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Researchers in the are part of a team that has discovered evidence of two “slow-slip” earthquakes in northeastern British Columbia. 

The timing of these slow slips, which occurred over periods of days, appears to correlate with hydraulic fracturing (fracking) operations. Using satellite Interferometric Synthetic Aperture Radar (InSAR) to measure ground movement of the Earth’s surface, they found that a few centimetres of ground movement had occurred.

was published Monday in the journal Scientific Reports.

Hydraulic fracturing is extensively used in Western Canada and, in rare cases, has been documented to cause earthquakes that would otherwise not be expected; these are known as induced earthquakes. Prior to this study, the largest induced earthquake associated with hydraulic fracturing in Western Canada had a magnitude of 4.55.

No associated shaking detected, despite magnitude

Slow earthquakes have been widely documented in natural tectonic settings such as subduction zones, plate tectonic boundaries where two plates converge, and one plate is thrust beneath the other.

From the satellite data, the size of the largest earthquake detected in this study (magnitude 5.0) is larger than any previous hydraulic fracturing-induced earthquake in Canada. Earthquakes are typically recorded using seismographs that measure ground motion; however, despite the size of the earthquakes as measured by satellite, the regional network of seismographs did not record any associated ground motion — the shaking that tends to characterize earthquakes.

“This is the first time that significant slow-slip events associated with hydraulic fracturing have been directly detected. Naturally occurring slow earthquakes have been widely documented. In these scenarios, slip occurs along a fault, just like regular earthquakes, but much more slowly, so that no detectable shaking occurs,” explains Dr. Thomas Eyre, PhD, the study’s lead author and geoscience research associate.

These slow-slip events may be more widespread than previously recognized, and an important way of releasing built up stress within the Earth in a manner that has minimal impact at the surface.

���������Dr. David Eaton, PhD, professor in the ,��“Since ground motion from slow-slip earthquakes occurs over a longer time span, improved understanding of this process could have profound implications for future risk analysis.”

Collaborators on the study include representatives from Natural Resources Canada, the Geological Survey of Canada, the University of Victoria, along with Sun Yat-sen University and the Southern Marine Science and Engineering Guangdong Labroratory in China. This work was funded in part by the Canada First Research Excellence Fund, through its support of the program at the ����ɫ��.