Earthquakes Swarm in Central Oklahoma

Earthquakes are shaking the midwestern state of Oklahoma, more than any other state in the country, even California.  Before 2009, it had about two earthquakes of magnitude 3.0 or greater annually. So far this year, the number has skyrocketed to more than 200.  As VOA’s Rosanne Skirble reports, a new study finds clues to that increase in underground wells drilled by the gas and oil industry.