Tiny seismic rumbles can warn that human activities such as fracking are putting enough stress on underground faults to trigger a larger earthquake. Analyses of a decade of seismic data from Alberta’s Western Canada Sedimentary Basin shows that 92 percent of earthquakes induced by fracking were preceded by smaller foreshocks, researchers report. However, significant uncertainties remain regarding how and why these foreshocks occur, meaning that while useful as short-term warnings, they can produce both false positives and false negatives.
A landmark study in 2015 was the first to conclusively demonstrate that fracking triggered dozens of earthquakes in Ohio. Since then, numerous studies have shown that human activities involving the injection of fluids into the ground—such as hydraulic fracturing, enhanced geothermal energy, or wastewater disposal—can trigger earthquakes. Most of the induced tremors are relatively small, but human-induced quakes can be powerful enough to shake nearby communities, such as the magnitude 5.6 earthquake in 2022 initiated by wastewater injection during oil extraction near Peace River, Canada.
Regulatory agencies worldwide have implemented a “traffic-light protocol” to manage this growing seismic hazard. A green light means operations proceed normally. When seismic data rises, indicating that a damaging quake may be imminent, a yellow light requires operations to stop, while there remains hope that a shutdown occurs before the status turns red. Small foreshock quakes are the primary way industrial operators know the system has switched to yellow. However, there is little understanding of what causes foreshocks and how often they truly signal a dangerous mainshock.
Bei Wang, a geophysicist at Zhejiang University of Technology in Hangzhou, China, and his colleagues analyzed seismic data from western Canada from 2014 to 2024, encompassing about 70,000 earthquakes. They identified 77 mainshocks of at least magnitude 3 linked to fracking, then searched for foreshocks occurring within five kilometers and five days of each mainshock. Foreshocks were detected before 71 of those fracking-related quakes—92 percent of the time.
This offers a yellow warning light that allows operators to halt fluid injection. However, the remaining 8 percent of the time, there is no warning, and operations jump straight from green to red. Even within the 92 percent, the foreshock sequences were highly inconsistent: some had a single foreshock, while others generated up to 700 tiny tremors.
Wang and his team propose three potential pathways through which fluid injection could lead to foreshocks and then a mainshock: fluids progressively weakening a main fault to cause slow slip, increasing strain on the region until sudden failure, or creating a domino effect causing slip on multiple fractures sequentially. Ryan Schultz, a seismologist at ETH Zurich not involved in the study, notes these are classic earthquake-earthquake interaction concepts. However, they remain hypotheses, and different geological conditions can trigger fault movements differently. Furthermore, understanding these mechanisms requires open access to seismic and pumping data, which companies are not always guaranteed to share.
As Schultz points out, the study highlights the flaws in the current traffic-light protocol, particularly the risk of skipping the yellow warning altogether. Moving forward, defining what constitutes unacceptable risk and positioning the red light far enough in advance of that threshold are key to improving the protocol’s effectiveness.
