4.2 Quake Shakes Desert

A magnitude 4.2 earthquake, the latest of about 70,000 aftershocks of the 1992 Landers quake, struck a remote Mojave desert area 27 miles southeast of Barstow late Monday night, the U.S. Geological Survey reported.

The 11:15 p.m. temblor was felt in San Bernardino and Riverside, but there were no reports of damage or injuries.

The magnitude 7.3 Landers quake of June 28, 1992, was the strongest quake in California since the 7.7 Tehachapi quake of July 21, 1952. Centered six miles north of Yucca Valley, the Landers temblor caused a 47-mile-long rupture in the earth’s surface.

North of this rupture was an unusual gap in seismic activity, and then, about 30 miles farther north, there was a cluster of hundreds of quakes northeast of Barstow.

Three experts on quakes in and near the Inland Empire on Tuesday placed the latest aftershock toward the northern end of the original rupture zone on the Camp Rock fault.

Sally McGill, a professor of geology at Cal State San Bernardino, and two Geological Survey scientists with offices in Riverside -- Katherine Kendrick and Doug Morton -- said it was not quite in the 1992 gap.

This, by definition, fits the scientific understanding of what aftershocks are. Their spatial patterns, in fact, delineate the original earthquake’s rupture zone, and quakes within that zone are said to be aftershocks just as long as their frequency exceeds the rate of earthquakes that struck before the big quake.

Aftershocks of the Tehachapi quake have lasted about half a century.

Until Saturday, California went for nearly eight days without a quake of magnitude 3.0 or larger, an unusually long time in this seismically active state.