Let's say it's a cold night, after a quick freeze in early January. You're woken up at 3 a.m. by a loud booming noise and the house shakes.
In the morning when you mention it to neighbors down the road, they have no idea what you're talking about. What happened? Was it an earthquake? Are you just losing your mind?
That middle-of-the-night disturbance might have been a frost quake.
The Shelburne News has reported that residents have been experiencing sounds and shaking that could have been caused by frost quakes.
The Vermont Geological Survey doesn't track the phenomena, but the Maine Geological Survey does. Vermont Edition spoke with Henry Berry, a bedrock geologist with the Maine Geological Survey about what a frost quake is and what could be causing them in the region.
What exactly is a frost quake?
“It's a naturally occurring phenomenon that has effects that are like a tectonic earthquake, but the same sort of deep forces do not cause them. It's something that happens because of temperature drops and contractions of the Earth's surface.
"For a frost quake to occur, specific things have to happen in the environment: the soil must be saturated with water, then experience a sharp temperature drop that goes from a little bit above freezing to quite cold in a short time.
“These things are very hard to study, because they happen fast and they only affect a very local area. So we don't really know a lot about exactly what the [ideal] conditions might be. But once we get the stories and put the information together, the patterns that show up [point us toward] the first cold snap of the year, especially if there's not much snow cover, so that the cold air has a chance to suddenly freeze the ground surface.”
Are what are being reported in Shelburne really frost quakes?
“I think it's a it's a good possibility. I saw the article … from the Shelburne News and I think that it actually does a nice job of getting [across] the kind of information that we look at in order to make this sort of decision.
“There are ways that these frost quakes are similar to tectonic earthquakes and there are ways that they're really different. A loud booming noise, or a sudden shock, or a jolt and shaking are the same sorts of effects you might experience in an earthquake.
“But the differences are that it only affects one house or one place, and a few hundred yards away nobody would even know it's happening. It is very localized. And it also doesn't really affect the deep earth, it doesn't send seismic waves through the earth's crust. So [frost quakes are] not detected by seismographs across New England."
So how did the Maine Geological Survey track frost quakes?
Berry says citizen reports are the main way frost quakes are tracked.
“[With] earthquakes, it's kind of a byproduct, we weren’t really looking for them, but we collect information on earthquakes when they occur. Vermont is a low-hazard state and Maine is a moderate-hazard state [for earthquakes]. Most of New England has some low level of earthquake susceptibility.
"For a while we had a website [where we were] collecting information, and we got a few of these odd ones that came in. People were experiencing 'earthquakes', but we knew that there hadn't been one. And so gradually, we realized that this was something worth tracking."
Would a frost quake register on a seismograph?
"Frost quakes are judged on the intensity scale, which measures what the effects of a quake are. The intensity scale really relies entirely on people telling us what happened and making observations. And it's in that way we try to connect the intensity scale with the magnitude scale.
"For tectonic earthquakes, things that are generated in the earth's crust, there's a pretty good correspondence [between what we measure on the magnitude scale and what people feel on the intensity scale].
"But with frost quakes, the amount of intensity that people are feeling just doesn't match up with the seismic waves that are generated. So there's almost nothing that shows up on the instruments.
"A study done in the early 1980s found that people were reporting some frost quakes, and so they put seismometers in neighbors' houses, a few hundred yards apart. And sure enough they picked up the vibrations. But different neighbors were reporting different events. So in one house, they would feel something and the instruments recorded it. But in the next house, the instruments didn't record that event."
Can frost quakes do any damage?
"It's the same sort of damage you'd expect [from] freezing ground. The most common thing that has been found associated with these is a crack in a driveway or something that was smooth beforehand. But the cracks generally don't go very deep, they're just at the ground surface. There was one report we had of somebody who said that a frost quake caused a crack in their foundation, but that’s a very rare occurrence, if ever."
