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Southern California's most active fault jolts residents awake with 5.2 quake

A 5.2 magnitude earthquake early Friday occurred on one of Southern California’s most active faults and triggered hundreds of aftershocks, but caused no major damage, experts and public safety officials said.

The quake occurred near Borrego Springs in San Diego County in a sparsely populated area. Still, the 1:04 a.m. quake was felt from San Diego to parts of L.A. and beyond.

“It’s the biggest one for a while,” said Egill Hauksson, a research professor of geophysics at Caltech.

The last notable quake in Southern California was in 2014 when a 5.1 magnitude quake hit La Habra. But that occurred on a different fault.

Deadly but little-known: Why scientists are so afraid of the San Jacinto fault »

Friday’s temblor occurred on the San Jacinto fault, the most active in the region, Hauksson said. More than 450 aftershocks have been reported since the initial quake.

The fault is characterized by less compression between its plates compared to the San Andreas or Newport-Inglewood faults, which means when there is slippage and a quake occurs, it’s less severe, Hauksson said.

But the fault is also remarkably long, which may explain why Friday morning’s quake was reportedly felt by people from Santa Barbara to the Mexican border, Hauksson said.

Reflexively, hundreds of people turned to social media to share their experience and also verify that the quake really happened.

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Read more: The rolling motion starts a beeline to Twitter »

Ron and Teri Walker were inside their hotel in Palm Springs when the room began to shake.

"We held each other, not sure what the next step was. What do we do?" Teri Walker told KNBC-TV Channel 4. 

A Downey woman called KNX-AM (1070) and said it struck with "a soft roll," then later "hit again stronger." A caller from Costa Mesa described a "back and forth" sensation.

According to the U.S. Geological Survey, the epicenter was 16 miles from La Quinta, 19 miles from Palm Desert and 20 miles from Rancho Mirage.

Aftershocks included a magnitude 3.3 jolt 13 miles from Anza at 1:46 a.m. at a depth of 6.8 miles. Anza is in southern Riverside County.

Seismologist Lucy Jones reported dozens of aftershocks on her Twitter feed.

There were at least four magnitude 3.0 aftershocks and a fifth recorded as a magnitude 3.3, Jones tweeted.

A telltale sign that a quake is going to be large is how long it lasts, she said.

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Video posted to YouTube shows cars in a driveway rocking for several seconds while a second video shows a chandelier swaying from the temblor.

The California Highway Patrol reported that boulders had fallen onto California 74 between Palm Desert and Pinyon, KESQ reported.

The San Jacinto fault stretches for 130 miles, from the Cajon Pass in San Bernardino County southeast toward the Mexican border. The 1987 Superstition Hills earthquakes, which hit about 90 miles east of San Diego, topped out at magnitudes 6.5 and 6.7, and caused $3 million in damage in Imperial County.

According to the USGS, a quake on the fault in 1918 caused significant damage and one death in San Jacinto.

There have been 19 quakes of 5.0 magnitude or larger on the fault since 1937, Hauksson said.

The largest was a 6.6. magnitude quake in 1968 south of Friday’s temblor. Others included a 5.3 magnitude quake in 1980 and a 5.4 magnitude quake in July 2010, Hauksson said.

”Most of the time when you have an earthquake in Southern California, it’s on the San Jacinto fault,” he said.

The last time Southern California experienced a quake larger than Friday's on any fault was in 2012, when Brawley in the Imperial Valley was shaken by 5.3 and 5.4 magnitude quakes, Hauksson said.

Borrego Springs is a community of about 3,000 people in eastern San Diego County, near the Imperial County line.

In the last 10 days, there have been two earthquakes of magnitude 3.0 or greater centered nearby.

Read more about Southern California earthquakes.

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UPDATES:

10:19 a.m.: This article was updated with more information about the San Jacinto fault and with comments from experts.

6:36 a.m.: This article was updated with comments from social media.

3:07 a.m.: This article was updated with comments from seismologist Lucy Jones.

2:21 a.m.: This article was updated with news about an aftershock near Anza.

1:31 a.m.: This article was updated to increase the magnitude of the earthquake to 5.2.

This article was originally published at 1:09 a.m.

 

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