A magnitude 6.1 earthquake struck a broad area of Southern California on Wednesday night, rocking high-rise office buildings in downtown Los Angeles for several seconds and sending out strong shock waves that were felt from Las Vegas to San Diego.
Seismologists from Caltech and the U.S. Geological Survey said the temblor was centered nine miles east of Desert Hot Springs on an unnamed north-south fault five miles northeast of the San Andreas Fault.
The quake jostled the Southland with a sustained rolling motion, temporarily knocking out telephone service from Riverside east to the Arizona border. Initial reports indicated that the quake caused little damage and no injuries.
There were a dozen aftershocks of magnitude 3.0 or greater following what officials designated as the Joshua Tree Earthquake.
A USGS seismologist said there will be a 10% chance within the next three days of a great quake on the San Andreas Fault stronger than Wednesday’s temblor.
“There is a certain level of concern that this could be a foreshock to something bigger,” said Lucile Jones, a seismologist in the field office.
The area where the larger quake would be most likely to occur is between Banning and Brawley in Imperial County, she said.
The quake hit shortly before 10 p.m. and was felt for at least 60 seconds in some areas. It temporarily knocked at least one television station off the air, but electrical service to downtown Los Angeles was unaffected.
The strong quake followed a more moderate 4.6 temblor centered in the same area.
“The conditions tonight where you have a 4.6 quake in this area at 7:25 p.m., followed by the 6.1 at 9:51, lead to a fairly serious concern that there could be a larger quake,” said Caltech seismologist Kate Hutton.
The Governor’s Office of Emergency Services has issued an advisory for six counties telling authorities in Riverside, San Bernardino, Imperial, Los Angeles, Orange and San Diego counties should be on alert for another, larger quake.
Geologists say it is common to feel a rolling motion after an earthquake over a wide area, following the initial jolt near the epicenter. The effect is like a pebble being thrown in a pond. The primary wave--the jolt--moves from the origin of the quake up toward the surface. The secondary waves--the rolling motion--are the ripples that spread along the surface.
Wednesday night’s quake was shallow, about 3 1/2 miles under the surface, said Russ Needham, a geophysicist with the U.S. Geological Survey National Earthquake Information Center in Golden, Colo., which measured the quake’s magnitude at 6.0. “A shallow earthquake would send out more surface waves and so be felt over a bigger area,” he said.
Needham said there wasn’t more damage because the quake was centered in a relatively unpopulated area. “The Whittier Narrows Quake in 1987 was a 5.9,” he said. “Tonight’s energy release was about double that. But there were a lot more people and a lot more buildings there and so there was more damage then.”
Needham added that California’s building codes have been relatively strict since 1932 and “an earthquake that might not cause much damage in California might cause a lot in Turkey or Armenia.”
Nevertheless, at the Hyatt Regency Suites in Palm Springs, director of security Jerry Iovine reported that guests on the top floor were evacuated temporarily while building experts checked for structural damage to the six-floor hotel.
“For precautionary reasons, we evacuated people from our sixth floor because there is a stress point we had wanted to check,” Iovine said. “The (guests) are back on the floor, a little shaken, but back on the floor.”
Iovine said that cracks had appeared at the stress point, but added that the building is “supposed to shift like that” when a major earthquake hits in the vicinity.
There were no injuries to the guests, he said.
Iovine described the earthquake as “sounding like thunder.”
Guests were evacuated for about 30 minutes from the 192-room hotel, which had few vacant rooms Wednesday night. Most people remained in the lobby, but a few went outside.
The quake frightened one guest at a Sheraton hotel in Riverside so much he “came down in his pajamas,” said hotel clerk Maria Hill. “He was so scared, he locked himself out of his room. He wanted another key.”
Los Angeles city and county fire officials said that as of midnight they had received no damage reports.
“At this point, we are in emergency earthquake mode with all the firetrucks moved to safe locations outside the station,” said City Fire Department spokesman Jim Wells.
The shaker was felt in Las Vegas, where Lourdes Mariano, a telephone operator at Harrah’s, said both of the hotel’s tower were swaying. “We had a call from our guests, saying their rooms were really shaking,” she said. “Just the high towers were bending. Nothing broken. Just shook.”
In Southern California, Stan Krejci, 49, a businessman from Alexandria, Va., was finishing his grilled vegetable salad at a Sherman Oaks restaurant when the temblor--his first--hit.
“You couldn’t help but know--the whole building was shaking,” said Krejci with a laugh. “I wasn’t frightened by it, but my wife was. She looked at me and said, ‘I think it’s time go to back to Washington,’ where there won’t be anything but a political earthquake or two.”
In Redondo Beach, where the South Bay Civic Light Opera was performing its debut of “Mame,” the show went on. Scenery shook on stage, the auditorium trembled and about a dozen audience members fled for the exits. When the scene was over, it got the biggest applause of the night.
“I thought someone was shaking my seat, and I turned around all annoyed,” said one woman. “But no one was there.”
The quake seemed to come in two waves in downtown San Diego, shaking a downtown high-rise building for about 30 seconds. Bill Robinson, spokesman for the San Diego Police Department, said police had “numerous callers saying things like, ‘Wow, wasn’t that something?’ But we have received no reports of damage.”
Orange County Fire Department spokesman Capt. Dan Young said that an emergency survey of the most hazardous sites in the county showed no damage as a result of the quake, and fire engines were continuing late Wednesday to check other sites.
Also contributing to this report were Greg Beckmann, Stephanie Chavez, David Dorion, Paul Feldman, George Frank, Joel Greenberg, Nieson Himmel, Kevin Johnson, Marc Lacey, Eric Lichtblau, Gebe Martinez, Victor Merina, Dean E. Murphy, Judy Pasternak, Jeffrey A. Perlman, Caitlin Rother, Danny Sullivan, Tracy Wilkinson and Eric Young.