5.0 Landers Aftershock Rocks Area Near Palm Springs

A magnitude 5.0 earthquake, the strongest aftershock of the 1992 Landers quake in nearly a year, struck before dawn Sunday in a sparsely populated, mountainous area of Joshua Tree National Park above Desert Hot Springs.

No damage or injury reports were received after the 4:03 a.m. temblor, the Riverside County Sheriff’s Department said. It was centered 15 miles northeast of Palm Springs and four miles south of the epicenter of the 6.1 Joshua Tree quake of April 22, 1992, that started the Landers sequence.

The Landers shock of June 28, 1992, measured a powerful magnitude 7.5, and the sequence has had more than 45,000 aftershocks. Sunday’s, as recorded at Caltech, was the strongest since June 16, 1994.

“We certainly felt it,” said John Hilton, owner of the Emerald Springs Resort in Desert Hot Springs. “This one was one big jolt, but it didn’t last 10 seconds. It was nowhere near as bad as the original quakes.”

The aftershock awakened residents in Palm Springs and was felt as far away as the San Gabriel Valley and Orange County.

Egill Hauksson, a Caltech seismologist, said six aftershocks, magnitude 3.0 or less, were measured in the first hours after Sunday’s large aftershock, which was located just five miles from the San Andreas fault as it runs along the northeast side of the Coachella Valley.

Normally, a temblor this close to California’s most dangerous fault would cause seismologists some concern about a bigger quake, Hauksson said. But the north-south orientation of Sunday’s temblor, as compared to the northwest-southeast alignment of the San Andreas, was more consistent with a Landers aftershock than a San Andreas foreshock, he said.

In January, a panel of scientists, working under the auspices of the Southern California Earthquake Center at USC, reduced their assessment of the probability of a huge earthquake occurring on the Coachella Valley segment of the San Andreas fault in the next 30 years, from 40% to 22%.

In another seismic development, a leading earthquake scientist with the U.S. Geological Survey is taking issue with a forecast by the chairman of the USC geology department of a 6.0 to 6.5 magnitude earthquake in coastal Central California, possibly close to Parkfield, by July 9.

Prof. Charles G. Sammis based his forecast last month on an increase in the region, since 1987, in earthquakes of magnitude 3.0 or greater. But Geological Survey scientist Allan Lindh, at Menlo Park, said “a much larger body of data and careful analysis” from this and other regions should have been undertaken before Sammis reached his conclusions.

“The base-line probability for a magnitude 6.0 to 6.5 by 9 July for the entire region (designated by Sammis) is in the 2 to 3% range,” Lindh said, “while in a weak moment Charlie did apparently say something about a probability greater than 50%.”

Lindh acknowledged that there has been an increase in seismic activity in the Central California area. He said many researchers might be willing to increase the base-line probability “as high as 5%.”