Data from UNH's seismometer, as represented on the Raspberry Shake network, following the earthquake that rattled New England on Jan. 27. The blue symbol labeled "3D" represents the location of the seismometer on campus, and the red dot in the center of the image is the epicenter of the earthquake. The waveform graph in the lower right shows the activity spike during the quake.
A 3.8 magnitude earthquake originating off the coast of Maine on Monday morning rumbled throughout the New Hampshire Seacoast region and was felt as far south as Boston and portions of coastal Rhode Island and Connecticut. The earthquake’s epicenter was less than 10 kilometers southeast of York Harbor, Maine.
It is the unique makeup of New England’s land mass that allowed the effects to be felt so far from the epicenter, says Sophie Coulson, assistant professor of geophysics in UNH’s Department of Earth Sciences.
“Where we are, we are surrounded by igneous rocks like granite, which are very dense and very structurally sound and solid. So they actually allow the shaking of earthquake waves to propagate through them for longer distances before the energy fades,” Coulson says. “That energy doesn’t dissipate as quickly as it can in other regions because we’re on such solid ground.”
Earthquakes of this magnitude aren’t necessarily common in New England, but they aren’t total anomalies, either. Coulson says we typically experience an earthquake of this size every five years or so in the region, noting that New Jersey experienced a similar one last year. There are often much smaller ones that occur between those instances, but they are usually around a magnitude of 2 or lower and are not felt.
The last earthquake with a magnitude of at least?3.8 to strike in Maine occurred?in Hollis in 2012, Coulson noted.
Earthquakes happen along faults, which are pre-existing planes of weakness, Coulson says. And New England happens to be home to many. They were created when the Appalachian Mountains were formed several hundred million years ago, though Coulson says they “probably haven’t been active for a very long time.”
When stress or pressure builds up in those areas, they experience a rupture as rock shifts, creating an earthquake.
“The most likely candidate to have caused this one is a large-scale tectonic process” Coulson says. “In the Atlantic Ocean you have the mid-Atlantic ridge, where two tectonic plates are actually spreading apart. What that means for us is the western portion of the Atlantic Ocean is moving toward us, and the plate we are on is being compressed. That could be one factor in creating that build up of stress or pressure near where we are in New Hampshire.”
The UNH Earth sciences department has a seismometer located in the basement of James Hall, primarily for teaching purposes, which recorded the quake activity. That seismometer is connected to the Raspberry Shake network, a global seismic monitoring network (sort of like Waze for earthquakes, featuring input from professional seismologists, hobbyists, educators and students), and UNH’s data was shared with that network.
The location of the epicenter offshore and not on land could provide some learning opportunities, Coulson says, as it “can give us some insight into what the crustal structure is out there and maybe allow us to extend what we haven’t been able to map there.”
While offshore data has been historically difficult to track, general tectonic trends have not. So should we be on the lookout for more frequent earthquakes in the region?
“These plates have been moving at about the same rate for tens of millions of years, and we’re talking by millimeters per year, so I don’t think this is a sign of things like this becoming more frequent,” Coulson says.
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Written By:
Keith Testa | UNH Marketing | keith.testa@unh.edu
