BBC: Scientists say wastewater injection from hydraulic fracturing was linked to a magnitude-5.7 earthquake that struck the US state of Oklahoma in 2011.
Fracking, as it is known, injects water and chemicals into petroleum wells in a bid to extract trapped natural gas.
Opponents of the practice say that it risks causing seismic events and contaminating groundwater.
The study in Geology shows that "induced seismicity" can occur years after wastewater injection begins.
Most seismic events linked...