EarthquakesOklahoma’s 5.7 tremor is biggest fracking-induced earthquake yet

Published 28 March 2013

Hydrofracking is used to crack open rocks to release natural gas, and for coaxing petroleum out of conventional oil wells. The process of fracking generates huge amounts of brine and chemical-laced wastewater, which are disposed of by injecting both back underground. The risk of setting off earthquakes by injecting fluid underground has been known since at least the 1960s, but the rapid expansion of fracking operations in the last decade has increased the number of fracking-induced earthquakes exponentially. The most powerful fracking-related earthquake – a 5.7 magnitude — occurred in Prague, Oklahoma, on 6 November 2011.

Damage from the 2011 deep-well-induced earthquake // Source: thegioianh.vn

A new study in the journal Geology is the latest to tie a string of unusual earthquakes, in this case, in central Oklahoma, to the injection of wastewater deep underground. Researchers now say that the magnitude 5.7 earthquake near Prague, Oklahoma, on 6 November 2011, may also be the largest ever linked to wastewater injection. Felt as far away as Milwaukee, more than 800 miles away, the quake — the biggest ever recorded in Oklahoma — destroyed fourteen homes, buckled a federal highway, and left two people injured. Small earthquakes continue to be recorded in the area.

A Columbia University release reports that the recent boom in U.S. energy production has produced massive amounts of wastewater. The water is used both in hydrofracking, which cracks open rocks to release natural gas, and in coaxing petroleum out of conventional oil wells. In both cases, the brine and chemical-laced water has to be disposed of, often by injecting it back underground elsewhere, where it has the potential to trigger earthquakes. The water linked to the Prague quakes was a byproduct of oil extraction at one set of oil wells, and was pumped into another set of depleted oil wells targeted for waste storage.

Scientists have linked a rising number of quakes in normally calm parts of Arkansas, Texas, Ohio, and Colorado to below-ground injection. In the last four years, the number of quakes in the middle of the United States jumped 11-fold from the three decades prior, the authors of the Geology study estimate. Last year, a group at the U.S. Geological Survey also attributed a remarkable rise in small- to mid-size quakes in the region to humans. The risk is serious enough that the National Academy of Sciences, in a report last year called for further research to “understand, limit and respond” to induced seismic events. Despite these studies, wastewater injection continues near the Oklahoma earthquakes.

Scientists in the Netherland have also found a connection between hydrofracking-related below-ground wastewater injection and an increase in the number of earthquakes (see “Parts of Low Country are Now Quake Country,” New York Times, 26 March 2013).

The magnitude 5.7 quake near Prague was preceded by a 5.0 shock and followed by thousands of aftershocks.

What made the swarm unusual is that wastewater had been pumped into abandoned oil wells nearby for seventeen years without incident. In the study, researchers hypothesize that as wastewater replenished