New England Aftershock Probabilities

This forecast is based on the statistics of aftershocks typical for New England.
This is not an exact prediction, but only a rough guide to expected aftershock activity.
This forecast may be revised as more information becomes available.

12/03/2015 Aftershock Probabilities

Aftershock Forecast was computed on: Friday, December 4, 2015 4:49 PM EST

Mainshock:  Thursday, December 3, 2015 7:12 PM EST, Magnitude 3.0
MA, 10.0KM (6.2 miles) SE OF WESTON, MA

Probability that this event is a foreshock and there will be an earthquake one unit of magnitude or greater in the next 30 days:


Probability that this event is a mainshock and will be followed by one or more aftershocks of any magnitude in the next 7 days:


Probability that this event is a mainshock and will followed by (one or more) aftershocks of magnitude 2.0 or greater:


Background Info About Aftershocks

Mainshock – the earthquake of greatest magnitude in a series of earthquakes which occur over a relatively short period of time in a particular area.

Aftershocks – additional earthquakes that occur after the mainshock and in the same geographic area. Usually an aftershock is smaller than the mainshock, but occasionally an aftershock may be strong enough to be felt widely throughout the area and may cause additional damage, particularly to structures already weakened in the mainshock.

Foreshock – an earthquake which occurs immediately preceeding a mainshock in the exact same area in which the mainshock occurs.


Like most earthquakes, the recent earthquake is expected to be followed by numerous aftershocks. Aftershocks are most common immediately after the mainshock; their average number per day decreases rapidly as time passes.

Aftershocks are most likely to be felt in the first few days after the mainshock, but may be felt weeks, months, or even years afterwards. In general, the larger the mainshock, the longer its aftershocks will be felt.

Aftershocks tend to occur near the mainshock, but the exact geographic pattern of the aftershocks varies from earthquake to earthquake and is not predictable. The larger the mainshock, the larger the area of aftershocks. While there is no “hard” cutoff distance beyond which an earthquake is totally incapable of triggering an aftershock, the vast majority of aftershocks are located close to the mainshock.

As time goes on, the aftershocks will subside. As they do, we will revise the table below to reflect the diminishing chances of large aftershocks.

New England Earthquake Information

New England Earthquake Info:


Earthquake Information by State:

If You’ve Felt an Earthquake

Normally, earthquakes between magnitude 2.0 and 3.0 can be felt near the epicenter but cause no damage. Earthquakes between magnitude 3.0 and 4.0 are more widely felt (between 10 and 100 miles from the epicenter) but almost never cause damage. Earthquakes above magnitude 4.5-5.0 can cause minor damage (cracks in plaster and brick walls) near the epicenter. Earthquakes above magnitude 6.0 or so can cause more severe damage to buildings.


If you believe you have felt an earthquake in New England, please do the following:

  • Email the Weston Observatory at or call at 617-552-8300 to tell us precisely when and where you felt the earthquake.
  • If there is damage, call the Massachusetts Emergency Management Agency at 508-820-2000.

Earthquake Safety: Before, During and After an Earthquake



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