On 5 November an earthquake measuring 5.6 rattled Oklahoma and was felt as far away as Illinois. Until two years ago Oklahoma typically had about 50 earthquakes a year, but in 2010, 1,047 quakes shook the state. Why? In Lincoln County, where most of this past weekend's seismic incidents were centered, there are 181 injection wells, according to Matt Skinner, an official from the Oklahoma Corporation Commission, the agency which oversees oil and gas production in the state. Cause and effect? The practice of injecting water into deep rock formations causes earthquakes, both the U.S. Army and the U.S. Geological...