Mild tremors rattle southern California.
Dozens of minor earthquakes have rattled parts of southern California and Arizona since Sunday.
The swarm of shakers were centered at the south end of the Salton Sea near Brawley, California.
According to the USGS, the largest quake was 5.5-magnitude that rattled Brawley 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.
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 says 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.
The San Onofre Nuclear Generating Station declared a ""Notice of Unusual Event" following the earthquakes around 12:30 p.m.
The declaration is part of protocol set by the Nuclear Regulatory Commission.