7.1 Quake Reveals Active Fault

CalTech seismologists have upgraded the magnitude of Saturday's Hector Mine earthquake, in the Mojave Desert, from 7.0 to 7.1, reports CBS News Correspondent David Dow.

The California quake rattled the Southwest, uncovered a fault seismologists thought was inactive and provided the perfect test run for the U.S. Geological Survey's (USGS) new quake data network.

The change in magnitude came after a review of data from the computer-linked network of 200 seismographic stations.

The temblor that struck at 2:46 a.m. Saturday near the remote desert town of Ludlow caused a passenger train derailment but only minor injuries and light damage.

No damage was reported from the hundreds of aftershocks, including several of magnitude-5.0 or greater that continued to rock the region.

The main temblor occurred along a 25-mile-long fault geologists had partly mapped, hadn't researched and didn't name because it was so far away from dense population areas, USGS geologist Ken Hudnut said Sunday.

"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 at the California Institute of Technology here.

Now it has a name: the Lavic Lake fault, named for a dry lake bed near the Mojave Desert through which the fault broke ground. The quake that rocked the Southwest will make Lavic one of the most studied faults these next few years.

"We got a lot of information about this quake, a ton," said Hudnut.

Hudnut and two colleagues took a helicopter over the area Saturday to inspect the fault. Most of Lavic is located inside a training field for the U.S. Marine Corps, so live-fire training was halted for three hours and two Marines accompanied the researchers as they periodically landed to measure the cracked earth.

Hudnut said colleagues marveled when they saw the giant fissure that moved a dry riverbed 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 more geologists can learn about the physics of earthquakes, he said, the more they can do to advise planners to avoid building on active faults and keep buildings already on them safer during temblors.

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

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

Some equipment, however, ended up with the Los Angeles Police Department.

Detectives recovered parts of a seismometer found partly buried Sunday in a wash near Reseda in the San Fernando Valley. Officers called in the bomb squad when they saw the unfamiliar blue boxes. Squad members dismantled one box to determine whther it was suspicious. They left the other seismometer in the ground.

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  • CBSNews.com staff CBSNews.com staff

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