A magnitude 6.4 earthquake hit Ridgecrest, California, Thursday, rattling residents as far south as Imperial Beach this Fourth of July.
San Diegans took to social media moments after the quake centered in Searles Valley, about 150 miles north of Los Angeles, at about 10:30 a.m. to describe the shaking.
"At work, downtown SD, on the 4th floor, the whole building shook!" Facebook commenter Susan Fleming said.
Melanie Peter said she also felt the quake downtown. "Swaying on the 26th floor downtown was NOT FUN. Definitely felt it!" she said.
The earthquake was 5.4 miles deep, which is considered moderate. The closer to the surface an earthquake is, the more it is usually felt.
Though any quake with a magnitude above 6.0 is substantial, according to San Diego State University Professor Emeritus Pat Abbott.
“If you’d of dumped that much energy there -- it would not be widespread death and destruction -- but what you would have is signature events, like a building collapsed over here or a gas line got ruptured here, this one caught on fire. There would be a lot of problems around town,” Abbott said. “It would be a major problem for the city."
Thursday’s earthquake was the largest with an epicenter in Southern California in two decades – since 1999’s Hector Mine earthquake with a moment magnitude of 7.1.
It was followed by a series of aftershocks ranging from magnitude 2.8 to magnitude 4.2. The strongest was a 5.4 temblor on Friday morning.
Others described feeling the temblor in Escondido, Pine Valley, Oceanside, Pacific Beach, La Jolla and Imperial Beach.
"Definitely felt it in National City, everything shook in my office," Leeann Johnson commented.
"Rockin' and rollin' here in Oceanside," Serena Reid said.
Did you feel it? Leave us a comment on our Facebook Page.
Abbot said if the quake hit San Diego or in a less mountainous region, there would have been a lot more damage.
Multiple aftershocks were reported after the main temblor, ranging from magnitude 2.8 to magnitude 4.2.
No damage was immediately reported but crews were responded to at least 24 medical or fire related incidents near the quake.
A magnitude-7.2 earthquake struck near Guadalup Victoria, Mexico, about 45 miles south of Calexico, California, on Easter Sunday in 2010.
The jolt shifted the Earth's crust near the epicenter about 10 feet, according to radar images and data collected by researchers at NASA's Jet Propulsion Laboratory.
Calexico was the U.S. area hardest hit by the earthquake. No injuries were reported but some buildings suffered broken windows and cracked masonry.
This is a developing story. Refresh for updates.