BUTSURI-TANSA(Geophysical Exploration)
Online ISSN : 1881-4824
Print ISSN : 0912-7984
ISSN-L : 0912-7984
Case Study
Estimation of S-wave velocity structures in Rikuzen-Takata City, Iwate Prefecture by microtremor observations
Hidekazu YamamotoWataru AsadaTsuyoshi Saito
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JOURNAL FREE ACCESS

2019 Volume 72 Pages 101-110

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Abstract

Microtremor observations were carried out for the purpose of exploring the S-wave velocity structures in order to clarify seismic risks in Rikuzen-Takata City, Iwate Prefecture, where severe damage occurred in the 2011 off the Pacific coast of Tohoku Earthquake and the great tsunami. Microtremor observations using a single seismometer were carried out at 78 points to examine the depth distribution of the bedrock was examined from the peak period of H/V spectral ratios. And, microtremor observations using a miniature array were also carried out at 14 sites to estimate the shallow S-wave velocity structures. As a result, the H/V peak period increases from the north area to the south area in the coastal plain, the H/V peak period increases from the east area to the west area, and it abruptly became shorter across the Kesen River. Therefore, the depth of bedrock gradually becomes deeper from the north area to the south area, from the west area to the east area, it is thought that the bedrock structure indicates a bowl-shaped one with a deep base near the center and with a shallow end at both ends. This result was similar to the geological cross section of Chida et al. (1984). In the place showing the basement depth of about 40 m, our S-wave velocity structure estimated using large size arrays and a miniature array were consistent with the geological cross section of Chida et al. (1984). The two dimensional shallow S-wave velocity structure obtained from the microtremor exploration using a single point and a miniature array was also in good agreement with the geological cross section by Chida et al. (1984).

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© 2019 The Society of Exploration Geophysicists of Japan
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