Rare 3.7 Magnitude Earthquake Shakes Southern Ontario Canada

After days of relentless snow shoveling and plows rumbling through the streets, residents across southern Ontario were reminded this week that not all unsettling forces come from winter storms.

Late Tuesday night, an earthquake shook parts of the province — a rare occurrence in a region far more familiar with extreme cold than ground tremors.

The quake struck just before 11 p.m., about 23 kilometers southeast of Orillia. It registered a magnitude of 3.7 and originated roughly five kilometers below the surface.

While a quake of that size is considered light on the Richter scale — which measures earthquakes up to magnitude nine — it is unusually strong for southern Ontario.

“This area, like southern Ontario and the Great Lakes region, is not prone to large earthquakes at all,” said Mareike Adams, a seismologist with Natural Resources Canada, in an interview with CTV News Toronto. “So this was quite a rare event for this region.”

Ontario sits within what scientists call an intraplate region — a stable section of the North American tectonic plate, far from the boundaries where most powerful earthquakes occur. As a result, seismic activity here is relatively low, though not impossible.

“On the West Coast, you have a major subduction zone where tectonic plates interact directly, producing very large and frequent earthquakes,” Adams explained. “That’s not the case here.”

In eastern Canada, earthquakes are typically caused by stresses that build up within the plate itself or by ancient fault lines buried deep in the Earth’s crust.

“These are very old faults that can sometimes become reactivated,” Adams said. “They can move slightly when stress builds up and release energy.”

Even so, she noted that the exact cause of Tuesday night’s quake remains unknown.

Despite its modest size, the tremor was felt widely. Reports came in from across southern Ontario, stretching as far south as St. Catharines and as far east as Kingston. More than 3,300 people reported feeling the shaking.

Because eastern Canada sits on older, denser rock, seismic waves can travel farther without losing much energy.

“This region has very low attenuation,” Adams said. “That means earthquake waves don’t weaken as quickly, so people can feel them much farther from the epicenter.”

Given the recent cold snaps and heavy snowfall, some residents wondered whether the shaking might have been caused by a frost quake — a phenomenon linked to sudden drops in temperature. Adams confirmed, however, that Tuesday’s event was a true earthquake.

“Earthquakes are caused by internal forces within the Earth,” she said. “Frost quakes are related to weather.”

Frost quakes typically occur when water in the soil freezes rapidly and expands, causing the ground to crack or pop. They are more common along the shores of the Great Lakes after heavy rain or snowmelt and do not cause structural damage.

Stronger earthquakes in southern Ontario are considered extremely rare. Still, Adams noted that history shows they are not impossible.

“There was a magnitude-five earthquake near Attica, New York, in the 1920s, and another of similar size near Cleveland,” she said.

According to Earthquakes Canada, the strongest quake ever felt in the Great Lakes region occurred on Aug. 12, 1929, with a magnitude of 5.5.