That Was No Earthquake — Mysterious Sonic Boom Rattles SoCal

LOS ANGELES, CA — What thousands of people across the Southland thought was an earthquake Friday morning turned out to be a sonic boom that rattled windows over hundreds of miles. What caused the sonic boom, however, is a mystery.

The jarring boom occurred at about 9:20 a.m., prompting hundreds of people from Thousand Oaks to Huntington Beach to report an earthquake to the U.S. Geological Survey. The bulk of the reports came in from the Los Angeles and San Gabriel Valley areas.

But it was no quake, confirmed seismologist Dr. Lucy Jones. Seismograms showed no earth movement at the time.

"People have been asking about the 'earthquake' in LA around 9:20 this morning. Many people report feeling it, but the seismograms clearly show the earth was not moving, only the air. So it was a sonic boom," tweeted Jones. "The distribution of people who felt the sonic boom from strongly suggests the source was a supersonic aircraft over the ocean."

Most military bases in Southern California don't operate supersonic aircraft. Edwards Airforce Base in Kern County is home to the Air Force Test Center.

"Our air space is the only supersonic flight corridor in the nation," said Edwards Airforce Base Public Affairs Specialist Grady Fontana.

"Sonic booms are caused by an object moving faster than sound -- about 750 miles per hour at sea level. An aircraft traveling through the atmosphere continuously produces air-pressure waves similar to the water waves caused by a ship's bow," according to the Base's website. "When the aircraft exceeds the speed of sound, these pressure waves combine and form shock waves which travel in all directions and eventually reach the ground. The sound heard on the ground is the sudden onset and release of pressure after the buildup by the shock wave."

Fontana confirmed aircraft did pass through the Edwards Airforce Base airspace Friday morning, but that activity didn't appear to coincide with the sonic boom that rattled the region.

A sonic boom can carry for hundreds of miles, and it's possible the supersonic jet took off from an aircraft carrier out to sea. Patch checked in with NASA, Camp Pendleton, Marine Corps Air Station Miramar, the Seal Beach Naval Weapons Station, the Los Alamitos Joint Forces Training Base, the Marine's 3rd Marine Aircraft Wing and the Naval Base Coronado. None said they were involved with supersonic flight operations in the area Friday.

The military doesn't always fess up to noisy operations. However, after startling residents across San Diego last month with an unanticipated sonic boom, Marine Corps Air Station Miramar sent out a cheeky tweet, "So, about the other night...#SanDiegoBoom."