[S07-P] Poster

[S07-P-08] Shallow to deep velocity structure modeling of Oita Plain, Japan, using microtoremor and borehole data

^○Masayuki Yoshimi¹, Takumi Hayashida², Shinichi Matsushima³, Hiroshi Kawase³, Hiroshi Takenaka⁴, Nobuyuki Yamada⁵, Hiroe Miyake⁶, Takeshi Sugiyama⁷, Tetsuyoshi Tokumaru⁷, Haruhiko Suzuki⁸, Atsushi Yatagai⁸, Hisanori Matsuyama⁸ (1.Geological Survey of Japan/AIST, Tsukuba, Japan, 2.IISEE, Building Research Institute, Tsukuba, Japan, 3.Disaster Prevention Research Institute, Kyoto University, Uji, Japan, 4.Okayama University, Okayama, Japan, 5.University of Teacher Education Fukuoka, Munakata, Japan, 6.University of Tokyo, Tokyo, Japan, 7.Tokumaru PE Office, Bungo-takada, Japan, 8.Oyo Corporation, Tokyo, Japan)

Shallow to deep velocity structure around Oita Plain, Kyushu Island, Japan, has been modeled using data obtained by dense microtremor array survey and boreholes. Large aperture microtremor array surveys of their radius about 20 to 1000 m were deployed at 12 sites in the Oita Plain using T=10s velocity seismometers to estimate the phase velocity of the Rayleigh wave to constrain S-wave velocity down to the seismic bedrock. In addition, small aperture array surveys with radius less than 20 m were conducted at about 100 sites to constrain shallow S-wave velocity structure. About 3,000 borehole data comprised of soil types and SPT values are carefully interpreted to create 250 m mesh model of a layered soil structure (down to 100 m depth at most) composed of three significant layers. S-wave velocity structure of each mesh has been converted from the layered soil structure using an empirical equation among the N-value, depth, soil type and S-wave velocity. Synthetic dispersion curve of the phase velocity calculated with the S-wave velocity model agree well with the observed ones.