Magnitude-7.1 quake uncovers new active fault

PASADENA, Calif. - An earthquake that rocked California and the Southwest has propelled the U.S. Geological Survey to focus its attention on a fault line it previously had ignored.

The newly coined Lavic Lake fault, named for a dry lake bed near the Mojave Desert through which it broke ground, will now become one of the most studied in the next few years.

''We got a lot of information about this quake, a ton,'' USGS geologist Ken Hudnut said Sunday.

The temblor that struck at 2:46 a.m. Saturday near the remote desert town of Ludlow, caused minor injuries during a passenger train derailment. Light damage was reported elsewhere.

The magnitude of the quake was put today at 7.1. It had been listed as a 7.0 quake, but the reading was upgraded after a review of data, said Robert Tindol, spokesman for seismologists at the California Institute of Technology.

The quake happened along a 25-mile-long fault geologists had only partly mapped, hadn't researched and hadn't yet named.

Those tasks were low priority because of the fault's location. Other faults, such as San Andreas, are constantly monitored because they are located near heavily populated areas.

''We weren't going to do a lot of research along a fault that would only bother a rattlesnake,'' said Lucy Jones, a USGS seismologist.

Hudnut said the more geologists can learn about the physics of earthquakes, the more they can do to advise planners to avoid building on active faults and keep buildings already on them safer during temblors.

Other things they learned: The 1992 Landers and Big Bear Lake earthquakes, which happened three hours apart and killed one person, may have had a large effect on the Lavic Lake fault and hastened Saturday's quake.

Hudnut, who flew over the area with two colleagues in a helicopter to inspect the fault, said they marveled at the giant fissure that moved a dry river bed 12 feet to the side.

''It had wonderful surface rupture,'' he said. ''It was exciting for us. Most geologists study things that happened thousands of years ago. This is something that happened yesterday.''

The quake also was the first major event recorded on the TriNet quake data system, a network of 200 seismographic stations that measure quake intensity and other properties. The system and stations are linked by computer.

''We had all this equipment in place,'' Jones said. ''We were looking for a model to test it. This was perfect.''

While geologists got down to business Sunday, the 50 residents of Ludlow near the quake's epicenter, had to fix mobile homes that slipped off foundations and broken glass and broken dishes that slowed service at the town's only diner.

The small town that heralded itself as ''famous for absolutely nothing'' is now known as the site of the strongest quake to hit California since Landers in 1992.