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SAN DIEGO – San Diegans reported hearing a loud boom and feeling some shaking similar to an earthquake Tuesday, but the source of the phenomenon was not immediately clear.

Dozens of tweets about the jolt came about 2:50 p.m., with many questioning whether what they’d felt was an earthquake. It was reported as being “very loud” in Poway and felt throughout the area from downtown San Diego to the South Bay.

“I think we had another earthquake, but could have been a sonic boom?” one Twitter user said. “I heard it more than felt it. #sandiego.”

It is unclear if an earthquake would have been the culprit, however. A small quake with a preliminary magnitude of 2.6 was recorded about 2:30 p.m. south of the border in Baja, California, according to the U.S. Geological Survey.

Camp Pendleton released a noise advisory active from 6 a.m. until midnight Tuesday for both artillery and mortar rounds training at the base in North County. The result of those noise-generating events, which are planned this week through Friday, can be heard from a great distance.

Another Twitter user surmised it could have been the result of a plane off the coast that was “very close to the sound barrier” and headed in the direction of San Diego.

At any rate, it’s been an increasingly common occurrence in San Diego with a mystery “boom” and shaking felt last year in mid-June and another coming in December.

For the June boom, officials from Marine Corps Air Station Miramar later took credit, saying the noise was “possibly due” to two aircraft that had been engaged in combat training off the coast of San Diego.