LOS ANGELES — THE two powerful earthquakes that hit near here Sunday - including the country's third largest this century - underline the hazard of seismic events that threatens the length of this fault-lined state.
They provide a catalyst for earthquake preparedness that seismologists have long warned is woefully inadequate, especially in more populated urban areas that escaped widespread damage from Los Angeles to San Diego.
And because of their close proximity, with epicenters only 20 miles apart, the back-to-back earthquakes are promising a greater-than-ever window into seismic events adjacent to the San Andreas fault where scientists have been gauging pent-up force for decades.
"Seismologists will be busy for several years analyzing what happened here today," said Dr. Egill Haukson, a seismologist at the California Institute of Technology in Pasadena.
The first quake hit 90 miles east of Los Angeles before dawn at 4:58 a.m., Pacific Daylight Time. It registered 7.4 on the Richter Scale, the largest United States quake in 40 years.
By opening an 18 ft.-wide fissure that stretched 43 miles, the earthquake will provide a wealth of information on past seismic events that will be invaluable for calculating future ones.
"This may completely revise our ideas about how the San Andreas [fault] behaves ... as well as the Central Mojave shear zone," said Dr. Lucy Jones, a geophysicist at Cal Tech.
Because the two earthquakes generated hundreds of aftershocks, including six of 5.0 magnitude or greater, the new seismic activity provided new grist for soul-searchers already reeling from drought, riots, recession, and other recent earthquakes.
[A third quake, measuring 5.6 on the Richter scale, hit 70 miles northwest of Las Vegas at 3:14 a.m. yesterday, the Associated Press reported. It was not considered an aftershock. No injuries or damage were immediately reported.]
"I want to move, I can't go through this anymore," said Yucca Valley resident Linda Durnell, who recalled a 6.1 magnitude earthquake in April and a 5.8 magnitude quake that hit Sierra Madre near here exactly one year before. Yucca Valley incorporated as a town just seven months ago, with a population of 25,000. The area is sparsely populated with military bases, children's camps and nature parks.
Three hours after the first quake hit the area, a second quake hit the desert community of Big Bear, 20 miles away, at 8:07 a.m. Seismologists warned state residents of a 50-50 chance that a 6.0-or-greater tremor would hit within a week.
The only stronger quakes in the US since 1900 were an 8.6 magnitude tremor that leveled San Francisco in 1906 and a 7.7 quake in Los Angeles in 1952. Seismologists warned, however, that Sunday's quakes in no way lowered the possibility of an 8.0 or greater quake, "The Big One," that has been predicted to hit within the next 100 years.
At press time, the quakes had injured more than 300 people, and one death was reported. Damage estimates were not complete but were in the millions of dollars. After touring the areas by helicopter, Gov. Pete Wilson declared a state of emergency in Riverside and San Bernardino counties, making state relief aid available and low interest loans for rebuilding.
State authorities put the National Guard on alert and closed several roads. In Washington, President Bush assured Governor Wilson of federal aid. The initial tremor was far greater than the 7.0 quake of 1989 that hit San Francisco. That temblor killed 70 and caused billions of dollars in damage.
Besides hundreds of homes that suffered severe structural harm, a trailer park was devastated and there was damage to hotels in Los Angeles and evacuations as far away as San Diego.
The water supplies of several communities were cut off indefinitely, depriving 40 percent of the desert area's customers. Though dozens of fires broke out during the peak of dry season, fire damage was minimal. In the town of Industry, near Los Angeles, the first quake caused about 4,000 gallons of acid to spill into the street. The wall of a bowling alley collapsed entirely, in what was widely considered the greatest physical devastation from the first quake.
Los Angeles Mayor Tom Bradley said his city escaped with few problems, however, over 500,000 suffered power outages.
Though California appears to have escaped "The Big One," for the moment, seismologists say that they are more concerned than ever about stress to the San Andreas fault.
Stretching 600 miles from Cape Mendocino in the north to the Imperial Valley in the south, the fault is the boundary between the Pacific tectonic plate that forms the bottom of the Pacific Ocean and the North American plate that makes up the rest of North America.
Since the Pacific plate is moving north at the rate of one inch per year, enormous energy and stress builds along the fault that must eventually be released in the form of a tremor.
As of Sunday, however, seismologists had not yet identified which of California's thousands of fault lines had shifted to cause the tremors.