SANTA CRUZ - Even though Central Coast residents felt rattled Wednesday morning, the source of the shaking was not under their feet, according to the U.S. Geological Survey.
At 9:15 a.m., USGS sensors detected ground movement, but the signals did not resemble an earthquake, said Leslie Gordon, a spokeswoman for the USGS.
The movement appeared to originate off the Monterey Bay coast, Gordon said.
"Our best guess is that it was a sonic boom from a jet off the coast," Gordon said. "That's all we can say scientifically."
Jet airplanes create sonic booms when they break the sound barrier. As a jet rips through the air at supersonic speeds, it emits shock waves that produce a tell-tale bang and rattle buildings.
The Air Force reports it did not have jets flying off the coast this morning, said Steve Bauer, a spokesman at Vandenberg Air Force Base.
After receiving calls about a boom in Southern California, the Federal Aviation Administration said it is searching through flights they monitored Wednesday morning to find the supersonic jet.
"We haven't found anything yet that would explain the sonic boom," said Ian Gregor, a spokesman for the administration.
Gregor said they will finish their search Thursday.
Officials at the NASA Ames Research Center at Moffett Field had not heard about the possible sonic boom, said Bruce Buckingham, the center's chief public affairs officer.
According to the Orange County Register, a
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sonic boom shook Southern California about 9:15 p.m. Tuesday.
Bob Dollar of the USGS told the Register Caltech scientists reviewed seismograms from Tuesday night's event in Orange County.
"These data are consistent with a sonic event coming onshore near Dana Point and traveling northward inland," Dollar said.
"The energy travelled across our seismic sensor network at the velocity of a compressional wave in air rather than the velocity of a similar wave through the ground, which is much faster," Dollar said.
The F/A 18 Super Hornet fighter jets used by the Navy and Marines in Southern California are capable of breaking the sound barrier and producing a sonic boom felt on the ground, the Register reported. When the space shuttle lands at Edwards Air Force Base it too produces a sonic boom. There are currently no shuttles in flight.
The Santa Cruz County Sheriff's Office started receiving phone calls from residents about a possible earthquake just after 9 a.m. Wednesday morning, said a lead dispatcher.
Julie Drysdale, who lives in Aptos, reported feeling a sonic boom or earthquake at about 9:17 a.m.
"I was outside and heard two loud booms. My husband said the house shook quickly, like a truck hit it, not the typical earthquake shaking, much quicker," Drysdale said.
Robert Diller, who lives on Glen Haven Road in Soquel, said he heard four loud booms this morning two before 10 a.m. and another two around noon.
"They made our windows rattle," Diller said. "It was like a blast, it sounded like a dynamite blast almost."
Residents in Salinas and Monterey also reported feeling the boom.
David Kellogg, city editor at the Monterey County Herald, said "It made his windows rattle."
The ground did move Wednesday morning also. The USGS Web site reported four minor earthquakes in the region. A magnitude 2.0 earthquake hit near Los Altos Hills at 8:40 a.m. Two quakes struck outside Tres Pinos: a 1.3 magnitude at 5:42 a.m. and a 1.6 at 7:52 a.m.
Gordon said the shaking detected at 9:15 a.m. was not posted on their site, because it was not classified as an earthquake.
At 11:12 a.m., a 1.7 movement was measured in a quarry near Portola Valley. The USGS attributed that to a probable quarry explosion.
The Orange County Register story can be found at http://www.santacruzsentinel.com/localnews/ci_11835292