Natural Resources Canada suspects the seismic activity measured on the Bruce Peninsula last week was not an earthquake after all, but a quarry blast.
Stephen Crane, research scientist with Natural Resources Canada, says the time of the day when the event happened, the location and the waveforms registered on the seismograph are consistent with a blast.
He says there a few quarries located nearby where seismic activity monitoring equipment recorded a 2.1-magnitude reading about 14km north of Wiarton, just after 5 p.m. on Friday, Dec. 13.
Six or seven reports have come in from people who felt vibrations from the blast, Crane notes, with the furthest away being about 20 km north near Lion's Head.
Crane says the reports sent to Natural Resources Canada from people about what they felt were also very consistent with an explosion or a blast, and not an earthquake.
“That helps confirm what we suspect,” Crane says. “But mostly, the reason why we think it was a blast is because of the time of day, the location it occurred and the fact it was very shallow at the surface.”
“Also, the difference between the blast and an earthquake is a blast will usually have a very strong onset and fade very quickly,” Crane continues. “An earthquake will have a slow onset and stronger shaking after, which lasts a little longer.”
Crane says it is very common for seismographs to detect activity such as blasts as the equipment is able to pick up the tiniest vibrations in the earth. He says Natural Resources Canada's automatic system initially categorizes a reading as an earthquake and it won't be converted to a blast until a seismic analyst reviews the event.
Anyone who felt the suspected blast is asked to fill out a report at earthquakescanada.gc.ca.