Lower 48 Maps and Data

2014

The 2014 U.S. Geological Survey (USGS) National Seismic Hazard Maps display earthquake ground motions for various probability levels across the United States and are applied in seismic provisions of building codes, insurance rate structures, risk assessments, and other public policy. The updated maps represent an assessment of the best available science in earthquake hazards and incorporate new findings on earthquake ground shaking, faults, seismicity, and geodesy. The USGS National Seismic Hazard Mapping Project developed these maps by incorporating information on potential earthquakes and associated ground shaking obtained from interaction in science and engineering workshops involving hundreds of participants, review by several science organizations and State surveys, and advice from expert panels and a Steering Committee. The new probabilistic hazard maps represent an update of the seismic hazard maps; previous versions were developed by Petersen and others (2008) and Frankel and others (2002), using the methodology developed Frankel and others (1996). Algermissen and Perkins (1976) published the first probabilistic seismic hazard map of the United States which was updated in Algermissen and others (1990).

The National Seismic Hazard Maps are derived from seismic hazard curves calculated on a grid of sites across the United States that describe the annual frequency of exceeding a set of ground motions. Data and maps from the 2014 U.S. Geological Survey National Seismic Hazard Mapping Project are available for download below. Maps for available periods (0.2 s, 1 s, PGA) and specified annual frequencies of exceedance can be calculated from the hazard curves. Figures depict probabilistic ground motions with a 2 percent probability of exceedance. Spectral accelerations are calculated for 5 percent damped linear elastic oscillators. All ground motions are calculated for site conditions with Vs30=760 m/s, corresponding to NEHRP B/C site class boundary.

Additional Information

The California portion of the 2104 NSHMP is based on the Uniform California Earthquake Rupture Forecast version 3 (UCERF3). The model was developed by Working Group on California Earthquake Probabilities (WGCEP). For more information see:

2008

The 2008 U.S. Geological Survey (USGS) National Seismic Hazard Maps display earthquake ground motions for various probability levels across the United States and are applied in seismic provisions of building codes, insurance rate structures, risk assessments, and other public policy. This update of the maps incorporates new findings on earthquake ground shaking, faults, seismicity, and geodesy. The resulting maps are derived from seismic hazard curves calculated on a grid of sites across the United States that describe the frequency of exceeding a set of ground motions. The USGS National Seismic Hazard Mapping Project developed these maps by incorporating information on potential earthquakes and associated ground shaking obtained from interaction in science and engineering workshops involving hundreds of participants, review by several science organizations and State surveys, and advice from two expert panels. The new probabilistic hazard maps represent an update of the 2002 seismic hazard maps developed by Frankel and others (2002), which used the methodology developed for the 1996 version of the maps (Frankel and others, 1996). Algermissen and Perkins (1976) published the first probabilistic seismic hazard map of the United States which was updated in Algermissen and others (1990). The national seismic maps represent our assessment of the “best available science” in earthquake hazards estimation for the United States.

Additional Information

2002

Following the release of the 2002 United States hazard maps and data, two subsequent updates were released. The first in April of 2003 and the second in October of 2003. Descriptions of each release can be found below. What is currently made available on our web site reflects the updated data and image files.

Additional Information

1996

In this release of hazard maps we present numerous maps and data with varying parameters. The computations for these maps and data used 50 year return periods on firm rock at 760 m/sec. All of the maps were prepared by combining hazard derived from spatially- smoothed historic seismicity with hazard from fault-specific sources. For more information please read our full documentation. Although these maps have been used by the U.S. Geological Survey, no warranty, expressed or implied is made by the USGS as to the accuracy of the maps and related material nor shall the fact of distribution constitute any such warranty, and no responsibility is assumed by the USGS in connection therewith.

Additional Information