Seismologists 'Keeping Close Eye' On Swarm Of Puget Sound Quakes

EDMONDS, WA - If you're worried about the recent spate of earthquakes in Puget Sound - in particular, the "swarm" of quakes near Bremerton - it's important to remember: the Pacific Northwest is earthquake country, so a certain level of seismic activity should be expected. That said, seismologists in the area are watching the quakes closely, even if they don't know for sure what's causing them.

The latest quake hit Thursday just before 11 a.m. The magnitude 3.3 struck off of Whidbey Island, and was felt around Puget Sound - as far east as Woodinville and Mercer Island. In Shoreline, one teacher said that she felt her classroom jolt.

But then there's that "swarm" of quakes near Bremerton. There have been dozens of very small quakes - some just a magnitude 1 or slightly higher - in a small area between Enetai and Manchester over the past week; that includes three quakes of a magnitude 3 or higher. The latest two large quakes hit at about 12:30 p.m. Thursday (a magnitude 3.6) and at 1:15 a.m. Wednesday (a magnitude 3.3).

Pacific Northwest Seismic Network seismologist Renate Hartog published a blog post on Thursday officially declaring the Bremerton-area quakes a "swarm."

"We are having a nice vigorous swarm deep below the Seattle Fault Zone. The focal mechanism of the bigger events are consistent with North-South contraction. But we don't really understand what causes these swarms. It is possible that more, and bigger, earthquakes happen. It is also possible that this area quiets down again. The swarm is providing us with some nice local waveforms that might be able to tell us more about the local crustal structure. For now, all we can do is what we do everyday, keep monitoring the seismicity in our region!"

U.S. Geological Survey seismologist Joan Gomberg told Patch.com that seismologists are watching the quakes closely. Under usual circumstances, seismologists will get alerts about quakes, and then work to figure out how strong they area and the exact location where they hit. With the recent swarm, seismologists will do more footwork to analyze the quakes to find out what's going on, she said.

At this point, there's no way to predict earthquakes, so no one can say whether these recent quakes are either foreshocks or just normal activity. Gomberg said that the area in question near Bremerton has seen similar activity before - there was a magnitude 4.9 there 20 years ago.

Gomberg said that there's "nothing we can hang our hats on" as far as a reason why the swarm is happening.

There's also been talk about the swarm's location near the Seattle Fault Zone. Although the quakes are located in the zone, they are occurring much deeper than where seismologists believe the Seattle zone runs. That fault has the potential to trigger a magnitude 6 or higher earthquake, which could be devastating for the Seattle area.

If anything, Gomberg said that the quakes are a good reminder to be prepared because one day, whether it's Cascadia or the Seattle fault or something else, a large quake will hit Puget Sound.

"These kinds of events are good reminders that people need to be prepared," Gomberg said.

Image via Pacific Northwest Seismic Network