When one thinks of a place in the U.S. where earthquakes tend to strike, California, with its famous San Andreas fault, probably springs to mind. It might come as a surprise to Harvard residents that Harvard, with harsh winters and the odd suspicious car as some of its typical natural hazards, is smack in the middle of what geologists call an intraplate earthquake zone within the North American tectonic plate. The last seismic event in the area radiated from Littleton’s town common two years ago.

So far there has been no need for concern: while a low rumble might pass through the land every now and then, the destructive power of these earthquakes has been minimal; they seldom measure at more than 3.0 on the Richter scale. At that level, sensitive seismologic equipment can have trouble recording it—an observer might mistake the event for a small, distant explosion or a bad car accident. Structural damage is unlikely. In terms of energy release, this can be compared to the detonation of several metric tons of TNT. As bad as this sounds, Earth is rather good at absorbing what, in a geologic sense, is a small amount of energy.

By contrast, the earthquake that recently devastated West Sumatra measured a 7.6 on that same scale, representing hundreds of millions of tons of TNT. It killed more than 1,000 people and caused millions of dollars in property damage. An earthquake that strong is out of character for New England. Seismic events occur most frequently around the boundaries of tectonic plates, the massive cracked pieces of crust and mantle that slowly but constantly push and pull against one another atop the liquid portion of the Earth. At their boundaries, tectonic plates will cause seismic events by smashing against each other. However, in intraplate zones, such as the one that sits under New England, and more specifically, Harvard, there is no such battle in the middle of a plate.

In fact, it is not known precisely what causes the quakes in this part of Massachusetts. Earthquakes here are uncommon; Harvard feels maybe one every two years. John Ebel, a professor focusing on earthquake seismology in Boston College’s department of geology and geophysics, has an analogy to explain the best scientific guess at what causes them. “Imagine a brick in a vice. As it gets squeezed, the center will crack.” This is, presumably, the case within central Massachusetts—ancient fault areas weaken and crack because of the pressure created by forces at work thousands of miles away. However, says Ebel, who is also the director of Boston College’s Weston Observatory, which monitors seismic activity in New England as part of the New England Seismic Network, it is still not entirely known that this is the case.

What, then, are the area’s seismological prospects? Will we experience a catastrophic earthquake here? The answer, Ebel says, is “yes,” but when it might happen is difficult to know. The science of geology is good at identifying where earthquakes are likely to occur, but not so good at predicting when they will happen.

“Any place with a lot of small earthquakes will [at some point] have a very large one,” he says, “but when you’re talking about a geologic time scale, that could be tomorrow or it could be 10,000 years from now.”