A scientific article (New window) was published in the journal Nature communications in November by researchers at the Geological Survey of Canada, McGill University and Ruhr University in Bochum, Germany.
Scientists have found that unlike conventional earthquakes of the same magnitude, these new earthquakes occur more slowly and are linked to landslides found at the San Andreas Fault in California.
Researchers made the discovery in the Montney Formation in northeastern British Columbia, where hydraulic fracturing is practiced. This process involves injecting water and chemical additives into the rock to release the oil and gas.
The injected fluid can increase the pressure on the rock enough to create a new network of fractures in the underground rocks or increase the pressure on existing faults and trigger an earthquake. The increase in pressure can also change the characteristics of the rock and cause earthquakes.
Using eight research stations, the researchers recorded about 350 earthquakes.
Usually, an earthquake occurs along a fault. So, it’s a fracture in the rock. When you put stress on it, when you put forces that act on the rock, at some point it’s going to exceed the resistance along the fault and it’s going to slide suddenly. When it suddenly slips, it generates seismic waves and that’s it, an earthquake, explains seismologist Maurice Lamontagne of the Geological Survey of Canada.
Researchers have found that some earthquakes do not occur so abruptly. It seems that the movement is rather slow and that it gives particular seismic traces, specifies Mr. Lamontagne.
These movements, it was the first time that they have been documented in an oil field, he adds.
Similarities to the San Andreas Fault in California
The researchers also observed a phenomenon that until now had only been considered by using numerical models and laboratory analyzes.
These models predicted that seismic landslides were occurring near the injection wells. A landslide is seismic when it is not accompanied by an earthquake and seismic when an earthquake occurs.
Seismic landslides are present on tectonic faults, such as the San Andreas fault in California, but this is the first time they have been observed near a field where there is hydraulic fracturing.
If it was possible to adjust the fluid injections below the seismic level, therefore at seismic slip or hybrid vibration frequency (EHW) earthquake levels, then we could reduce or eliminate the seismic events., explains researcher Honn Kao.