Avian Flu Diary: USGS Seismic Hazard Map Update: 75% of Americans At Risk Of Experiencing A Damaging Earthquake

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In 2006 the USGS calculated that earthquakes posed a significant risk to 75 million Americans living in 39 States. Since then, populations have changed and/or shifted, ongoing research has uncovered new seismic risks, and geologists have a better understanding of the extent of ground shaking from these quakes.

A 2015 study, published in the journal Earthquake Spectra, nearly doubled – to 143 million - the number of Americans who live or work in areas susceptible to potentially damaging ground shaking (see USGS: Nearly Half Of U.S. Population Exposed to Potentially Damaging Earthquakes).

Last week the USGS unveiled a new seismic risk map (see above), and increased the percentage of the population at risk of experiencing a damaging earthquake to nearly 75% (roughly 240 million people).

USGS scientists and our partners recently revealed the latest National Seismic Hazard Model, showing that nearly 75% of the United States could experience a damaging earthquake, emphasizing seismic hazards span a significant part of the country.

GOLDEN, Colo. – Nearly 75 percent of the U.S. could experience damaging earthquake shaking, according to a recent U.S. Geological Survey-led team of 50+ scientists and engineers.

This was one of several key findings from the latest USGS National Seismic Hazard Model (NSHM). The model was used to create a color-coded map that pinpoints where damaging earthquakes are most likely to occur based on insights from seismic studies, historical geologic data, and the latest data-collection technologies.

The congressionally requested NSHM update was created as an essential tool to help engineers and others mitigate how earthquakes affect the most vulnerable communities by showing likely earthquake locations and how much shaking they might produce. New tools and technology identified nearly 500 additional faults that could produce a damaging quake, showcasing the evolving landscape of earthquake research.

“This was a massive, multi-year collaborative effort between federal, state and local governments and the private sector,” said Mark Petersen, USGS geophysicist and lead author of the study. “The new seismic hazard model represents a touchstone achievement for enhancing public safety.”

The latest iteration, the first 50-state comprehensive assessment, was updated from previous versions published in 2018 (conterminous U.S.), 2007 (Alaska) and 1998 (Hawaii).

Noteworthy changes in the new model show the possibility of more damaging earthquakes along the central and northeastern Atlantic Coastal corridor, including in the cities of Washington D.C., Philadelphia, New York and Boston. In addition, there is a chance for greater shaking in the seismically active regions of California and Alaska. The new model also characterizes Hawai‘i as having greater potential for shaking because of observations from recent volcanic eruptions and seismic unrest on the islands.

"Earthquakes are difficult to forecast but we’ve made great strides with this new model," said Petersen. "The update includes more faults, better-characterized land surfaces, and computational advancements in modeling that provide the most detailed view ever of the earthquake risks we face."

Key findings from the updated seismic hazard model include:

Risk to People: Nearly 75% of the U.S. could experience potentially damaging earthquakes and intense ground shaking, putting hundreds of millions of people at risk.
Widespread Hazard: 37 U.S. states have experienced earthquakes exceeding magnitude 5 during the last 200 years, highlighting a long history of seismic activity across this country.
Structural Implications: The updated model will inform the future of building and structural design, offering critical insights for architects, engineers, and policymakers on how structures are planned and constructed across the U.S.
Unified Approach: This marks the first National Seismic Hazard Model to encompass all 50 states simultaneously, reflecting a massive collaborative effort with federal, state, and local partners.
Not a Prediction: No one can predict earthquakes. However, by investigating faults and past quakes, scientists can better assess the likelihood of future earthquakes and how intense their shaking might be.
To read the full findings of the scientific assessment, which was published in the journal Earthquake Spectra, please visit: https://doi.org/10.1177/87552930231215428

While most people immediately think of California and the `big one', the New Madrid Seismic Zone (NMSZ), the Pacific Northwest (Cascadia fault), coastal South Carolina, Alaska and Hawaii, and even New York City and parts of New England are at risk of seeing significant seismic activity.

Additionally, there are nearly a dozen `very high risk' volcanoes in the continental US (4 in Washington, 4 in Oregon & 3 in California), along dozens of `lesser' threats. While earthquake damage is generally localized, volcanic eruptions can affect property and populations thousands of miles away.

Over the past 100+ years the United States (excluding Alaska & Hawaii) has experienced a `seismic drought', with relatively few big quakes or volcanic eruptions. As a result, most people assume the next `big one' won't happen in their lifetimes.

In 2019 the SSA (Seismological Society of America) held their annual meeting, and a study was presented that concludes that California's recent lack of major quakes has no precedent in the past 1000 years.

California, they announced, has been in an earthquake drought for the past 100 years. One, that the SSA warns, is unlikely to continue. In a news release they wrote:

They agree that the next 100 years of California earthquakes along these faults could be a busy one. “If our work is correct,” Scharer and Biasi note, the next century isn’t going to be like the last one, but could more like the century that ended in 1918.”

All reasons why I blog on the importance of earthquake preparedness every September for National Preparedness month (see #Natlprep: You Don't Have To Live In A High-Risk Seismic Zone To Need An Earthquake Plan).

For more on earthquake preparedness, both here in the United States, and around the world, you may wish to revisit: