OK

A new study currently in press at Geology strongly suggests a link between the November 5, 2011 earthquake near Oklahoma City and a process well known and used all over the world by the oil and gas industry (and others) involving wastewater injection.

Now, I wrote about this quake shortly after it happened. Highly skeptical of claims that the quake was the oil and gas industry's fault, I laid it all out.

I still am, but this is very compelling. Very compelling, and perhaps should force some regulatory changes in states where wastewater injection is ongoing (so far, only Ohio has tightened things up.)

oh, and our FishOutOfWater totally nailed this. Mad props, man.

The Abstract:

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. 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.
Follow me and we'll talk a little bit about it.

The study, by Katie M. Keranen, Heather M. Savage, Geoffrey A. Abers, and Elizabeth S. Cochran is actually quite simple. Beginning in 2009, seismicity began to increase in Oklahoma. As a result a new seismograph network was deployed. This network captured the November 5th quake's foreshock and large mainshock. The quake was perhaps one of the biggest in 1,000 plus years for Oklahoma.

The newly deployed network was able to pinpoint aftershocks that otherwise would have been missed. They illuminated the region of fault rupture. All were in areas near to wastewater injection wells, and by near, I mean within distances that were practically on top of the fault system that ruptured.

Now, these wells were old. The injection was not new. They'd been used for over 20 years in some cases, to extract all the possible oil from the field through which the Wilzetta Fault (a fairly interesting structure in its own right) traversed. In previous induction earthquake sequences, the quakes began fairly soon---within months. This new study suggests that perhaps there can be a delay, perhaps as long as several decades, before seismicity begins. Also, what changed is in 2006, the pressure at which the water was forced into formations within and beneath the oilfield greatly increased. The strain induced the first quake, an Mw 5.0, which then triggered the mainshock, an Mw 5.7, which then triggered a vigorous aftershock sequence that is still ongoing.

That's a problem. And injection is still ongoing.

Like I said, this is very compelling. I have my reasons for still remaining somewhat skeptical , but they're greatly lessened now in the case of this quake. A prominent theory that areas of elevated seismicity move naturally around the stable continental interiors really has a lot of resonance with me, and these are the hypotheses I laid out when I wrote about this in 2011:

1. The earthquakes are entirely natural
2. They're induced entirely by human activity
3. They're natural, but indicative (warning) of a coming, larger and more significant quake i.e., the Wilzetta Fault (PDF), which appears to be the culprit, has turned itself on, perhaps due to stress transfer from the New Madrid quakes that occurred to its east 200 years ago.
4. Hypothesis 3, but the threat mitigated somewhat, because the strain was partially released due to hypothesis 2.
Mother Jones has a surprisingly good piece on it(I like them, but have found their science writing hit or miss.) The fluid injection industry is barely regulated, whether its for gas and oil extraction or geothermal energy creation or toxic waste storage (yes, really.) This is a problem. A big one.

Potentially induced earthquakes in Oklahoma, USA: Links between wastewater injection and the 2011 Mw 5.7 earthquake sequence is the paper's title.

Originally posted to SciTech on Thu Mar 28, 2013 at 04:38 PM PDT.

Also republished by Oklahoma Roundup and Community Spotlight.

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