After a flurry of minor earthquakes struck the Seattle area Thursday, local seismologists aren’t sure if the quakes will continue, or if they portend a more powerful and dangerous event to come.
Concerns shifted from “Did you feel it?” to “What does it mean?” Thursday after two morning earthquakes near Bremerton, one with a magnitude of 3.6, and another quake off Whidbey Island with a 3.4 magnitude.
The Bremerton quakes were the latest in a swarm of 13 minor earthquakes that have hit the Kitsap Peninsula since May 3.
A much smaller 1.7 magnitude quake was recorded Thursday near Granite Falls at 2:37 p.m.
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Earthquakes registering between magnitudes 2.0 and 3.9 are considered minor.
Seismologists at the University of Washington’s Pacific Northwest Seismic Network (PNSN) are particularly interested in whether the swarm might be related to the Seattle fault zone.
It is possible that more, and bigger, earthquakes happen. It is also possible that this area quiets down again.
Renate Hartog of the Pacific Northwest Seismic Network
The Seattle Fault is an area of thrust faults that run through Seattle and across the Puget Sound. The last time the fault ruptured in a big way was about 1,100 years ago. The resulting quake measured at least magnitude 7 and thrust up shorelines in West Seattle and Bainbridge Island by 20 feet or more. It also triggered a tsunami that swept through Puget Sound.
In PNSN’s “Seismo blog” Thursday afternoon, Renate Hartog wrote that the Seattle Fault runs right through the area of the current swarm. But the quakes were deep, striking at about 25 kilometers.
“But, remember, these earthquakes are very far below the surface and can therefore not be of any of the Seattle Fault strands,” Hartog wrote.
“So, to answer,” she continued, “what is going on?”
Swarms of small earthquakes are not unusual in our region. But we don’t really understand what causes such swarms, she wrote.
“It is possible that more, and bigger, earthquakes happen. It is also possible that this area quiets down again.”
For now, she continued, “all we can do is what we do everyday, keep monitoring the seismicity in our region!” What you can do, she wrote, is to make sure you’re prepared for emergencies.