[S-SS11] Strong Ground Motion and Earthquake Disaster

[SSS11-P06] Strong Ground Motion Characteristics and Subsurface Structure of the Mino Fault in the Median Tectonic Line Based on Microtremor Survey

*Tatsuya Noguchi¹, Aoyama Yuna¹, Moe Hirashima¹, Takao Kagawa¹, Masanori Kohno¹ (1.Faculty of Engineering, Tottori University)

Keywords:microtremor, H/V, S-wave velocity, the Mino Fault, the Median Tectonic Line

Microtremor surveys were conducted to understand the seismic characteristics and subsurface structure of the Mino Fault and its surrounding area, which is part of the Median Tectonic Line Fault System. The geology of the area around the Mino Fault consists of conglomerate, sandstone and mudstone deposited on the seabed, and large-scale fracture zones are exposed along the Mino Fault. Microtremor observations were carried out in two areas: one on the west side of the Mino Fault where fault gouge is exposed at the surface, and the other on the east side of the fault where a combination of fault and landslide zones are present. On the west side of the fault, L-shaped array observations were carried out at six locations with a seismic station interval of 2 to 128 m, crossing the fault. In the area to the east side of the fault, single-point three-component observations were carried out over a wide area at intervals of approximately 100 m to cover the landslide area, and L-shaped array observations were carried out at nine locations with seismometer intervals of 2 to 8 m. The H/V shape changes just above the fault. On the west side of the fault, the subsurface structure changed drastically at shallow structure (Vs=200~900m/s) and deep structure (Vs=1100~2100m/s) depths along the fault. On the east side of the fault, the subsurface structure changed drastically near the fault line, in addition to changes in the sedimentary layer (Vs=200~400m/s) caused by landslides.