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Earthquakes in Southern California |
There have been many earthquake occurrences in Southern California. This set
of slides shows earthquake damage from the following events: Imperial Valley, 1979,
Westmorland, 1981, Palm Springs, 1986; and Whittier, 1987. These events were all earthquakes
with a magnitude of 5.9 or higher with damage estimates of one million dollars or
more. Imperial Valley Earthquake of October 15, 1979. Epicenter 32.6 N, 115.3 W; depth:
7 km; magnitude 6.8; damage: $30 million; no deaths. The earthquake was felt over
approx. 128,000 sq km. The worst damage occurred in southern Imperial County and northeastern
Baja California where eleven businesses and two homes were destroyed. Four hundred
forty businesses and 1565 homes were damaged. Although there were no deaths, ninety-one
people were reported injured mainly by flying glass or by falling objects. The greatest
single structural loss was to the Imperial County Services Building in El Centro.
Non-structural damage included damage to bridge abutments that were cracked and roadbeds
that shifted due to slumping or faulting. The agriculture industry incurred damage
to canals and irrigation ditches, damage to subsurface drain tiles which were disturbed
by the movement along the Imperial Fault. The worst damage incurred by the agriculture
industry wasto the All-American Canal which brings Colorado River water into the Imperial
Valley. Ground shaking caused the collapse of levees on both sides of the canal along
a 13-km stretch of the canal east of Calexico. Extensive lateral slope failure occurred
along this and other canals. In some places canal banks settled by more than 1 m.
Westmorland Earthquake of April 26, 1981. Epicenter 33.1 N, 115.6 W; depth: 4 km;
magnitude 6.3 ML(B); damage: $1-3 million; no deaths. Twelve buildings in Westmorland
were severely damaged, ten beyond repair, and an additional 30 sustained minor damage.
Seventy percent of the town's 900 homes (many of which were built of adobe and brick)
were damaged, and five homes were condemned. Six mobile homes were knocked off their
foundations and nine homes sustained minor damage to foundations, porches, and walls.
Electrical service was interrupted for onehour and the water supply was interrupted
for 10 hours. The sewage plant sustained an estimated $40,000 damage. Total damage
was estimated at $1.5 million. Subsidence was reported on several rural roads in the
area. Liquefaction caused scores of "mudpots," and oozing soil in nearby fields. One
country road west of Westmorland collapsed, producing a 2-footdrop-off. In rural areas
$100,000 in damages was incurred when unreinforced, concrete-lined irrigation canals
were broken. Palm Springs Earthquake of July 8, 1986. Epicenter 34.0 N, 116.6 W; depth:
10 km; magitude 6.0; damage: $4.5 million; no deaths. At least 29 people were injured
and some damage occurred in the Palm Springs-Morongo Valley area. Landslides ccurred
in the area. The quake caused serious damage at the Devers substation of Southern
California Edison Company. Some residences in the Whitewater Canyon area were badly
damaged. Damage from this quake was approximately $4.5 million. Minor damage occurred
at Angelus Oaks, Desert Hot Springs, North Palm Springs, Palm Desert, Palm Springs,
and Yucca Valley. The quake was felt throughout much of southern California and in
Las Vegas, Nevada, Lake Havasu City, Arizona and in the northern Baja California area
of the United States and Mexico. Whittier Narrows Earthquake of October 1, 1987. Epicenter
34.0 N, 118.1 W; depth: 11 km; magnitude 5.9; damage: $358 million; 8 deaths. At 7:42
A. M (Pacific Daylight Time), on October 1, 1987, a fault located about 11 km below
the surface and 20 km east of downtown Los Angeles, California, began to rupture.
The fault was an extension of the previously identified Whittier fault. The resulting
earthquake caused about $358 million in property damage and the loss of 8 lives. Severe
damage was confined mainly to communities east of Los Angeles and near the epicenter.
No severe structural damage to high-rise structures in downtown Los Angeles was reported.
Non-structural damage did occur, however. In Whittier the most severe damage occurred
in the "Uptown" business district. Similar damage was observed in the old downtown
section of Alhambra and in the "Old Town" section of Pasadena. These areas had high
concentrations of unreinforced masonry buildings. Residences which sustained damage
usually were constructed of masonry, were not fully anchored to foundations, or were
houses built over garages with large door openings. Many chimneys collapsed and in
some cases, fell through roofs. Wood frame residences sustained relatively little
damage. Damage often occurred around large windows. Light fixtures and suspended ceilings
fell in many buildings within a 10-km radius of the epicenter. A student at California
State University, Los Angeles was killed when the connectors for a precast concrete
fascia panel failed and the panel fell two stories crushing her. Damage was incurred
on a bridge at the interchange of I-605 and I-5, where the columns in the center were
severely damaged.
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