Researchers size up seismic activity

Earthquake activity in Maupin, ORe. has OSU scientists looking for cause

By: Rebecca Johnson

Posted: 1/14/09

The small town of Maupin, located in Eastern Oregon, has been experiencing a large number of earthquakes over the past two years, and OSU researchers are trying to figure out why.

There have been around 350 earthquakes since December 2006. While most of them go unnoticed except by the seismometers, around 15 have reached a magnitude strong enough to be felt by the surrounding community, according to Jochen Braunmiller, research assistant for the OSU College of Oceanic and Atmospheric Sciences (COAS).

Braunmiller explained that there have been several questions that have arisen while researching these earthquakes.

One is that these swarms do not follow the mainshock/aftershock sequence of most earthquakes. In many cases, there will be a large earthquake (the mainshock) followed by numerous smaller earthquakes that decrease over time, also known as the aftershocks.

In Maupin, there was no large earthquake, only numerous small ones that have not stopped, the last of which occurred Dec. 27 of last year.

The fact that the activity has been going on for two years is also unusual because with many swarms, the tremors will begin to taper off as stress is released from the fault.

These swarms have also been occurring in other parts of the nation. The United States Geological Survey reported several hundred small earthquakes at Yellowstone National Park at the end of December 2008. While swarms are not uncommon for Yellowstone, the activity was much higher than the area is used to seeing.

The occurrence in Yellowstone also raises another question: the depth at which the Maupin earthquakes are occurring. In Yellowstone, the small quakes are fairly shallow, originating only three miles below the surface. In Maupin, the earthquakes are occurring at a depth of around 10 miles.

This depth causes a problem for one of the theories regarding the activity's causes. Braunmiller explained that there have been some fluid pressure changes locally along the fault. The presence of water in a fault can make it easier for plates to break away and start sliding.

What makes this fault unusual is that researchers did not think water could be present at that depth.

OSU researchers were able to take advantage of equipment that was present in 2007 for an ongoing project called Earthscope. The goal of the project is to better understand the geology and seismic activity of the nation.

The equipment is placed in an area, beginning on the West Coast, and left there for two years to record data. Once the two years are up, the equipment is picked up and moved east along a grid until the entire country has been studied.

In 2007, when half of the earthquakes were occurring, Earthscope was able to record the activity and provide data to researchers at OSU.

Braunmiller said the data collected by this equipment is the best they have seen so far.

The equipment is no longer there, but the Oregon Department of Geology and Mineral Industries (DOGAMI) adopted three of the Earthscope stations in Oregon, one being near the town of Maupin; therefore, researchers are confident that they will still receive quality information.

"Our efforts now are to get a handle on the area," Braunmiller said. "We want to see how much we can condense it by looking at the seismograms."

Past data has been showing an area of activity around three square miles. Braunmiller believes that research will prove the area is actually smaller, less than one square mile.

He explained that knowing the size of the area of activity is important because it indicates the size of the fault. Braunmiller is also interested in seeing if snowmelt and rainfall have anything to do with water being present in the fault, but he says he will have to observe the earthquake activity for a few more years.

According to Anne Trehu, a member of the research team and professor in the COAS, researchers are still awaiting the approval of funds from the United States Geological Survey. Trehu said that until funding is approved, they have been "bootlegging" the research in their free time.

"It's interesting because it's in our own backyard," Trehu said.

Other major contributors to the research were John Nabelek, an associate professor for the COAS, and Mark Williams, a Master's student in geophysics.

Rebecca Johnson, staff writer

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