Gilroy Quake Is Vivid Reminder of ’89 Shaker

The Gilroy earthquake Monday night was small by Bay Area standards, but a reminder of what quakes there can be.

The quake’s magnitude was revised Tuesday from the original 5.2 to 4.9. Bill Ellsworth, the scientist in charge of earthquake studies for the U.S. Geological Survey in the West, and Doug Dreger of the UC Berkeley Seismographic Laboratory, changed the figure based on more readings from various stations in the state’s new Trinet system.

Still, it was one of the strongest quakes in the area since the 1989 Loma Prieta quake, which had a magnitude of 6.9 And scientists said there is a 70% chance of a tremblor as strong as the 1994 Northridge quake striking the Bay Area by 2030.

There were no injuries or significant damage from Monday’s quake, which was centered three miles southwest of Gilroy, best known for its annual garlic festival.

Scientists said Tuesday that, contrary to initial word, the jolt was on the Sargent fault next to the San Andreas fault, not on the San Andreas.

The jolt sparked a house fire in San Jose when flammable liquids spilled near a water heater and the vapors ignited. It took 40 firefighters an hour to knock down the fire, said San Jose fire spokesman Rob Piper. The house was destroyed, he said. Elsewhere the damage was considered minor.

“It felt really strong,” said Joe Kline, a Gilroy city spokesman. “But I was pleasantly surprised at how little damage was reported. It was more of a wake-up call to reinforce the need to be prepared.”

The quake was felt throughout the Bay Area, however, and scientists attributed the wide scope to the comparatively shallow depth of the quake, centered just five miles below the surface

The heavy volume of calls after the temblor caused service delays for half an hour throughout the Bay Area. “Any time you have a natural disaster, there is network congestion,” said Pacific Bell spokeswoman Jenny Conradi. Phone service was back to normal about 25 minutes after the quake.

The quake also caused a stir at the National Hockey League playoff game then underway between San Jose and Colorado in San Jose. “This again focuses our attention on the Bay Area [seismically speaking],” Ellsworth said Tuesday.

He said there have been several moderately strong quakes in the Gilroy area in the last half a century, including a magnitude 5.3 temblor in 1959 at the same spot as Monday’s quake.

Gilroy is near two major faults, the San Andreas and the Calaveras, and not far from a third, the Hayward. All three faults are capable of a 6.7 quake or stronger.