Did fracking cause Oklahoma’s largest recorded earthquake?

Scientific American : Oklahoma’s largest recorded earthquake, registering 5.6, struck on 5 November. Seismic activity in Oklahoma has increased sharply over the past three years. From 1972 to 2008, six or fewer earthquakes were reported each year, many too small for people to notice. Nearly 50 earthquakes were recorded in 2009, and 1047—103 of them strong enough to be felt—were recorded in 2010. Hydraulic fracturing, known as “fracking,” uses millions of gallons of fluid to break apart rock to release natural gas. It generates a significant amount of waste liquid that’s often disposed of by injecting it into rock formations, where it can lubricate faults and make it easier for the land to shift. Fracking is common in Oklahoma, and although it’s not unreasonable to ask if the practice is the cause of the state’s recent uptick in earthquakes, it has only been linked to small quakes thus far. The US Geological Survey is deploying about 30 additional seismographs to the epicenter of the 5 November quake to determine its origin more precisely.