New maps offer the most detailed look yet at the geologic forces controlling the locations, types, and magnitudes of earthquakes in Texas and Oklahoma.
These new “stress maps,” published in the journals Geophysical Research Letters and Bulletin of the Seismological Society of America, provide insight into the nature of the faults associated with recent temblors, many of which the injection of wastewater deep underground appears to have triggered.
“These maps help explain why injection-induced earthquakes have occurred in some areas, and provide a basis for making quantitative predictions about the potential for seismic activity resulting from fluid injection,” says coauthor Mark Zoback, professor of geophysics in Stanford University’s School of Earth, Energy & Environmental Sciences.
To create these stress maps, Zoback and his graduate students Jens-Erik Lund Snee and Richard Alt interpreted data from different parts of Texas and Oklahoma donated by oil and gas companies. “Companies routinely collect data that can be used for assessing the state of stress in the Earth as part of their normal oil and gas operations,” Lund Snee says.
When combined with information about the faults present in a given area, the scientists could assess which faults are likely to be problematic and why. In the areas where induced earthquakes have occurred in Texas and Oklahoma, the scientists show that a relatively small increase of pore pressure—the pressure of fluids within the fractures and cavities of rocks—would have been sufficient to trigger slip.
In a related paper published recently in the journal Geology, graduate student F. Rall Walsh and Zoback present a methodology for assessing which faults are susceptible for earthquake triggering and which are not.
The scientists also found that many of the recent earthquakes in Texas that have been suspected as being triggered by wastewater injection occurred on faults that—according to the new map—have orientations that are nearly ideal for producing earthquakes. Doing this kind of study in advance of planned injection activities, then, could be very helpful.
“By identifying which faults are potentially active in advance, companies and regulators can avoid problematic faults during fluid injection and prevent the induced earthquakes from happening before they do,” Zoback says.
Mark Zoback is also a senior fellow at Stanford’s Precourt Institute for Energy, an affiliate of the Stanford Woods Institute for the Environment, and the director of the Stanford Natural Gas Initiative.
Funding came from the Stanford Center for Induced and Triggered Seismicity.
Source: Stanford University