“It doesn’t increase the risk,” Dr. Jones told reporters at a news briefing. “It also doesn’t decrease it.”

A simulation a decade ago of a 7.8-magnitude earthquake on the San Andreas fault estimated that it would cause 2,000 deaths, 50,000 injuries and $200 billion in damage.

Geological research along the southern portion of the San Andreas suggests the fault is due for a major rupture. The last big earthquake on the southern San Andreas was 162 years ago. Katherine M. Scharer, a geologist with the U.S.G.S., said the average interval between the previous nine earthquakes in that area was 135 years. But the intervals have been highly variable — ranging from 44 years to 305 years.

In Lake Isabella, some 60 miles west of Ridgecrest, Reyanna Denier, 39, was doing laundry when she felt shaking and figured the washing machine needed to be leveled to the ground of her modular home, which sits on an elevated foundation, almost as if on stilts.

“I told my husband, and he said, ‘It’s not the washing machine. That’s an earthquake!’” she said.

The couple moved under the door jamb, which Ms. Denier said she could feel “flex, like loping waves on the ocean, kind of like on a boat.”

“It wasn’t that it was violent jerking, but it was steady,” she said. “Our chandelier was rocking back and forth, and the T.V. — the flat screen — was wavering. It was really disconcerting because you’re going, ‘Oh my gosh, it’s not stopping.’”

A few hours later, Ms. Denier could see emergency vehicles driving past. A helicopter buzzed in the sky.