Seismic strong motion with long path and risk evaluation in Mexico City

1985年9月19日发生的希乔阿坎地震（震级为8.1级）对墨西哥山谷内的墨西哥城造成了非常严重的破坏，距离太平洋震中约400公里。虽然地震在震中产生的加速度很低，但在山谷内，地震波却被惊人地放大了，尤其是在湖床地带，而且湖床地震记录的长时间持续确实令人惊讶。我们假设湖床带的长尾波是由多路径产生的，这是由于湖床带的长尾波路径和振动特性取决于山谷结构和非常柔软的表层。进行了以下3项研究。第一个主题是墨西哥城的波场解释，由4个主题组成。第一个课题是强震记录数据库软件的构建。第二个主题是通过对长路径强震记录的基本分析来估计长路径效应。第三个主题是对墨西哥城数组记录的分析。第四个主题是沿长路径的微震测量，以检查强震台站的场地效应。第二个课题是墨西哥城地震危险性综合评价体系的开发。第三，在考虑土-结构相互作用的情况下，对墨西哥城软土地基上结构的响应进行了估计。

The 19 September 1985 Hichoacan earthquake (Hs=8.1) caused very severe damage in Mexico City inside the Mexico Valley, which is approximately 400 km from the epicenter in the Pacific Ocean. Whereas the earthquake produced very low accelerations at epicentral stations, seismic waves were amazingly amplified inside the valley, especially in the lakebed zone, and the long duration of the lakebed seismograms was a real surprise. We hypothesize that the long coda in the lakebed zone are produced by multipathing due to the long-distance path and the vibration characteristics, which depend on the valley configuration and the very soft surficial layrs. The following 3 study subjects have been performed. The first subject is the interpretation of wave field in the Mexico City and is composed of 4 topics. The first topic is the construction of database software for strong-motion records. The second topic is the estimation of the long-path effects by basic analysis of strong-motion records along the long path. The third topic is the analysis of array records in Mexico City. The fourth topic is the microtremor measurements along the long path to examine site effects of strong-motion stations. The second subject is the development of general seismic risk evaluation system for Mexico City. Thirdly, we estimate the response of structures on the soft ground of Mexico City, considering soil-structure interaction.