Oklahoma has had nearly double the number of earthquakes as California, local news reported after five earthquakes on Thursday morning rattled an area of the state where oil and gas drilling is prevalent.
While California recorded 88 earthquakes of a magnitude 3.0 or greater this year, 174 of the same intensity have shaken Oklahoma. On Thursday, the region was hit by five quakes with magnitudes higher than 3.0 — the magnitude at which tremors can easily be felt, Oklahoma City’s KOCO news reported.
Whereas California’s quakes are spread throughout the state, seismic activity in Oklahoma is concentrated in the central and northern part of the state — areas where oil and gas drilling, otherwise known as hydraulic fracturing or fracking, has increased in recent years. In Oklahoma as a whole, drilling doubled between 2009 and 2012.
The rise in oil and gas drilling in the state has paralleled increasing earthquake activity. Previously, the state averaged about one quake per year, but that has increased to at least one a day, KOCO reported.
Seismologists have concluded that fracking — a process where water, sand and chemicals are shot underground at high pressure to release trapped oil and gas deposits — can cause small earthquakes.
At the Seismological Society of America’s annual meeting in May, scientists said that underground disposal of vast amounts of wastewater generated by fracking likely induce earthquakes by changing the state of stress on existing faults.
Researchers hypothesized that as more wastewater is sequestered underground, it could trigger larger faults tens of miles away from fracking sites.
While researchers initially believed such fracking-triggered quakes could not exceed 5.0 magnitude, the U.S. Geological Survey reported a 5.7-magnitude "human-induced" earthquake in a heavily drilled area near Prague, Oklahoma, in 2011.
Another quake stronger than magnitude 5.0 occurred in 2011 near Trinidad, Colorado, another heavily fracked area. On Tuesday, Colorado officials shut down a fracking wastewater well in Greeley after the second earthquake in less than a month was felt.
Scientists believe wastewater disposal could have a cumulative effect and that as more wastewater is shot underground, more intense earthquakes could become the norm.
The Red Cross recommended a free earthquake app after an earthquake swarm — a series of small earthquakes — hit the state. The organization cited the skyrocketing numbers of quakes since 2009.
Hundreds of Oklahomans were expected at a town hall meeting in Edmond Thursday that the Oklahoma Geological Survey, the agency that regulates the Oklahoma's 11,000 injection wells, will attend. The state government has begun reviewing scientific data, holding public discussions, and considering new regulations.
“This is all about managing risks,” said Oklahoma Corporation Commission spokesman Matt Skinner. “It’s a little more complicated than that because, of course, we’re managing perceived risks. There have been no definitive answers, but we’re not waiting for one. We have to go with what the data suggests.”