A fault under Hollywood and increased earthquake activity east of Los Angeles provide new reasons to fear Southern California is heading toward a killer jolt measuring 7 or more on the Richter scale, scientists say.
"Throughout Southern California, the earthquake threat is always lurking. These new studies help us understand the wide range of potential earthquakes we might face," said Shirley Mattingly, emergency services director for Los Angeles.The studies by the U.S. Geological Survey and the California Institute of Technology prompted Richard Andrews, the state's emergency services chief, to urge citizens and local officials to review and complete their plans for surviving a seismic disaster.
The research was announced Tuesday during the American Geophysical Union's fall meeting.
The findings show "there is a significant likelihood a large-magnitude quake will occur in Southern California sometime in the future, and we don't know when that is," Andrews said.
Scientists found the 18-mile-long Santa Monica-Hollywood Fault may be active and capable of producing a quake measuring 6.5 to 7 or more, and the San Gabriel Valley east of Los Angeles may be heading toward a magnitude-7 jolt.
The Oct. 17, 1989, quake that rocked the San Francisco Bay area measured 7.1, killed 63 people and injured 3,757. It was centered roughly 50 miles south of San Francisco. The new studies deal with faults directly under Los Angeles and its heavily populated suburbs.
A 1988 Geological Survey study identified the San Andreas Fault as 60 percent likely to produce a magnitude-7.5 to 8 quake by the year 2018 - a quake that officials say could kill up to 14,000 people and injure another 55,000 even though the fault is about 40 miles from Los Angeles.
Scientists also previously identified Los Angeles' Newport-Inglewood, Elysian Park and Torrance-Wilmington faults as possible sources of magnitude-6.5 to 8 quakes that could be even more deadly because they pass directly under the city.
The San Gabriel Valley, which includes cities such as Pasadena and West Covina, had six damaging quakes measuring 4.5 to 5.9 since 1987, after a 50-year period without a single quake that size, said Geological Survey seismologist Lucile Jones, chief author of one study.
"This increase in the numbers of moderate earthquakes is of concern," Jones said. "It's certainly possible we could have a magnitude-7 earthquake in the San Gabriel Valley, but whether that's going to happen this decade or within the next century or not for hundreds of years, we can't tell from the present data."
She said a similar series of moderate jolts preceded the 1989 Bay area disaster, but the San Gabriel Valley might face either more moderate quakes or an end to the recent activity.
In the yards of homes along the Santa Monica-Hollywood Fault, Caltech geologists Jim Dolan and Kerry Sieh identified embankments created by ground movements within the past 11,000 years or so. That suggests the fault is active, contrary to the long-held belief it was inactive, Sieh said.
The fault passes beneath Hollywood, West Hollywood, Beverly Hills, West Los Angeles, Santa Monica and Pacific Palisades.
"It does go down parts of Hollywood Boulevard" and near UCLA's campus, Sieh said.