New Brunswick town plagued for weeks by earthquake swarm and no one knows why

April 19, 2012 – CANADA – “Everybody is talking about the earthquakes,” says David Blair, a retired science teacher and lifetime McAdam resident from his home on Old Harvey Road, just east of downtown. “You’ll be out and about and people will say, ‘Did you feel the one last night, or did you feel the one this morning? Some people will say yes, others might say no. It really depends on what you are doing.’ “If you are quiet at home and there is not a lot of noise you are probably going to feel or hear it. But if you are banging around, or if the grandkids are banging around, you sometimes won’t know if it’s the kids — or if it was an earthquake — they are about the same magnitude, I guess.” Residents were initially rattled awake at 1:40 a.m. on March 10 by a 2.4-magnitude earthquake that was followed three minutes later by a 1.4-magnitude aftershock. People described hearing what sounded like an explosion. Pictures fell off walls. Window panes rattled. Floorboards creaked and groaned. Some houses even shook, while locals, initially, felt a surge of panic that eased, somewhat, by morning with the realization that a bomb had not gone off but a small earthquake had. Three days later: two more earthquakes. And in the five weeks since there have been 35 additional shakes, a steady tide of minor tremors that is a popular topic of conversation among villagers and a seismic anomaly that scientists can’t entirely explain. “What is happening in McAdam is something called an earthquake swarm,” says Stephen Halchuk, a seismologist with Natural Resources Canada. “It is a series of earthquakes, which is rare. But what is particularly unusual about what is happening in McAdam is that it is basically happening directly beneath the village — and at a depth of less than one kilometre. “When these earthquake swarms occur they are typically in a remote area where nobody feels them.” Mr. Halchuk can’t say how long the earthquakes will continue for, or if a big one, capable of causing serious property damage and endangering lives, could be lurking among all the little ones. “We can never say never,” he says. “I wouldn’t rule out a very large event occurring but, typically, in situations like this, the magnitude of the earthquakes is modest and doesn’t increase.” Researchers from the University of New Brunswick addressed community members at an atypical town hall meeting Monday night, answering questions and assuaging lingering fears. One working theory they have to explain the quakes is an early spring thaw. A rapid change in groundwater levels could, perhaps, be causing the underlying rocks to slip and stress, unleashing the multiple shocks. –National Post

contribution by Emanni