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Two damage-causing earthquakes have been linked to fracking operations in China's Sichuan Province.
The two earthquakes, which originated in the South Sichuan Basin, registered magnitudes of 5.7 and 5.3. Though no one was killed, 17 people were hurt. Farmhouses, barns and local infrastructure suffered $7.5 million in damages.
When scientists analyzed the seismic data, they traced the earthquakes to shallow origins, between one and six miles beneath the surface. Human activities, including oil and gas extraction, are often responsible for shallow earthquakes.
Hydraulic fracturing involves the injection of high-pressure fluids deep into rock, most commonly shale, in order to trigger the release of oil and gas trapped between the rock layers. Often, wastewater left over from the activity is treated and then injected back into the ground.
Fracking operations are plentiful in the South Sichuan Basin, home to the Changning shale gas block. Gas companies first moved into the region beginning in 2010, and, in 2014, several new wells were constructed. Since the increase in fracking activity, the region's earthquake rate has risen dramatically.
Studies have previously linked fracking with earthquakes in Oklahoma, Kansas, Ohio and Western Canada.
Fracking-caused earthquakes tend to be shallow, and they also tend to feature few aftershocks. The seismic patterns registered by the two Sichuan earthquakes showed most of the shaking occurred during the initial shock.
In a paper detailing the link between fracking and earthquake activity in Sichuan -- published this week in the journal Seismological Research Letters -- scientists claimed the injection of wastewater would increase the pressure in underground rocks enough to cause preexisting faults to slip.
Unlike other faults, which are less likely to slip in the aftermath of a sizable earthquake, the faults in Sichuan are likely to continue producing moderate earthquakes as long as wastewater injections continue.
"In my opinion, repeated moderate earthquakes can be caused as long as the injection is continuing, since a moderate earthquake releases very limited strain," Xinglin Lei, researcher at the Geological Survey of Japan, said in a news release. "The national regulations in China should be updated with the requirement for operators to take action if some signs of fault reactivation were observed."
Lei and his colleagues hope to map the faults in the South Sichuan Basin so they can predict where earthquakes are likely to happen as fracking operations continue.
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