A rash of up to 70 moderate earthquakes were felt on Sunday from Orange County and San Diego County into Arizona as part of a swarm of shakers located at the south end of the Salton Sea near Brawley, Calif.
The aftershocks continued Monday morning throughout San Diego and parts of Arizona.
UPDATE: Monday evening at about 7 p.m., a magnitude 4.2 earthquake hit brawley and was felt in some parts of San Diego.
According to the USGS, the largest quake was 5.5-magnitude that rattled Brawley, Calif., just before 2 p.m. on Sunday.
A 5.3-magnitude quake centered in Brawley was felt throughout San Diego county at 12:30 p.m. Sunday and a 4.9-magnitude quake followed minutes later, as well as several lower magnitude earthquakes and aftershocks.
The epicenters of the bigger earthquakes were 11 to 12 miles from Imperial, Calif., and 15 to 16 miles from El Centro, Calif., the USGS reported.
According to the USGS, there have been roughly 70 lower magnitude earthquakes in the Brawley area on Sunday alone.
In San Diego, residents across the county reported feeling the quake in places including downtown San Diego, Mission Valley, Santee and Chula Vista. No injuries were reported.
San Diego State University geology expert Pat Abbott told NBC 7 San Diego that Sunday’s earthquakes were in the middle of the Brawley Seismic Zone, famous for swarms of quakes. He said Southern California residents should expect aftershocks.
“[The Brawley Seismic Zone] is a broad zone with lots of little faults,” explained Abbott.
“This area has clearly activated. We will likely experience swarms of 3, 4 and 5-magnitude [earthquakes] but they are not likely to increase in intensity. Of course, there are no guarantees on this, but history says they likely won’t get bigger – that we will experience more of the same or smaller quakes,” he added.
As of 1:30 p.m., San Diego Fire Dispatch had no reports of earthquake-related damages or injuries in San Diego county.
The San Onofre Nuclear Generating Station declared a “Notice of Unusual Event” following the earthquakes around 12:30 p.m.
“An earthquake was detected by the station’s monitoring system. The station subsequently received reports of earthquakes near the Mexico border. The plant has been off-line since earlier this year, and there is no safety risk for the public or SONGS employees,” a statement from the plant read.
The declaration is part of protocol set by the Nuclear Regulatory Commission.
At around 1:40 p.m. Southern California Edison posted this update to their Twitter feed: "Earthquake felt in [San Onofre power plant] SCE _SONGS control room. Plant is safely shutdown."
At 1:57 p.m., USGS reported another 5.4-magnitude earthquake centered three miles from Brawley, Calif. USGS later upgraded the quake's magnitude to 5.5.
In compliance with regulations, the San Onofre Generating Station issued a second “Notice of Unusual Event” at 2:03 p.m., following the 5.5-magnitude quake.
Southern California Edison posted this update on its Twitter feed following the second Notice:
“Once again, no plant systems harmed at @SCE_Songs and no risk to public safety. Will update when second NOUE has been closed.”
As of 4 p.m., Pioneer Memorial Hospital in Brawley, Calif., was beginning to evacuate patients due to the ongoing quakes in the area. About a dozen patients were transferred to hospitals in San Diego and Riverside Counties, but the majority of the hospital was operating with a generator.
Brawley Mayor George Nava said all damage to the area was mostly cosmetic damage to businesses and homes. About 30 mobile home residents were displaced, and Red Cross helped them find shelter.
Five of those displaced took shelter at Imperial Valley College, where the American Red Cross set up a temporary shelter.
Several outages were also reported following the earthquakes in Brawley. Workers were repairing low pressure instances and power outages in the hours following the quakes.
Monday marks the first day of school for Brawley students, but all schools will be closed to assess the damages.