In the months following the 7.1 magnitude earthquake in Ridgecrest, California on July 5, 2019, seismologists recorded thousands of aftershocks in the area. Surprisingly, there is no observation in the Corso geothermal field, and the area is only about 10 kilometers away from the surface rupture caused by the main shock.
Now, researchers at the California Institute of Technology have discovered that operations related to Coso’s geothermal energy production have reduced the pressure on the area for the past 30 years, making the area less prone to earthquakes. These findings can point to ways to systematically reduce pressure in high-risk earthquake areas, while also building clean energy infrastructure.

The study was conducted by Jean Philippe Avoac, Earle C. Anthony Professor of Geology, Mechanical and Civil Engineering. An article describing this research was published in the July 1 issue of Nature.
Geothermal fields, such as the Corso area, are areas with particularly high underground temperatures, for example due to volcanic or tectonic activity. This heat can be used to create clean energy without burning fossil fuels. To harness this energy, water is pumped to the ground, where it is heated to high temperatures; When the water returns to the surface, the heat is used to generate electricity.

It is important that in the process of geothermal field development, many small earthquakes (approximately magnitude 4) are triggered when water is pumped. This is often considered a matter of concern, many geothermal projects have been abandoned due to this “induced” seismic activity. However, in this new study, the researchers found that these small earthquakes and the “silent” or seismic deformation (which occurs without an earthquake) caused by the injected fluid actually reduce the pressure, thus reducing the risk of a larger earthquake. Area.
“Geothermal energy is clean energy and we want to have as much clean energy as possible,” Avouac said.

“The induced seismic activity, the triggering of many small earthquakes, was seen as an obstacle to building more infrastructure of this type during the initial development of the geothermal field. But our research shows that this is really beneficial. For example, you can imagine developing a geothermal field along the San Andreas fault, where you can get clean energy and reduce the risk of a major earthquake.

Led by Kyungjae Im, a postdoctoral fellow at the California Institute of Technology, the team is trying to simulate what is happening below the surface of a geothermal field developed for energy production. Geoscientists use a method called synthetic aperture radar (SAR) interferometry. The technology measured that the surface of the Coso geothermal field has warped and sunk tens of centimeters in the following decades.

Its development. I built a model of this deformation and determined that the underground heat contracts due to the pumping of water.
I concluded that this thermal contraction not only relieved some of the stress in the Coso area, but also caused the ground to slide “quietly”, that is, in a smooth way that does not generate earthquakes. This explains why there were no major aftershocks in the Coso area after the July 5th, 2019 earthquake-the underground pressure is less because it has been relieved by geothermal activity.

“Our research shows that by injecting cold water, seismic activity can be suppressed in the future,” Im said. “But it is still not without risk: when the oil field starts to develop, there is a risk that small induced earthquakes may turn into large earthquakes. However, in principle, over time, the risk of large earthquakes in the area is less than if you This field has not been developed. You have been accelerating seismic activity for a while, so the highest risk is temporarily higher. But if you look at the risk of level 7 or 8 for a long time, it will be much less than 15 years or so. Developing methods to accurately quantify this impact is part of our research goals.

 

It will never be zero risk, but our research shows that we should do more research on this method to reduce the probability of a major earthquake. Both the ”
” thermal stress release and the hydrofoil can release the accumulated stress, thereby reducing future major earthquakes. However, at the same time, there is still a risk of inducing a major earthquake during the stress release process, “I explained.” Coso’s case is an ideal example. In this example, the stress release is performed without triggering a major earthquake. Finished.

This may be due to the nature of thermal stress, which is slow, intense and local compared with hydrofracturing. But to confirm this, more research is needed. ” The title of this article is “Ridgecrest Replicas at Coso Suppressed by Thermal Attrition”. Kyungjae Im is the first author of the study. In addition to Im and Avouac, the other co-authors are the California Institute of Technology postdoctoral researcher Elias. Pennsylvania State University Heimisson and Derek Elsworth. Funding was provided by the National Science Foundation through the Collaborative Research Center for Geomechanics and Geological Disaster Mitigation of the University of Technology and the Southern California Seismic Center.

 

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