4.7 Quake Hits Area of Seismic Concern : Geology: Experts have alerted authorities in Barstow to prepare for possibility of stronger temblor. The latest was one of 130 quakes there since 7.5 Landers shaker.

A magnitude 4.7 earthquake that may have been related to the June 28 Landers quake struck Wednesday in the Mojave Desert six miles northeast of Barstow, an area where scientists and state emergency officials have alerted authorities to prepare for the possibility of a stronger temblor.

Although there were no reports of damage or injuries from the 3:22 p.m. shock, it was the largest of more than 130 earthquakes that have occurred in the Barstow area since the magnitude 7.5 Landers quake. Thirty-one of those were above magnitude 3 and seven were above magnitude 4.

Four hours after the Barstow quake, an unrelated earthquake of magnitude 3.0 hit the Los Angeles area. A Caltech spokesman said the mild jolt was centered three miles northeast of Hollywood. There were no immediate reports of injuries or damage, authorities said.

Richard Andrews, head of the state Office of Emergency Services, said Wednesday that scientists have been closely monitoring the Barstow area in recent weeks. Authorities there have been urged to undertake various earthquake preparedness measures, he said.

Andrews said earthquake scientists have expressed concern that the Barstow area is in a “seismic gap” between the Landers aftershock zone and an area of quake activity to the northwest near the town of Mojave and in the Owens Valley.

“We have been told that if there is a 6-magnitude Landers aftershock, it could occur in this gap,” Andrews said.

Barstow Mayor Mel Wessel confirmed Wednesday that the city of 22,000 people recently received “a notification from the state that we were in an area that could have aftershocks.” City manager Eric Ziegler said no specific preparedness steps were suggested.

Seismologist Lucile M. Jones of the U.S. Geological Survey said Wednesday’s temblor occurred on the northern end of the Calico Fault, about 15 miles north of the end of the Landers aftershock zone.

“This is an obvious place to have the 6-magnitude aftershock we have been talking about,” Jones said. “A lot of earthquake sequences have late, large aftershocks that extend the aftershock zone.”

She noted, by way of example, that aftershocks well away from the original main shock occurred after both the magnitude 6.3 Long Beach earthquake of 1933 and the magnitude 7.7 Tehachapi quake of 1952. The aftershock to the Tehachapi quake struck a month later in Bakersfield and killed two people.

As officials pondered the Barstow quake, Andrews joined Dalles Peck, national director of the U.S. Geological Survey, in announcing that a 12-member scientific review panel has been named by the two agencies to re-evaluate the probability of catastrophic earthquakes occurring in Southern California.

The panel is expected to present its initial conclusions for review by national and state experts in about two months. Specifically, it will try to recalculate the 1988 conclusion by a scientific task force that there is a 60% probability of the so-called Big One striking along the southern San Andreas Fault by 2018.

“Many of us in the scientific community feel intuitively that the Landers-Big Bear quake sequence has increased the probability of large damaging earthquakes over the next few years,” Peck said. “But we can’t ask public agencies or individual citizens to make preparedness or emergency plans based on intuition. Instead, we must provide the best scientific review.”