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Research about Coalinga, California

Source-linked reports with geographic coverage including Coalinga, California.

7 recordsLinked to original sources
USGS1990

The Coalinga, California, earthquake of May 2, 1983

At 2342 G.m.t. May 2, 1983, a magnitude (ML) 6.7 earthquake occurred about 12 km northeast of the town of Coalinga, approximately halfway between Los Angeles and San Francisco. The shock was felt from Los Angeles to 200 km north of Sacramento and as far east as Las Vegas. Unlike other well-documented, major earthquakes in California in the 20th century, this event was not associated with any previously known or suspected active fault. Comprehensive geologic and geophysical investigations begun soon after the event have demonstrated the absence of a near-surface fault responsible for the earthquake. Instead, the earthquake was closely associated with a fault zone concealed beneath folds developed along the structural boundary between the Coast (Diablo) Ranges and the San Joaquin Valley.

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USGS1988

Crustal velocities near Coalinga, California, modeled from a combined earthquake/explosion refraction profile

Crustal velocity structure for the region near Coalinga, California, has been derived from both earthquake and explosion seismic phase data recorded along a NW-SE seismic-refraction profile on the western flank of the Great Valley east of the Diablo Range. Comparison of the two data sets reveals P-wave phases in common which can be correlated with changes in the velocity structure below the earthquake hypocenters. In addition, the earthquake records reveal secondary phases at station ranges of less than 20 km that could be the result of S- to P-wave conversions at velocity interfaces above the earthquake hypocenters. Two-dimensional ray-trace modeling of the P-wave travel times resulted in a P-wave velocity model for the western flank of the Great Valley comprised of: (a) a 7- to 9-km-thick section of sedimentary strata with velocities similar to those found elsewhere in the Great Valley (1.6 to 5.2 km/sec); (b) a middle crust extending to about 14 km depth with velocities comparable to those reported for the Franciscan assemblage in the Diablo Range (5.6 to 5.9 km/sec); and (c) a 13- to 14-km-thick lower crust with velocities similar to those reported beneath the Diablo Range and the Great Valley (6.5 to 7.30 km/sec). This lower crust may have been derived from subducted oceanic crust that was thickened by accretionary underplating or crustal shortening.

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USGS1985

Effects of the 1983 Coalinga, California, earthquake on creep along the San Andreas fault

The M//L approximately equals 6. 5 earthquake that occurred near Coalinga, California, on May 2, 1983 induced changes in near-surface fault slip along the San Andreas fault. Coseismic steps were observed by creepmeters along a 200-km section of the San Andreas. some of the larger aftershocks induced additional steps, both right-lateral and left-lateral, and in general the sequence disrupted observed creep at several sites from preseismic long-term patterns. Static dislocation models can approximately explain the magnitudes and distribution of the larger coseismic steps on May 2. The smaller, more distant steps appear to be the abrupt release of accumulated slip, triggered by the coseismic strain changes, but independent of the strain change amplitudes.

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USGS1984

Seismic potential revealed by surface folding: 1983 Coalinga, California, earthquake

The 2 May 1983 Coalinga, California, earthquake (magnitude 6.5) failed to rupture through surface deposits and, instead, elastically folded the top few kilometers of the crust. The subsurface rate of fault slip and the earthquake repeat time are estimated from seismic, geodetic, and geologic data. Three larger earthquakes (up to magnitude 7.5) during the past 20 years are also shown to have struck on reverse faults concealed beneath active folds.

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USGS1984

On the front lines in Coalinga

I have often been asked, "As a city manager, what is the first thing you do in an earthquake?" I generally say, "Look up, something heavy might be falling on you. Actually, the first step is to declare an emergency. The city council can ratify it later. The declaration is in your emergency preparedness plan, if you can find it. Mine was under a pile of debris; but after, I turned it up, I located an old declaration from a flood disaster and inserted the word "earthquake" wherever I found the word "flood." The declaration is necessary to give the city some protection from liability, which unfortunately, it will need.

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