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Locations of earthquakes in a recent swarm. Courtesy Pacific Northwest Seismic Network (PNSN)

Scientists’ perspectives on recent earthquake “swarm” near Bremerton

Yesterday, a blog post on the Seismo Blog by Research Scientist Renate Hartog of the Pacific Northwest Seismic Network (PNSN) set out to describe a recent sudden up-tick of seismic events recorded in the vicinity of Bremerton, Washington (approximately 90 miles south of Ferndale).

Hartog explained, “The Seattle Fault Zone runs West to East right through downtown Seattle and has the potential of being the source of a large (M6+) earthquake.” So it was exciting, according to Hartog, when 3.4-magnitude (M3.4) earthquake happened below the fault zone last week and was followed by aftershocks. Soon after there were more earthquakes ranging from  M2.6 to M3.6. In addition to these larger events, there have been dozens of much smaller bursts of energy in the same area over the same period.

Hartog points out in her blog post that “swarms,” as these series of frequent seismic events over a relatively short period of time are referred to, are not that uncommon in the Puget Sound region. But, “this swarm is interesting in that it might be related to the Seattle Fault Zone.”

After detailing the locations and depths of the recent seismic events, Hartog points out that while the Seattle Fault runs right through the area of the current swarm, the depths of the events indicates they cannot be on the plate along the Seattle Fault.

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To answer the question, “What is going on?” Hartog explained, “We are having a nice vigorous swarm deep below the Seattle Fault Zone. But we don’t really understand what causes these swarms.” She also said it is possible more and or bigger earthquakes may happen but it is just as possible activity in the area will quiet down.

In an interview with Q13FOX television, PNSN Director John Vidale said one possibility was the ocean floor being dragged down underneath Western Washington, “So we think the water is pulsing through all these cracks in the ground and just flowing continuously. And sometimes the [water] pressure builds up and pushes aside the fault and lets there be some [seismic] activity.”

Hartog concluded her blog post with, “all we can do is what we do everyday, keep monitoring the seismicity in our region! What you can do is to make sure to be prepared for emergencies, check out the CREW website for ideas: http://crew.org/what-you-can-do.”

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