A mysterious swarm of noisy earthquakes unnerves Spokane

Long after the last Fourth of July firecracker burst in Spokane, nerve-rattling explosions still shake the city. There has been a swarm of earthquakes that boom like dynamite, surprising residents and seismologists alike.

Since a 3.7-magnitude quake rumbled through town June 25, there have been more than 30 recorded tremors. If you add in the tremors felt by residents but undetected by monitors, the number easily tops 50 seismic events. On Monday night, a 3.2-magnitude quake shook the town.


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"They get your heart racing," said resident Keri Yirak.

They also have scientists scratching their heads and searching for funds to investigate the mysterious swarms, shallow quakes and trembling faults.

"We didn't know there were active faults in the Spokane area," said Tom Yelin, seismologist with the U.S. Geological Survey.

The quakes in Spokane have been shallow, sometimes only a mile or two deep. This probably has contributed to all the noise they're making. Higher-frequency vibrations make the booming sound and when quakes are deeper, those vibrations are gone by the time they reach the surface. Sometimes the quakes boom even when no vibration is felt.

From his home on basalt cliffs overlooking town, the sound "is a lot like thunder or the old sonic booms," said Spokane resident Tim Ray. "It definitely unnerves my wife."

Yirak has been surprised at how localized the quakes are.

"It's just so bizarre. Seattle can have one and we feel it (hundreds of) miles away. And we have one and you can't feel it two miles away," she said. Yesterday she counted what she thought were 18 little quakes in a four-hour period.

The series of temblors is called a swarm because they are close in magnitude, as opposed to a single large quake followed by aftershocks. In the early 1970s Seattle experienced two swarms, each lasting several months.

The swarm process remains poorly understood. And the Spokane quakes "could go on for months," Yelin said.

It's been difficult for researchers to determine just what's going on in Eastern Washington because seismology recording devices there are few and far between.

Scientists deployed five seismic monitors in the area after the first large quake. The equipment was on loan and had to be returned before the Monday quake, but the short window of readings should be helpful. A permanent monitoring device already has been placed in Spokane and there are hopes that another will join it.

Guy Medema, a graduate student in the geophysics department at the University of Washington, said California could have something to do with the rumblings in Eastern Washington.

California is creeping north but Canada's landmass is holding its ground.

"Washington and Oregon are getting squeezed in the middle," he said.

Bob Derkey, a geologist with the state Department of Natural Resources in Spokane, has identified a new fault in the area and dubbed it Latah Creek Fault because it runs near a creek of the same name. It could be the cause of the recent activity, but most scientists say it's too soon to know.

Quake damage has been limited mostly to listing chimneys, cracked walls and crumbling mortar, but the state emergency management division has been keeping an eye on the events.

"Eastern Washington is part of earthquake country," said George Crawford, earthquake program manager for the agency. "There is potential for quakes and therefore we need to be prepared for them. These are wake-up calls."

There were small quakes in Spokane intermittently from 1915 to 1962.

The largest quake to strike Eastern Washington in the last 100 years was a 5.5-magnitude temblor in 1942 centered 35 miles northeast of Spokane.

Yelin said the chances that the small quakes are a precursor to something larger is low. But "I can't guarantee we won't have a large event."

P-I reporter Lisa Stiffler can be reached at 206-448-8042 or lisastiffler@seattlepi.com

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