PLAINFIELD — At first, town officials didn’t have an answer.
More than 50 people had called the police shortly after 9:30 a.m. Thursday to report a boom and a shake. The town fire marshal’s office had ruled out blasting as the cause, and there were no crashes on nearby I-395. Neither was there any work being done on the Providence and Worcester railroads.
An earthquake, with a preliminary magnitude of 2.0 to 2.2, had occurred in the northern part of town, about 2 miles south of Danielson, they learned. It was nearly 6 kilometers underground and caused no damage.
Earthquakes happen fairly regularly in Connecticut, but they rarely amount to more than a murmur. For centuries, the residents of the Moodus section of East Haddam have heard the rumblings of earthquakes in the area.
The Plainfield area, where Thursday morning’s temblor struck, has now experienced four small earthquakes since October, according to data collected by the Weston Observatory at Boston College
at 6:08 PM January 08, 2015.
The number of quakes has increased across the New England area over the last 10 years — part of a natural geologic process, said John E. Ebel, the chair of the Department of Earth and Environmental Sciences at Boston College.
“From the late 1970s into the early 1990s, it was much more active,” he said. “Then things dropped off. In the early 2000s, the activity got very low throughout New England. And it seems to have come back since then.”
The observatory recorded fewer than 40 earthquakes per year in the area from 1990 through 2005. Then activity increased — to 80 in 2006, 94 in 2010, 154 in 2011 and 182 in 2012.
More earthquakes have been reported in recent years in some areas with new oil and gas exploration, according to the U.S. Geological Survey. But New England’s earthquakes are naturally occurring.
“There are spots all over the eastern United States where there has been wastewater injection due to hydrofracking,” Ebel said. “And there are earthquakes associated with those areas,” even in eastern Ohio.
“But not in New England. We don’t have the right geology,” he said.