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doi:10.3850/978-981-08-7920-4_S2-G21-cd
Identification of Engineering Bedrock using H/V Spectral Ratio of Microtremors
Terumasa Okamoto1 and Osamu Tsujihara2
1Department of Civil and Engineering, Okayama, Maniwa City, Japan.
2Department of Civil Engineering, Wakayama National College of Technology, Gobo City, Japan.
ABSTRACT
This study presents amethod of identifying S-wave velocity structure and the depth of engineering
bedrock using the H/V spectral ratio (the spectral ratio of horizontal to vertical components)
of microtremors which are assumed to be dominated by Rayleigh wave. The real subsurface
grounds are modeled by an equivalent two layered model with one surface layer and the
bedrock. S-wave velocity and depth of engineering bedrock are identified in two steps: In the
first step, S-wave velocities of the engineering bedrock are estimated by using microtremors at
several sites where the depth of engineering bedrock is known from borehole tests, and these Swave
velocities are averaged. In the next step, the depths of engineering bedrock are identified
by microtremors at other locations, assuming that the S-wave velocity of engineering bedrock is
known (it is estimated in the first step). This method is applied to Arida City in Japan and the
maps describing the characteristics of surface ground are drawn.
Keywords: Microtremors, H/V spectral ratio, Engineering bedrock.
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