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'Swarm of earthquakes' jostles Deer Island, southwest Washington

Largest tremor measured at magnitude 2.9


by: SPOTLIGHT PHOTO ILLUSTRATION - Although University of Washington seismologist Paul Bodin said he does not think the series of small earthquakes near Deer Island that began Sunday, Jan. 26, are any cause for alarm, he said the event is a good reminder that Pacific Northwest residents should keep emergency supplies on hand in case of a major earthquake. A series of small earthquakes struck near Deer Island early this week, with the most powerful tremor clocking in at magnitude 2.9 on the Richter scale Sunday, Jan. 26.

The 2.9 quake was recorded by the University of Washington's Pacific Northwest Seismic Institute at 9:31 a.m. Sunday morning. Seismologists at the institute said about 25 people reported having felt the earthquake, with all of those reports coming from Washington residents across the Columbia River, according to Paul Bodin.

Bodin and fellow seismologist Bill Steele described the group of small earthquakes, which continued into Monday night, as a “swarm.”

“This is an area that has produced, you know, significant earthquakes in the past. And they're kind of swarm-like in nature sometimes, so there will be a number of little ones,” Steele said. “They aren't all typical main-shock, aftershock type sequences.”

Seismic swarms are poorly understood, Bodin and Steele said, and seismologists take an interest in them when they happen.

“The character of seismic swarms is one of those open scientific questions,” said Bodin. “We're not sure we know that much about how they're generated.”

In the Pacific Northwest, Steele remarked, “It's not unusual to find areas where we have clusters of earthquakes over time. And we don't well understand why here and not somewhere else.”

Earthquakes as small as those recorded this week near Deer Island are generally not significant enough to cause injury or damage to property, according to Bodin.

“In general, I don't expect to see damage for earthquakes less than magnitude 3,” said Bodin. “That would be surprising. And in fact, I wouldn't expect significant damage for earthquakes smaller than, I don't know, [magnitude 4.5].”

Although Bodin said seismologists do not believe seismic swarms are predictive of larger earthquakes to come, he and Steele both noted that the Pacific Northwest is a seismically active region, and he said residents should be prepared with emergency supplies in the event of a major temblor.