Many Mainers felt firsthand Monday morning that the earth below them isn’t as still as it seems.
The state isn’t a seismic hotspot, but earthquakes like Monday’s magnitude 3.8 happen on occasion.
But what causes the ground to rumble beneath our feet?
Since 1997, there have been more than 150 recorded earthquakes in the state, according to the agency. Those tend to be weak movers and shakers ranging from magnitude 0.7 to 2.8. You may not even feel many of those.
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Monday’s quake struck about 10:22 a.m. approximately 8 miles southeast of York Harbor at a depth of nearly 12 miles, according to the U.S. Geological Survey. (The agency initially reported the quake had a magnitude of 4.1.) That makes it one of the stronger quakes felt here in recent decades.
That level of seismic activity is typically of the Appalachian Mountains, according to a Maine Geological Survey report.
What causes earthquakes here isn’t well understood. It may be stress released along zones of weakness. Maine State Geologist Ryan Gordon told Maine Public on Monday that the movement of tectonic plates may be causing cracking and the occasional rumbling we feel. Or it could be, according to Gordon, the ground rebounding from the last ice age.
But, without a doubt, there aren’t any active faults near Maine. That geological survey report noted that our fault lines haven’t been active since the Appalachians formed — 300 million years ago. And there hasn’t been any significant motion evident in the past 20,000 years.
So earthquakes aren’t a rarity here, and there aren’t any active faults. Will one happen near you? That depends.
Recorded quakes tend to be clustered near Passamaquoddy Bay, the Dover-Foxcroft-Milo area and southwestern Maine. Of course, earthquakes have been felt across Maine, even as far north as the St. John Valley.
Every so often quakes happen in clusters. That happened near Jonesboro between Aug. 11 and Sept. 1, 2022, when about nine earthquakes ranging from magnitude 1.7 to 3 shook the ground. Before that there was the cluster of six quakes east of Cadillac Mountain on Mount Desert Island from Sept. 22 to Dec. 29, 2006, the strongest of which measured a magnitude 4.2.
One last fact stands out about earthquakes in Maine. Unlike their West Coast cousins, none has caused any significant or widespread damage here.