The New England region was shaken by an earthquake on the evening of October 16. The magnitude 4.0 earthquake occurred at a depth of 5 km approximately 30 km west of Portland, Maine. The earthquake was recorded on the EEAS seismometer (l). The duration, as shown on the seismogram (r), was approximately 1 minute although most observers only felt the quake for a few seconds. Although this was a relatively small earthquake, given the geology of New England which is largely composed of crystalline bedrock the earthquake was felt over a wide area, from northern Maine to Connecticut.
Approximately 40 small earthquakes occur in New England each year. Many of these are concentrated in central New Hampshire on a N-S trend in the Ossipee region. These earthquakes are largely due to strain that has built up in the North American plate as it moves away from its spreading center (the Mid-Atlantic ridge). Large earthquakes are rare. The most famous was the 1755 earthquake located off Cape Ann that had an estimated magnitude of 6.0.