Earthquakes cause an estimated annualized loss to the U.S. of several billions of dollars. To mitigate earthquake losses, it is necessary to evaluate the earthquake hazards across the country.
The seismic hazard maps address this need by integrating what scientists have learned about earthquake sources, crustal deformation, active faulting, and ground shaking. This information is translated into a form that can be used to reduce the risk from earthquakes and to improve public safety. The resulting seismic hazard maps are improved and updated on a periodic basis by incorporating new information. The USGS maps are the basis for seismic provisions in building codes and for risk models used in insurance rate structures. An integral part of this project is a database describing Quaternary faults and digital maps of those faults for the U.S. and its territories.
Earthquake hazard map showing peak ground accelerations having a 2 percent probability of being exceeded in 50 years, for a firm rock site. The map is based on the USGS models for the conterminous U.S. (2023), Hawaii (2021), and Alaska (2023). The models are based on seismicity and fault-slip rates and take into account the frequency of earthquakes of various magnitudes. Locally, the hazard may be greater than shown, because site geology may amplify ground motions.
2023 50-State Update of the NSHMThe USGS has completed and released the 2023 updated hazard model for the 50 states. The 2023 NSHM includes recently updated ground motion models for subduction-zone faults (present in the Pacific Northwest and Alaska) as part of its updated national hazard assessment. The Hawaii portion of the NSHM has already been updated to reflect, in part, a swath of new earthquakes related to volcanic eruptions that have changed the way we understand ground shaking on the Island of Hawai‘i. The 2023 update for the lower 48 states includes targeted characterizations of shaking within sedimentary basins, large geological depressions generally filled with soft sediments down to deep bedrock, where major urban areas are often centered. New studies in southern and central California, Seattle, Portland, Reno, and Las Vegas have been performed to determine if these basin regions need special treatment within the NSHM. To broaden the utility of the NSHM beyond traditional design and assessment of buildings, USGS engineers and scientists are currently exploring potential applications that assess seismic risk for other critical infrastructure systems such as gas pipelines, highway bridges, and dams. Other engineering and risk research efforts related to the NSHM include 1) developing earthquake scenarios for response planning, 2) extending the ground shaking forecast to ground failures such as soil liquefaction that can cause additional damage, and 3) studying the interactions of multiple hazards for engineering and risk assessments of infrastructure systems. |
The 2023 National Seismic Hazard Model – What's Shaking?
Earthquakes cause an estimated annualized loss to the U.S. of several billions of dollars. To mitigate earthquake losses, it is necessary to evaluate the earthquake hazards across the country.
The seismic hazard maps address this need by integrating what scientists have learned about earthquake sources, crustal deformation, active faulting, and ground shaking. This information is translated into a form that can be used to reduce the risk from earthquakes and to improve public safety. The resulting seismic hazard maps are improved and updated on a periodic basis by incorporating new information. The USGS maps are the basis for seismic provisions in building codes and for risk models used in insurance rate structures. An integral part of this project is a database describing Quaternary faults and digital maps of those faults for the U.S. and its territories.
Earthquake hazard map showing peak ground accelerations having a 2 percent probability of being exceeded in 50 years, for a firm rock site. The map is based on the USGS models for the conterminous U.S. (2023), Hawaii (2021), and Alaska (2023). The models are based on seismicity and fault-slip rates and take into account the frequency of earthquakes of various magnitudes. Locally, the hazard may be greater than shown, because site geology may amplify ground motions.
2023 50-State Update of the NSHMThe USGS has completed and released the 2023 updated hazard model for the 50 states. The 2023 NSHM includes recently updated ground motion models for subduction-zone faults (present in the Pacific Northwest and Alaska) as part of its updated national hazard assessment. The Hawaii portion of the NSHM has already been updated to reflect, in part, a swath of new earthquakes related to volcanic eruptions that have changed the way we understand ground shaking on the Island of Hawai‘i. The 2023 update for the lower 48 states includes targeted characterizations of shaking within sedimentary basins, large geological depressions generally filled with soft sediments down to deep bedrock, where major urban areas are often centered. New studies in southern and central California, Seattle, Portland, Reno, and Las Vegas have been performed to determine if these basin regions need special treatment within the NSHM. To broaden the utility of the NSHM beyond traditional design and assessment of buildings, USGS engineers and scientists are currently exploring potential applications that assess seismic risk for other critical infrastructure systems such as gas pipelines, highway bridges, and dams. Other engineering and risk research efforts related to the NSHM include 1) developing earthquake scenarios for response planning, 2) extending the ground shaking forecast to ground failures such as soil liquefaction that can cause additional damage, and 3) studying the interactions of multiple hazards for engineering and risk assessments of infrastructure systems. |