Plainfield - The 11 earthquakes that have shaken the town since Jan. 8 are the first known to have occurred there in more than 375 years of historical records, and present seismologists with an "intriguing enigma" they are eager to study.

So said Alan Kafka, director of the Weston Observatory at Boston College, during a presentation Friday night to about 800 residents gathered in the high school auditorium for a public information session about the earthquake "swarm" that last rattled the town Thursday morning. The strongest of the quakes hit Monday morning, measuring 3.1 on the Richter scale. Another measurement put it at 3.3. No major damage or injuries have been reported from the quakes.

"This is the first case of known earthquakes in this part of Connecticut dating back to 1638," Kafka said. "Seismologists don't know why these earthquakes decided to happen at this place at this time, but from now on you will be seeing a lot of us. You have become for eastern seismologists a famous place. From now on we are going to think of the Danielson-Plainfield area as holy ground."

As part of its research, scientists from his office this week set up four portable seismographs in and around the epicenter of the strongest quake.

Kafka was invited by Police Chief Michael Surprenant and First Selectman Paul Sweet, who said the series of tremors have caused a lot of anxiety in town. He noted that with the early morning timing of several of the tremors and accompanying explosive sounds, "earthquakes are substituting for alarm clocks." His office provided residents attending the meeting with packets about earthquake preparedness.

Kafka said Weston Observatory, the leading agency studying earthquakes in New England and eastern Canada, is searching for other locations with characteristics similar to Plainfield that have also had earthquakes. While the town sits near the Honey Hill-Lake Char fault, it is not believed to be an active fault, he said. And unlike faults in California, there is no clear correlation between faults in this part of the country and earthquakes.

"For it to be an active fault, we would actually have to see it in motion, and no one has ever seen it move," he said. "So far there are no places east of the Rocky Mountains where we have seen the faults move."

New England earthquakes typically occur in the vicinity of past earthquakes, he said, but since that is not the case with the current swarm, the Plainfield episode is even more puzzling.

The timing of the quakes in the morning hours, he said, could have something to do with freezing and thawing of the ground causing underground movement.

About 40 minutes into his PowerPoint presentation, Kafka was interrupted by a member of the audience who had grown impatient waiting for a chance to ask questions.

Reisa Mello said she had already done a lot of Internet research on earthquakes, and wanted more information specific to her town.

"Do you know why this is happening in Plainfield?" she asked. "What's going on?"

"No, we do not know," Kafka responded. "We've been going around the world trying to find a comparable place, and so far we have not found any."

Resident Alvin Wagner asked whether hydraulic fracturing, also called fracking, could be causing the quakes - even though the closest fracking areas are hundreds of miles away in Pennsylvania. Fracking has been linked to earthquakes in Texas and other areas where it is occurring.

"You have to be pretty close to cause that problem, within one to two and no more than 10 miles," Kafka said.

Another resident asked why the quakes sound like explosions.

"These are very shallow earthquakes, about a mile or two down," Kafka said. "If it was deeper you probably wouldn't be hearing that boom."

Before Kafka's presentation, Paul Yellen, the town's fire marshal and director of emergency management, said his office has contacted various utilities and state agencies and has verified that no road, bridge, gas line or other infrastructure has been damaged. The town highway department and sewage treatment plant, along with Northeast Utilities, Yankee Gas, Algonquin Gas Transmission Co., Providence & Worcester Railroad, the state Department of Transportation and the Tilcon Connecticut asphalt plant in the Wauregan section of town are among those contacted, he said.

j.benson@theday.com

Twitter: @BensonJudy

How to be quake-ready

The state Department of Emergency Services and Public Protection advises these actions to prepare your home for an earthquake:

• Identify a safe place in each room of your home, under a piece of sturdy furniture, or against an interior or load-bearing wall.

• Practice "drop, cover and hold on" in each safe place.

• Bolt and brace water heaters, gas appliances, bookcases, china cabinets and other tall furniture to wall studs.

• Locate the gas and water valves in your home and learn how to shut them off.

• If you use propane gas, make sure it is securely anchored and the shutoff valve can be easily reached. If you smell gas, do not turn on electrical appliances or lights, evacuate the home and call the utility from a safe place.

• Keep and maintain an emergency supply kit that is easily accessible and includes basic supplies, including a portable radio, flashlight, fresh batteries, a first aid kit and bottled water.

• Check your home for structural damage or cracks, including foundations, chimneys and wood stove piping, on a regular basis. Contact your local building official if you notice any damage.

• To prepare for any incident, including an earthquake, have family and workplace emergency plans.

• Sign up with www.CTAlert.gov to receive any emergency information sent out in your town.

• For additional preparedness information, go to: www.redcross.org and www.211ct.org.