Historic Earthquakes
Near Coalinga, California
1983 05 02 23:42 UTC
Magnitude 6.4
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 kilometers 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 spalling at the top of the support columns, fracturing and displacement of wingwalls 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 kilometers 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.
This earthquake triggered thousands of rockfalls and rockslides as far as 34 kilometers northwest, 15 kilometers south, and 26 kilometers southwest of the epicenter. Only a few slope failures occurred east of the epicenter because of the absence of steep slopes in that direction.
This damaging earthquake was caused by an 0.5-meter uplift of 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 kilometers of the instrumental epicenter, none of which appeared to represent movement on deeply rooted fault structures. About 5 weeks later, on June 11, however, an aftershock caused surface faulting about 12 kilometers northwest of Coalinga.
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.
Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.
