- Ground-motion model is:
where y is in g, C1 = -1.482, C2 = 0.264, C4 = -0.883, h = 2.473, CA = 0.117, CS = 0.101,
CN = -0.088, CR = -0.021, σ1 = 0.243 (intra-event) and σ2 = 0.060 (inter-event).
- Use four site conditions but retain three (because only three records from very soft (L) soil which combine with
soft (S) soil category):
- Rock: V s > 750m∕s, ⇒ SA = 0,SS = 0, 106 records.
- Stiff soil: 360 < V s ≤ 750m∕s, ⇒ SA = 1,SS = 0, 226 records.
- Soft soil: 180 < V s ≤ 360m∕s, ⇒ SA = 0,SS = 1, 81 records.
- Very soft soil: V s ≤ 180m∕s, ⇒ SA = 0,SS = 1, 3 records.
- Use same data as Ambraseys et al. (1996).
- Use three faulting mechanism categories:
- Strike-slip: earthquakes with rake angles (λ) -30 ≤ λ ≤ 30∘ or λ ≥ 150∘ or λ ≤ -150∘,
⇒ FN = 0,FR = 0, 47 records.
- Normal: earthquakes with -150 < λ < -30∘, ⇒ FN = 1,FR = 0, 146 records.
- Reverse: earthquakes with 30 < λ < 150∘, ⇒ FR = 1,FN = 0, 229 records.
Earthquakes classified as either strike-slip or reverse or strike-slip or normal depending on which plane is
the main plane were included in the corresponding dip-slip category. Some records (137 records, 51 normal,
10 strike-slip and 76 reverse) from earthquakes with no published focal mechanism (80 earthquakes) were
classified using the mechanism of the mainshock or regional stress characteristics.
- Try using criteria of Campbell (1997) and Sadigh et al. (1997) to classify earthquakes w.r.t. faulting
mechanism. Also try classifying ambiguously classified earthquakes as strike-slip. Find large differences in
the faulting mechanism coefficients with more stricter criteria for the rake angle of strike-slip earthquakes
leading to higher CR coefficients.
- Note that distribution of records is reasonably uniform w.r.t. to mechanism although significantly fewer
records from strike-slip earthquakes.
- Try to use two-stage maximum-likelihood method as employed by Ambraseys et al. (1996) but find
numerical instabilities in regression.
- Also rederive mechanism-independent equation of Ambraseys et al. (1996) using one-stage