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'Mystery booms' on Orcas Island source of Pacific Northwest Seismic Network investigation

A mystery boom recorded across the seismic network in the San Juan Islands is catching the attention of researchers. What could be the source?
Credit: Pacific Northwest Seismic Network
Seismograms show the nearest 10 operating seismograph stations for several minutes around the mystery boom, according to Steve Malone with the Pacific Northwest Seismic Network.

EASTSOUND, Wash. — The Pacific Northwest Seismic Network (PNSN) is investigating a "mystery boom" heard coming from Orcas Island last week. 

The boom was heard early in the morning on March 7 by a retired seismologist, Tom Owens, according to PNSN. He also reported a similar boom that was accompanied by a flash of light back in December. 

Owens checked the PNSN seismic records and found that a "short pulse of seismic energy" was picked up by PNSN seismic stations on the San Juan Islands. He contacted the seismic network to see if researchers had any thoughts on what the sound could have been, according to a blog posted by PNSN. 

Steve Malone, a Professor Emeritus at the University of Washington and former director of PNSN, was able to get an approximate location for the source of the boom by looking at the time the boom registered on different instruments across the network. Malone determined the boom occurred near Crescent Beach Preserve just east of Eastsound on Orcas Island.

Malone discovered the boom was not made by any shaking in the ground, saying the seismic recordings were consistent with the "velocity of acoustic (sound) waves in the air." 

Atmospheric conditions for what was a "relatively small explosion" had to be just right for the boom to be clearly recorded up to 23 miles away from the origin of the sound, Malone wrote. Little wind and a stable atmosphere without much fluctuation in temperature are required for the sound waves to cover that distance. 

Was it a meteor? A fireball? Booms have originated from these sources before, and a meteor was caught on a doorbell camera in Bellingham that same night. However, it occurred 15 minutes later than the boom that registered on PNSN's seismic records. 

"There are only a couple of possible very small signals that could be attributed to it," Malone wrote. "So our mystery boom was not a high atmospheric explosion."

More nighttime booms have been recorded by the San Juan Islander and on Social media, but only one appeared to be similar to the sound heard on March 7. According to PNSN records, a nighttime boom was heard on Dec. 5, 2021, which was registered on area seismic stations. 

The noise seemed to originate slightly south of Crescent Beach, out in Ship Bay. However, error estimates could put the source of the boom back on land, near the same location of the boom recorded on March 7, Malone said.

"At this point, we are left with explosive sources that are probably not legal for at least some if not all of these booms," Malone wrote.

PNSN has detected and located accidental explosions before, including one in north Seattle and one in Port Orchard that resulted in fatalities. 

"The early morning times and no one taking credit for these booms makes them less than innocent," Malone wrote. 

The San Juan County Sheriff's Office has been investigating similar reports of mysterious booms and asks that anyone who has information contact them at (360) 378-4151 or at the anonymous tip line at (360) 370-7629. Anyone who hears any strange nighttime booms is invited to email PNSN at pnsn@uw.edu with the times and general area of the noise to see if they were seismically recorded.

    

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