Historic Earthquakes

Coyote Lake, California
1979 Augsut 06 17:05 UTC
Magnitude 5.7

No fatalities occurred, but 16 people were injured in Hollister and Gilroy. Property damage in the two towns, estimated at $500,000, consisted mainly of damaged chimneys, broken glassware in stores, and structural damage to five buildings in Gilroy.

Many chimneys were damaged in older houses near Gilroy's downtown area. A crack split a wall in the City hall, and the ceiling in a court room of the Municipal Courthouse caved in. Beams and uprights were damaged at Fords Department Store and the store was closed. At Hollister, a parapet toppled and caved in the roof of a real estate office; a ceiling partly collapsed at a new building on San Felipe Road. The J.C. Penny store sustained a 3 meter hole in its ceiling, and extensive cracks formed in the ceiling throughout the store. A service station at nearby Casa de Fruta sustained extensive damage, including fallen bricks from the chimney, bulging of exterior walls, and separation of interior walls from ceiling or floor. The fire station at Pacheco Pass, about 16 km northeast of Hollister, sustained extensive damage, and the nearby lookout station was vacated because of structural damage.

Ground displacement was observed along the Calaveras fault zone from Hollister north to the Anderson Lake area, about 39 km. The maximum horizontal displacement, 5-6 mm, occurred about 10 km east of Gilroy, where the Calaveras fault zone intersects Highway 152. Ground lurching, settlement , and slumping were observed in many places between Anderson Lake and Hollister. Felt from about 60km north of Bakersfield, north to Sacramento, east to the Pacific Ocean. During August, most of the 312 located aftershocks were clustered in the area south of the epicenter of the main shock.

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.