The Risk-Targeted Maximum Considered Earthquake (MCER) spectral response acceleration (SS and S1) values of the 2015 NEHRP Recommended Seismic Provisions, the 2016 ASCE/SEI 7 Standard, the 2017 ASCE/SEI 41 Standard, and the 2018 and 2021 editions of the International Building Code are calculated from the data in the downloadable files below, via the following equations:
SS = min[ SSUH * CRS , max( SSD84th , 1.5 ) ];
S1 = min[ S1UH * CR1 , max( S1D84th , 0.6 ) ];
where
SSUH & S1UH = uniform-hazard spectral accelerations at periods of 0.2 & 1.0 seconds, respectively;
CRS & CR1 = risk coefficients at spectral periods of 0.2 & 1.0 seconds, respectively;
SSD84th & S1D84th = 84th-percentile spectral accelerations at periods of 0.2 & 1.0 seconds, respectively.
The spectral accelerations are each for the direction of maximum horizontal response and a site shear wave velocity (VS30) of 760 m/s. For more information, see the "Related External Resources" below.
Note: The corresponding USGS Seismic Design Web Services first spatially interpolate the uniform-hazard (SSUH & S1UH), risk coefficient (CRS and CR1), and 84th-percentile (SSD84th & S1D84th) gridded values, and then combine the interpolated values via the equations above. If instead one first combines the gridded values (via the equations above) and then spatially interpolates, the resulting values will not necessarily be equal to those from the web services.
