More shaking and booming noises were reported across San Diego County on Monday afternoon, with residents reporting their windows rattling. A similar incident occurred Friday.
The incidents appear unrelated to any seismic activity, as data from the U.S. Geological Survey show no earthquakes in the region at the time of the reported incidents.
Joseph Katz, an aerospace engineering professor at San Diego State University, said Tuesday one likely explanation for the widespread phenomenon is shock waves from supersonic aircraft — sonic booms.
"It's nothing dramatic," Katz said during an interview at the university's supersonic wind tunnel. "The sonic boom is simply a pressure wave that you hear. When an airplane moves fast, at the front, it compresses the air (and) in the back, there's decompression. Your ear hears the pressure difference."
The reason, Katz said, people miles apart experience that shock wave with similar intensity is that the wave isn't a one-time occurrence when the aircraft breaks the sound barrier. It follows the aircraft as it flies. Shock waves from a sonic boom can be felt on the ground — depending on atmospheric conditions — from a jet flying above 30,000 feet, Katz said.
"(The shock wave) is a cone that follows the airplane," Katz said. "So if you stand on the ground, then it just passes you by. It will follow the airplane's flight path."
Another possible military explanation for the booms and shaking is artillery and ground-based explosions at Marine Corps Base Camp Pendleton. This type of training is routine at the base and the sounds of those explosions can carry up to 50 miles given the right atmospheric conditions, according to the Marine Corps.
Those sound waves, however, Katz said, will dissipate over distance and are generally localized near the base. Other potential sources of sonic booms include meteorites. However, Katz said because meteorites travel downward, the effect of the shock wave would also be localized.
Military officials in San Diego offered no explanation for either Friday's or Monday's events. A Naval Air Forces spokesperson said they weren't tracking any Navy jet activity in the area. A Marine Corps Air Station Miramar spokesperson could not confirm what caused the booms but said in an email that although the Marines conduct routine flights in the region daily.
