Estimation of Horizontal Seismic Bedrock Motion From Vertical Surface Motion Based on Horizontal-To-Vertical Spectral Ratios of Earthquake Motions

Abstract eng:
Estimating bedrock motion is a popular method to understand the amplification characteristics of the observation site and investigate strong ground motion characteristics without any site effects. We calculated average Horizontal-to-Vertical spectral ratios of weak motions and identify the subsurface structure as a ratio of transfer functions of horizontal and vertical components based on the diffuse field theory. Then, we attempted to estimate the horizontal seismic bedrock motions of weak motions and strong motions using the proposed method and compared with results from the equivalent linear analysis for non-linear soil response. For the weak motions, the bedrock spectra and the bedrock motions estimated by both analyses were consistent. The estimated bedrock spectra of strong motions were similar, but the bedrock waveform estimated by the equivalent linear analysis at MYG006 was larger than the one estimated by the proposed method. The cause of this larger amplitude was the excessive amplitude reduction of the transfer function that is used to divide the surface spectrum in order to get the bedrock spectrum. Except for that case, the results of the proposed method basically corresponds to the previous methods, and so we have shown here a new possibility of the application of the diffuse field theory.

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