Between 2022 and 2023, three earthquakes shook the Peace River oilsands area. They constituted the largest human-induced seismic event in Canadian history, felt by residents across central Alberta.
An initial investigation in March 2023 linked the earthquakes to subsurface injection of wastewater from bitumen extraction, but just how that triggered a seismic reaction has remained a mystery.
Now, new research involving University of Alberta geophysicists Wenhan Sun and Jeff Gu shows how the wastewater migrated into a nearby fault about 50 kilometres from the town of Peace River, and how the three earthquakes may have influenced one another.
“We interpret the earthquakes as a domino‐like sequence triggered by wastewater injection and sustained by interactions between fault structures,” says Gu. “The geologic setting near the earthquakes formed a natural ‘drainage’ system that channels injected fluids into a deep, ancient fault zone.”
Wastewater injection at wells identified in Sun’s study caused a magnitude 5.6 earthquake on Nov. 30, 2022. That was followed by two more moderate earthquakes of magnitudes 4.8 and 5.0 on March 16, 2023. One of the three nearby disposal wells was the primary trigger of the earthquakes, “with secondary contributions from multiple wells more than 20 kilometres away,” progressively destabilizing the fault, says Sun.