Historic Earthquakes

Imperial Valley, Mexico-California Border
1979 10 15 23:16:54 UTC
Magnitude 6.5
Intensity IX

This major earthquake injured 91 people and caused an estimated $30 million in property damage in the Imperial Valley area. It destroyed two houses and 11 commercial buildings and damaged 1,565 houses and 440 commercial buildings. The most severe damage (MM intensity IX) was to the Imperial County Services building in El Centro, which had to be razed. The support pillars failed on this six-story reinforced concrete-frame structure, causing partial collapse of the east part of the building. It was designed under the 1967 provisions of the California Uniform Building Code. Other property damage caused by this earthquake at El Centro, Brawley, and Calexico and at Mexicali, Mexico, is typical of MM intensity VII, which is the highest intensity assigned to any location except the Imperical County Services Building.

Movement along the Imperial fault also caused damage to the irrigation system in the Imperial Valley. The All American Canal, which brings water form the Colorado River to the Imperical Valley, was damaged most severely. East of Calexico, the earthquake shook down levees on both sides of the canal. The banks settled more than 1 meter in places.

Ground displacment on the Imperial fault extended from about 4 kilometers north of the International Border to about 4 kilometers south of Brawley. The maximum lateral displacement - about 55 centimeters - was observed in Heber Dunes; the maximum vertical displacement - 19 centimeters - occurred southeast of Brawley. Ground rupture followed the same trace as that in the shock of May 18, 1940, and showed many of the same features and characteristics. Aftershock activity shifted to the north in both earthquakes, and both sustained damaging aftershocks near Brawley. There also is evidence that the Brawley fault experienced sympathetic movement in both earthquakes.

Felt over a large area, including southern California, southern Nevada, western Arizona, and an unknown area of Mexico. Many aftershocks occurred, the most damaging of which were on October 16 and December 21.

Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.