PhysOrg: Earthquakes used to be almost unheard of on the vast stretches of prairie that unfold across the U.S. Midwestern states of Texas, Kansas and Oklahoma.
But in recent years, they have become commonplace. Oklahoma recorded nearly 150 between January and the start of May. Most were too weak to cause serious damage or endanger lives. Yet they've rattled nerves and raised suspicions that the shaking might be connected to the oil and gas drilling method known as hydraulic fracturing, or fracking, especially...