A minor earthquake that shook parts of Maine at 8:07 p.m. local time Monday caused water to drop 2.5 feet at a U.S. Geological Survey monitoring well.

Nearly 17 hours later, the water level was still dropping, scientists announced today.

Hydrologists call the change in the well “dramatic,” and said well-water users might notice changes in their drinking water.

The preliminary magnitude 3.9 earthquake was the third such event to shake the state in the past few weeks. It was centered about 4 miles south-southeast of Bar Harbor, or 45 miles southeast of Bangor. A magnitude 2.5 earthquake on Sept .28 and a magnitude 3.4 on Sept. 22 were centered in the same location.

“It isn’t unusual for earthquakes to cause minor changes in water levels in wells, but this is the most memorable in Maine in the last decade,” said USGS hydrologist Gregory Stewart. “Users of well water could notice cloudy water and possibly a change in availability of water.”

The 98-foot-deep well is in Acadia National Park in Bar Harbor and is drilled into bedrock. On a normal day the water-level changes 3-4 inches. One other well near the epicenter also showed a drop in water level after the quake.

“Water-level responses can occur over time periods of a few minutes to several months," Stewart said.

Monday’s earthquake was widely felt in coastal and central Maine.

Though major earthquakes are rare in the Northeast, moderate to strong temblors have struck the region in the past.

The largest earthquake centered in Maine was a magnitude 5.1 event on March 21, 1904. It toppled chimneys and was widely felt throughout New England. Historic earthquakes centered outside Maine have been large enough to cause damage in the state.

The largest historic earthquake in the region was a magnitude 7.0 temblor in 1663, centered in Quebec along the St. Lawrence River. It knocked down chimneys in eastern Massachusetts. In 1755, a magnitude 6.0 earthquake brought down chimneys and several brick buildings in eastern Massachusetts.

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