Alan L. Kafka

Weston Observatory
Department of Earth and Environmental Sciences
Boston College

Yes, the Earth Does Quake in New England!

In the evening of October 16, 2012 residents of Hollis Center, Maine felt the ground shake from a magnitude 4.0 earthquake centered in southern Maine. This earthquake was widely felt across New England and into adjacent New York, New Jersey and Canada. Near the epicenter people reported that their whole house shook and that it felt like a train going right through their house.

On the morning of December 20, 1940, the Earth suddenly quaked near Lake Ossipee, New Hampshire. An earthquake with a magnitude of about 5.5 had occurred. Damage was reported in a broad region across New England, including chimneys thrown down, cracked plaster, broken dishes, and overturned objects.

On November 20, 1755, the Boston Weekly News-Letter reported "a most terrible Shock of an Earthquake: The conditions were so extreme as to wreck the Houses in this Town to such a degree that the Tops of many Chimnies, and some of them quite down to the Roofs, were thrown down. . . ." This earthquake, with a magnitude of about 6.2, was centered off the coast of Cape Ann, MA.

Yes, it's true. Earthquakes really do occur on a regular basis in New England. Notable examples of earthquakes that caused damage in New England and adjacent areas are: the earthquake off the coast of Cape Ann, MA in 1755; two earthquakes near Ossipee, NH in 1940; and an earthquake near New York City in 1884. In spite of this regular occurrence of earthquakes in the northeastern United States, most people living in New England probably think of places like California or Japan, rather than New England, when they hear the word "earthquake." While Californians have learned to expect earthquakes, residents of New England more likely consider the ground beneath their feet to be "solid as a rock." Nonetheless, the record of earthquake activity in the United States shows that, while the highest level of activity is, of course, in the western part of the country, earthquakes are quite common in many areas of the eastern United States, including New England.

Why then do earthquakes occur in New England? What causes earthquakes in major seismic zones like California and Japan? Why are earthquakes more common in California than in the northeastern United States, and how does earthquake activity in California differ from that in the Northeast?

Plate Tectonics and California Earthquakes

Unlike the situation in the northeastern United States, most California earthquakes occur near a major boundary separating two of the Earth's tectonic "plates", the North American plate and the Pacific plate. In the late 1960s, a revolution occurred in the geosciences when scientists discovered that earthquakes, volcanoes and geological activity are concentrated in well-defined zones that outline the edges of plates. There are about a dozen such plates. This theory of the Earth, known as plate tectonics, is now accepted as the overall explanation of how the Earth works. Plate interiors are much more stable than plate boundaries, and the theory of plate tectonics accounts for most of the large earthquakes in California, Japan, and Alaska, to name a few of the infamous seismic zones.

Of course, the real world is more complicated than this model suggests. While the two largest historically-documented earthquakes to occur in California (1906, San Francisco and 1857, Fort Tejon) did rupture a plate boundary along the well-known San Andreas fault, when looked at in detail, earthquakes in California are rather diffusely distributed in the vicinity of the plate boundary. Furthermore, earthquakes are scattered throughout the interior of the North American plate (as well as throughout the interiors of all plates).

With this perspective on plate boundary earthquakes, let us look at earthquakes in the northeastern United States.

Earthquakes in the Northeastern United States

The historical record of earthquakes in the northeastern United States and adjacent areas goes back to the 1500s, and a number of seismographs were operating in this region beginning in the early 1900s. Routine reporting of instrumental data on earthquakes in this region began in the late 1930s. The number of seismic stations in the Northeast increased significantly between 1970 and 1974. By 1974, area seismologists were operating a regional seismic network in the northeastern United States. With the advent of modern computers and the internet, high-quality digital recordings of earthquakes in this region are now available for research and public information purposes within minutes of when a northeastern US earthquake occurs. The figures shown below illustrate the pattern of earthquake activity in New England and surrounding areas.