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