Seismic map of North America reveals geologic clues, earthquake hazards

April 23, 2020

How do mountains form? What forces are needed to carve out a basin? Why does the Earth tremble and quake?

Earth scientists pursue these fundamental questions to gain a better understanding of our planet's deep past and present workings. Their discoveries also help us plan for the future by preparing us for earthquakes, determining where to drill for oil and gas, and more. Now, in a new, expanded map of the tectonic stresses acting on North America, Stanford researchers present the most comprehensive view yet of the forces at play beneath the Earth's surface.

The findings, published in Nature Communications on April 23, have implications for understanding and mitigating problems associated with induced seismicity - human-caused earthquakes - from unconventional oil and gas recovery, especially in Oklahoma, Texas and other areas targeted for energy exploration. But they also pose a whole new set of questions that the researchers hope will stimulate a wide range of modeling studies.

"Understanding the forces in the Earth's crust is fundamental science," said study co-author Mark Zoback, the Benjamin M. Page Professor of Geophysics in Stanford's School of Earth, Energy & Environmental Sciences (Stanford Earth). "In some cases, it has immediate application, in others, it may be applied decades later to practical questions that do not exist today."

First continental synthesis of data

The new research provides the first quantitative synthesis of faulting across the entire continent, as well as hundreds of measurements of compressive stress directions - the direction from which the greatest pressure occurs in the Earth's crust. The map was produced by compiling new and previously published measurements from boreholes as well as inferences about kinds or "styles" of faults based on earthquakes that have occurred in the past.

The three possible styles of faulting include extensional, or normal faulting, in which the crust extends horizontally; strike-slip faulting, in which the Earth slides past itself, like in the San Andreas fault; and reverse, or thrust, faulting in which the Earth moves over itself. Each one causes very different shaking from a hazard point of view.

"In our hazards maps right now, in most places, we don't have direct evidence of what kind of earthquake mechanisms could occur," said Jack Baker, a professor of civil and environmental engineering who was not involved with the study. "It's exciting that we have switched from this blind assumption of anything is possible to having some location-specific inferences about what types of earthquakes we might expect."

Zooming in

In addition to presenting a continent-level view of the processes governing the North American plate, the data - which incorporates nearly 2,000 stress orientations, 300 of which are new to this study - offer regional clues about the behavior of the subsurface.

"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," said lead author Jens-Erik Lund Snee, PhD '20, now a postdoctoral fellow with the United States Geological Survey (USGS) in Lakewood, Colorado. "We've detailed a few places where previously published geodynamic models agree very well with the new data, and others where the models don't agree well at all."

In the Eastern U.S., for example, the style of faulting revealed by the study is exactly the opposite of what would be expected as the surface slowly "rebounds" following the melting of the ice sheets that covered most of Canada and the northern U.S. some 20,000 years ago, according to Lund Snee. The discovery that the rebound stresses are much less than those already stored in the crust from plate tectonics will advance scientists' understanding of the earthquake potential in that area.

In the Western U.S., the researchers were surprised to see changes in stress types and orientations over short distances, with major rotations occurring over only tens of miles - a feature that current models of Earth dynamics do not reveal.

"It's just much clearer now how stress can systematically vary on the scale of a sedimentary basin in some areas," Zoback said. "We see things we've never seen before that require geologic explanation. This will teach us new things about how the Earth works."
Zoback is also a senior fellow at the Stanford Precourt Institute for Energy, co-director of the Stanford Center for Induced and Triggered Seismicity (SCITS) and director of the Stanford Natural Gas Initiative. Baker is also an affiliate at the Stanford Precourt Institute for Energy.

The study was supported by SCITS, an industrial affiliates program that studies scientific and operational issues associated with triggered and induced earthquakes.

Stanford's School of Earth, Energy & Environmental Sciences

Related Stress Articles from Brightsurf:

Stress-free gel
Researchers at The University of Tokyo studied a new mechanism of gelation using colloidal particles.

Early life stress is associated with youth-onset depression for some types of stress but not others
Examining the association between eight different types of early life stress (ELS) and youth-onset depression, a study in JAACAP, published by Elsevier, reports that individuals exposed to ELS were more likely to develop a major depressive disorder (MDD) in childhood or adolescence than individuals who had not been exposed to ELS.

Red light for stress
Researchers from the Institute of Industrial Science at The University of Tokyo have created a biphasic luminescent material that changes color when exposed to mechanical stress.

How do our cells respond to stress?
Molecular biologists reverse-engineer a complex cellular structure that is associated with neurodegenerative diseases such as ALS

How stress remodels the brain
Stress restructures the brain by halting the production of crucial ion channel proteins, according to research in mice recently published in JNeurosci.

Why stress doesn't always cause depression
Rats susceptible to anhedonia, a core symptom of depression, possess more serotonin neurons after being exposed to chronic stress, but the effect can be reversed through amygdala activation, according to new research in JNeurosci.

How plants handle stress
Plants get stressed too. Drought or too much salt disrupt their physiology.

Stress in the powerhouse of the cell
University of Freiburg researchers discover a new principle -- how cells protect themselves from mitochondrial defects.

Measuring stress around cells
Tissues and organs in the human body are shaped through forces generated by cells, that push and pull, to ''sculpt'' biological structures.

Cellular stress at the movies
For the first time, biological imaging experts have used a custom fluorescence microscope and a novel antibody tagging tool to watch living cells undergoing stress.

Read More: Stress News and Stress Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to