There are no reports of injuries or property damage after an earthquake rumbled around New England Tuesday.
The 4.0 magnitude earthquake hit at 7:12 p.m. on Tuesday and was centered about 20 miles west of Portland, Maine, sending tremors as far south as Boston and into Connecticut.
John Ebel, director of the Weston Observatory, joined WBUR's Morning Edition to discuss earthquakes in the northeast.
Bob Oakes: So tell us what we know about the quake this morning that we might not have known last night
John Ebel: Well, the initial magnitude was 4.6 that got released, and then after an analysis of some of the seismic waves, it was put at 4.0. The epicenter is in the Hollis area of Maine, and very widely felt across New England and even eastern New York state.
How does 4.0 compare to the typical earthquake in New England, if there is such thing as a typical New England earthquake?
Well, most earthquakes in New England, just like in any part of the world, are smaller magnitude events. We average an earthquake above magnitude of 4.0 once every half decade or so, somewhere in our New England region. The last one that was above 4.0 was a 4.2 that was also in Maine at Bar Harbor in 2006.
How is it that, then at 4.0 this quake was so widely felt, reports around southern New England that some people could feel the earth move, so to speak?
We see this with some earthquakes that they get felt over a wider area than others. Obviously, the larger the magnitude of the earthquake, the wider the area over which it will be felt. This one, the preliminary magnitude we computed at Weston Observatory was 4.5. So, I wouldn't be surprised if over the next couple days as we study the magnitude more, the size might come up a little bit again.
I'm wondering about a geological question. Because we sit on so much granite and bedrock, is a quake therefore maybe more widely felt around here?
Well, quakes are more widely felt in the eastern part of the United States than in the west because our rock is colder, actually, than the rock out west. So, an earthquake of this size would not have been felt over nearly the area if it had occurred out in California. The type of rock, actually, granite and the various rock types in New England, are very similar to what they have in California. It's the temperature that causes it to be felt so much more widely here.
Well very interesting. What do we know about the likelihood of aftershocks? Have there been any yet from this quake, and is it possible that this quake could be a foreshock, maybe a precursor of a larger quake to come?
As of about 6 a.m. this morning no aftershocks were detected by our seismic instruments. I wouldn't be surprised if there were some small aftershocks right in the area that were too small to be detected or even felt. Aftershocks probably will occur after this event, but I don't know how many, and they'll be small, probably not felt as far away as Boston. Could this be a precursor of a larger event? Not impossible. Very rarely we've had larger events follow within, say, a few days or more of an earthquake of this size, but I'm not sitting and necessarily expecting that.
And how frequent are earthquakes in this part of the country?
An earthquake in New England? We pick up about 20 per year, and about half a dozen of those are felt. As I said, an earthquake as large as magnitude 4.0 is a relatively rare occurrence. We only see something like that once every several years or even longer.
This program aired on October 17, 2012.