Series of Small Quakes Unrelated, Experts Say

Weekend earthquakes in Northern and Southern California were “totally unrelated,” Caltech seismologist Kate Hutton said Monday. The quakes all occurred on different faults, she said, and their coincidental timing, although “slightly odd,” did not augur a future quake.

No injuries were reported in any of the quakes, and the only significant damage was a disruption of electricity at two pumping stations on the California Aqueduct. A spokesman for the Department of Water Resources said Monday that the damage should be repaired and the pumping stations back in operation today.

The weekend activity began Friday at 4:06 p.m. with a magnitude 5.1 temblor on the Garlock fault, 11 miles north-northeast of Gorman. An aftershock of magnitude 4.0 was recorded at 4:23 p.m. and another of magnitude 3.4 at 6:56 p.m. About a dozen smaller aftershocks have since been recorded, Hutton said.

Hutton noted Friday that about one in 20 quakes such as that on the Garlock fault are foreshocks of larger quakes. But by Monday, she said, the chance that a larger quake would follow it had dropped to less than 1%.

At 2:22 p.m. Sunday, a magnitude 3.4 quake was recorded 5 miles east of Ontario. Hutton noted that no effort is made to assign such small quakes to specific faults.

About 22 minutes later, a magnitude 3.3 temblor occurred at Lake Berryessa in Napa County, about 60 miles north of San Francisco. It was followed at 6:45 p.m. by a magnitude 5.1 quake on the Calaveras fault about 10 miles northeast of San Jose. That quake rattled buildings and knocked goods off shelves in supermarkets.

A mild temblor, measuring 3.0, rolled through the Santa Barbara area Monday evening. There were no reports of injuries or damage.

The quake struck at 5:59 p.m. and was centered seven miles west of Santa Barbara, Caltech spokesman Robert Finn said. It followed a magnitude 2.3 quake at 8:42 a.m., centered in the Playa del Rey area.

Hutton said that the Caltech seismic monitoring network in Southern California records 20 to 30 earthquakes each day with magnitudes below 3.