考虑海域衰减特性的日本相模湾海底场地放大研究

为研究海底场地放大特征，选取日本相模湾地区6个海底强震台站和附近23个陆地台站，共188次地震的8199条地震动记录；采用广义反演法研究了海域与陆域数据反演震源位移谱的一致性；借助非参数广义反演法不受传统衰减函数形式限制的优势，分析了衰减函数的特征，反演了日本相模湾地区海域品质因子；最后分离并研究了海底台站的场地放大效应。相模湾地区海域与陆域地下介质存在明显不同，在震源、传播路径和场地条件三种效应解耦过程中，海域与陆域采用相同的衰减函数，会影响海底场地放大效应的估计精度。该文在海底场地放大的研究中区分考虑了陆域与海域的衰减函数，结果表明：日本相模湾地区海域品质因子在高频处对几何衰减模型十分敏感，且小于陆地上的品质因子，即水平方向的地震动在海域衰减速度高于陆域；考虑海域衰减特性进一步提高了海底强震动台站的场地放大估计精度。

Study on site amplification of strong ground motion stations considering attenuation characteristics of the sea area in the Sagami Bay area,Japan

In order to study the site amplification characteristics of submarine sites, 8199 acceleration recordings are selected from 6 offshore strong motion stations and 23 nearby onshore strong motion stations in 188 earthquakes in the Sagami Bay area of Japan. The consistency of seismic source displacement spectrum is studied by generalized inversion method. The characteristics of the attenuation function are analyzed by using the non-parametric generalized inversion method, which is not constrained by the traditional attenuation function. Finally, the site amplification of submarine station is separated. The subsurface structure is obviously different for the sea area and the land area of the Sagami Bay area. When the attenuation function of the sea area and the land area is assumed same in the decoupling process of source, propagation path and site conditions, the estimation precision of amplification of the submarine site will be influenced. The attenuation functions of the land and the sea area are both considered differently in the study of submarine site amplification. The results show that the quality factor of the sea area in the Sagami Bay area in Japan is very sensitive to the geometric attenuation model at high frequency and smaller than that on land. The attenuation rate of horizontal ground motion in sea area is higher than that in land area. It is also shown that the site amplification estimation accuracy of the submarine strong seismic station can be further improved by considering the attenuation characteristics of the sea area.