Disaster Preparedness & Recovery

Nearly Every State Is at Risk of a Damaging Earthquake, Report Says

The updated National Seismic Hazards Maps from the U.S. Geological Survey show the most current understanding of where future earthquakes will occur.

Northridge Earthquake 1994
The Northridge earthquake struck California’s San Fernando Valley in 1994, killing 57 people, injuring another 5,000 and causing more than $20 billion in damage. FEMA News Photo
 

While no state is ruled out of the possibility of experiencing an earthquake, 42 states have a “reasonable chance” of having damaging ground shaking from an earthquake, according to recently updated information from the U.S. Geological Survey (USGS). The agency’s research also determined that 16 states — those that have experienced a magnitude 6.0 earthquake or larger — have a “relatively high likelihood” of having a damaging quake in the future.

The updated U.S. National Seismic Hazard Maps were released July 17 to reflect current understanding of where future earthquakes will occur. The data reflected what researchers have known: The earthquake hazard is highest on the West Coast, intermountain West and in regions of the Central and Eastern U.S., including near New Madrid, Mo., and Charleston, S.C. “While these overarching conclusions of the national-level hazard are similar to those of the previous maps released in 2008, details and estimates differ for many cities and states,” reported the USGS. “Several areas have been identified as being capable of having the potential for larger and more powerful earthquakes than previously thought due to more data and updated earthquake models.”

“What we’re doing is trying to forecast future shaking based on past behavior,” said Chuck Mueller, a research geophysicist with the USGS.

National+Seismic+Hazard+Maps+2014Mueller, a member of the team that makes the hazard models, said two models are created, one for the Central and Eastern U.S. and another for the Western part of the country. “The things that usually change in going from the 6-year-old model to the new model is we make new earthquake catalogs, we try and characterize earthquake potential faults with new information wherever we can,” he said. “And sometimes the biggest changes just come from new estimates of the way the ground shakes as a function of distance and magnitude away from these earthquakes.”

There are two parts to the hazard models: the source, which is the catalogs and faults, and the ground motion, the estimate of the shaking that comes from an earthquake of a given size and distance.

States at Greatest Risk

The 16 states at highest risk of experiencing damaging ground breaking from an earthquake are: Alaska, Arkansas, California, Hawaii, Idaho, Illinois, Kentucky, Missouri, Montana, Nevada, Oregon, South Carolina, Tennessee, Utah, Washington and Wyoming.

Since the previous maps were released, events — including the magnitude 5.8 earthquake in Virginia in 2011, magnitude 9.0 quake in Tohoku, Japan, in 2011, and Chile’s magnitude 8.2 event this year — have led scientists to see increased potential for larger and more damaging earthquakes in some areas like the East Coast.

“We understood that the central Virginia seismic zone was a fairly active region historically, and we had accounted for earthquakes of that size in that region,” Mueller said. “But the exciting new information that comes from an earthquake like that, a fairly rare earthquake especially in the east, is this ground shaking information, the second part of the model, because now all of a sudden whether it’s actual measurements with instruments or the 'Did You Feel It' kind of information that comes from the USGS, we have a lot more control now on the way the ground shakes for some of these earthquakes.”

Key updates to the seismic hazard maps included:

  • In New York City the maps show a lower hazard for tall buildings because scientists think there will be a lower likelihood for slow shaking, which causes more damage to tall structures when compared to fast shaking.
  • In response to an assessment of earthquakes in South Carolina, estimates of hazards near Charleston have increased.
  • New research indicated there’s a larger range of potential earthquake magnitudes and locations in the New Madrid Seismic Zone than previously thought.
  • New faults were discovered in California, leading to an increase in earthquake hazard estimates for San Diego, San Jose and Vallejo. There were also increases for parts of the San Francisco Bay Area and Los Angeles region.
  • New research shows increased estimates for the Cascadia Subduction Zone to as large as a magnitude 9.3 earthquake.

The maps are used by planners and engineers to understand potential ground shaking levels, which can aid the development of building codes and understanding the seismic risk to structures. The information also can help determine emergency preparedness plans and insurance rates.

Elaine Pittman  |  Associate Editor

Elaine Pittman is the associate editor of Emergency Management magazine. She covers topics including public safety, homeland security and lessons learned. Pittman is also the associate editor for Government Technology magazine. She can be reached via email and @elainerpittman on Twitter.

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