1985年9月19日メキシコ地震に関する研究 I : 地盤震動特性と被害との関係について

Abstract

The damage in Mexico city during the Mexico Earthquake of September 19,1985 was studied in relation to seismic characteristics of soils in Mexico Valley. Mexico city is nowadays one of the biggest cities in the world with population of about 18 million. A sudden increase in population since 1940 caused a rapid expantion of urban area to the Lake Zone composed of extremely soft sediments of Lake Texcoco. Damages during the earthquake concentrated in this area. Microtremor measurements and spectrum analisis of strong motion records were carried out. The results obtained suggest that predominant periods in highly damaged area are from 1 to 2.5 seconds, which are the same as natural periods of buildings having 9 to 17 floors. It means that sever damages of buildings are easily caused by resonance with soil motions. It is one of the reasons that caused damages in Mexico city. The questionnaire survey to the citizens of Mexico city was performed to estimate seismic intensity during the earthquake of 1985. The result shows that seismic intensity was very high in the damaged area. This is the reason why comparatively low houses were also damaged.