Re: Mystery disturbance traced to sound wave. No source known ?


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http://www.signonsandiego.com/news/metro/20060427-9999-1n27boom.html#
Mystery disturbance traced to sound wave


Scripps scientists say it traveled over the ocean to desert
By Alex Roth
UNION-TRIBUNE STAFF WRITER
April 27, 2006

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.

The April 4 disturbance hit San Diego County shortly before 9 a.m. A
quake was quickly eliminated as the cause, leaving a mystery that has
been the source of three weeks of speculation from Pacific Beach to
Lakeside to the Internet.

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. It was picked up by more than two
dozen seismometers in San Diego and eastern Riverside counties, the
researchers said.

According to data analyzed by the scientists, the wave was felt on San
Nicolas Island, northwest of San Clemente Island, at 8:40 a.m. It hit
Solana Beach at 8:46 a.m., the western edge of the Cleveland National
Forest at 8:47.30 and the eastern side of the Salton Sea at 8:53 a.m.
From there, it appears to have dissipated.

Elizabeth Cochran, the lead researcher on the project, said the wave
moved at 320 meters per second, roughly the speed that sound travels
through the air. Its velocity was too slow to be that of an earthquake,
she said.

Cochran, a postdoctoral researcher in the geophysics and planetary
physics department, said the only explanation is that the wave was
traveling through the atmosphere, not through the ground. At each
location, the wave could be felt for roughly 10 seconds, she said.

Several months before the April 4 incident, the team had begun studying
other nonquake disturbances that were registering on San Diego County
seismometers, including 76 that apparently originated in that same
general area of the ocean in 2003. Shearer said he and his colleagues
figured that some of those disturbances surely must have come from
offshore military exercises.

The researchers haven't been able to determine whether the April 4 wave
was more powerful than the earlier ones or whether it simply felt that
way because of atmospheric conditions.

If the disturbance was caused by the military, no one has owned up to it.
The Navy and Marines say none of their planes were flying at supersonic
speeds that morning.

"I'm told that a sonic boom would not cover that distance at all," said
Fiebing, the Navy spokesman.

The Navy uses Warning Area 291 for a wide range of training, including
large-scale ship maneuvers and battle exercises, but Fiebing and Fenick
said they were unaware of any such training April 4 that would have
caused such a disturbance.

Authorities have said a meteor probably wasn't the cause because it would
have been noticed by the scientific community. The American Meteor
Society reported no fireball sightings over Southern California on that
day.


I was working on an archeological project in the Ohio Valley in 1982.
While in a trench conducting an excavation, there was a loud boom which
shook the ground intensely. It was felt in three counties that day.
Neither the military nor the local quarries claimed any responsibility for
the boom. Local meterologists assumed that it was an exploding bolide, but
they really had no evidence to support that assumption. As far as I know,
no one has ever figured out what the source of the boom was.

George


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