Two Tremors Echo July 13 Earthquake

Two strong aftershocks were recorded early Tuesday from the July 13 earthquake off the coast of San Diego that rattled Southern California. There were no reports of damage, although many residents in San Diego County coastal areas who felt the quakes called local police agencies.

Seismology experts at the California Institute of Technology in Pasadena said the first quake occurred at 1:18 a.m. and measured 4.4 on the Richter scale. A second temblor at 4:23 a.m. measured 3.9.

The Richter scale is a measure of energy released by a quake, with each numerical increase on the scale (e.g., from 4 to 5) representing a tenfold increase in energy release.

Both of Tuesday’s quakes took place along the same fault line 28 miles southwest of Oceanside, the location of the July 13 5.3 magnitude quake. That temblor was the largest ever recorded in San Diego County or offshore and caused an estimated $500,000 in minor damage.

A Caltech spokeswoman said Tuesday that the two quakes represented fairly strong aftershocks but that such continuing seismic activity could be expected for several weeks, if not months.

“Given the magnitude of the (July 13) quake, it takes a while for things to settle back down and the aftershocks could continue for some time to come,” Dolores Page said.

The offshore aftershocks were not the only ones to shake California Tuesday. Caltech also reported two aftershocks from the 6.1 temblor July 21 near Crowley Lake in the Sierra Nevada which caused an estimated $2.7 million in damage, mainly to mobile homes shaken off their foundations.

A 3.9 quake occurred at 12:12 a.m. 15 miles east of Crowley Lake and a second hit at 2:58 a.m. 20 miles northeast of the lake.

In addition, a small quake registering 3.6 was recorded 20 miles southeast of San Jose at 1:04 a.m.