The Mexican Earthquake: A Firsthand Report

by Emilio Rosenblueth, Prof. of Civ. Engrg.; Universidad National Autonomo de Mexico, Mexico City, Mexico,


Serial Information: Civil Engineering—ASCE, 1986, Vol. 56, Issue 1, Pg. 38-40


Document Type: Feature article

Abstract:

The Mexican earthquake of September 19, 1985 was most peculiar, because of the combination of its intensity, regularity, and duration. No other earthquake has had an intensity of IX, at such a focal distance, and with a magnitude of 8.1. There is also no record of horizontal peak ground acceleration of 0.20 G associated with a two-second period. The result was a double-resonance phenomenon (earthquake-ground, ground-building) that accounts for much of the damage. Most collapsed or damaged buildings were in the two period range, between 8 and 15 stories high. Mexico City is built on an old lakebed of volcanic origin, and soils in the upppermost clay formations often exceed water content of 400%. In general steel buildings survived the quake better than concrete ones. Friction piles also accounted for some failures where designers apparently counted on these to resist overturning moment. The city fared better than it might have had not the building code been revised in 1978.

Subject Headings: Earthquakes | Volcanic deposits | Soil water | Water content | Urban areas | Steel structures | Steel

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