Did You Feel It? Orange County Reports 'Earthquake-Like' Shaking

ORANGE COUNTY, CA — When is an earthquake not an earthquake? There was a whole lot of shaking going on in Orange County Monday morning as residents reported feeling earthquake-like activity between 8:15 and 8:30 a.m.

Residents from Newport Beach to San Clemente reported two distinct "jolts," though the United States Geological Survey has no record of an earthquake happening in the region.

"We didn't see anything on the waveforms during that time," Julie Dutton, Geophysicist for the U.S. Geological Survey tells Patch. Still, sonic waves or booms can often feel like earthquakes, she said. Sonic booms typically have "did you feel it" reports in a "succession of cities" due to the nature of airplane flight, according to Dutton.

Seismologists at Cal Tech concurred as they reported that Sonic Booms were the most likely cause when an earthquake-like shaking is felt, but there is no activity below the surface.

In Laguna Beach, over 100 residents report feeling shaking on the Laguna Locals Facebook page. The general consensus was the event felt more like an explosion than a traditional earthquake.

Those with experience in sonic booms were leaning in that direction. Residents said that windows and doors rattled during both incidents.

Camp Pendleton reported a noise advisory this week as they are firing "high explosive ammunitions" in the Quebec and Zulu portion of the base, which can be felt to the northwest of the base.

Though originally thought the likely source of the incident, Camp Pendleton says that no training took place Monday morning. All signs now look to the sonic boom as the source of the shaking.

According to the USGS, here are some interesting facts about Sonic Booms:

• Most sonic booms aren't felt on land (most supersonic training flights are out over the ocean).
• Atmospheric conditions like temperature inversions and calm surface winds can make sound propagate farther than normal.
• Aircraft actually produce two booms, but they usually arrive so close together that they're indistinguishable.
• "Under certain aircraft operating conditions (e.g., acceleration, dives, turns, and climbs), the sonic boom conoids generated by the aircraft may intersect one another. This effect is known as sonic boom focusing. Such focusing may also result from refraction effects caused by variations in atmospheric sound and wind speed. Focused sonic booms may be of much greater intensity than unfocused booms and are typically generated by fighter aircraft in "dogfight" maneuvers." USFWS)
• USGS instruments are not designed to detect or analyze atmospheric phenomena, and atmospheric research is not part of the USGS mission.

The source of the shaking remained a mystery as of Monday morning.