1983 Coalinga earthquake
Encyclopedia
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.
The Coalinga earthquake was felt from the Los Angeles area north to Susanville
(Lassen County) and from the coast east to western Nevada
. Through July 31, more than 5,000 aftershocks were recorded, of which 894 had a magnitude of 2.5 or larger. Most of the larger magnitude shocks were felt in Coalinga.
of the anticline ridge
northeast of Coalinga, but surface faulting was not observed. Ground and aerial searches immediately after the earthquake revealed ground cracks and fissures within about 10 kilometres (6.2 mi) of the instrumental epicenter
, none of which appeared to represent movement on deeply rooted fault structures. About five weeks later, on June 11, however, an aftershock caused surface faulting about 12 km (7.5 mi) northwest of Coalinga.
The Coalinga earthquake suggested to geologists that the State of California was in even worse seismological condition than had been thought. The pace of earthquake activity along the Pacific coast was identified as a relevant subject for further study; and the investigation of earthquakes stemming from unknown faults caused concern. California officials emphasized that the predicted great quake would do far more damage than this one and that if it struck in a densely populated area the damage would be incalculable.
This earthquake caused an estimated $10 million in property damage (according to the American Red Cross
) and injured 94 people. Damage was most severe in Coalinga, where the 8-block downtown commercial district was almost completely destroyed. Here, buildings having unreinforced brick walls sustained the heaviest damage. Newer buildings, however, such as the Bank of America
and the Guarantee Savings and Loan buildings, sustained only superficial damage. The most significant damage outside the Coalinga area occurred at Avenal
, 31 kilometres (19.3 mi) southeast of the epicenter.
A disaster assessment by the American Red Cross
listed the following statistics on damage in the area: almost destroyed - 309 single-family houses and 33 apartment buildings; major damage - 558 single-family houses, 94 mobile homes, and 39 apartment buildings; and minor damage - 811 single-family houses, 22 mobile homes, and 70 apartment buildings. Most public buildings, including the City Hall, hospital, schools, fire house, post office, and police station, sustained only minor damage.
Only six bridges of 60 surveyed in the area sustained measurable structural damage. This damage consisted of hairline cracks and spall
ing at the top of the support columns, fracturing and displacement of wing walls and parapets, and settlement of fill
.
All public utilities were damaged to some degree. The water system continued to function despite many leaks in its transmission piping. Gas was shut off for several days because of broken piping and leaks, but only temporary interruptions of electric and telephone services were reported. One large section of old concrete sewer pipe west of the downtown area partly collapsed, but this system also continued to function.
In the oil fields near Coalinga
, surface facilities such as pumping units, storage tanks, pipelines, and support buildings were all damaged to some degree. One oil company administration building, about 7 km (4.3 mi) north of Coalinga, sustained major structural damage and its two brick chimneys were toppled. Subsurface damage, including collapsed or parted well casing, was observed only on 14 of 1,725 active wells.
s and rockslides
as far as 34 km (21.1 mi) northwest, 15 km (9.3 mi) south, and 26 km (16.2 mi) southwest of the epicenter. Only a few slope failures occurred east of the epicenter because of the absence of steep slopes in that direction.
. In addition, the commission member's per diem expenses were raised from $50 to $100 per day and their duties specific to the 1983 Coalinga earthquake were deleted before the comprehensive report was prepared.
Coalinga, California
Coalinga is a city in Fresno County, California. The population was 13,380 at the 2010 census, up from 11,668 at the 2000 census. It is the site of both Pleasant Valley State Prison and Coalinga State Hospital. Coalinga is located southwest of Fresno, at an elevation of 673 feet .-Early...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. The 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...
recorded 6.5 on the Richter scale. The earthquake was caused by an unknown fault buried under the surface.
The Coalinga earthquake was felt from the Los Angeles area north to Susanville
Susanville, California
Susanville is the county seat of Lassen County, California, United States. Susanville is located on the Susan River in the south-central part of the county, at an elevation of 4186 feet . The population was 17,974 at the 2010 census, up from 13,541 at the 2000 census...
(Lassen County) and from the coast east to western Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
. Through July 31, more than 5,000 aftershocks were recorded, of which 894 had a magnitude of 2.5 or larger. Most of the larger magnitude shocks were felt in Coalinga.
Tectonics
The Coalinga earthquake was caused by an 0.5-meter upliftTectonic uplift
Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic uplift:...
of the anticline ridge
Anticline
In structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...
northeast of Coalinga, but surface faulting was not observed. Ground and aerial searches immediately after the earthquake revealed ground cracks and fissures within about 10 kilometres (6.2 mi) of the instrumental epicenter
Epicenter
The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates...
, none of which appeared to represent movement on deeply rooted fault structures. About five weeks later, on June 11, however, an aftershock caused surface faulting about 12 km (7.5 mi) northwest of Coalinga.
