Whittier Narrows earthquake
Encyclopedia
The 1987 Whittier Narrows earthquake struck the southern San Gabriel Valley
and surrounding communities of southern California
at 7:42 a.m. (PDT
) 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 in the town of Rosemead, California
, at a depth of 9.5 kilometres (5.9 mi).
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
.
A magnitude 5.6 strike-slip aftershock
occurred three days later, on October 4, causing additional damage, and one additional death.
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
. Lupe Elias-Exposito was killed when a concrete slab fell on her as she, her sister and a friend were exiting a parking structure at California State University, Los Angeles. Five other deaths are attributed indirectly to the event. About $358 million USD
in damage resulted.
The Whittier Narrows earthquake along with two other events - the 1983 Coalinga earthquake
, and the 1994 Northridge earthquake, brought blind thrusts to the attention of seismologists and policy makers. As a result, other significant blind thrusts have been identified in Southern California.
San Gabriel Valley
The San Gabriel Valley is one of the principal valleys of Southern California, United States. It lies to the east of Los Angeles, to the north of the Puente Hills, to the south of the San Gabriel Mountains, and west of the Inland Empire. It derives its name from the San Gabriel River that flows...
and surrounding communities of southern California
Southern California
Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...
at 7:42 a.m. (PDT
Pacific Time Zone
The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time . The clock time in this zone is based on the mean solar time of the 120th meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC-7.In the United States...
) on October 1, 1987. The magnitude 5.9 earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
was originally assigned a magnitude of 6.0 but was revised a few days later when additional data became available. Its epicenter was in the town of Rosemead, California
Rosemead, California
Rosemead is a city in Los Angeles County, California, United States. As of the 2010 census, it had a population of 53,764. Rosemead is part of a cluster of cities, along with Arcadia, Temple City, Monterey Park, San Marino, and San Gabriel, in the west San Gabriel Valley with a growing Asian...
, at a depth of 9.5 kilometres (5.9 mi).
The earthquake was caused by slip on a blind thrust fault
Blind thrust earthquake
A blind thrust earthquake is an earthquake along a thrust fault that does not show signs on the Earth's surface, hence the designation "blind" . Such faults, being invisible at the surface, have not been mapped by standard surface geological mapping...
near the northern end of the Whittier Fault
Whittier Fault
The Whittier Fault is a geologic fault located in eastern Los Angeles County in Southern California, that is one of the two upper branches of the Elsinore Fault Zone, with the Chino Fault the second.-Geology:...
, part of the Elsinore Fault Zone
Elsinore Fault Zone
The Elsinore Fault Zone is a large right-lateral strike-slip geological fault structure in Southern California. The fault is part of the trilateral split of the San Andreas fault system and is one of the largest, though quietest faults in Southern California....
, 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
Puente Hills Fault
The Puente Hills Fault, or the Puente Hills thrust system, is a thrust fault located across the Los Angeles Basin, discovered in 1999. It runs about 25 miles from the Puente Hills region in the southeast to just south of Griffith Park, Los Angeles in the northwest...
.
A magnitude 5.6 strike-slip aftershock
Aftershock
An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock...
occurred three days later, on October 4, causing additional damage, and one additional death.
Three people died as a direct result of the earthquake. One death was of a Southern California Edison
Southern California Edison
Southern California Edison , the largest subsidiary of Edison International , is the primary electricity supply company for much of Southern California, USA. It provides 14 million people with electricity...
worker buried by a landslide in the Muir Peak area of the San Gabriel Mountains
San Gabriel Mountains
The San Gabriel Mountains Range is located in northern Los Angeles County and western San Bernardino County, California, United States. The mountain range lies between the Los Angeles Basin and the Mojave Desert, with Interstate 5 to the west and Interstate 15 to the east...
while working with a crew installing the footings for a high tension power tower north of Pasadena, California
Pasadena, California
Pasadena is a city in Los Angeles County, California, United States. Although famous for hosting the annual Rose Bowl football game and Tournament of Roses Parade, Pasadena is the home to many scientific and cultural institutions, including the California Institute of Technology , the Jet...
. Lupe Elias-Exposito was killed when a concrete slab fell on her as she, her sister and a friend were exiting a parking structure at California State University, Los Angeles. Five other deaths are attributed indirectly to the event. About $358 million USD
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in damage resulted.
The Whittier Narrows earthquake along with two other events - the 1983 Coalinga earthquake
1983 Coalinga earthquake
The 1983 Coalinga earthquake occurred on May 2, 1983 at exactly 23:42 UTC in Coalinga, California. The earthquake recorded 6.5 on the Richter scale. The earthquake was caused by an unknown fault buried under the surface....
, and the 1994 Northridge earthquake, brought blind thrusts to the attention of seismologists and policy makers. As a result, other significant blind thrusts have been identified in Southern California.
External links
- NOAA images of earthquake damage
- Whittier Narrows earthquake on Southern California Earthquake CenterSouthern California Earthquake CenterThe Southern California Earthquake Center , headquartered at the University of Southern California, was founded in 1991 with a mission to:* gather new information about earthquakes in Southern California;...
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