92% of Fracking Earthquakes Had Warning Tremors — But Not All

Tiny seismic rumbles can signal that fracking and other fluid-injection activities are putting enough stress on underground faults to trigger a larger earthquake, according to a study published August 27 in the journal Science. Researchers led by Bei Wang, a geophysicist at Zhejiang University of Technology in China, analyzed a decade of seismic data from Alberta's Western Canada Sedimentary Basin and found that 92 percent of earthquakes induced by fracking were preceded by smaller foreshocks.

The team examined about 70,000 earthquakes recorded in western Canada between 2014 and 2024, identifying 77 mainshocks of at least magnitude 3 linked to fracking. Foreshocks — smaller quakes occurring within 5 kilometers and five days of a mainshock — appeared before 71 of those 77 events. But the pattern was inconsistent: some mainshocks were preceded by a single foreshock, while others had as many as 700 tiny quakes in the warning window.

Regulators typically use a "traffic-light protocol" to manage this risk: injection continues under a green light, but ticking-up seismic activity triggers a yellow light that halts operations before a red-light, damaging quake occurs. Foreshocks are the main way operators detect that yellow warning. "Eight percent of the time there's no warning; you would skip right past the yellow light," said Ryan Schultz, a seismologist at ETH Zurich who was not involved in the study. Most human-triggered quakes are small, but some have been damaging, including a magnitude 5.6 earthquake in 2022 near Peace River, Canada, caused by wastewater injection during oil extraction.

The researchers propose three possible ways injected fluid could produce foreshocks before a mainshock: gradually weakening the main fracture until it slowly slips, building strain until the fault suddenly fails, or triggering a domino effect across several fractures in succession. Schultz said these mechanisms have been discussed since the 1990s but remain unconfirmed, and improving the traffic-light system further will require open access to the seismic and injection data that companies collect — access that currently varies by country and, in the United States, by state.