The Coalinga earthquake suggested to geologists that the State of California was in even worse seismological condition than had been thought. The pace of earthquake activity along the Pacific coast was identified as a relevant subject for further study; and the investigation of earthquakes stemming from unknown faults caused concern. California officials emphasized that the predicted great quake would do far more damage than this one and that if it struck in a densely populated area the damage would be incalculable.
Damage and casualties
American Red Cross
The American Red Cross , also known as the American National Red Cross, is a volunteer-led, humanitarian organization that provides emergency assistance, disaster relief and education inside the United States. It is the designated U.S...
) and injured 94 people. Damage was most severe in Coalinga, where the 8-block downtown commercial district was almost completely destroyed. Here, buildings having unreinforced brick walls sustained the heaviest damage. Newer buildings, however, such as the Bank of America
Bank of America
Bank of America Corporation, an American multinational banking and financial services corporation, is the second largest bank holding company in the United States by assets, and the fourth largest bank in the U.S. by market capitalization. The bank is headquartered in Charlotte, North Carolina...
and the Guarantee Savings and Loan buildings, sustained only superficial damage. The most significant damage outside the Coalinga area occurred at Avenal
Avenal, California
Avenal is a city in Kings County, California, United States. Avenal is located southwest of Hanford, at an elevation of 807 feet . It is part of the Hanford–Corcoran Metropolitan Statistical Area , which encompasses all of Kings County. In area, it is the largest city in Kings County...
, 31 kilometres (19.3 mi) southeast of the epicenter.
A disaster assessment by the American Red Cross
American Red Cross
The American Red Cross , also known as the American National Red Cross, is a volunteer-led, humanitarian organization that provides emergency assistance, disaster relief and education inside the United States. It is the designated U.S...
listed the following statistics on damage in the area: almost destroyed - 309 single-family houses and 33 apartment buildings; major damage - 558 single-family houses, 94 mobile homes, and 39 apartment buildings; and minor damage - 811 single-family houses, 22 mobile homes, and 70 apartment buildings. Most public buildings, including the City Hall, hospital, schools, fire house, post office, and police station, sustained only minor damage.
Only six bridges of 60 surveyed in the area sustained measurable structural damage. This damage consisted of hairline cracks and spall
Spall
Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure...
ing at the top of the support columns, fracturing and displacement of wing walls and parapets, and settlement of fill
Fill dirt
Fill dirt is earthy material which is used to fill in a depression or hole in the ground or create mounds or otherwise artificially change the grade or elevation of real property....
.
In the oil fields near Coalinga
Coalinga Oil Field
The Coalinga Oil Field is a large oil field in western Fresno County, California, in the United States. It surrounds the town of Coalinga, about half-way between Los Angeles and San Francisco, to the west of Interstate 5, at the foot of the Diablo Range...
, surface facilities such as pumping units, storage tanks, pipelines, and support buildings were all damaged to some degree. One oil company administration building, about 7 km (4.3 mi) north of Coalinga, sustained major structural damage and its two brick chimneys were toppled. Subsurface damage, including collapsed or parted well casing, was observed only on 14 of 1,725 active wells.
Mudslides and rockslides
This earthquake triggered thousands of rockfallRockfall
Rockfall or rock-fall refers to quantities of rock falling freely from a cliff face. A rockfall is a fragment of rock detached by sliding, toppling, or falling, that falls along a vertical or sub-vertical cliff, proceeds down slope by bouncing and flying along ballistic trajectories or by rolling...
s and rockslides
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
as far as 34 km (21.1 mi) northwest, 15 km (9.3 mi) south, and 26 km (16.2 mi) southwest of the epicenter. Only a few slope failures occurred east of the epicenter because of the absence of steep slopes in that direction.
Response
In response to the earthquake, the California Seismic Safety Commission was tasked with conducting a specific comprehensive investigation into the 1983 Coalinga earthquake, providing funding and expert technical assistance to the people of Coalinga for planning and reconstruction, and preparing and publishing a comprehensive report on the Coalinga earthquake. Coalinga recovered 98 percent of their expenses in repairing and rebuilding public buildings at a time when an 85 percent recovery rate was considered the standard success rate. In September 2006, the California Seismic Safety Commission was renamed the Alfred E. Alquist Seismic Safety Commission in honor of the then recently deceased California politician Al AlquistAl Alquist
-Biography:Born in Memphis, Tennessee, the son of a Swedish immigrant who worked for the railroads, he was barely a teenager when he started carrying water to railroad work crews. He became a timekeeper, switchman, brakeman and conductor, before serving with the Army Air Forces during World War II...
. In addition, the commission member's per diem expenses were raised from $50 to $100 per day and their duties specific to the 1983 Coalinga earthquake were deleted before the comprehensive report was prepared.