What's shaking? Induced seismicity

The U.S. Geological Survey (USGS) has long studied and prepared hazard maps predicting the risks of natural earthquakes. Now the USGS plans to integrate information relating to induced earthquakes and potentially induced earthquakes into its National Seismic Hazard Map. Since its last earthquake map in 2008, the USGS has identified a “remarkable” spate of earthquakes triggered by industrial activities in parts of the country. The USGS sees this increased induced seismicity to be a hazard that should be analyzed. In assessing the risk, the scientists need to determine whether the activity causing the earthquakes is likely to end quickly or whether the shaking is likely to become a “normal” event.

Some recent earthquakes have occurred in areas where there are deep disposal wells in which wastewater from oil and gas operations is injected 10,000 to 20,000 feet underground. USGS geophysicist Dr. William Ellsworth who has studied injection-induced seismic events, opines that “the mechanism responsible for inducing these events appears to be the well-understood process of weakening a preexisting fault by elevating the fluid pressure.” In Oklahoma where there are approximately 4,400 disposal wells, there were almost 3,000 earthquakes in 2013, when there were only 50 in the previous 30 years. In south-central Kansas, where there are over 5,000 injection wells, there was a series of earthquakes in the fall of 2013, culminating in a 3.8 earthquake in December. In the area surrounding Azle, Texas, where there are a number of disposal wells, from November 1, 2013 through the end of the year, there were approximately 30 earthquakes.

The citizens of Azle met with a representative of the Texas Railroad Commission in early January 2014. As a result of that meeting, the Commission hired a California seismologist to study the possibility of a correlation between oil and gas activities and the earthquakes. In addition, in the Texas legislature, the House Energy Resources Committee has formed a subcommittee on seismic activity to study allegations that the quakes are linked to the injection wells. This subcommittee is to consider past studies, ongoing research, expert testimony, and input from the Commission and the University of Texas’ Bureau of Economic Geology. Currently, researchers from the USGS and Southern Methodist University have placed monitoring instruments around Azle to pinpoint the location of the seismic events.

So far, there has been no definitive link between the seismic activity in Kansas, Oklahoma, and Texas with disposal wells. A representative of the Oklahoma Corporation Commission has stated that there is not enough evidence to say that the events were caused by injection of oil and gas waste and urges everyone to keep an “open mind” regarding the cause of the earthquakes.

For additional information, see previous blogs, including “Injection wells and their possible link to seismic activity” and “House Democrats request hearing on induced seismicity.”
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