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How 'mystery boom' on Orcas Island was studied by local scientists

Seismologists hope sharing that process will inspire interest in education on available resources and data.

WASHINGTON — In March, the Pacific Northwest Seismic Network (PNSN) shared a blog post about their efforts to identify the source of a "mystery boom" on Orcas Island. 

Now, they're sharing more about their collaboration with the Cascades Volcano Observatory and about how increasing data points are making it easier to gain a timely understanding of seismic events. 

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

PNSN's inquiry into a reported "mystery boom" on Orcas Island started after an email from a now-retired seismologist living in the area, who woke up to shaking and wanted to know if there'd been an earthquake.

"There was a signal on our seismographs, but it was not the kind of signal that's generated by an earthquake," said Paul Bodin with the PNSN. "So it wasn't something in the rocks that moved- the usual tectonic earthquake. Instead, it had the signature of something acoustic in the air- like an explosion in the air, a firecracker or something like that, that causes a pressure wave in the atmosphere, and you can tell the difference. What happens is that a pressure wave hits a place where there's a seismic station and it shakes the building or whatever and that registers on our equipment, but not like an earthquake. It's a different kind of signature."

Bodin said a wide variety of things can cause this to happen, with varying degrees of impact. Anything from a truck going by to animals walking by to a tree falling can register. 

"In order for us to understand- what are earthquakes and what are ground motions, we have to look at this whole mess of stuff, so what we do is we have a lot of automatic processes to identify what we expect to be earthquakes," Bodin said. "In a case like...what happened in the Orcas island case was, there weren't earthquakes and we knew that pretty quickly actually."

Bodin said PNSN works closely with the Cascades Volcano Observatory, the US Geological Survey's office in Vancouver, Washington. He says for the past few years they've been adding both seismic and infrasound stations around Mount Rainier- and they were able to share some of that infrasound data. 

"He wrote back, and said, well, yeah, and showed us data showing, there is this weird signal and using my seismic stations as an array I can tell the signal's coming from the north, so it kind of fits- but it's not at the right time," Bodin said.

Through continued inquiry, PNSN concluded that the source of the boom was likely a man-made device like an amateur explosive- perhaps, a firework. Investigating that falls under the purview of other organizations and authorities.

But Bodin said the assessment they were able to do is a testament to the tools that are now available to closely analyze seismic activity. PNSN, operated by the University of Washington and University of Oregon, has continued to add new seismic stations across the region, now numbering in the hundreds. 

The hope is that more Washington residents will educate themselves on the processes and available data involved - in line with the Network's mission to provide accurate, fast information about earthquakes and ground motions to scientists, engineers, planners and community members.

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