Earthquakes happen often in Maine and likely will rattle state again

Posted March 31, 2010, at 10:09 p.m.
Last modified Jan. 30, 2011, at 11:46 a.m.
Dr. Robert G. Marvinney, Maine state geologist and director of the Maine Geological Survey. w/Hewitt story
Dr. Robert G. Marvinney, Maine state geologist and director of the Maine Geological Survey. w/Hewitt story

ORRINGTON, Maine — The shaking and rattling that rolled around eastern Maine on Tuesday afternoon was a relatively minor quake compared to the devastating temblors that struck Haiti and Chile earlier this year.

But the tremor that shook up residents in parts of Hancock and Penobscot counties and the smaller aftershock that followed were just the latest in a long history of earthquakes in Maine. On average, an earthquake such as the magnitude 3.0 quake that centered in Orrington near the Bucksport town line on Tuesday happens about once a year in the state, according to Maine State Geologist Robert Marvinney.

Many quakes in Maine, those with a magnitude of less than 2.0, are too mild to be felt, but even without those, the Maine Geological Survey notes that since 1997, about 50 quakes have been documented throughout the state. The strongest in recent years was in 2006 when a magnitude 4.2 quake struck east of Mount Desert Is-land. The strongest Maine earthquake on record occurred in Eastport in 1904 and registered a magnitude of more than 5.0 that caused chimneys to tumble and was felt as far away as Montreal. A magnitude 4.0 earthquake struck the Albion-Unity area in 1988.

Before Tuesday’s quake, the most recent was a magnitude 1.7 quake that struck on Feb. 17 offshore of Trescott township about 14 miles south-southwest of Eastport, according to the Maine Geological Survey Web site.

It has happened pretty often before and very likely will happen again.

“Earthquakes can occur anywhere in the state,” Marvinney said Wednesday.

The bedrock of Maine is creased with fault lines, breaks in the earth where rock has moved. But those faults are older, are not geologically active and do not move the way the younger, more active fault lines do. According to Marvinney, they have little to do with the earthquakes that occur in Maine.

“We don’t have active faults as they do in California,” he said. “We’re in a geological setting that is very quiet.”

The Earth’s crust is composed of a group of plates that move slowly atop a sea of magma. Maine sits in the middle of one of those geologic plates — the North American Plate — which acts as a buffer from the sometimes violent activity at either end of the plate. California, on the other hand, sits on one edge of that plate, which is rubbing against another tectonic plate. Likewise, Marvinney said, Haiti and the nearby Caribbean islands all lie on the edge of a very active plate.

Still, the movement of the North American Plate — westward at about 1 centimeter a year — results in earthquakes in the state.

“It’s moving toward the west,” Marvinney said. “That puts stress on the entire crust of North America. When that stress is released, it creates the kind of small earthquake like the kind we had yesterday.”

That release of built-up stress also can result in the kind of explosive sound that many people in the Bucksport area reported hearing during Wednesday’s earthquake. The earthquake creates a wave that moves through the crust of the Earth, Marvinney said. In some cases, the release can come as a sharp jolt, creating the cannon-shot noise.

Marvinney said it’s likely that quakes such as Wednesday’s temblor occur at some weak point in the Earth’s crust. Because Maine’s quakes are relatively mild, he said, it would be difficult to map those areas the way geologists have been able to do with the older, major fault lines.

There is nothing geologically significant about the area in Orrington where the earthquake hit that made it more or less susceptible to a quake, according to Marvinney, and the same can be said for other areas of the state.

“The plate is always moving, and that movement doesn’t happen uniformly,” he said. “It can move in fits and starts, and this can generate some earthquakes anywhere in the plate.”

A map of the state pinpointing earthquakes in Maine for the nearly 200 years that records have been kept shows some small quake clusters in some regions of the state. But it also shows that most areas of the state have had some earthquake activity during that time.

More information about earthquakes is available on the Maine Geological Survey Web site at www.maine.gov/doc/nrimc/mgs/mgs.htm.

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