- Ground-motion model is:
where x is in cm∕s2, b1 = 3.40, b2 = 0.89, b3 = -1.17, b4 = -0.20 and σ = 0.62.
- Uses two site categories:
Y s = 0
- Rock: sedimentary or basement rock or soil less than 10m thick, 11 records.
Y s = 1
- Soil: alluvium or other soft material greater than 10m thick, 59 records.
- Uses records from basement of buildings or from ‘free-field’. Uses no more than seven records from same
earthquake and no more than nine from a single site to minimize underestimation of calculated variance.
Retains records which give a large distance and magnitude range.
- Notes that near-field ground motion governed by different physical laws than intermediate and far field
so excludes near-field data, for example El Centro (19/5/1940) and Cholame-2, from Parkfield earthquake
- Considers a distance dependent site term but not statistically significant. Also uses a magnitude dependent
site term and although it was statistically significant it did not reduce the scatter and also since largest
magnitude for a rock site is 6.5, result may be biased.