Microtremor array surveys and development of the velocity model in the Hakodate Plain, Hokkaido, Japan

Abstract The Hakodate Plain in the southern part of Oshima Peninsula, Hokkaido, Japan, is a sedimentary basin surrounded by mountains. vertical displacements caused active faults along western margin increased depth Plain. Small-to-large-sized microtremor array surveys were conducted at five sites to estimate S-wave velocity structure down seismic bedrock for each site develop detailed model. A new three-dimensional model was developed integrating results and other existing geophysical explorations data. This modeled as stack homogeneous isotropic layers facilitate its incorporation into present nation-wide ground motion prediction. bottom Quaternary sediments deep total thickness Neogene reaches 2.9 km proposed validated gravity anomaly modeling simulation moderate-sized inland earthquake. location low-gravity around coastline Bay improved using numerical FDM also demonstrated that amplification long duration observed reproduced effectively this spatial variation long-period amplifications (period > 1 s) discussed based on simulations utilizing our highest periods 4 5 s expected southwestern period 3 relatively high near plain. Conversely, characteristics below 2 quite complex due interference wavefield inside structure. Variation source shorter range. Graphical abstract