New Seismic Map of North America Reveals a Highly Stressed Continent

Scientists have compiled the most comprehensive map yet of tectonic stress magnitudes across North America, highlighting regions most vulnerable to earthquakes.

And this new map of North America reveals a continent under tremendous stress.

The map and associated study showcase the dynamic subterranean forces at play on a continental scale.

According to their authors, it’s “the first comprehensive view of the relative principal stress magnitudes throughout North America.”

The new seismic map

The new map incorporates thousands of horizontal stress orientations, revealing the directionality of high-pressure zones within the continent’s crust. This allowed them to pinpoint seismic hotspots across North America.

The new map highlights previously known earthquake risks (especially in California, New Mexico, and Texas). Rediscover the 6 most dangerous faultlines in the US here.

It also shows earthquakes linked to human activity or fracking (especially in Oklahoma and Texas).

“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,” explained Lund Snee in a press release. “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.”

How did they create the map?

To create the map, the researchers amassed over 2,000 stress orientations taken across North America, of which 300 are brand new.

These measurements were taken from boreholes — long, narrow shafts drilled into the ground for geophysical analysis.

The authors also assessed faults based on a locality’s prior earthquake history. This provided for a highly granular view of the seismic situation at local levels, but also across the entire North American continent.

How to read the map

Looking at the map, the black lines show areas of maximum horizontal stress, and the black arrows indicate the directionality of the plates.

Colors represent the style of faulting found in a particular region, in which:

• bluish areas experience normal faulting (where the crust stretches horizontally)
• greenish-yellow areas experience strike-slip faulting (vertical fractures where blocks mostly move horizontally)
• reddish areas experience reverse faulting (where fractures move atop another).

Each fault style produces its own distinctive shaking during an earthquake, highlighting another valuable aspect of this map.

“In our hazards maps right now, in most places, we don’t have direct evidence of what kind of earthquake mechanisms could occur,” said Baker, who wasn’t involved in the new 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.”

The new map clearly corroborates the major fault lines in the U.S. as highlighted in the USGS map below:

New findings

The new research has already yielded some interesting findings:

• In the western U.S. pronounced changes to stress types and orientations were seen across short distances, sometimes measured in tens of miles — a level of detail not exposed in previous maps.

• The new research shows that postglacial rebound pressures are lower than those seen in crusts along faults.

This new map has revealed things we’ve never seen before and that now require geologic explanation. This will teach us new things about how the Earth works. [Nature, Gizmodo]