1987 Whittier Narrows earthquake

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The Whittier Narrows earthquake struck the southern San Gabriel Valley and surrounding communities of southern California at 7:42 a.m. (Pacific Daylight Time) on October 1, 1987. The magnitude 5.9 earthquake was originally assigned a magnitude of 6.0 but was revised a few days later when additional data became available. Its epicenter was actually in the town of Rosemead, California, at a depth of 11 km.

The earthquake was caused by slip on a blind thrust fault near the northern end of the Whittier Fault, part of the Elsinore Fault Zone, on a previously unknown fault structure. There was no surface rupture. It has been proposed that the event occurred on an extension of the recently recognized Puente Hills thrust system.^[1]

A magnitude 5.3 strike-slip aftershock occurred three days later, on October 4, causing additional damage.

Three people died as a direct result of the earthquake. One death was of a Southern California Edison worker buried by a landslide in the Muir Peak area of the San Gabriel Mountains while working with a crew installing the footings for a high tension power tower north of Pasadena, California. Five other deaths are attributed indirectly to the event. About $358 million USD in damage resulted.^[2]

The Whittier Narrows earthquake along with two other events -- the May 1983 Coalinga earthquake, M6.5, and the January 1994 Northridge earthquake, M6.7 -- brought blind thrusts to the attention of seismologists and policy makers. As a result, other significant blind thrusts have been identified in Southern California.