A study on estimation method of a site effect of local government observation sites based on earthquake ground motion records in Kansai region

摘要

本論文では地震波形が得られていない自治体観測点を対象として，最大加速度とスペクトルの卓越振動数からサイト特性を推定する手法を提案する．まず，関西地方のK-NET，KiK-net観測点の地震記録を用いてスペクトルインバージョンによって，経験的なサイト特性を求めた．続いて，最大加速度の地盤増幅度とサイト特性，基盤スペクトルの関係式を導き，実観測記録においても関係式が概ね成り立っていることを明らかにした．サイト特性を推定するにあたり，地震動スペクトルの卓越振動数と1次ピーク振動数をパラメータとするサイト特性モデル式を考案し，各観測記録に対してサイト特性を推定した．推定したサイト特性とインバージョンによるものを比較したところ，ほとんどの観測点でサイト特性の形状や増幅度がよく対応していた． We propose a method to evaluate a site effect using peak ground acceleration (PGA) and predominant frequency of spectrum obtained at local government observation sites where seismic waveform records were not stored. Firstly, the site effects at K-NET, KiK-net observation sites in Kansai region were evaluated by the spectral inversion method. A relationship among amplification factor of PGA and the site effect, bedrock spectrum was derived. As a result, it was clarified that the relationship is valid for the observed records used in this study. In evaluation of the site effect, site effect model in terms of the predominant and first peak frequencies of the spectrum was proposed and the site effect at each observation record was evaluated using the proposed model. In comparison of the evaluated site effects with inverted one, the shape and amplification of the site effects at most observation sites were in good agreement with those of the inverted site effects.