PR 26

by R.D. McJunkin and J.T. Ragsdale

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A moderate-magnitude earthquake (ML = 6.6, California Institute of Technology, Seismological Laboratory) occurred at 16:16 (PDT) on 15 October 1979, approximately 15.5 km east-southeast of Calexico, California (location map - page 2). The main shock, a shallow focus event centered in Baja, California, was located at 32.64°N latitude and 115.33°W longitude (CIT, Seismological Laboratory). The earthquake was generated by right-lateral slip on the northwest trending Imperial fault and produced approximately 30 km of surface rupture that extends northward from the international border into the United States.

Damage from the earthquake, estimated to exceed $30,000,000, was most pronounced in residential areas of southern Imperial County and northeastern Baja, California. Agriculture also sustained high-dollar losses from seismic shaking and faulting. Much of the agricultural damage was generated by lateral slope failures into irrigation canals, including the All American Canal, that blocked and in places breeched these structures and subsequent crop damage resulting from insufficient irrigation. Much of the subsurface drain tile in fields cut by surface rupture was broken and will need to be replaced; in addition, many of these fields will need to be re-leveled to facilitate flood irrigation.