The 2008 U.S. Geological Survey (USGS) National Seismic Hazard Maps were originally released in April of 2008. In early May 2008 they were modified slightly. As of May 13, 2008, the content available for download on our website is up-to-date and the following changes are reflected in the open file report (v1.1). Please take a moment to read an important note below regarding appropriate usage of this release.
- Table 1, Item F magnitude bins updated.
- Figures 34-38. Figures now correspond to their respective figure caption.
- Figure H-1 updated to show traces of the South Whidbey Island fault and differentiation of reverse/thrust faults from oblique reverse faults used in the 2008 model.
- Table H-1 identifies oblique reverse faults in the 2008 model.
- Figure J-1 replaced.
Although it is anticipated that the new 2008 USGS hazard data will be the basis for the seismic design maps in future editions of the NEHRP Recommended Provisions, the ASCE/SEI 7 Standard, and the International Building and Residential Codes, the values on those seismic design maps are expected to be materially different from the values on the 2008 hazard maps. More specifically, it is anticipated that …
- the USGS hazard values will be amplified by factors that convert (approximately) to spectral response accelerations in the maximum direction of ground motion,
- these factored hazard values will be multiplied by “risk coefficients” that adjust for a target risk (namely 1% probability of collapse in 50 years), and
- these factored and adjusted hazard values will be capped near known active faults by so–called deterministic ground motions (like the USGS hazard values were for the design maps in current editions of the model building codes).
Thus, the 2008 USGS hazard maps should not be substituted for the model building code design maps nor should they be used with ASCE/SEI 41 or 31 for seismic rehabilitation or evaluation.
For more information, please click on the following link to a recap of the Building Seismic Safety Council (BSSC) Seismic Design Procedures Reassessment Group (SDPRG -- a.k.a., Project ‘07) Workshop .