A new map reveals which parts of the US are most at risk of earthquakes in unprecedented detail — including quakes caused by people

Jens-Erik Lund Snee and Mark D. Zoback

Scientists have mapped seismic stress across North America in unprecedented detail, revealing the areas most at risk of earthquakes.

“We see things we’ve never seen before that require geologic explanation. This will teach us new things about how the Earth works,” Mark Zoback, a Stanford geophysics professor behind the new map, said in a press release.

Zoback and his team described their mapping work in a study published Wednesday in the journal Nature Communications, calling it the first “quantitative synthesis of faulting across the entire continent.” The map and study offer detailed data about the tectonic forces at work beneath the Earth’s surface.

By incorporating nearly 2,000 “stress orientations” – measurements indicating the direction that pressure gets exerted underground in high-stress areas – as well as 300 measurements not included in previous studies, the map provides a higher-resolution picture of regional seismic activity than ever before.

To make the map, the researchers compiled new and previously published measurements from boreholes (narrow shafts drilled into the ground), then used information about past earthquakes to infer which types of faults were likely to be found in different locations.

“If you know an orientation of any fault and the state of stress nearby, you know how likely it is to fail and whether you should be concerned about it in both naturally triggered and industry-triggered earthquake scenarios,” Jens-Erik Lund Snee, a lead author of the study and postdoctoral fellow with the US Geological Survey, said in the release.

The term “Industry-triggered” earthquakes refers to seismic activity caused by humans, which is most common in parts of Oklahoma and Texas where hydraulic fracturing, or “fracking,” commonly occurs.

This method of oil and gas extraction involves injecting water deep into the Earth’s layers of rocks to force open crevices and extract the oil or gas buried inside. But it destabilizes the ground: In 2018, USGS found that Oklahoma’s earthquake threat level was roughly the same as California’s.

“The new map confirms that most of the earthquakes in Texas/Oklahoma occurred on pre-existing faults that were already ‘critically stressed,'” or those that are under intense pressure and likely to lead to faulting, Lund Snee said in an email to Business Insider. “Using this dataset, operators, regulators, and academia can identify the pre-existing structures of concern and take steps to reduce the risk of triggering earthquakes.”

While some of the researchers’ findings in the new map reaffirmed existing knowledge, they also made new discoveries about the types of earthquakes that are most likely to occur across the continent. That information could have profound implications for how regions prepare for disasters.

In the Western US, for example, the researchers observed that the direction of pressure under the Earth’s surface changed by up to 90 degrees over distances as short as 10 kilometers. That means the fluids injected into the ground in the fracking process could get pushed around in completely different ways even just a short distance from where they get injected.

“The new map may help with efforts to build seismic hazard maps because it illustrates the style of earthquakes that could occur throughout the continent, each of which produces a different kind of shaking,” Lund Snee told Business Insider.

See the full map

In the map below:

  • Black lines indicate the direction of pressure in maximum stress areas;
  • Blue areas represent extensional, or normal faulting, where the crust extends horizontally;
  • Green areas represent strike-slip faulting, where the Earth slides past itself (like the San Andreas fault);
  • Red areas represent reverse, or thrust faulting, where the Earth moves over itself.
Seismic stress map stanfordJens-Erik Lund Snee & Mark D. Zoback

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