Destructive strong ground motion in Mexico City: Source, path, and site effects during the great 1985 earthquake

Simultaneous consideration of source, path, and site effects on ground motion during the Michoacan earthquake of 1985 allows us to draw coherent conclusions regarding the roles played for the disaster in Mexico City by the rupture process, the mode of propagation of the waves between the epicentral zone and Mexico City, and the local amplification. In contrast to the horizontal component which showed dramatic amplification for the 2 to 3 sec motion at lake sediment sites, we observe almost identical vertical displacement seismograms containing rip-ples with 2 to 3 sec period throughout he Mexico City valley whether the recording site is on the lake sediments or on hard rock. We, therefore, conclude that the 2 to 3 sec motion responsible for the destruction of Mexico City was present in the incident field. After performing a phase analysis, we interpret he signal as the superposition of long-period Rayleigh waves and short-period Lg with a dominant period of about 3 sec. The analysis of the teleseismic records indicates that the radiation of this event is enhanced for waves around the 3 sec period. Except i