On Tuesday 16 October 2012, slightly after 7.10 pm local time (slightly after 11.10 pm, GMT) the United States Geological Survey recorded a Magnitude 4.0 Earthquake 5 km underground, roughly 30 km southwest of Portland, Maine. This is not an especially large quake, but it was quite shallow and is far larger than the area is used to, leading the USGS estimate that there was a 24% chance of the quake resulting in at least one fatality. There have not been any reports of damage or casualties, but the quake appears to have caused widespread alarm over much of New England.
The location of the 16 October 2012 Earthquake. Google Maps.
Earthquakes in Maine are an uncommon occurrence, but they do occur, with six Earthquakes of Magnitude 4.0 or greater being recorded in the twentieth century, the largest being the Magnitude 4.8 Bowmantown quake of 1973. The precise cause of these quakes is unclear, though they are thought to be associated with tectonic stresses in the Appalachian Mountains. The state is cross-cut from north-to-south by a number of ancient faults associated with the formation and breakup of the ancient supercontinent of Pangea, between 300 and 200 million years ago, though no sign of modern movement on these faults has been discovered.
Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake you can report it to the USGS here.
See also Earthquake in Labrador, Canada, Quebec Earthquake, 27 August 2011, Virginia Earthquake shakes Washington, New York, Earthquake in South Dakota, 9 August 2011 and Earthquakes on Sciency Thoughts YouTube.
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