4.7 Earthquake Jolts S.D.; Little Damage

A sharp earthquake measuring 4.7 on the Richter scale shook San Diego at 6:38 p.m. Tuesday, but no significant damage was reported by police or disaster authorities in the San Diego area or in Tijuana.

The quake was centered in the ocean off Imperial Beach near the Mexican border, according to the California Institute of Technology in Pasadena, which monitored the temblor.

A seismological specialist at Scripps Institution of Oceanography at UC San Diego said Tuesday night that the epicenter appeared to be on the southward extension of the Rose Canyon Fault, based on the Caltech information. The Rose Canyon Fault is a major seismological cleavage running north-south along San Diego’s coastal region.

Scripps scientist John G. Anderson said the fault is capable of seismic activity although its slip rate--a measurement of fault activity--is 20 to 30 times less than those of faults such as the Imperial or San Andreas.

“That means that it (moves) less frequently to maintain its geological slip rate,” Anderson said.

The Tuesday quake continues a pattern of increasing seismic activity in San Diego County during the past two years, but scientists are extremely cautious in predicting whether the quakes are related or will lead to larger tremors.

On July 13, a 5.3 magnitude quake took place 28 miles southwest of Oceanside. It was the largest ever recorded in San Diego County and caused an estimated $500,000 in minor damage. Several aftershocks on the same fault have been in the 4.0 Richter range.

The Richter scale is a measure of energy released by a quake. Each numerical increase on the scale (from 4 to 5, for example) represents a tenfold increase in energy released.

Fourteen quakes ranging from 2.5 to 4.2 were felt during a four-day period in June, 1985, most of them centered in San Diego Bay near the 32nd Street Naval Station.