Major Earthquake Shakes Southern California

SAN DIEGO, CA — A major earthquake rattled Southern California on Monday morning. Initial reports had the quake measuring 6.0 magnitude, but it was quickly downgraded to 5.2.

The quake struck at 10:08 a.m. and was centered near the Julian area of San Diego County, according to the U.S. Geological Survey. The quake had a depth of about 8.3 miles.

For reference, the U.S.G.S. says these cities were located the following distances from the quake:

• Julian: 2.5 miles north of the quake
• San Diego Country Estates: 11.2 miles west, southwest of the quake
• Pine Valley: 15.8 miles south, southeast of the quake
• Escondido: 28.7 miles west, northwest of the quake
• San Diego: 36.8 miles west, southwest of the quake
• Palm Springs: 54.1 miles north of the quake
• El Centro: 62.7 miles east, southeast of the quake

The shaking was felt in Orange and Riverside counties and as far away as Los Angeles.

At least six smaller aftershocks with magnitude readings of less than 3.0 happened within the 10 minutes following the quake, according to the USGS. Another quake near Borrego Springs registered 3.5.

A 3.9 magnitude quake was recorded at 11:23 a.m. near Julian.

• Also see: Multiple Aftershocks Rattle San Diego Area Following Strong Earthquake

A ShakeAlert notice was sent to cell phones throughout much of Southern California, initially putting the magnitude of the quake at 6.0, but the USGS later downgraded it to 5.1, then revised it again to 5.2.

Alerts were sent to mobile phones across the region, warning area residents to "drop, cover, hold on!"

Damage Assessments Underway

"San Diego experienced a strong earthquake centered near Julian," San Diego Mayor Todd Gloria said on social media. "There's no known visible or major damage to the city so far and I'm in communication with local, state and federal officials."

The California Governor's Office of Emergency Services said the agency was working with local agencies to assess any possible damage or impacts from the quake. The governor's office issued a statement saying Gov. Gavin Newsom had been briefed on the temblor.

"The state is coordinating with local authorities to assess any damage and if emergency response is needed," the office said.

Seismologist and Southern California earthquake expert Lucy Jones said the quake appeared to have been felt "over a very large area," stretching into Los Angeles. She said given the size and depth of the quake, it was unlikely to cause any series damage "to a normal California building," although it may have knocked some items off shelves.

"There shouldn't be structural damage," she said. "If there is, it's in a pretty bad building."

One resident in San Diego's East County said her mother was in a Home Depot when the quake struck, and customers ran out of the building.

Another resident in the Vista area noted online that the quake "sounded and felt like a bomb went off."

The San Diego County Sheriff's Office said it had not received any reports of injuries or major damage caused by the earthquake.

Caltrans, however, warned drivers to watch out for obstacles in the roadway after boulders fell onto state Route 76, east of East Grade Road near the Lake Henshaw area.

"Caltrans crews are out assessing the highway infrastructure for any damage from this morning's earthquake," the agency said on social media.

The U.S. National Tsunami Warning Center said a tsunami was not expected following the quake.

Fault Zone

The earthquake struck near Julian, a community situated along the Elsinore Fault Zone — one of the major fault systems in Southern California.

The Elsinore Fault is known for its right-lateral strike-slip movement, similar to the more famous San Andreas Fault.

The Elsinore Fault has the potential to produce large earthquakes, posing a significant seismic hazard to the region, according to the San Diego County Earthquake Alliance. Despite its size, the fault zone has remained relatively quiet in recent history.

The Southern California Earthquake Data Center notes that the main trace of the Elsinore Fault has experienced only one notable event greater than magnitude 5.2 — a magnitude 6.0 earthquake in 1910 near Temescal Valley. That quake caused little damage and left no visible surface rupture. However, the fault's southeastern extension, known as the Laguna Salada Fault, ruptured in a magnitude 7.0 event in 1892.

The Elsinore Fault Zone consists of several strands, each with its own designation. To the northwest of Lake Elsinore lie the Glen Ivy North and Glen Ivy South faults, while to the southeast are the parallel Wildomar and Willard faults. The fault eventually splays into the Chino and Whittier faults at its northern end and is intersected by the Yuha Wells Fault at the south, forming a complex and active seismic network.

City News Service contributed to this report.