Today there was a small earthquake about 7 miles from Augusta Maine. The quake was a 2.6 on the Richter Scale. Because the Richter scale is logarithmic, each point it rises means the quake is 10 times stronger. By extension, this quake was about 100 times gentler than the 4.5 that many of us in southern Maine felt last October 16th.
We're used to hearing about big earthquakes: The 2010 Haiti earthquake (7.0), the 2011 Japan earthquake (9.5, 10,000,000 times as powerful as the one felt today) or the ones that occur along the San Andreas in California. All of these occur on active plate boundaries where one plate is shoving under or, in the case of California, past another, but what's happening in Maine? There haven't been any active plate boundaries in Maine for more than 200 million years.
If you could look at Maine's Carfax report it would not look good. Maine is the victim, nay product, of several collisions with other landmasses. Each one left Maine with several small faults, where the old continents docked. Then there was the stretching. When Pangaea split the continent spread to fill up the old space. Some parts of once solid rock sank down, while others remained aloft. The result: despite it's beautiful exterior, our state has some pretty severe internal damage.
There are faults on the surface within 15 miles of today's earthquake, but the earthquake occurred 3.1 miles underground. It's difficult to assign blame for the earth shift that occurred, but we can be assured that it is a result of Maine's storied tectonic history.
"Central Maine Feels 2.6 Magnitude Earthquake." Bangor Daily News. 21 June 2013. Web. 21 June 2013. <http://bangordailynews.com/2013/06/21/news/state/central-maine-feels-2-6-magnitude-earthquake-sidney/>.
"M2.6 - 2km W of Sidney, Maine." Earthquake Hazards Program. United States Geological Survey, 21 June 2013. Web. 21 June 2013. <http://earthquake.usgs.gov/earthquakes/eventpage/usc000hx15#summary>.
"Maine Earthquakes 1997 to Present." Maine Geological Survey. State of Maine. Web. 21 June 2013. <http://www.maine.gov/doc/nrimc/mgs/explore/hazards/quake/quake-recent.htm>.