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

of Oklahoma.”

The risk of setting off earthquakes by injecting fluid underground has been known since at least the 1960s, when injection at the Rocky Mountain Arsenal near Denver was suspended after a quake estimated at magnitude 4.8 or greater struck nearby — the largest tied to wastewater disposal until the one near Prague, Oklahoma. A series of similar incidents have emerged recently. University of Memphis seismologist Stephen Horton in a study last year linked a rise in earthquakes in north-central Arkansas to nearby injection wells. University of Texas, Austin, seismologist Cliff Frohlich in a 2011 study tied earthquake swarms at the Dallas-Fort Worth Airport to a brine disposal well a third of a mile away. In Ohio, Lamont-Doherty seismologists Won-Young Kim and John Armbruster traced a series of 2011 earthquakes near Youngstown to a nearby disposal well.

That well has since been shut down, and Ohio has tightened its waste-injection rules.

Wastewater injection is not the only way that people can touch off quakes. Evidence suggests that geothermal drilling, impoundment of water behind dams, enhanced oil recovery, solution salt mining, and rock quarrying also can trigger seismic events (hydrofracking itself is not implicated in significant earthquakes; the amount of water used is usually not enough to produce substantial shaking).

The largest known earthquakes attributed to humans may be the two magnitude 7.0 events that shook the Gazli gas fields of Soviet Uzbekistan in 1976, followed by a third magnitude 7.0 quake eight years later. In a 1985 study in the Bulletin of the Seismological Society of America, Lamont-Doherty researchers David Simpson and William Leith hypothesized that the quakes were human-induced but noted that a lack of information prevented them from linking the events to gas production or other triggers. In 2009, a geothermal energy project in Basel, Switzerland, was canceled after development activities apparently led to a series of quakes of up to magnitude 3.4 that caused some $8 million in damage to surrounding properties.

In many of the wastewater injection cases documented so far, earthquakes followed within days or months of fluid injection starting. In contrast, the Oklahoma swarm happened years after injection began, similar to swarms at the Cogdell oil field in West Texas and the Fort St. John area of British Columbia.

The Wilzetta fault system remains under stress, the study’s authors say, yet regulators continue to allow injection into nearby wells. Ideally, injection should be kept away from known faults and companies should be required to provide detailed records of how much fluid they are pumping underground and at what pressure, said Keranen. The study authors also recommend sub-surface monitoring of fluid pressure for earthquake warning signs. Further research is needed but at a minimum, “there should be careful monitoring in regions where you have injection wells and protocols for stopping pumping even when small earthquakes are detected,” said Abers. In a recent op-ed in the Albany (New York) Times Union, Abers argued that New York should consider the risk of induced earthquakes from fluid injection in weighing whether to allow hydraulic fracturing to extract the state’s shale gas reserves.

— Read more in Katie M. Keranen et al., “Potentially induced earthquakes in Oklahoma, USA: Links between wastewater injection and the 2011 Mw 5.7 earthquake sequence,” Geology (26 March 2013) (doi: 10.1130/G34045.1); and Induced Seismicity Potential in Energy Technologies (National Research Council, 2012)