The Mexican earthquake of 1985 vis-à-vis great Indian earthquakes: Field and seismological aspects

Abstract

The great Mexican earthquake or 19 September 1985 (Magnitude 8.1 ) and its aftershocks caused the worst disaster in Mexico city about 350 km away from its epicentre. Through field surveys undertaken by the author, typical damages particularly on taller buildings in the city area have been discussed in the light of strong motion results vis-a-vis engineering aspects. The damage in Mexico city has been attributed to the largest spectral accelerations, longest duration and occurrence of two shallow focus events with an interval of 27 sec besides efficient generation of surface waves (0.2 to 1 Hz) towards Mexico city. The urban reconstruction plan has also been briefly described.

Comparison of the source dynamics of the Mexico earthquake near subduction boundary of the Cocos South American plate with the great Himalayan earthquakes near the Indian Eurasian plate boundary shows that in spite of tectonically different environments (low stress drop of the Mexical1 earthquake compared with high stress drops of great Indian earthquakes), there .was a similarity in development of secondary miezoseismal areas for the great earthquakes of 1905 and 1934 which can be potentially hazardous zones for taller structures/ buildings.