"The new exposure estimate is nearly double the previous 2006 estimate, based on population growth and advances in science," said William Leith, A senior science adviser for earthquakes at the USGS.
More than 143 million Americans could be exposed to potentially damaging ground shaking caused by earthquakes
, the study concludes. Researchers looked at how populations have grown in earthquake-prone areas, and they say improvements in data collection provide a more accurate estimate than in years past.
The study looked at ground shaking, which is caused by the passage of seismic waves. This shaking causes most property damage during an earthquake and can range from weak and barely noticeable to violent or extreme, with catastrophic damage.
As you might expect, California tops the list of states most at risk
, but others may surprise you. Based on this new assessment, states in the eastern United States have a greater chance of having a damaging quake than was previously thought. A lot was learned from the magnitude-5.8 earthquake that hit Virginia in 2011
, researchers say
; the quake caused considerable damage and forced the Washington Monument to close for repairs, which were just completed in May 2014.
The New Madrid earthquake zone in the central United States has more potential for a larger quake than previous estimates suggested. The zone could have a devastating earthquake that would be felt in nearly a dozen states, researchers say, threatening large cities such as St. Louis, Memphis, Nashville and Atlanta.
The magnitude-9.0 earthquake that hit Japan in 2011
, triggering a Pacific-wide tsunami and causing a series of meltdowns at the Fukushima nuclear plant
, along with the 8.2 earthquake that hit Chile
in April 2014, have given scientists valuable data and insight into the U.S. Pacific Northwest earthquake zone. Scientists say they think that a quake with a magnitude as high as 9.3 is possible, a number previously thought to be impossible for the region.
The USGS' new assessment of California's earthquake risk was mixed. More faults were discovered, raising the earthquake threat for cities like San Jose and San Diego, while the estimated threat decreased for Santa Barbara and Oakland. Hazard probabilities increased for parts of San Francisco and Los Angeles, but they decreased in other parts of the cities, based on the new data.
"This research helps us better understand the scale of earthquake hazards," and it strengthens "the nation's ability to protect Americans," Kishor Jaiswal, a USGS engineer and lead author of the study, said in a statement.
The new USGS earthquake hazard map continues to show the highest threat levels in the western U.S. But other areas of the country, such as the central states surrounding the New Madrid fault, and Charleston, South Carolina, also show a high risk.