The swarm, which caused no reported damage, came on the heels of a 3.3 magnitude earthquake registered on Feb. 2 in Passamaquoddy Bay, 6 miles north of Eastport.
The epicenters of the swarm of tremors were in McAdam, New Brunswick, beginning at 4:43 a.m. Monday and continuing through 5:59 p.m., Berry said.
As many as 21 earthquakes were recorded with only a few strong enough to be felt, he said. One of the earthquakes in the swarm had a magnitude of 2.9, but the rest were closer to 2.0 or below.
Tremors of 2.5 or less on the earthquake magnitude scale, are “usually not felt but can be recorded by seismograph,” according to UPSeis, an educational site for budding seismologists. Anything registering a 2.5 to 5.4 is “often felt, but only causes minor damage.”
A swarm of tremors is not unusual, Berry said Wednesday.
“These swarms happen every once in awhile,” he said. “They start and they just go for a while, and then they stop.”
Other such swarms previously reported in Maine included a series on Sept. 22, 2006, near Bar Harbor. Another swarm was reported in April and May 2011 in the Bucksport area. A third was reported Feb. 17, 2012, in Machias, according to Berry.
A statement released by the Canadian government about the most recent tremors, said: “In the past few days, numerous earthquakes have again been felt by residents of McAdam and recorded by the regional seismograph network operated by Natural Resources Canada and the University of New Brunswick.
“These events are considered to be a resumption of ‘earthquake swarm’ activity. … The current swarm began on Feb. 3. A swarm usually has many similar-sized earthquakes within a short period of time occurring in a small area. It is not unusual for swarm activity to start, stop and restart again. A swarm can last for days, weeks or months.”
Although a larger earthquake is unlikely, it’s not impossible, the statement concludes.
Berry said a similar swarm of microearthquakes hit the McAdam area between Nov. 30 and Dec. 9, 2015. The magnitudes were 1.0 to 2.2, according to a list of earthquakes on the Maine Geological Survey website.
The largest earthquake centered in Maine was a magnitude 5.9 registered Down East on March 21, 1904, according to Boston College’s Weston Observatory website.
Centered in southeast Maine, “This strong earthquake overthrew chimneys in Washington County, in the area of Calais and Eastport, Maine, and at St. Stephen, New Brunswick. Felt throughout most of New England and the provinces of New Brunswick and Nova Scotia. It was observed west to the Hudson River and Montreal, Canada, and south to southern Connecticut,” according to the U.S. Geological Society’s website.
“This was the largest earthquake in New England for the last two centuries,” Berry said.
Other strong earthquakes to be felt in Maine in the recent past had epicenters in Canada, he said.
The largest was a magnitude 5.4 on March 6, 2005, with an epicenter northeast of Quebec City. The Maine Geological Survey website describes this quake as “felt widely across Maine.”
A magnitude 5.1 was reported Nov. 5, 1997, near Quebec City and also “felt widely across Maine.”
A magnitude 5.0 was reported June 23, 2010, about 35 miles north-northeast of Ottawa and “felt in southwestern Maine,” according to the Maine Geological Survey website.