A Canadian-German research team have found out a new type of earthquake. These earthquakes are slower and last longer. This new type of earthquake is triggered by hydraulic fracturing. This method is mainly used in Canada to extract oil and gas.
Researchers from Geological Survey of Canada and McGill University have recorded seismic data of approximately 350 earthquakes with a network of eight seismic stations surrounding an injection well. Ten percent of these recorded earthquake’s showed unique features. They were slower, as it was recorded in volcanic areas.
This research paper has been published in the journal Nature Communications.
Theories behind their origin
Researchers have explained two main reasons behind these earthquakes. One is, the fluid pumped into the rock creates pressure and generates a new network of fractures in the subsurface rocks near the well. This pressure triggers an earthquake.
Another reason is, the fluid pressure increases from injection in the subsurface make elastic stress changes on the surrounding rocks which are transmitted over longer distances. These leads to changes that cause the earthquake.
A new model in lab has analysed the process of faults near injection wells and researchers have observed that. Researchers have termed it as aseismic slip. This kind of slip starts out as slow slip and does not release any seismic energy.
This slow slip causes a stress on nearby faults and slip rapidly and make an earthquake. The lack of seismic energy and the size of the faults involved in it make it difficult to observe in natural settings. So, researchers haven’t got any chance to document aseismic slip broadly to induce earthquake. The new research provides insights of aseismic loading and its transformation from aseismic to seismic slip.
The researchers think the slow earthquake is an intermediate form of conventional earthquake and aseismic slip.