The 2014 Update of the United States National Seismic Hazard Maps
Abstract
The USGS is in the process of updating the U.S. National Seismic Hazard Maps for the lower 48 States that will be considered for inclusion in future building codes, risk assessments, and other public policy applications. These seismic hazard maps are based on our assessment of the best available science at the time of the update, and incorporate a broad range of scientific models and parameters. The maps were discussed in regional workshops held across the U.S., reviewed by our Steering Committee, and available on-line during a 45-day period for public comment. The USGS hazard maps depict earthquake ground-shaking exceedance levels for various probabilities over a 50-year time period and are based on calculations at several hundred thousand sites across the U.S. Inputs to the hazard maps are based on scientific estimates of the locations, magnitudes, and rates of earthquakes as well as ground motion models describing each earthquake's ground shaking. We model rates of earthquakes either on known faults or as seismicity-based background earthquakes that account for unknown faults and an incomplete fault inventory. Probabilities of ground shaking are calculated from ground motion models that estimate the likely shaking caused by an earthquake. Several new datasets and models have been developed since the 2008 update of the maps. For the Central and Eastern U.S. we implemented a new moment magnitude catalog and completeness estimates, updated the maximum magnitude distribution, updated and tested the smoothing algorithms for adaptive and fixed-radius methods, extended the fault model -including the sizes and rates of New Madrid Seismic Zone earthquakes, considered induced earthquakes, and included updated and new ground motion models along with a new weighting scheme. In the Intermountain West we implemented new smoothing algorithms, fault geometry for normal faults, Wasatch fault model, and fault slip rates based on models obtained by inverting geodetic and geologic data together. For the Pacific NW we developed new Cascadia fault rupture models that incorporate additional earthquakes in the south and implemented subduction ground motion models that fall off with distance faster than those applied in earlier models. For California we implemented the new UCERF3 model that allows for a more complete inventory of fault ruptures and is based on new deformation models, magnitude-area equations, and seismicity input parameters. For the western U.S. region, we applied several new published ground motion models for shallow crustal earthquakes that are based on a new ground motion database. The equations incorporate larger uncertainties than in previous models. Changes in the earthquake catalog and seismicity, faults, and ground motion models have caused significant hazard changes that vary by × 25% at 1 Hz and 5 Hz spectral accelerations across broad sections of the country. The changes in hazard are highly variable from region to region and ratio maps with respect to 2008 maps are available on-line at: http://earthquake.usgs.gov/hazmaps/ . These changes are currently being discussed by the building code committees. Final versions are expected in winter/spring of 2014.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.S51F..08P
- Keywords:
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- 7212 SEISMOLOGY Earthquake ground motions and engineering seismology;
- 7221 SEISMOLOGY Paleoseismology;
- 7230 SEISMOLOGY Seismicity and tectonics