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EARTHQUAKES IN CENTRAL CALIFORNIA, 1980-1984

The Livermore Earthquake of January 24, 1980.

At 11 A.M. PST on January 24, 1980, an earthquake occurred that was felt over an area of approximately 75,000 km2 of central California. The epicenter was 20 km north of Livermore in the vicinity of the Greenville fault. Most of the damage was of a non-structural type.

The most commonly reported damage consisted of broken gas and water lines, broken windows and glassware, chimney damage, overturned furniture, mobile homes knocked off supports, cracked plaster, and fallen ceiling tile. Most of the damage, (about $10 million) occurred in the Lawrence Livermore Laboratory nuclear research center. Expensive laser equipment was knocked out of alignment or thrown off supports. Many of the tanks partially or totally failed at the Wente Brothers Winery on Tesla Road, 4 km southeast of Livermore, causing the loss of more than 90,000 liters of wine.

The overpass at Interstate 580 and Greenville Road had to be repaired because the paving settled nearly 30 cm during the quake.

One death (possibly from a heart attack) and 44 injuries resulted from this earthquake. Most of the injuries were due to flying glass, overturned furniture, and falling ceiling tile and light fixtures

The Coalinga Earthquake of May 2, 1983.

The earthquake struck the town of Coalinga, California, (population 7,000) at 4:42 p.m. PDT on May 2, 1983, and was followed by a large aftershock 3.5 minutes later. The main shock occurred near Anticline Ridge about 15 km northeast of Coalinga. It was felt from the Los Angeles area north to Susanville and from the Pacific Coast to western Nevada, an area of about 205,000 km2.

The most serious damage occurred in the eight-block downtown commercial district extending from Third to Seventh Street between Durian and Forest Streets. Of 139 buildings in this area, 59 collapsed or were heavily damaged. The most severe damage occurred to the old (usually pre-1930) one- and two-story buildings of unreinforced brick masonry wall construction, with floors and roofs of wood.

In contrast to the severe damage to old brick buildings, the newer buildings of reinforced concrete-block walls or prefabricated metal had little structural damage. Most of the public buildings including the firehouse, post office, city hall, police station, hospital, and schools suffered only minor damage. Public utilities (water, electricity, gas, sewerage) performed well inspite of damage to some units.

Private residences were heavily damaged. More than eight hundred single-family houses were destroyed or incurred major damage. The majority of the 94 injuries occurred in residential sections of the city.

The Morgan Hill Earthquake of April 24, 1984.

On April 24, 1984 at 1:15 p.m. PST, a moderate-size earthquake occurred on the Calaveras fault to the east of San Jose, California. This earthquake was felt over an area of approximately 120,000 km2 in California and western Nevada. The area of moderate damage extended southward from the epicenter rather than centering on the epicenter. This pattern indicates that the Morgan Hill earthquake may have been a double event with the second event being located about 17 km southeast of the main shock.

In Santa Clara County, where most of the damage occurred, more than 550 structures incurred minor damage. Major structural damage was mainly confined to a very small area on two streets of the Jackson Oaks subdivision located east of Morgan Hill (population 19,000). Five houses were condemned; two of these had fallen off their concrete foundations and suffered partial collapse. Several masonry buildings on Main Street in Morgan Hill were damaged and later condemned. Well-engineered industrial buildings and residential structures sustained only minor damage, but many mobile homes fell off their supports causing considerable damage to the furnishings inside. There were many reports of fires resulting from the quake. Minor damage also occurred at San Martin and Coyote. Twenty-seven people were injured.