“Efforts to monitor and characterize the recent increasing seismicity in central Oklahoma”

CITATION:
D. E. McNamara et al. 2015. The Leading Edge, June 2015, pp. 628-639.
ON-LINE AVAILABILITY:
ABSTRACT:
The sharp increase in seismicity over a broad region of central Oklahoma has raised concerns regarding the source of the activity and its potential hazard to local communities and energy-industry infrastructure. Efforts to monitor and characterize the earthquake sequences in central Oklahoma are reviewed. Since early 2010, numerous organizations have deployed temporary portable seismic stations in central Oklahoma to record the evolving seismicity. A multiple-event relocation method is applied to produce a catalog of central Oklahoma earthquakes from late 2009 into early 2015. Regional moment tensor (RMT) source parameters were determined for the largest and best-recorded earthquakes. Combining RMT results with relocated seismicity enabled determination of the length, depth, and style of faulting occurring on reactivated subsurface fault systems. It was found that the majority of earthquakes occur on near-vertical, optimally oriented (northeast-southwest and northwest-southeast) strike-slip faults in the shallow crystalline basement. In 2014, 17 earthquakes occurred with magnitudes of 4 or larger. It is suggested that these recently reactivated fault systems pose the greatest potential hazard to the region.

I live in central Oklahoma, so the recent increase in seismicity is very much on my mind. I experienced the magnitude 5.6 2011 Prague earthquake—it was pretty dramatic (though I’m glad to say the recently completed renovation of my house came through unscathed). Hardly a day goes by without an item in the news about quakes north of us (there is a cluster in the northeast part of Oklahoma City; Norman is a southern suburb). And, increasingly, there are stories in local media about demands on the state government to respond to the problem; quakes in the well-to-do northern suburb of Edmond prompted a heated public meeting with the state representative as well as a lawsuit against oil and gas companies, and citizens have expressed their anger at the state capitol. Our local NPR affiliate, KGOU, has done a splendid job of reporting on this topic on its StateImpact Oklahoma series—both with specific stories, as well as general background. (I learned about McNamara’s work from KGOU.)

The “induced seismicity” we are experiencing here in Oklahoma seems like a perfect metaphor for the Anthropocene. At its root the Anthropocene is a geological idea, suggesting that human beings have become, in effect, a geological force. Human beings have many obvious impacts on the world—from shaping the landscape, to driving species extinct, even to changing the climate. But earthquakes? This impact seems even more dramatic—not just a change in what happens upon the planet’s surface, but a reaching down to the depths, to the fundamental processes that shape the planet itself. This metaphor perhaps does not precisely capture the idea of the Anthropocene as a period, demarcated by a permanent trace that human activity is leaving in the rock strata that measure time. But it does seem to encapsulate the notion that human beings have assumed the role of a force of nature, able to shake the very Earth.

Metaphors aside, Oklahoma’s experience with earthquakes provides a direct example of what is involved in inhabiting the Anthropocene. Among its many meanings the term “Anthropocene” has come to refer to the grand total of externalities—the aggregate of harmful unintended consequences of the activities human beings engaged in to inhabit the world. Not least of these, of course, is burning fossil fuel; it seems somehow fitting that induced seismicity is associated with modern techniques for extracting oil and gas. (The primary culprit appears to be the injection into disposal wells of wastewater produced from oil and gas wells by fracking.) So induced seismicity is yet another externality of the energy system the developed world depends on for its mode of habitation.

And now it is something we have to live with. Though the residents of central Oklahoma, and other (but not all) places fracking is conducted, are most immediately subject to seismic hazard (next time my house might not fare so well), in fact the risk affects millions. It turns out that a crucial hub in the infrastructure that distributes oil (indeed a terminus for the Keystone pipeline) is in Cushing, Oklahoma—directly on top of a fault system that appears to have been “reactivated” by wastewater injection. A major earthquake there could damage the many storage tanks—risking an environmental catastrophe for the local community, and a massive disruption in the energy economy for the nation as a whole. This is the more telling sense in which induced seismicity encapsulates the problem of inhabiting the Anthropocene: it raises the question of how we can live in an environment transformed and made more hazardous by the activities by which we live in it.

The McNamara et al. paper, and the others in the Further Readings below, illustrate a particular type of response to what is a specific version of the question of how to inhabit the Anthropocene. That version asks how to inhabit central Oklahoma, where habitation includes the production of oil and gas. The paper by no means recommends a blanket cessation of production (with the associated wastewater injection) across the state. Rather, it illustrates a position we might call good environmental governance. Not all injection wells are associated with earthquakes—seismicity depends on the geology of the region, as well as the specific technique by which water is injected (see Weingarten et al.). Thus, a good understanding of the factors contributing to induced earthquakes can enable the state to regulate the industry appropriately—determining where injection wells should be permitted and how they should be operated. Ideally, regulation can be responsive to real-time conditions and risks. For example, McNamara et al. declare their goal of contributing “to the assessment of earthquake hazard for the short-term ‘traffic-light’ system implemented by the Oklahoma Corporation Commission” (p. 628).

