Section 11.4.1/Mapped Acceleration Parameters (7-16 Edition)
ASCE 7-16 Section 11.4.1 covers mapped SS and S1 from 2014 USGS hazard maps, referenced by IBC 2018.
The mapped spectral response acceleration parameters SS (short period) and S1 (1-second period) must be determined from Figures 22-1 through 22-8 in ASCE 7-16. These maps provide the maximum considered earthquake spectral response acceleration (MCER) based on the 2014 USGS National Seismic Hazard Model. The parameters are then adjusted for site class effects using Fa and Fv coefficients from Tables 11.4-1 and 11.4-2 to produce the design spectral acceleration parameters SDS and SD1.
Key differences from ASCE 7-22
ASCE 7-22 uses updated seismic hazard maps based on the 2018 USGS National Seismic Hazard Model, which revised hazard estimates at many locations. The 7-22 edition also revised the site coefficients Fa and Fv, with notably different Fv values for soft soils (Site Class D and E) at high S1 values. These changes can significantly affect the seismic design category and design forces at some sites. The 7-16 edition uses the older 2014 hazard model and the original site coefficient tables.
What plan reviewers look for
Plan reviewers verify SS and S1 values against the correct edition's maps (USGS online tool with the correct dataset). They check the site class determination from the geotechnical report. They verify Fa and Fv from the correct edition's tables. They compute SDS and SD1 and verify the seismic design category assignment. Using the wrong edition's maps is a common and consequential error.