- See Section 2.234.
- Response parameter is acceleration for 5% damping.
- Only use spectral accelerations within passband of filter (1.25fl and fh) where fl is the low cut-off
frequency and fh is the high roll-off frequency.
- Note that after 0.8s the number of records available for regression analysis starts to decrease rapidly and
that after 4s there are few records available. Only conduct regression analysis up to 2.5s because for longer
periods there are too few records to obtain stable results. Note that larger amplitude ground motions are
better represented in the set for long-periods (> 1s).
- Find that logarithmic transformation may not be justified for nine periods (0.26, 0.28 and 0.44–0.65s) by
using pure error analysis but use logarithmic transformation since it is justified for neighbouring periods.
- By using pure error analysis, find that for periods > 0.95s the null hypothesis of a magnitude-independent
standard deviation cannot be rejected so assume magnitude-independent σ. Note that could be because
magnitude-dependent standard deviations are a short-period characteristic of ground motions or because
the distribution of data w.r.t. magnitude changes at long periods due to filtering.
- Find that different coefficients are significant at different periods so try changing the functional form to
exclude insignificant coefficients and then applying regression again. Find that predicted spectra show
considerable variation between neighbouring periods therefore retained all coefficients for all periods even
when not significant.
- Note that smoothing could improve the reliability of long-period ground-motion estimates because they
were based on less data but that smoothing is not undertaken since the change of weighted to unweighted
regression at 0.95s means a simple function cannot fit both short- and long-period coefficients.