View Approximate epicenter of quake in a larger map

December 4, 2012

Tuesday's earthquake in York County no cause for alarm, expert says

A few small earthquakes close together in time are not unusual in Maine, the state geologist says.

By David Hench dhench@pressherald.com
Staff Writer

The magnitude 2.3 earthquake that hit part of York County on Tuesday may have been an aftershock from the bigger quake on Oct. 16 that was centered in Hollis.

LEARN MORE . . .

USGS: Real-Time Earthquake Map

USGS: Maine Earthquake Information

 

The earthquake that hit around 6 a.m. Tuesday was centered south of Lake Arrowhead in Waterboro.

"I felt it in Hollis. It shook the whole house," said Tom Hawley of the National Weather Service. "My neighbor felt it too."

Carrieann Bedwell, a geophysicist with the U.S. Geological Survey, said the quake was centered 18 miles northwest of Biddeford.

Dave Francoeur of the York County Emergency Management Agency said emergency dispatchers received a few calls but there were no reports of damage.

The earthquake on Oct. 16 was magnitude 4.0.

Small earthquakes, even a few close together, are not unusual in Maine, said Robert Marvinney, the state geologist.

"We've seen this kind of behavior before in our region," Marvinney said. "In 2006, there was a whole sequence of earthquakes in the Bar Harbor area. Really, this is all within the statistical norm for earthquakes in Maine."

Maine has had eight earthquakes since Oct. 1, according to Boston College's Weston Observatory.

Aftershocks usually hit soon after major earthquakes in areas with a lot of seismic activity, but New England tends to be relatively quiet.

Earthquakes are caused by movement of the earth's tectonic plates. In an area like California, where the volatile San Andreas fault is, plates pushing together create pressure that is released in sometimes violent earth movements.

By contrast, the East Coast is in the middle of a plate and is relatively stable. The plate still moves, generating small quakes, but not the violent collisions that characterize the Ring of Fire circling the Pacific.

"The earthquakes we experience in Maine or throughout New England are not tied to any faults we've mapped," said Marvinney. The faults that do underlie the state are millions of years old and not active, he said.

East Coast quakes tend to be felt much farther from the epicenter than those in seismically active areas because the region's bedrock is dense, without major faults, and movements of the earth tend to travel efficiently through it, Marvinney said.

If a major quake did hit the Eastern United States, the damage could be extensive, he said. The damage would be spread over a wide area, and the construction is not designed to withstand earth movements.

Earthquakes are rarely the result of human activity, though there is evidence they can be precipitated by disposal of wastewater in deep underground wells, a practice associated with the "fracking" technique of drilling for natural gas, Marvinney said.

The military triggered a small quake by saturating underground layers where pressure already exists, he said.

There is no evidence that extracting drinking water or similar activity could produce a quake in Maine, he said.

 

Staff Writer David Hench can be contacted at 791-6327 or at:

dhench@pressherald.com

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