- Ground-motion model is: where y is in g, α = -1.02, β = 0.249, b = -0.00255, h = 7.3 and σ = 0.26.
- Use two site categories (not all records have category):
S = 0
- Rock: sites described as granite, diorite, gneiss, chert, greywacke, limestone, sandstone or siltstone
and sites with soil material less than 4 to 5m thick overlying rock, 29 records. Indicate caution in
applying equations for M > 6.0 due to limited records.
S = 1
- Soil: sites described as alluvium, sand, gravel, clay, silt, mud, fill or glacial outwash except where soil
less than 4 to 5m thick, 96 records.
- Restrict data to western North American shallow earthquakes, depth less than 20km, with M > 5.0. Most
records from earthquakes with magnitudes less than 6.6.
- Exclude records from base of buildings three or more storeys high and from abutments of dams.
- Exclude records associated with distances which had an uncertainty greater than 5km.
- Exclude records from distances greater than or equal to the shortest distance to an instrument which did
- Six earthquakes recorded at only one station so not included in second stage regression.
- Include quadratic dependence term, γM2, but not significant at 90% level so omitted.
- Include site term, cS, but not significant so omitted.
- Examine residuals against distance for difference magnitude ranges, no obvious differences in trends are
apparent among the different magnitude classes.
- Consider a magnitude dependent h = h1 exp(h2[M - 6.0]) but reduction in variance not significant. Also
prefer magnitude independent h because requires fewer parameters.
- Examine effect of removing records from different earthquakes from data.
- Examine effect of different h on residuals and b. Note coupling between h and b.
- Note coincidence of anelastic coefficient, b, and measured Q values. Also note similarity between h and
proportions of depth of seismogenic zone in California.