To help make the best decisions to protect communities from earthquakes, new USGS maps display how intense ground shaking could be across the nation.
The USGS recently updated its U.S. National Seismic Hazard Maps, which reflect the best and most current understanding of where future earthquakes will occur, how often they will occur, and how hard the ground will likely shake as a result.
While all states have some potential for earthquakes, 42 of the 50 states have a reasonable chance of experiencing damaging ground shaking from an earthquake in 50 years (the typical lifetime of a building). Scientists also conclude that 16 states, including Arkansas, have a relatively high likelihood of experiencing damaging ground shaking. These states have historically experienced earthquakes with a magnitude 6 or greater.
The hazard is especially high along the west coast, intermountain west, and in several active regions of the central and eastern U.S., such as near New Madrid, Missouri. The 16 states at highest risk are Alaska, Arkansas, California, Hawaii, Idaho, Illinois, Kentucky, Missouri, Montana, Nevada, Oregon, South Carolina, Tennessee, Utah, Washington, and Wyoming.
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. 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.
With an understanding of potential ground-shaking levels, various risk analyses can be calculated by considering factors like population levels, building exposure, and building construction practices. This is used for establishing building codes, and in the analysis of seismic risk for key structures. This can also help in determining insurance rates, emergency preparedness plans, and private property decisions such as re-evaluating one’s home and making it more resilient.
These maps are part of USGS contributions to the National Earthquake Hazards Reduction Program (NEHRP), which is a congressionally-established partnership of four federal agencies with the purpose of reducing risks to life and property in the U.S. that result from earthquakes. The contributing agencies are the USGS, Federal Emergency Management Agency (FEMA), National Institute of Standards and Technology, and National Science Foundation (NSF). As an example of the collaboration, the hazards identified in the USGS maps underlie FEMA-sponsored seismic design provisions that are incorporated into building codes adopted by states and localities. The maps also reflect investments in research by academic and other scientists supported by grants from the USGS and the NSF.
“The standards for seismic safety in building codes are directly based upon USGS assessments of potential ground shaking from earthquakes, and have been for years,” said Jim Harris, a member and former chair of the Provisions Update Committee of the Building Seismic Safety Council. “The committees preparing those standards welcome this updated USGS information as a basis for making decisions and continuing to ensure the most stable and secure construction.”
Some states, including Arkansas, have experienced increased seismicity in the past few years that may be associated with human activities such as the disposal of wastewater in deep wells.
One specific focus for the future is including an additional layer to these earthquake hazard maps to account for recent potentially triggered earthquakes that occur near some wastewater disposal wells. Injection-induced earthquakes are challenging to incorporate into hazard models because they may not behave like natural earthquakes and their rates change based on man-made activities.
The USGS is the only federal agency with responsibility for recording and reporting earthquake activity nationwide and providing a seismic hazard assessment. The USGS regularly updates the national seismic hazard models and maps, typically every 6 years, in sync with the building code updates. View the maps online at: http://pubs.usgs.gov/of/2014/1091/