- Ground-motion model is:
where h is focal depth, y is in cm∕s2, a = 0.578, b = 0.00355, e = 0.00661, S = -0.069, SR = -0.210,
SH = -0.114, SM = 0.023, SS = 0.237 and σT = where σ = 0.213 and τ = 0.162.
- Use four site categories (most data from medium and hard soils):
Sk = SR
Sk = SH
- Hard soil
Sk = SM
- Medium soil
Sk = SS
- Soft soil
S is the mean site coefficient, i.e. when do not consider site category.
- Records interpolated in frequency domain from 0.02 to 0.005s interval and displacement time history
calculated using a fast Fourier transform (FFT) method having perpended to beginning and appended to
end at least 5s of zeros to record. Number of samples in FFT is large enough that duration used in FFT is
at least twice that of selected duration for processing window so that numerical errors are small. Bandpass
Ormsby filter used, with limits 0.2 and 24.5Hz, and displacement time history plotted. If displacement in
pre- and appended portions is large then increase lower frequency limit in filter until displacements are
small, using smoothed Fourier spectral amplitudes from 0.05 to 25Hz to make choice.
- Most earthquakes are intra-slab.
- Note lack of near-field data for all magnitudes, most data from > 100km, therefore use coefficients, c and
d, from an early study.
- Excludes data from distances greater than the distance at which an earlier study predicts PGA < 0.02m∕s2.
- Consider residuals of earthquakes in western Japan (a small subset of data) and find small difference in
anelastic coefficient and focal depth coefficient but note may be due to small number of records or because
type of source not modelled.
- Note model predicts intraslab motions well but significantly over predicts interface motions.
- Plots site correction factors (difference between individual site factor and mean factor for that category)
and find rock sites have largest variation, which suggest due to hard and soft rock included.
- Examine residual plots. Find no significant bias.