Important Note on Use of New 2008 USGS Hazard Maps

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 …

1. the USGS hazard values will be amplified by factors that convert (approximately) to spectral response accelerations in the maximum direction of ground motion,
2. 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
3. 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 attend the upcoming Building Seismic Safety Council (BSSC) Seismic Design Procedures Reassessment Group (SDPRG -- a.k.a., Project ‘07) Workshop .