Human-induced earthquakes raise seismicity risk in Oklahoma

New York Times : Oklahoma now outranks California as second in the nation in earthquake frequency, surpassed by only Alaska, according to a recent report by the US Geological Survey. The cause of the uptick is underground wastewater disposal from oil and gas production. Since 2001, those industries have experienced an economic boom, and the amount of wastewater generated has greatly increased. To get rid of it, companies reinject the wastewater into rock thousands of meters below the surface, where it increases the pressure on subterranean faults and causes them to slip. As a result, the number of earthquakes of magnitude 3 or greater in Oklahoma shot up from a historic average of fewer than two per year to 907 last year. Already this year, Oklahoma has experienced 160 quakes, three of which have been the largest in the state’s history. Although Oklahoma’s earthquake rate appears to be slowing since steep reductions in underground waste disposal were imposed earlier this year, the effects from the high volume of waste already buried are likely to be felt for many years to come.