Stress in Earth's crust determined without earthquake data

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Los Alamos National Laboratory scientists have created a method that determines the location of mechanical stress in the earth’s crust. This is without the need for drilling or earthquake data. This method is cheaper than current ones, has broad application in geophysics, and can provide insight into regions of continental continents that lack historical geologic information.

Andrew Delorey, Los Alamos: "We used the nonlinear elastic behaviour in rocks and applied new techniques to monitor the orientations of the maximum horizontal compression stress in rocks. "The orientation of the maximum horizontal compressive stresses in rocks will reveal which fractures are active."

North-central Oklahoma was chosen because of the ongoing induced seismic activity in the area after decades of oil and gas operations. The faults that are optimally aligned in the regional stress field are where seismic activity takes place. North-central New Mexico was chosen to test the results in a geologic setting that straddles a continental fault, which separates the Colorado Plateau and a stable section the earth's crust.

Scientists determined that earth has stress-induced anisotropy nonlinear susceptibility. This is the same as the maximum horizontal compressive stresses in the two geologic settings. The effect of rock compression on rocks becomes more rigid and less elastic when they are extended. However, this effect doesn't happen instantly. This rate is greater in the direction where the ambient stress field has the greatest compressive force. Scientists can measure this rate in various orientations to determine which orientation has the highest ambient stress.

Borehole drilling is a common way to determine the geophysical stress orientation or direction of maximum horizontal compressive strain. Borehole drilling can be expensive and provides only one data point.

Geophysical data is not available for large areas because it is too costly. This alternative is available.

This approach could prove to be crucial for the oil and natural gas industry, which is trying to minimize hazards and maximize production. Hydro fracking will cause fractures to open in the direction that the minimum horizontal compressive stresses is. Scientists can now establish this before drilling.

"Estimation of stress orientation in the Earth's crust" by Andrew A. Delorey and Christopher W. Johnson with Gtz Bokelmann of University of Vienna was published September in Nature's Communication Earth and Environment journal.

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More information: Andrew A. Delorey et. al. Estimation the orientation of stress within the Earth's crust, without earthquake or borehole data. Communications Earth & Environment (2021). Information from the Journal: Communications Earth & Environment - Nature Andrew A. Delorey et all, Estimation the orientation of stress within the Earth's crust, without earthquake or borehole data (2021). DOI: 10.1038/s43247-021-00244-1