An earthquake that shook homes and rattled people in the Esterhazy, Sask., area on Tuesday morning was likely caused by mining activity, according to Natural Resources Canada (NRCan).
The earthquake — measured at a 3.4 magnitude — struck at 7:04 a.m. CST. Its epicentre was about nine kilometres east-northeast of Esterhazy, according to the NRCan’s Earthquake Canada website.
The federal agency says the earthquake was “a suspected mining-induced event,” which is categorized as an anthropogenic — or human-caused — seismic event.
The Mosaic Company operates a potash mine about 15 kilometres northeast of Esterhazy.
Last year, the area was hit by three earthquakes, including two within three months. Earthquake Canada said those were also likely caused by mining activity.
Jason Whitby and his wife were just starting their morning when they felt Tuesday’s earthquake. They heard a loud booming noise and their house shook, tipping over cups on the shelf and shifting art on the walls.
At first, he thought someone had hit their house.
“It was a crazy bang. It was a couple seconds then it was over,” Whitby said in an interview with CBC. “I’ve never felt anything like that.”
Whitby said he didn’t feel the earthquakes that happened in the area last year, but he’s concerned about damage to his home if the earthquakes become more frequent.
“It happens here and there, but nothing to this magnitude,” Whitby said. “To shake a house is pretty crazy. It might get worse, too, who knows?”
All Mosaic employees are accounted for and post-earthquake safety inspections are finished, the company said in a statement. About 1,200 people work below and above ground at the site, according to the Mosaic website.
Potash production was not interrupted and the earthquake happened “in a mined-out area of the older workings of the K3 Mine,” according to the statement.
“Mining induced seismic activity in this area is common, and our facilities are engineered with seismic loading in mind,” Mosaic said in the statement.
“While the recent event occurred far from current mining areas and presents no immediate safety concerns, we continue to advance our understanding of the geological properties of the K3 ore body and will work with external experts to review seismic activity.”
The Mosaic Company operates the K3 Esterhazy mine. (CBC)
NRCan has recorded anthropogenic seismic activity in the Esterhazy area for decades, NRCan seismologist Claire Perry said.
“The number of natural earthquakes in this area is very low. It’s not a tectonically active zone, far from active plate boundaries, far from the subduction zone,” Perry said.
“So this is a stable region where we don’t see a lot of earthquakes. And so we see these shallow events around Esterhazy, we know that they are related to industry activity and they’ve been going on for years.”
NRCan has not yet received any reports of damage to houses or other structures.
Esterhazy Mayor Randy Bot said the town “is no stranger to seismic events” because of the mine’s proximity.
“With one of the richest potash deposits beneath our feet, occasional ground movement is something our community has experienced over the years,” Bot said in a statement to CBC.
“Our primary concern is always the safety of our residents and everyone working in the area. We have confidence in Mosaic and the monitoring, safety protocols, and regulatory oversight that are part of our mining industry.”
The most significant seismic event in the area — with a magnitude of 4.1 — happened in 2019, but most measure in a range of 2.0 to 3.0 magnitude and only those above 2.8 are typically felt by people.
But Perry said it’s still important to take precautions.
“Nothing is impossible and everyone should remember to be prepared and have an emergency kit ready,” she said.
“Even if we don’t live in an earthquake prone region … it’s good to be prepared and know what to do should you feel shaking. The reflex should be to get under a desk or a table or something close by, take cover, protect your head and wait for that shaking to subside.”
Potash mines excavate massive amounts of material from deep below the surface and create large cavities that can eventually shift or alter the rock strata above it, which in turn can create “cracking” or “fracturing” that produce seismic activity, said Andrew Frederiksen, a professor in the earth sciences department at the University of Manitoba.
“Even if you stopped all mining now, there are enough areas that were excavated already that this activity would likely continue,” Frederiksen said. “Once you’ve got these open cavities from the mining, this kind of [seismic] activity is probably pretty inevitable.”
The seismic activity is relatively safe compared to areas near tectonic faults and isn’t indicative of future, larger earthquakes, he said.
“Something in the magnitude three or four range happening a couple of times a year is quite small potatoes on the global scale,” Frederiksen said.
“The mechanism that produces these earthquakes [around the potash mine] has sort of a maximum size to it … whereas earthquakes caused by tectonic plate motions could scale up to be very large.”
