Historic Earthquakes

Whittier Narrows, California
1987 October 01 UTC 14:42
Magnitude 5.9

The Whittier Narrows earthquake caused eight fatalities, injured several hundred, and left property damage estimated at $358 million in the east Los Angeles area, mainly at Whittier. MM intensity VII to VIII covered an area of about 500 km2from Monrovia and Pasadena in the north to beyond Whittier in the southeast. MM intensity VI was assigned to an additional area of 1,500 km2.

Business structures in the old Whittier commercial district were the most severely damaged by the main earthquake. In the 24-square-block shopping area known as Whittier Village, 12 commercial buildings had to be razed, and another 20 buildings were declared unsafe. An inspection of residential houses in Los Angeles, Orange, and Ventura Counties indicated that 123 single-family houses and 1,347 apartment units were destroyed, and about 513 single-family houses and 2,040 apartment units sustained major damage. Property damage on the Los Angeles campus of California State University (about 10 km west of the epicenter) was estimated at more the $20 million.

The most severe damage to transportation systems was the Interstate 605Interstate 5, a major nine-span bridge that was built in 1964. The five supporting columns sustained severe shear fractures and the overpass was closed temporarily. Minor damage also occurred on 23 other bridges in the area.

Damage and dysfunction of lifelines included the often observed failure of ceramic elements on high-voltage substation equipment, damage to large liquid-storage tanks, and saturation of the telephone system with inappropriate calls. The natural-gas transmission system was not damaged, and only one cast-iron pipe failed in the distribution system. However, about 1,400 gas leaks occurred on customer property, and many fires were ignited.

This earthquake sequence ruptured a small and previously unidentified, gently north-dipping,west-striking thrust fault beneath the uplifted Puente Hills and Elysian Park-Montebello Hills. However, tectonic slippage was not observed during a field study of the faults in the epicentral area. Geologic surface expression appeared to be limited to secondary nontectonic breaks caused by acceleration at the surface. Although many ground cracks formed along the base of the Puente Hills between Turnbull Canyon and Norwalk Boulevard, ground breakage in that area was limited to slope failures, including extensional cracks, minor landslides, and rockfalls. Ground-surface cracks also were observed at Worsham Creek oil field and Whittier Narrows golf course.

The main shock was followed by about 500 locatable aftershocks, an unusually small number for an earthquake of this magnitude. The largest aftershock, which occurred on October 4 about 3 km northwest of the epicenter of the main shock, caused further damage to weakened buildings.

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.