5% chance even bigger quake will hit same area of Southern California in next 3 days, USGS says

Dozens of large and small aftershocks are shaking Southern California after a 6.4-magnitude earthquake near Searles Valley on July 4, 2019. Dozens of large and small aftershocks are shaking Southern California after a 6.4-magnitude earthquake near Searles Valley on July 4, 2019. Photo: USGS Photo: USGS Image 1 of / 4 Caption Close 5% chance even bigger quake will hit same area of Southern California in next 3 days, USGS says 1 / 4 Back to Gallery

After a magnitude 6.4 earthquake rattled Southern California Thursday morning, aftershocks rocked the region, one after another.

Experts say this is normal. Residents can expect the shaking to continue for days.

"For a 6.5 quake you'd expect a lot of aftershocks," said U.S. Geological Survey seismologist Susan Hough. "You'd expect the biggest to be 5.5 and so far the biggest has been 4.7."

Hough says with a 6.4 earthquake, on average you can expect one 5.5 aftershock, 10 4.5s and 100 3.5s.

"Some aftershock sequences are more lively than others," she said. "This part of California tends to produce more aftershocks."

There's also the slight chance of something even bigger.

"With any earthquake, there is a 5 percent chance something even bigger will happen within the next three days," she said. "If it did, it would be in the same remote area."

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The magnitude 6.4 earthquake rocked Southern California at 10:33 a.m. Thursday with a depth of about 5 miles.

The largest temblor to strike the region in 20 years, it was centered about a 100 miles northeast of Los Angeles in the remote Kern County community of Searles Valley. It was widely felt around Southern California.

"The shaking was pretty low and rolling, but it was the longest earthquake I've felt in Los Angles in my seven years living here," Echo Park resident Annie Powers said. "It was long enough that I definitely started to wonder if this was the big one." (Find more reactions to the earthquake in the gallery above.)

This is the largest quake to hit Southern California since the 1999 magnitude 7.1 Hector Mine earthquake in the remote Mojave Desert that caused little damage. In 1994, the 6.7 Northridge temblor struck in a highly populated area, resulting in 57 deaths, more than 8,700 injuries and billions of dollars in damage.

The quake's epicenter was 11 miles northeast of Ridgecrest, 109 miles north of San Bernardino and 121 miles northeast of Los Angeles, according to the USGS. The Naval Air Warfare Center Weapons Division at China Lake, the location of a desert test range, is within the epicenter area.

"The closest town of any size is Ridgecrest, which is about 10 miles away," Hough said. "It's a good size community of 30,000 people. It grew up around the China Lake Navy Base. I haven't heard about injuries. I would expect some light damage based on the magnitude and distance. A tiny town called Trona is near the epicenter. I wouldn't be surprised if there were reports of injuries and damage in these very small towns."

The quake didn't occur on the San Andreas Fault. Dr. Lucy Jones, a seismologist who wrote the book "The Big Ones," shared on Twitter the quake happened on what's known as a strikeslip fault.

"It is an area with a lot of little faults but no long fault," Jones wrote.

Amy Graff is a news producer for SFGATE. Have information or photos from the earthquake? Email her at agraff@sfgate.com.