[S-SS10] Strong Ground Motion and Earthquake Disaster

[SSS10-P16] Microtremor Survey near the Mino Fault, the Median Tectonic Line, Miyoshi City, Japan

*Tatsuya Noguchi¹, Shota Sasaki¹, Masanori Kohno¹, Yusuke Ono¹, Takao Kagawa¹ (1.Faculty of Engineering, Tottori University)

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

Microtremor surveys were conducted in the vicinity of the Mino Fault in the Median Tectonic Line fault system to understand the characteristics of strong ground motion and subsurface structure. The Mino Fault is a 13.5-km fault located in Miyoshi City, Tokushima Prefecture, Japan. The Izumi Group, which includes the Mino Fault, is composed of conglomerates, sandstones, and mudstones that were deposited on the seafloor, and there are large-scale fracture zone exposures along the Mino Fault. Microtremor observations were conducted across the fault near the outcrop of the fault gouge of the Mino Fault. Single-point three-component observations were conducted at 41 points at 100 m intervals over a wide area, linear array observations were conducted on the fault at 2 m and 10 m intervals with four 3-line arrays (total of 12 arrays), and L-shaped arrays were conducted at 2 to 62 m intervals at one site. H/V was calculated from the three-component records, and the predominant period was read. Phase velocity dispersion curves were obtained from the array records to estimate the subsurface structure. The H/V characteristics were as follows: the peak of H/V was flattened just above the fault, and the peak was clearly defined on the south or north side of the fault. The phase velocity dispersion curves show that the velocity differs on the north or south side of the fault, and that the S-wave velocity structure changes drastically before and after the fault. Further study is needed to include the deep structure of the fault, taking into account the results of gravity survey.