That wasn’t an earthquake that shook your windows—it was sonic booms from military aircraft flying over the Central Coast.
According to a press release from the San Luis Obispo County Sheriff’s Department , dispatchers received several reports of what appeared to be seismic activity in the county the morning of Dec. 20.
“[The department] confirmed through various state and federal agencies that there has been no seismic activity in our area. It’s believed the activity was caused by sonic booms from military aircraft flying over this region of California,” officials said in the release. “The United States Geological Survey (USGS) confirms there was a sonic boom reported at 9:26 a.m. and again at 9:40 a.m. No damages have been reported.”
Officials at Vandenberg Air Force Base in Lompoc said they were fielding calls all morning about the incident, but they deal exclusively with rocket launches, not super-sonic jets.
The noises came from two military aircraft being tested on an authorized flight path some 50 miles off the coast by teams at Edwards Air Force Base in California’s southeastern desert, base spokesperson John Haire told New Times. Super-sonic tests are done routinely in that airspace, but cold, condensed air allowed the sonic boom to travel farther than normal, he said, adding that people should be prepared for more booms in the winter months.
“It’s not the end of the world—the Mayans weren’t right,” Haire said.
According to a National Aeronautics and Space Administration fact sheet, sonic booms are actually a constant noise produced by compacted air, or “overpressure.” People hear them as a single, staccato boom, but the thick sound wave hits everyone under the flight path. Two pounds per square foot of overpressure will rattle houses, but structures in good condition can handle up to 11 pounds of overpressure.
Responding to some people’s belief that the world would end on Dec. 21, 2012, via a natural disaster—as seemingly indicated by the Mayan calendar—USGS sent out information about monitoring natural disasters and staying safe should a disaster occur.
“Others believe that instead of doomsday and destruction, the day will mark a new era for humanity and will be a time for celebration,” USGS officials said in an e-mail to the media. “Such beliefs aside, what we know with certainty is that Earth has a tremendous capacity to generate natural disasters on any day of any year.”
According to USGS, there’s no reliable short-term earthquake prediction method. Nor do scientists expect to develop a method in the foreseeable future.
However, probabilities can be calculated based on scientific data. For example, officials said, assessments of long-term earthquake rates in California reveal there’s roughly a two-in-three chance that a magnitude 6.7 or greater earthquake will strike the greater San Francisco Bay Area in the next 30 years.
Experts predict with 99 percent certainty that such a quake will occur somewhere in California in the same timeframe.
To learn more about USGS earthquake forecasting and hazards, visit earthquake.usgs.gov/hazards.