Stress in the Earth’s crust is determined without earthquake data

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Scientists at Los Alamos National Laboratory have developed a method for determining the direction of mechanical stress in the Earth’s crust without relying on data from earthquakes or craters. This method is less expensive than current methods, can have wide application in geophysics and provide insight into continental regions that lack historical geological information.

“We have used nonlinear elastic behavior in rocks and applied a new technique to monitor the trend of maximum horizontal compressive stress in rocks in parts of Oklahoma and New Mexico,” said Andrew Delury of Los Alamos. “The direction of this maximum horizontal pressure reveals the fractures in the rock that will be active.”

North Central Oklahoma was chosen because induced seismic activity has been ongoing in the area after decades of sewage injection from oil and gas operations. This seismic activity occurs on optimally directed faults in the regional stress field. North central New Mexico was chosen to compare the results to a geological setting that extends across a continental fault separating the Colorado Plateau from a stable section of the Earth’s crust.

Scientists determined that the Earth exhibits stress-induced anisotropy of nonlinear susceptibility consistent with maximum horizontal stress in these two different geological settings. Rocks become stiffer when compressed and softer when stretched, but this effect is not immediate. The rate is faster in the direction where the ambient pressure field is more compressible. By measuring this rate in different directions, scientists can determine which direction the ambient pressure is most compressible.

The direction of geophysical pressure, or the direction of maximum horizontal pressure, is usually determined by drilling narrow and deep wells. However, well drilling is expensive and only provides a single data point.

In addition, for large areas, geophysical data is not collected because it is too expensive. This method provides an alternative.

Their approach could be essential to the oil and gas industry in an effort to avoid risks and improve production. In the case of hydrofracking, the fractures will open toward the minimum horizontal compressive stress, which scientists can now determine before any drilling.

“Estimation of the stress trend in Earth’s crust without earthquake or well data” by Andrew A. Delory, Christopher W. Johnson, Paul A. Johnson, and Gotze Böckelmann of the University of Vienna was published in September in the “Nature Communications” journal Earth and Environment.

Wastewater did not significantly change the direction of seismic stress in southern Kansas More information: Andrew A. Delorey et al, Estimation of stress direction in Earth’s crust without earthquake or well data, Earth and Environment Communications (2021). DOI: 10.1038/s43247-021-00244-1 Submitted by Los Alamos National Laboratory

Quote: Earth’s crust stress determined without earthquake data (2021, Oct 8), retrieved Oct 8, 2021 from https://phys.org/news/2021-10-stress-earth-crust-earthquake.html

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