- Ground-motion model is:
where Y is in g, for site category B: a = -2.342699, b = 1.091713, c

_{1}= 0.413033, c_{2}= 0.623255, d = -1.751631, e = 0.087940 and σ = 0.427787 and for site category C: a = -2.353903, b = 0.838847, c_{1}= 0.305134, c_{2}= 0.640249, d = -1.310188, e = -0.051707 and σ = 0.416739. - Use four site categories,
_{s}is shear-wave velocity in upper 100ft (30m):- A
- Rock:
_{s}≥ 2500fps (_{s}≥ 750m∕s), 33 records - B
- Soft rock or stiff soil: 1200 ≤
_{s}≤ 2500fps (360 ≤_{s}< 750m∕s), 88 records - C
- Medium stiff soil: 600 ≤
_{s}< 1200fps (180 ≤_{s}< 360m∕s), 101 records - D
- Soft clay:
_{s}< 600fps (_{s}< 180m∕s), 16 records

- Use two source mechanisms: reverse (R): ⇒ F = 1, 81 records and strike-slip (S) ⇒ F = 0, 157 records.
Most (77) reverse records from M
_{s}≤ 6.7. - Most (231) records from small building (up to 3 storeys in height) or from instrument shelters to reduce effect of soil-structure interaction. 6 records from 6 storey buildings and 1 record from a 4 storey building, included because lack of data in site or distance range of these records. Structures thought not to appreciably affect intermediate or long period and at large distances short period ground motion more greatly diminished than long period so less effect on predictions.
- Exclude records from Eureka-Ferndale area in N. California because may be associated with subduction source, which is a different tectonic regime than rest of data. Also excluded Mammoth Lake records because active volcanic region, atypical of rest of California.
- Include one record from Tarzana Cedar Hills although exclude a different record from this station due to possible topographic effects.
- Most records between 6 ≤ Ms ≤ 7.25 and 10 ≤ R ≤ 80km.
- Apply weighted regression separately for site category B and C. Data space split into 4 magnitude (6.0–6.25, 6.25–6.75, 6.75–7.25, 7.25+) and 5 distance intervals (≤ 10km, 10–20km, 20–40km, 40–80km, 80km+). Each recording within bin given same total weight.
- So that Y is increasing function of M and decreasing function of R for all positive M and R apply
constraints. Define g = b∕d and h = -(g + c
_{2}), then rewrite equation lnY = a + d{gM + ln[R + c_{1}exp(c_{2}M)]} + eF and apply constraints g ≤ 0, d ≤ 0, c ≥ 0, c_{2}≥ 0 and h ≥ 0. - Check plots of residuals (not shown in paper), find uniform distribution.
- Find e not significantly different than 0 and inconsistency in results between different soil classes make it difficult to attach any significance to fault type.
- Lack of records for A and D site categories. Find scale factors k
_{1}= 0.998638 and k_{2}= 1.200678 so that Y_{A}= k_{1}Y_{B}and Y_{D}= k_{2}Y_{C}, where Y_{S}is predicted ground motion for site class S. Find no obvious dependence of k_{1}or k_{2}on acceleration from examining residuals. Find k_{1}and k_{2}not significantly different than 1. - Note limited data for R < 10km, advise caution for this range.
- Note equation developed to estimate site-amplification factors not for seismic hazard analysis.