Industrial activities like hydraulic fracturing and wastewater disposal can disturb underground rock layers, sometimes causing earthquakes. These activities change the stress and pressure in the subsurface, which can be hard to detect directly. In this study, we used a technique called ambient noise coda wave interferometry to track tiny changes in the speed of seismic waves (dv/v), which reveal how the subsurface is responding to fluid injection.
Focusing on the Montney region in western Canada, we analyzed data from 66 seismic stations collected between 2018 and 2024. We found that after fluid is injected, dv/v tends to drop—indicating weakening rock conditions—and later recovers once injection stops. In one location, the seismic velocity dropped by 0.12% in a year. These changes likely reflect increased underground pressure, cracks forming, or small earthquakes.
We also found patterns linked to seasonal changes and ocean waves, and interestingly, a dv/v drop occurred before a magnitude 4.5 induced earthquake in 2018, suggesting dv/v might help forecast such events.
Overall, dv/v is a powerful tool for monitoring how the Earth responds to human activities, but combining it with other data is essential for a clearer picture.