Research: Sharp increase in central Oklahoma seismicity

Oklahoma has had more earthquakes over magnitude 3 in 2014 than California.

“Seismic swarms” of earthquake activity have been recorded in Oklahoma, according to just-released research led by Dr. Katie Keranen at the Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York.

Oklahoma earthquakes in areas of high-rate water disposal constitute nearly half of all central and eastern US seismicity from 2008 to 2013.

Unconventional oil and gas production provides a rapidly growing energy source; however high production states in the United States, such as Oklahoma, face sharply rising numbers of earthquakes.

In the research findings, reported in SCIENCE, Dr. Keranen writes, “Subsurface pressure data required to unequivocally link earthquakes to injection are rarely accessible. Here we use seismicity and hydrogeological models to show that distant fluid migration from high-rate disposal wells in Oklahoma is likely responsible for the largest swarm. Earthquake hypocenters occur within disposal formations and upper-basement, between 2-5 km depth.

Seismicity in the United States midcontinent surged beginning in 2008, predominantly within regions of active unconventional hydrocarbon production. In Arkansas, Texas, Ohio, and near Prague, Oklahoma, recent earthquakes have been linked to wastewater injection although alternative interpretations have been proposed, writes Dr. Keranen.

Sharp increase in Oklahoma magnitude 3+ earthquakes.

Sharp increase in Oklahoma magnitude 3+ earthquakes.

Conclusively distinguishing human-induced earthquakes based solely on seismological data remains challenging. Seismic swarms within Oklahoma dominate the recent seismicity in the central and eastern United States, contributing 45% of M3 and larger earthquakes between 2008-2013. No other state contributed more than 11%.

Our work demonstrates that a very small number of wastewater disposal wells, operating at exceedingly high volumes, create substantial anthropogenic seismic hazard, Dr. Keranen writes. Four of the highest-volume disposal wells in Oklahoma (~0.04% of wells) are capable of triggering ~20% of recent central US earthquakes in a swarm covering nearly 2000 square kilometers, as shown by our analysis of modeled pore pressure increase at relocated earthquake hypocenters. This massive Jones seismic swarm is in sharp contrast to the oft-cited aseismic behavior of the majority of active disposal wells. The area of increased pressure related to these wells continually expands, increasing the probability of encountering a larger fault and thus increasing the risk of triggering a higher-magnitude earthquake.

These results from Oklahoma, where the rate of M3+ earthquakes is now double that of California, are broadly relevant for understanding fluid-related earthquake triggering and rapid fluid transmission in the shallow crust to great distances. Our results illuminate the sharp response of faults in critical equilibrium to the strong forcing mechanism of massive subsurface fluid injection.

With growing development of unconventional reservoirs, the number of new disposal wells drilled and the volume of water disposed at individual wells have abruptly increased. The burgeoning hydrocarbon production from unconventional reservoirs has sharply changed energy and energy politics, and states from California to New York are currently debating permitting and regulation of hydraulic fracturing and wastewater disposal.

Read the story in SCIENCE.

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Earth increasingly shakes in Oklahoma

(TIME, February 18, 2014)

An unusually high number of tremors have shaken the state lately, leading some to point their fingers at the emerging hydraulic fracturing industry, though the real culprit might be a type of wastewater storage system.

No strangers to nature’s fury, Oklahomans grow up accustomed scorching heat, blizzards, wrecking-ball thunderstorms and tornadoes. What they don’t see a lot of are earthquakes, which have been rattling the Sooner State with rare frequency of late — at least 115 earthquakes of varying intensities in the first two months of 2014.

fracking_Oklahoma

The question on everyone’s mind is: why? The area has been seismically active since time immemorial but the latest swarm of earthquakes is unheard of. According to earthquake monitors EQ Charts, between 1990 and 2008 there were between 0 and 11 earthquakes of magnitude 2.0 or greater in Oklahoma every year. In 2009 there were 49. In 2010 there were 180. In 2013 there were 291, and so far in 2014 there have been 59-plus and counting. More than a dozen notable earthquakes have shaken north-central Oklahoma in the past three days.

Spent drilling water injected back into the ground for storage at high pressure, some scientists believe, may be forcing fault lines under pressure to shift. Katie Keranen, a geophysics professor at Cornell, says “the evidence is strong” that the earthquakes are caused by fracking and wastewater disposal, both of which have become more frequent amid today’s boom in oil and gas drilling.

(Click here for the full story.)

Links between wastewater injection and 5.7 earthquake

(GeoScienceWorld)

Significant earthquakes are increasingly occurring within the continental interior of the United States, including five of moment magnitude (Mw) ≥ 5.0 in 2011 alone. Concurrently, the volume of fluid injected into the subsurface related to the production of unconventional resources continues to rise.

Waste water injection well.

Waste water injection well.

Here we identify the largest earthquake potentially related to injection, an Mw 5.7 earthquake in November 2011 in Oklahoma. The earthquake was felt in at least 17 states and caused damage in the epicentral region. It occurred in a sequence, with 2 earthquakes of Mw 5.0 and a prolific sequence of aftershocks. We use the aftershocks to illuminate the faults that ruptured in the sequence, and show that the tip of the initial rupture plane is within ∼200 m of active injection wells and within ∼1 km of the surface; 30% of early aftershocks occur within the sedimentary section.

Subsurface data indicate that fluid was injected into effectively sealed compartments, and we interpret that a net fluid volume increase after 18 yr of injection lowered effective stress on reservoir-bounding faults. Significantly, this case indicates that decades-long lags between the commencement of fluid injection and the onset of induced earthquakes are possible, and modifies our common criteria for fluid-induced events. The progressive rupture of three fault planes in this sequence suggests that stress changes from the initial rupture triggered the successive earthquakes, including one larger than the first.

(Click here for the full report.)