- See Section 2.70.
- Ground-motion model is:
- Response parameter, Sv, is velocity
for 5% damping
- Develop relationships for ratio Sv∕amax because there is a much more data for PGA than spectral ordinates
and use of ratio results in relationships that are consistent over full range of magnitudes and distances.
- Calculate median spectral shapes from all records with 7.8 ≤ Mw ≤ 8.1 (choose this because abundant
data) and R < 150km and one for R > 150km. Find significant difference in spectral shape for two distance
ranges. Since interest is in near-field ground motion use smoothed R < 150km spectral shape. Plot ratios
[Sv∕amax(Mw)]∕[Sv∕amax(Mw = 8)] against magnitude. Fit equation given above, fixing C8 = 10 (for
complete saturation at Mw = 10) and C9 = 3 (average value obtained for periods > 1s). Fit C7 by a linear
function of lnT and then fix C6 to yield calculated spectral amplifications for Mw = 8.
- Calculate standard deviation using residuals of all response spectra and conclude standard deviation is
governed by equation derived for PGA.