Lessons from the 1985 Mexican earthquake

Severe damage during the September 19, 1985 Mexican earthquake prompted a site visit by three engineers and two seismologists representing the Canadian National Committee on Earthquake Engineering. This paper includes background information on earthquake history of the region, details of the 1985 earthquake and its strong ground motion, subsoil conditions, and building code provisions. The team's observations of moderate damage in the epicentral area are consistent with the relatively low near-field accelerations (15% g). In the damaged parts of Mexico City, soft soil conditions amplified the ground motion and resulted in almost pure harmonic motion with a period of about 2 s. These characteristics, together with the long duration and high accelerations (20% g) caused severe damage to many structures, as is illustrated in the paper. Lessons learned from the earthquake together with the Mexican emergency code changes are discussed.