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Aspenites on shaky ground

Tim Mutrie

Locals who claimed yesterday that they felt an earthquake in the middle of the night weren’t telling an April Fools’ Day joke. The quake was real.

An earthquake registering about 2 on the Richter Scale subtly shook the upper Roaring Fork Valley at 2:56 a.m. Thursday morning.

But the bizarre natural phenomena for the day didn’t end with the shaky ground. Locals arose to find a thick blanket of “desert dust” deposited on the valley yesterday.

The epicenter of the quake, which lasted only about three seconds according to witness accounts, was somewhere in the Aspen area, said Don Blakeman, geophysicist/earthquake analyst with the U.S. Geological Survey National Earthquake Information Center in Golden.

There were no reported injuries or damages caused by the quake.

“There are characteristics in the data that indicate that it was very local to the Aspen area,” Blakeman said.

“It was an approximate magnitude 2 earthquake,” Blakeman said. “And that’s a very approximate magnitude because we only recorded this quake on one of our seismometers in Idaho Springs. As a result, we don’t know exactly where the epicenter was; if we had more data we cold pin it down.”

The seismometer in Idaho Springs is the closest instrument to Aspen, he said.

Blakeman explained that a magnitude 2 quake is very mild.

“As a general rule of thumb, usually it takes a magnitude 5 earthquake before you get any damage,” Blakeman said.

Each step in the magnitude scale, or Richter Scale, indicates a tenfold increase in the power of the earthquake, Blakeman said.

Like Thursday’s quake, earthquakes in Colorado are typically mild. They typically occur five to 10 times a year in the state, Blakeman said. The last quake to shake Aspen was in July 1993, Blakeman said. It notched a 3.1 on the Richter Scale.

“We’re right on a fault zone, and that’s one of the reasons we have the mountains we do, from the plates pushing against one another,” explained Rebecca Houston, environmental educator with the Aspen Center for Environmental Studies. “This is still a pretty geologically active area.”

Houston said the Castle Creek Valley is on a major fault line, and that Ajax’s Bell Mountain is situated between two minor faults, under Spar Gulch and Copper Bowl. Another sizable fault line is in the vicinity of Red Butte, she said.

Earthquakes, Houston ex-plained, are the result of shifting along fault lines.

Apparently, some residents sensed the seismic activity. The Pitkin County Sheriff’s Office said residents reported pictures falling off walls and furniture shaking.

In an unrelated but equally strange natural phenomenon, Roaring Fork Valley residents awoke Thursday morning to find a thin layer of red dirt blanketing everything. The dust, most easily discernible on vehicles, blew into the valley from Utah and fell to the ground along with Thursday’s precipitation, experts agreed.

“My understanding is that there was a tremendous dust- storm in Utah and that’s where it came from,” said Lee Cassin, Aspen’s environmental health director. Cassin said Aspen’s PM-10 count spiked Wednesday coinciding with the duststorm. PM-10 refers to airborne particles.

“To some degree, long-range dust transport is possible, but due to all the mountains, we wouldn’t anticipate as much dust getting through,” said Sheila Burns, program manager with the Colorado state health department.

“Anytime particles stay suspended in the atmosphere,” Burns continued, “they get washed out by precipitation. That may be why it looks like there are concentrations on vehicles. There is usually an air quality benefit because of that washout feature.”


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