This type of response does not aim to reform our mode of habitation, but rather to facilitate it by managing its externalities. But induced seismicity makes the task of accomplishing habitability where it occurs much more complicated. Earthquakes are a hazard societies must cope with; an important role of the United States Geological Survey is to assess earthquake risks across the country, in order advise planners on design standards for buildings and infrastructure. An earthquake-prone region is made more habitable if the structures people use to inhabit it are built to withstand expected shaking. The National Seismic Hazard Model (NSHM) provides that information; it “affects economic and safety decisions across the United States” (Peterson, 2). However, the 2014 NSHM does not take account of induced seismicity, and as a result underestimates the risk of earthquakes in precisely an area, central Oklahoma, where seismic activity has spiked.

The reason for not including induced seismicity in the NSHM is that “Forecasting the seismic hazard from induced earthquakes is fundamentally different from forecasting the seismic hazard for natural, tectonic earthquakes. This is because the spatio-temporal patterns of induced earthquakes are reliant on economic forces and public policy decisions regarding extraction and injection of fluids” (Petersen, 1). Induced seismicity, that is, arises from a melding of social and geological factors. But the bodies of knowledge we use to understand those factors do not lend themselves to being melded in any obvious way. With induced seismicity, the understanding needed to inform habitation and preserve habitability is thus in principle hard to attain. In this respect induced seismicity is again a fitting emblem for the Anthropocene.

FURTHER READING:
D. E. McNamara et al. 2015b. “Reactivated faulting near Cushing, Oklahoma: Increased potential for a triggered earthquake in an area of United States strategic infrastructure.” Geophysical Research Letters, 42, 8328–8332. Cushing is the location of the oil terminal that is threatened by induced seismicity.
Mark D. Petersen et al. 2015. “Incorporating Induced Seismicity in the 2014 United States National Seismic Hazard Model—Results of 2014 Workshop and Sensitivity Studies.” USGS Open-File Report 2015–1070. Petersen et al. report on a 2014 workshop aimed at measuring the earthquake risk associated with induced seismicity.
M. Weingarten et al. 2015. “High-rate injection is associated with the increase in U.S. mid-continent seismicity.” Science, Vol. 348 No. 6241, pp. 1336-1340. Weingarten et al. review the association between wastewater injection and seismicity; they show it is dependent on geological factors as well a injection technique.
KGOU maintains a list of readings on induced seismicity.
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3 thoughts on ““Efforts to monitor and characterize the recent increasing seismicity in central Oklahoma”

  1. I hate to say it but the simple answer is that it’s complicated.

    First–in my post I only spoke about the earthquake hazard. But there are other problems that have been associated with fracking/wastewater disposal . . . those might well warrant ending this practice, at least in some places. But let me focus on only on earthquakes.

    So from a climate perspective there is an argument in favor of fracking–I don’t have a reference for this claim, but I believe that one explanation for a recent decline in the US carbon footprint is the increased use of natural gas. (I am not factoring in the serious problem with methane escape–for the sake of argument let’s say that can be solved.) To the extent that fracking contributes to increasing the supply of natural gas, it seems to be worth doing–meaning it is worth doing the wastewater injection.

    But what about the induced seismicity. Here again it is complicated. For, according to Weingarten et al., around 10% of injection wells have earthquakes associated with them (see p. 1336 and fig’s 1-2 of the article in the Further Reading) . . . meaning 90% of wells do not seem to induce seismicity. The difference has to do with the geology of the areas being drilled–in particular the present of inactive fault systems which can be reactivated by the pressures created by the injected wastewater. (See Keranen et al., “Sharp increase in central Oklahoma seismicity since 2008 induced by massive wastewater injection,” Science, Vol. 345, Is. 6195, pp. 448-451, do: 10.1126/science.1255802.) So, if it turns out that the geology of a location is such that induced seismicity will not occur, it seems that injection wells are acceptable (notwithstanding the possibility of other concerns).

    What about places like central Oklahoma where the geology is liable to induced seismicity? Injecting wastewater would involve asking residents to bear an external cost, in order to gain possible benefits (e.g. lower carbon emissions), which obviously isn’t fair–so that looks like a very good reason not to use that technology. However, again there are complications. For, according the Weingarten et al. and Keranen et al. seismicity is not inevitable even when wastewater is injected. It seems to depend on the way in which injection is carried out. In particular, according to Weingarten et al. what matters is the rate at which wastewater is injected: “Our analysis shows that injection rate is the most important well operational parameter affecting the likelihood of an induced seismic event in regions and basins potentially prone to induced seismicity” (p. 1339). And Kearney et al. argue that for a swarm of earthquakes near Jones between 1995 and 2002 4 out of 89 injection wells contributed ~85% of the pressure that cause the quakes. Those four wells were high injection rate wells.

    In other words–focusing on induced seismicity alone, it appears as if injection of wastewater in and of itself is not the problem. Induced seismicity results from a complicated combination of geological factors and the technique used. Thus the logical response is to stop injecting–in certain ways in certain places. In my view this speaks to the need for strict and very thoughtful regulation.

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