4.5 and 4.4 quakes rattle region over weekend

A magnitude 4.4 earthquake hit the Imperial Valley on Sunday at 9:42, and six quakes in the magnitude 3 range rattled the area in a three-hour period today, automated seismographs report.

A magnitude 4.5 quake early Saturday morning at the northern end of the Laguna Salada Fault woke up people in San Diego, the Palm Springs area and southern Orange County, according to reports filed with the USGS.

Kathy Svitil, a spokeswoman at Caltech, said the increased seismic activity is being reviewed by scientists.

The epicenters for today’s quake cluster generally were on the U.S.-Mexico border about 11 miles west of downtown Calexico. But the California Integrated Seismic Network computers initially placed the largest quake epicenter 14 miles southeast of Calexico, and Svitil said scientists were reviewing computer data to see if that was correct.

Scientists have said that automatic plotting of exact epicenters south of the border is not always exact, because there are is real-time seismographic data flow.

Sunday’s quake swarm is generally at the northern end of the Laguna Salada Fault, which extends from the Imperial Valley town of Seeley, west of El Centro, to the southeast, towards the Mexican resort town of San Felipe. Last Sunday’s 7.2 earthquake, which killed two people in Mexicali and did $100 million in damage in California, was centered on that fault about 31 miles south of the border.

Stivil said Sunday’s earthquake cluster is not related to a computer glitch Saturday that caused a flood of false reports of seismic activity to be relayed by the California Integrated Seismic Network.