- Ground-motion model is:
where am is in unknown unit, Δ = , DE is epicentral distance, H is focal depth, S is
fault area and C0′ = -1.23, C1 = 0.068, C2 = -0.001 and C3 = -0.043 (σ is not given). Note that there
are typographical inconsistencies in the text, namely Sr maybe should be replaced by Sal.
- Use two site categories (based on Argentinean seismic code):
Sr = 1
- Stiff soil (IIA).
Sr = 0
- Intermediate stiff soil (IIB).
Since there is no geotechnical data available, classify sites, assuming a uniform surface layer, using the
predominant period of ground motions estimated using Fourier spectra to get an equivalent shear-wave
velocity (mainly these are between 100 and 400m∕s).
- Records from instruments located in basements or ground floors of relatively small buildings.
- Records from SMAC and SMA-1 instruments.
- Uniform digitisation and correction procedure applied to all records to reduce noise in high and low
- Calculate fault area using log S = Ms + 8.13 - 0.6667log(σΔσ∕μ) where Δσ is stress drop, σ is average
stress and μ is rigidity.
- Most magnitudes between 5.5 and 6.0.
- Most records from DE < 100km.
- Most focal depths, H ≤ 40km. One earthquake with H = 120km.
- Use weighted regression because of a correlation between magnitude and distance of 0.35. Weight each
record by ωi = (ωM + ωDH)∕2 where (note there are typographical errors in formulae in paper):
where ΔM(ni) is the width of the nith magnitude interval and Δlog DH(ni) is the width of the nith
distance interval, ncat is total number of intervals, ni the index of the interval, ne(ni,is) is the number
of records in interval ni from site classification is and ns is the number of records from site classification
is. Use two site classifications, three magnitude intervals and four epicentral distance intervals so ncat =
2 × 3 × 4 = 24.
- First do regression on log ai = C0 + C1M + C2Δ + C3 log Δ and then regress residuals, ϵi, against
C4Sr + C5Sal where Sal = 1 if site is intermediate stiff soil and Sal = 0 otherwise. Then C0′ = C0 + C5
and C4′ = C4 + C5. Similar method to that used by Ambraseys et al. (1996).