Chance Seen of a Bigger S.D. Quake

Earthquake experts familiar with minor earthquakes such as the one that hit San Diego Monday and Tuesday say there is a “slight” chance that San Diego might be hit by a more powerful, perhaps even destructive, quake in the next few days.

“I don’t know exactly what the chances are but I’d say it’s slight, about 5%,” said Kate Hutton, staff seismologist at the California Institute of Technology in Pasadena. “We’re not talking about evacuating buildings, it’s too much of a long shot, but maybe they ought to think about putting their fire engines outside and things like that for better emergency response.”

Hutton said she based her estimate on past earthquake patterns in California, in which large quakes have sometimes followed a series of smaller ones. Chances of danger diminish as the days pass following the temblors, she said.

Officials at the San Diego County Office of Disaster Preparedness said they had been alerted by the U.S. Geological Survey to a 1-in-20 chance of an earthquake of Richter scale magnitude 5 or greater within five days of Monday’s three mild earthquakes.

A quake of Richter magnitude 6 would be roughly equivalent to the 1971 San Fernando earthquake, which killed 65 people and caused more than $500 million in property damage.

“We’re calling all of the cities (in San Diego County) and simply letting them know what the USGS has told us,” said disaster preparedness operations officer Marian Wright. “It’s up to them to decide what they want to do about it. They know their structures better than we do.”

A San Diego Fire Department spokesman, Mel Young, said the department rolled its engines out of fire houses after each of Monday’s quakes and rolled them back in after the ground stopped rumbling. However, there are no immediate plans to keep pumpers and ladder trucks parked outside, he said.

“If we get a good tremor, we’ll pull the apparatus out,” Young said.

The most recent seismic activity in the San Diego area occurred at 2:41 p.m. Tuesday when an aftershock from Monday’s activity was felt in central San Diego. The aftershock, measuring 2.8 on the Richter scale, was centered about a mile southeast of downtown, according to Caltech sensors.

During a 4 1/2-hour span Monday, three quakes rattled buildings briefly throughout much of the county. The largest registered 4.0 on the Richter and was sandwiched between two jolts that each measured 3.9. All were centered in coastal waters off Coronado.

There were no reports of damage or injury.

In June, 1983, the most powerful earthquake ever recorded near San Diego, a jolt of 4.6 magnitude, chipped building plaster, shook windows and awakened thousands of residents but had little other significant effect.

Although San Diego is traversed by a series of faults and fault lines, seismologists have long regarded the area as relatively inactive. But it is the area’s past inactivity that now concerns some experts.

“Many of the large earthquakes have ‘foreshock’ patterns in areas that don’t have many earthquakes, as in San Diego,” Hutton said. “Not every big quake turns out to be preceded by foreshocks, but there are some.”