Something Went Boom

April 4th, near San Clemente Island, but the Navy denies all:

A group of local scientists has uncovered some clues to the source of a mysterious disturbance that rattled San Diego County on the morning of April 4, shaking windows, doors and bookcases from the coast to the mountains.

The scientists, based at Scripps Institution of Oceanography in La Jolla, say the disturbance was caused by a sound wave that started over the ocean and petered out over the Imperial County desert. Using data from more than two dozen seismometers, they traced its likely origin to a spot roughly 120 miles off the San Diego coast.

That spot 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 researchers also have charted dozens of similar, if less dramatic, incidents that seem to have originated in the same general area of the ocean. They aren't sure what caused any of them.

Peter Shearer, a Scripps professor involved in the research, has no idea whether the April 4 disturbance was natural or made by humans. “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,” he said. “But it was certainly a big disturbance in the atmosphere.”

Steve Fiebing, a Coronado-based Navy spokesman, 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 area, also known in military circles as Whiskey 291, covers 1 million square miles and is off-limits to civilian planes and ships, Fiebing said. “There was no unusual training that would have caused anything close to what people here felt,” he said.

Cmdr. William Fenick, another local Navy spokesman, said no San Diego-based warships were conducting operations in Warning Area 291 that day. “We don't know at this time where this earthquakelike sensation came from,” Fenick said.