Williams says the chances for a larger earthquake in Oklahoma have significantly increased. He points out, however, that this concern is based on the behavior of natural earthquakes. No one can yet confirm that the same relationship between small and large earthquakes takes place during anthropogenic, or man-induced, seismic events. While not all agree, Williams and a growing number of other scientists believe the underlying cause of the state’s recent M3+ seismic events is indeed of anthropogenic origin.
“I do believe that wastewater disposal in injection wells is contributing to the cause of some of the earthquakes,” Williams says. “Some of the earthquakes also could be natural tectonic events. However, a number of peer-reviewed research papers on the Oklahoma earthquakes published in the last three years support the conclusion that wastewater disposal is part of the problem. One of these publications showed how the increased rate of M3+ quakes does not appear to be related to natural causes when looking back at the rate of Oklahoma earthquakes prior to 2009. Human-induced earthquakes are not a new phenomenon; we’ve known for decades that injecting or withdrawing fluids from deep underground can cause earthquakes.”[pullquote]At this point in time, the evidence points to a human origin for the remarkable rise in earthquake activity in Oklahoma. I am not aware of a viable alternative hypothesis.”[/pullquote]
One of those studies linking injection wells to Oklahoma’s increase in earthquakes was published last year in the journal Science by Dr. William Ellsworth, senior research geophysicist at the Earthquake Science Center of the U.S. Geological Survey in Menlo Park, Calif. Ellsworth, a Tulsa native, says he never once experienced an earthquake while growing up in the Sooner State.
Ellsworth explains that earthquakes occur as rocks move rapidly along a fault line. Certain stresses, such as increasing the fluid pressure along a fault line, can overcome the fault’s natural friction, causing a slip, and subsequently an earthquake.
“Although Oklahoma is far from the actively deforming plate boundary that rims the western United States and where most U.S. earthquakes occur, stresses are high and faults are close to the breaking point everywhere on Earth,” Ellsworth says. “So, it may take only a small increase in the stress or a small decrease in the friction to induce an earthquake.”
Both hydraulic fracturing, or “fracking” – the injection of high-pressure fluid to increase the permeability of previously difficult-to-penetrate rock formations – and oil and gas wastewater disposal via injection deep into the earth’s crust have been proven to cause earthquakes.
Fracking typically causes very small micro-earthquakes that are rarely felt on the surface. Injection wells, however, have been the culprits in larger-scale seismic activity. While there has been debate as to whether Oklahoma’s earthquakes are the result of natural or man-made forces, more research, including Ellsworth’s findings, is substantiating the latter. Ellsworth cites, for example, a recent study of disposal wells and earthquakes in Arkansas, Colorado, Ohio, Texas and Oklahoma that indicates long-term, high-volume injection (greater than 100,000 barrels per month) into deep earth is a risk factor for inducing earthquakes.
But fracking and wastewater disposal are not new practices in Oklahoma. Indeed, some have argued that the decades-long history of such practices in the state proves they cannot be responsible for the recent, sudden onslaught of earthquakes. Others, however, say the science regarding the source is clear.
“Science doesn’t move forward by either popular opinion or consensus, but rather by formulating hypotheses that can be tested,” Ellsworth says. “A hypothesis can only be disproven. That is the scientific method. At this point in time, the evidence points to a human origin for the remarkable rise in earthquake activity in Oklahoma. I am not aware of a viable alternative hypothesis.”
Ellsworth points to the recent research regarding the 5.7 magnitude event near Prague that rattled buildings in the region and nerves around much of the state.
“The November 2011 earthquake near Prague ruptured an ancient fault that was well-oriented in the present-day stress field for slip,” he says. “Several papers have been published in scientific literature that examined potential causes of the Prague earthquake. They all concluded that wastewater injection very close to where the earthquake sequence began was sufficient to destabilize the fault and cause it to rupture in an earthquake, although there is a difference of opinion about which specific wastewater wells would have contributed most to destabilizing the fault. They also note that there were no significant earthquakes anywhere in the vicinity until after high-volume wastewater [injection].”
Regardless of the potential causes and the controversy surrounding them, one thing is certain: Oklahomans are on edge about their state’s newfound status as a tectonic hotspot. Damage from such events as the 2011 Prague earthquake have Oklahomans flocking to buy earthquake insurance for their properties.
“Adequate insurance coverage can give Oklahoma families a great peace of mind,” says Oklahoma State Insurance Commissioner John Doak. “We encourage homeowners to consider adding earthquake insurance to their policy, as it is not included in a standard policy.”
Doak says that typically, an Oklahoma homeowner may pay between $1,000 and $1,500 per year for earthquake insurance. The deductibles for such insurance, however, can run high – sometimes between $5,000 and $10,000 or more – and the fine print is legion. For example, Doak says that separate deductibles may apply for individual structures, such as garages or fences or for personal items. In addition, earthquake insurance does not cover damage to land, such as sinkholes, or vehicle damages. Each company is different; Doak urges Oklahomans to obtain thorough details from their insurance brokers.
Insurance only goes so far in allaying fears, say some Oklahoma citizens.
“It feels scary that Oklahoma has become so seismically active lately,” says Sara, a Norman resident. “I don’t know anyone here who feels adequately prepared or sure of what to do when they happen. So far, everyone’s collective response seems to be to freeze where they are and wait until it’s over. It’s always a surprise, and since I have not grown up with the threat of earthquakes, I have no instinctive response like I do with a tornado.”