[S07-7] Site effects II

[S07-7-05] The spatial variability of the directionally dependent microtremor horizontal-to-vertical spectral ratios at the boundary of the basin edge in Uji, Japan

^○Shinichi Matsushima¹, Keita Sato², Yuri Fukuoka³ (1.DPRI, Kyoto University, Uji, Japan, 2.Sch. Eng., Kyoto University, Kyoto, Japan, 3.Grad. Sch. Eng., Kyoto University, Kyoto, Japan)

Directionally dependent microtremor horizontal-to-vertical spectral ratios (MHVRs) have been observed in Uji, Japan, close to the basin edge which is formed as a result of the reverse fault movement of Obaku fault, in the south-eastern part of Kyoto basin and the directionally dependent MHVRs are assumed to be a result of the effect of the two dimensional basin structure from on the theoretical MHVR calculated based on the diffuse field assumption (Matsushima et al., 2014). The study was focused on the MHVRs where the directional dependence of the MHVRs were very clear.
In this study, we have conducted microtremor observations in a wider area compared to the previous studies in order to investigate the spatial variability of the directionally dependent MHVRs in and around the target area. We extended the observation area to sites further away from the basin edge, i.e. closer to the central part of the basin, and sites up the hills to the hanging wall side of the Obaku fault. The observed MHVRs showed that if the site is further enough from the basin edge it does not show much directional dependency, where we can assume that the subsurface structure is flat-layered. On the other hand, if we go up the hills, the peak diminishes as predicted by numerical calculations by Matsushima et al. (2014). These information obtained from MHVRs can be used to specify the detailed shape of the basin edge combined with numerical calculations of MHVRs assuming the diffuse field.