku Research Institute Inc., 2109 Yashimanishimachi, Takamatsu 761-0192, Japan;bGeodynamics Research Center, Ehime University, 2-5 Bunkyocho, Matsuyama 790-8577, Japan;cDepartment of Civil and Architectural Engineering, Shikoku Electric Power Co., 2-5 Marunouchi, Takamatsu 760-8573, Japan |
| |
| Abstract: | We conducted a seismic tomographic analysis to estimate the crustal structure beneath the Shikoku and Chugoku regions in Japan. The Philippine Sea slab (PHS slab) subducts continuously in a SE–NW direction beneath this region, and the crustal structure is complex. Furthermore, the Median Tectonic Line (MTL), one of the longest and most active arc-parallel fault systems in Japan (hereafter, the MTL active fault system), is located in this area, and the right-lateral strike–slip movement of this fault system is related to the oblique subduction of the PHS slab. The MTL active fault system has ruptured repeatedly during the last 10 000 years, and has high seismic potential. Our tomographic analysis clarified the heterogeneous crustal structure along the MTL active fault system. This fault system in Shikoku can be divided into two segments, an east segment and a west segment, on the basis of the velocity structure. This segmentation model is consistent with other such models that have been determined from geological and geomorphological data such as fault geometry, slip rate, and faulting history. This consistency suggests that the surface characteristics of the MTL active fault system are related to structural properties of the crust. In particular, a prominent low-velocity (low-V) zone is present in the lower crust beneath the east segment. Our tomographic images show that the lower crust structure beneath the east segment is obviously different from that of the other segment. Furthermore, this low-V zone may indicate the presence of fluid, possibly related to dehydration of the PHS slab. As the presence of fluid in the lower crust affects the activity of the fault, stress accumulation and the fault failure mechanism may differ between the two segments of the MTL active fault system. |
| |
| Keywords: | Median Tectonic Line (MTL) Fault segmentation Crustal structure Philippine Sea slab Seismic tomography |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
