More than 4,000 earthquakes have struck all around the United States over the last 30 days; from New York City to Los Angeles and from Alaska to Hawaii, dozens of earthquakes strike all around the country. While this shaking is going on, USGS has released an updated seismic hazard map showing what recent earthquake activity has proved: large parts of the country are vulnerable to earthquake damage.
According to the new data, nearly 75% of the U.S. could face potentially damaging earthquakes and intense ground shaking over the next 100 years.
The U.S. National Seismic Hazard Model (NSHM) was updated in 2023 for all 50 states using new science on seismicity, fault ruptures, ground motions, and probabilistic techniques to produce a standard of practice for public policy and other engineering applications. The new model data, just released, reflects substantial changes because the new model considers more data and updated earthquake rupture forecasts and ground-motion components.
“In developing the 2023 model, we tried to apply best available or applicable science based on advice of co-authors, more than 50 reviewers, and hundreds of hazard scientists and end-users, who attended public workshops and provided technical inputs,” project authors wrote. “The hazard assessment incorporates new catalogs, declustering algorithms, gridded seismicity models, magnitude-scaling equations, fault-based structural and deformation models, multi-fault earthquake rupture forecast models, semi-empirical and simulation-based ground-motion models, and site amplification models conditioned on shear-wave velocities of the upper 30 m of soil and deeper sedimentary basin structures.”
A recent joint study led by the US Geological Survey (USGS) and Federal Emergency Management Agency (FEMA) forecasted direct average economic losses of $14.7 billion per year from ground-shaking–related damage to buildings across the United States. “The USGS National Seismic Hazard Model (NSHM) forms the underlying ground-shaking hazard layer applied in this risk assessment and is made by developing the nation’s fault and fold deformation databases, interpreting crustal and volcanic seismicity, and evaluating the probabilistic ground-shaking levels for various earthquake sizes, distances, tectonic regimes, and site conditions,” the program authors wrote in their introduction of the new model data. They added, “The projected rates of earthquakes and economic risk in some urban areas pose a threat to citizens and infrastructure.”
The USGS has continued to develop the NSHM over the past 50 years and revises these models regularly to reflect newly published earthquake science on earthquake hazards for areas they cover. Recent updates have been made for the continental U.S., Hawaii, Alaska, Puerto Rico, and American Samoa.
Based on the 2023 update, there is a chance for damaging earthquakes everywhere in the US except for the Upper Mid West, Northern Great Lakes, central and southern Texas, and central and southern Florida. The greatest threat of damaging earthquakes exists on the Big Island of Hawaii, in much of central Alaska, around the New Madrid Seismic Zone (NMSZ) around Missouri, Illinois, Kentucky, Tennessee, Mississippi, and Missouri, northwestern Wyoming, southern Montana, northeastern Idaho, California, western Nevada, and western portions of Oregon and Washington.
Through work done on this 2023 update, scientists were able to identify 500 new faults in the U.S. that could be a source for a damaging earthquake.
In the last 200 years, 37 states have seen quakes exceeding a magnitude 5 rating, highlighting a long history of seismic activity that’s occurred around the country.
While this model update doesn’t forecast a specific seismic event, USGS has recently said both California and Hawaii have high odds of seeing a damaging earthquake soon. In California, scientists say there’s a better than 99% chance that one or more major earthquakes will strike there within the next 30 years. In Hawaii, scientists say there’s a 90% chance that the islands of Hawaii and Maui will see a destructive quake in less than 100 years.