3.6 Quake Hits Close to Home for Many

There have been 25 earthquakes in Southern California so far this year at least as strong as the magnitude 3.6 quake that struck Thursday at 8:26 a.m. three miles east-southeast of downtown Los Angeles. But an earthquake’s proximity is everything, so this one--which caused no damage or injuries but was felt as a distinct jolt in the city’s central core and on the Eastside--got quite a bit more attention than most of the others.

Not only was it close to downtown, but it occurred in a sensitive fault zone that has had frequent quakes in recent years and, scientists agree, has the potential for bigger ones.

The temblor was centered about five miles underground within the Elysian Park thrust fault system, the same welter of faults responsible for the 5.9 Whittier Narrows earthquake of Oct. 1, 1987, which killed eight people, injured 200 and did $358 million in damage.

This system also underlies Hollywood and the eastern part of the Santa Monica Mountains, downtown Los Angeles, and extends southeastward through the Whittier Hills into Orange County.

Because it passes underneath such a highly populated area, it is potentially one of the most dangerous fault zones in California. To the experts, it provides special cause for proceeding with seismic retrofits on major high-rise buildings, such as Los Angeles City Hall.

“The best estimates are that the fault system is slipping at about a tenth of an inch a year,” James Dolan, assistant research professor of earth sciences at USC, said Thursday. Dolan is a leading authority on the Elysian Park fault zone.

“If it were to break in its entirety, we could get something in a magnitude 7 or 7-plus range,” he said. “But that’s a big ‘if,’ and it’s equally possible the system could break [in segments] in more frequent but smaller earthquakes.

“If it does occur in larger earthquakes, they might happen every couple of thousand years,” he added.

Because this is a “blind” fault system that leaves no visible surface traces, scientists have no indication when or whether such a quake might have occurred in the past, Dolan said.

Lucy Jones, a seismologist with the U.S. Geological Survey, noted that there have been half a dozen noticeable temblors since 1992 in the immediate vicinity of Thursday’s quake, and quite a few more over the last quarter-century.

The largest of these were two quakes on June 12, 1989, assessed at magnitude 4.6 and 4.4. Those are nearly as strong as the quake near San Jose that was felt throughout the San Francisco Bay Area this week.

The Whittier Narrows quake was centered about a dozen miles farther southeast along the fault system on a different segment.

In comparison to the 1994 Northridge earthquake, Thursday’s was small potatoes.

Caltech seismologist Egill Hauksson said Southern California’s growing network of strong-motion recording devices measured the quake at 0.014 of the force of gravity at USC and 0.005 at Compton.

This compared to readings ranging from 0.3 to 2.0 in the San Fernando Valley and other damaged parts of Los Angeles in the Northridge quake, meaning that the shaking then was 20 to 150 times more violent.

Still, for some people who felt Thursday’s 3.6 shaker, it was memorable.

At the El Tepayac cafe in East Los Angeles, cashier Vanessa Macias, 19, said she got scared.

“One cook yelled . . . ‘Temblor! Temblor! “‘ she said. “I just ran outside into the street.”

Others took it in stride.

UPS driver Michael Williams was in the back of his truck with 200 packages when the quake occurred.

“It was kind of a slow rock, like the Michael Jackson song, ‘I Want to Rock With You,’ ” he said. “I just stayed in the back of the truck. I wasn’t scared. Earthquake is my middle name.”