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

1985年9月19日，墨西哥城发生了一场8.1级的地震，造成了墨西哥山谷内的墨西哥城严重破坏，该山谷距离太平洋震中约400公里。尽管地震在震中台站产生了非常低的加速度，但地震波在山谷内，特别是在湖床区，被惊人地放大了，而且湖床地震图的持续时间之长是一个真实的惊喜。我们假设，长尾波在湖底区产生的多路径，由于长距离的路径和振动特性，这取决于山谷的配置和非常软的表层。已进行了以下3项研究受试者。第一个主题是墨西哥城的波场解释，由四个主题组成。第一个课题是强震记录数据库软件的建设。第二个主题是通过对长路径上沿着强震记录的基本分析来估计长路径效应。第四个课题是强震台站场地效应的长路径沿着地脉动观测。第二个课题是墨西哥城地震危险性综合评估系统的开发。第三，考虑土与结构的相互作用，对墨西哥城软土地基上的结构进行了动力响应分析。

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.