About a week ago, the U.S. Geologically Survey (USGS) hit send on a press release titled: "Record number of Oklahoma tremors raises possibility of damaging earthquakes." The first two paragraphs of the release detailed the recent increase in quakes in the state. As of May 2, Oklahoma had already had more earthquakes of magnitude 3.0 or greater (145) than in all of 2013 (109). In the fifth paragraph, the USGS offered a bit about why these quakes might be happening more frequently.
The analysis suggests that a likely contributing factor to the increase in earthquakes is triggering by wastewater injected into deep geologic formations. This phenomenon is known as injection-induced seismicity, which has been documented for nearly half a century, with new cases identified recently in Arkansas, Ohio, Texas, and Colorado.
In other words, this increased activity isn't naturally occurring. To be clear, the USGS isn't referring to hydraulic fracturing wells. (Fracking is a controversial process used to extract oil and gas locked in dense rock formations beneath the earth.) However, the fracking process does produce wastewater that is sometimes disposed of by injecting it back into the earth at a separate well site. We asked Robert Williams, a scientist with the USGS, to explain the difference: "There is not a one-to-one link between a single hydraulic fracturing well and a wastewater disposal well," Williams says. "Frack wells generally operate for a much shorter time than a disposal well. The disposal well can take water from many frack wells or other wastewater from other types of oil and gas production activity."
Naturally, we also began to wonder whether Colorado has experienced any increased seismic activity. Here's what Williams had to say on that topic: "Central Oklahoma is definitely more seismically active than Colorado since 2009. This despite many new wastewater disposal wells developed in the last few years in association with the hydraulic fracturing boom. Much of this new oil and gas activity is in the Denver-Julesburg Basin north and east of Denver. I'm not aware of any felt or instrumentally-detected earthquakes in this area."
He went on: "There have been earthquakes in the Raton Basin (Southern Colorado), including an August 2011 magnitude 5.3, in an area of wastewater injection west of Trinidad Colorado. The wastewater comes from the nearby coal-bed methane field.... Another area of induced seismicity occurs in Western Colorado in the Paradox Basin. The earthquakes occurring there are within several kilometers of an active brine deep injection well, and, based on their timing and location, the U.S. Bureau of Reclamation interprets them to be induced by injection operations."
Point is, Colorado hasn't seen the kind of record seismic activity that Oklahoma has. Nevertheless, this is is just one more thing to keep an eye on as oil and gas development continues to boom around the Centennial State.
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