Friday, April 22, 2016

McAdam earthquake swarm remains a mystery

Canadian seismologist sharing details of ‘swarm’ at U.S. conference Friday

A few small earthquakes continue to occur underneath the village of McAdam, but the reason behind the swarm, that began two months ago, remains a mystery to scientists.
One Natural Resources Canada seismologist is hoping to find some answers at a Seismological Society of America meeting in Reno, Nevada, on Friday, where she'll present details of the village's recent experience.
Since Natural Resources Canada installed four seismometers in the McAdam area in early February, the devices have recorded 101 earthquakes in and around the village, a phenomenon known as a swarm. 
The equipment recorded 82 in February, 14 in March and five so far in April. A map plotting their exact epicentres shows most to be directly beneath McAdam.
The seismometers were installed on the heels of reports of dozens of quakes over a period of a few weeks, the largest having a magnitude of 3.7.
Natural Resources Canada is now hoping to share details of its data with fellow seismologists, in an effort to pool knowledge about earthquake swarms in North America.
Allison Bent, a seismologist from Natural Resources Canada, is presenting details of the 2012 and 2016 McAdam earthquake swarms at the conference.
"She actually submitted [the information]
before the activity kicked up again in 2016, but she is going to be presenting all of the data that we've recorded up until the end of March," said Stephen Halchuk, another Natural Resources Canada seismologist.
"She is looking for insights from her colleagues and other researchers in the area who have looked at swarms in other areas across North America, and even globally."
Bent's abstract on her presentation says there are no known faults in the McAdam area.
Halchuk says she intends to write and publish a paper for a scientific journal on the subject in the coming months.
"They remain a mystery, because there is not a lot of concrete evidence that we can point to, to say that this is the fault, or this is what's driving the release of energy at this particular location," said Halchuk.
"But we're hopeful that we may be able to come up with some answers."
Halchuck said there is no evidence to indicate that the earthquakes are as a result of human activity and the most likely cause is a very small fault.
Bent was unavailable for an interview.

Aquifer theory

One of the four seismometers has been installed in David Blair's basement in McAdam.
Blair says the recent map of exact earthquake locations caught his eye.
This seismometer is one of 4 installed in and around the village of McAdam. (CBC)
"The map that Earthquakes Canada released showed the earthquakes were within the village limits, and actually within the perimeter of the outside roads of the village," said Blair.
"So that's kind of surprising and kind of wondering why that would be and why there wouldn't be some outside the village limits."
Blair said he think it's something that the scientists should at least investigate.
"I have my own personal theory, that it's maybe something to do with the aquifer," said Blair.
"In the old days people had shallow wells. Now we have deep wells drawing a lot more water out. Whether that's caused some changes in the aquifer that's causing this, I'm not sure."
Halchuk said Natural Resources Canada may remove some of the seismometers in the coming months, but that they may keep one in the village on a more permanent basis.
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