Mysterious Booms Remain Unknown

SAN DIEGO -- La Jolla-based scientists say a mysterious boom heard and felt throughout San Diego County earlier this month originated from an area over the ocean, but the source of the disturbance remains unknown.

According to scientists at the Scripps Institution of Oceanography, the thunderous noise heard April 4 started over the ocean about 120 miles off the San Diego coast and petered out over the Imperial County desert, The San Diego Union-Tribune reported.

Scientists said the spot where the rattling boom originated is in the general vicinity of Warning Area 291, a huge swath of ocean used for military training exercises. The Navy operates a live-fire range on San Clemente Island, which is within Warning Area 291 and sits about 65 miles from Mission Bay, the newspaper reported.

But Steve Fiebing, a Coronado-based Navy representative, said the live-fire range on San Clemente Island was inactive April 4. He also said there was no Navy or Marine Corps flight activity in Warning Area 291 on that day that would have caused a sonic boom or a countywide tremor, the Union-Tribune reported.

Peter Shearer, a Scripps professor involved in the research, has no idea whether the disturbance was natural or made by humans, the Union-Tribune reported.

"I would guess it's either an explosion that somebody hasn't told us about or it could have been a meteor coming into the atmosphere," Shearer told the newspaper.

The Scripps researchers believe the disturbance was the result of a low-frequency wave that traveled through the air at the speed of sound as it moved from the ocean to the desert. They said it was picked up by more than two dozen seismometers in San Diego and eastern Riverside counties, the newspaper reported.

The boom heard around 8:45 a.m. rattled homes and buildings all throughout San Diego County, including residences in Ramona and the county sheriff's building in Clairemont Mesa.

Some people speculated the disturbance was the result of an earthquake. But the U.S. Geological Survey said no measurable seismic activity was recorded in the county that morning.