Quake Sensors Check on Kern County Wave : Aftershocks: Scientists express concern about recent movements. But they hope swarm will proceed without a large temblor.

After a spasm of Sunday night and Monday morning aftershocks from last week’s desert earthquake, the U.S. Geological Survey has sent one of its five portable seismographic stations in the Southland to the China Lake Naval Air Weapons Station area to better monitor what is going on.

There were five sizable aftershocks between 9:21 p.m. Sunday and 3:33 a.m. Monday. The strongest of them, magnitude 4.9, moved the quake sequence into a new area 13 miles northeast of the Kern County town of Ridgecrest, very close to a longer fault that scientists say could generate a large quake in the magnitude 6 range.

Caltech and Geological Survey seismologists Monday expressed some concern about the apparent migration of the 5-week-old quake sequence. But they said they still believe the odds are that the quake swarm will proceed without such a large quake, which, even if it did occur, would be strongly felt but probably not damaging in the Los Angeles area, more than 100 miles away.

The new aftershocks of last week’s magnitude 5.8 quake, all more than eight miles north of Ridgecrest on the naval base, did no further damage to the town of 28,000.

The $20,000 worth of equipment moved to the area by truck Monday has components capable of measuring quakes more precisely than most permanently located seismometers. All five of the transportable stations have been roving in the vicinity of the 1994 Northridge quake, and four of them are being left there.

Survey seismologist Lucy Jones said that one component of the equipment will measure small earthquakes, three others will measure quakes in the magnitude 3 range, and three “force-balance accelerators” will measure larger quakes, in the 4- and 5-magnitude range.

The portable stations have radio links to the Caltech Seismological Laboratory, which correlates Southland quake information.

Jim Mori, in charge of the Geological Survey’s Pasadena field station, and Caltech seismologist Egill Hauksson said that Sunday night’s largest aftershock approached a lengthy fault scarp, or vertical displacement, to the east of the welter of short faults that had been giving rise to the recent quakes.

“Maybe it’s a lead up to a big earthquake,” said Mori. “Sometimes you get events that begin to pop. But I think this is different, with maybe only small to moderate quakes popping on a complicated fault system.”

Jones and Hauksson also mentioned a possible volcanic connection to the quake swarm, saying the whole area--which is near the relatively youthful Coso volcanic field--may be underlain by magma, or molten rock, although they acknowledged it might simply be hot water from a geothermal field.

Meanwhile, Tom Henyey, executive director of the Southern California Earthquake Center at USC, said that the quakes are taking place in “a well known seismic belt which branches off the San Andreas Fault near Palm Springs.”

Henyey noted that the Landers-Big Bear quakes of 1992 also took place in what is known as the eastern California shear zone, as did one of the state’s three biggest earthquakes, in 1872 in the Owens Valley.

“These earthquakes now are not really unexpected in that we’re dealing with a moderately active level of seismicity through all this area,” he said.