Earthquakes swarm Marlin

Basin center of 29 tiny seismic shakes

MARLIN — For sale: Alpine property at Marlin.

Yes, you read correctly. Just a short drive north from Moses Lake, the plateau landscape is experiencing an earth heaving phenomenon in the very slow process of creating tally craggy mountains better suited for goats than wheat, so science predicts.

In the past couple of weeks, 29 very small earthquakes south of Marlin, Odessa and Wilson Creek were recorded by 20 seismograph stations of the Pacific Northwest Seismograph Network.

According to Steve Malone, director of the Network which is part of the University of Washington Earth and Space Sciences department in Seattle, a rash of quakes like this are called a "swarm." Considering the location, it's a highly unusual occurrence though not unprecedented, he said in a telephone interview.

The middle of Eastern Washington is normally a quiet place with not much shaking, Malone explained.

"If you include the whole Columbia River Basin, only about 200 earthquakes a year are the average, and most of those occur on the flank of the Cascades," he said.

An earthquake swarm is defined as a series of shocks that are similar to aftershocks but happen without a main shock, Malone said. "A swarm may last a few weeks to a few months, with as many as 100 shocks."

The recent Marlin quakes are low in magnitude, measuring between 1.1. and 2.1 on the Richter scale. They're shallow quakes, geologically close to the surface, most at a depth of less than a mile. "They're occurring in the Columbia River basalt layer which is between 1 kilometer to 2 kilometers deep in that area," Malone noted. The 1.5 quake near Odessa on Aug. 11 actually shook right on the surface.

Not that locals are in a panic. In fact, few seem to be aware of the phenomenon, which doesn't surprise Malone. "At that magnitude you won't feel anything unless you're right over the epicenter and sitting quietly, and then you'd feel it as a little thump."

Historically, the 1970s and 1980s were marked by a series of earthquake swarms in eastern Washington, Malone said. "There used to be one to two swarms a year," he recalled. "The one at Saddle Mountain lasted a few months. Another one occurred north of Richland."

At that time some scientists hypothesized that the Columbia Basin Irrigation Project might have something to do with the quaking, since the water delivery beginning in the 1950s had affected a change in aquifer levels. "It's a far-from-proven theory that water table changes trigger earthquakes," Malone noted.

Not that he discounts the theory altogether. "Mother Nature keeps her cards close to her vest, so we scientists hedge our bets," he said. "The thought that quakes can be triggered by a change in the hydrostatic head could be true, but even a change in a water table as large as the Odessa aquifer is just a tiny blip in geological terms.

Potential triggers aside, more certain is what's causing the quakes, Malone said. "There is a north-south compression from south British Columbia is not moving, while California and Nevada are trying to move north."

So the Inland Northwest is in a mountain building epoch? "Yes," Malone answered. "The movement is occurring very slowly, at a tiny fraction of an inch a year. It'll take several 100,000 years for the mountains to form."

So maybe the sale of alpine property's slightly premature at Marlin. But big earthquakes in Eastern Washington could happen in a relatively short span. "The largest quake here in the last 50 years was only magnitude 4," Malone said. "The biggie occurred in the North Cascades in 1872, near Entiat. That was pre-instrumental, scientists think it was a magnitude 7. It caused a large landslide, you can see the deposit of that to this day."

On a personal note, Malone said that he studied Eastern Washington seismic action for 10 years. "Now my specialty are volcanoes. They're a little more interesting, there is faster movement than in mountain building," he related.

At UW, his department is a small one with a few graduate students, he said. The seismograph network under his direction consists of 250 seismograph stations. "The instruments are so sensitive that they pick up the noise of a train several miles away. We try to locate the stations in remote areas away from what we call 'cultural noise.' In your area we have one station near Ephrata, and one near Odessa."

Mark Amara, Moses Lake, earned a geology degree from the University of California, Davis, and is co-author of the popular "Geologic Road Trips in Grant County, Washington."

Perhaps not surprisingly, Amara finds charm in the swarm. Our area is a geological wonder because many features of the landscape are a expression of nature's cataclysmic might: At first there was sea, an ocean supporting primordial life forms after millions of years of sediment deposits the land rose, pressured by a tectonic plate pushing against the continent's western edge. But the Cascades didn't exist yet when volcanoes became active here, shield-like volcanoes that oozed molten rock from 17 million to 6 million years ago, Amara said.

Geologists envision lava flowing at a sluggish rate due to low viscosity, spreading over hundreds of miles, Amara explained. The basalt built up flow by flow to as much as 10,000 feet in total thickness, its weight so great it warped the underlying crust of rock which, in turn, caused the warping of the basalt.

And now the basalt is shaking at Marlin. "Overall, I'm surprised that we don't have more stress-relievers like this, even in Eastern Washington, considering the seismic activity occurring due to plate tectonic activity," Amara put it.

For humans, the quake swarm is a grand reminder, Amara summed up. "The forces of nature reassert themselves in the landscape."