- Ground-motion model is:
where a is in gal, for ML ≤ 6 b1 = 0.318 × 291.14b, b2 = 1.03, b3 = 1.14b and σ = 0.930 (in terms of
natural logarithm) and for ML > 6 b1 = 26.0 × 291.22b, b2 = 0.432, b3 = 1.22b and σ = 0.592 (in terms
of natural logarithm).
- Assumes all earthquakes have focal depth of 8km.
- Makes no distinction for site conditions in first stage where uses only earthquake records.
- Studies effects of PGA cutoff (no cutoff, 0.01, 0.02 and 0.05m∕s2), distance cutoff (no cutoff and < 150km)
and magnitude cutoff (all, ≥ 5, ≥ 6, ≥ 6, ≥ 6 and ≤ 6).
- Selects 6 as optimum magnitude cutoff but uses all data to derive equation for ML ≤ 6 because not
much difference and dispersion is slightly lower (in terms of ±1 standard deviation have 2.53 and 2.61).
- In second stage uses only records from underground nuclear explosions, consistent with natural earthquake
records, to derive site factor.
- Uses 1911 alluvium and 802 rock records and derive PGA ratio of alluvium to rock assuming their PGAs
equal at 4km.
- Finds site impedance ρV s, where ρ is density and V s is shear-wave velocity under site, is best measure of
site condition. Use 2000fps (600m∕s) as shear-wave velocity of alluvium stations.
- Multiplies equation (after taking logarithms) by b = log 10(ρV s) and normalise to 4km.
- Notes may not be a good model for other regions.