UCLA

Site response effects are accounted for in the development of risk-targeted maximum considered earthquake (MCER) ground motions in two ways: (1) as site factors incorporated within ground-motion models, as implemented in the National Seismic Hazard Model, and (2) from the use of site response analyses that model wave propagation through a geotechnical model of the project site. Site response analyses are the subject of Section 21.1 in the NEHRP Provisions and the ASCE-7 Standard. As part of a provisions update cycle concluding in Fall 2026 for the NEHRP Provisions and 2028 for ASCE-7, Section 21.1 was rewritten to permit the use of probabilistic methods for combining site response with reference site ground motions, as well as to incorporate significant improvements related to parameter selection, uncertainty evaluation, and analytical approaches. Included within the updates are procedures that allow for the use of non-ergodic (site-specific) site response, including guardrails.