- Ground-motion models are (if define site in terms of local geological site classification):
or (if define site in terms of depth of sediment):

where

_{0}= S_{0}(T) represents the coherence radius of the source and can be approximated by S_{0}~ C_{s}T∕2, C_{s}is shear-wave velocity in source region (taken to be 1km∕s), T is period, S is ‘source dimension’ approximated by S = 0.2 for M < 3 and S = -25.34 + 8.151M for 3 ≤ M ≤ 7.25 and v is component direction (v = 0 for horizontal 1 for vertical). - Use two types of site parameter:
- Local geological site classification:
- s = 0
- Sites on sediments.
- s = 1
- Intermediate sites.
- s = 2
- Sites on basement rock.

- Depth of sediments from surface to geological basement rock beneath site, h.

- Local geological site classification:
- Response parameter is pseudo-velocity for 0, 2, 5, 10 and 20% damping.
- Equations only apply in range M
_{min}≤ M ≤ M_{max}where M_{min}= -b_{1}(T)∕(2b_{6}(T)) and M_{max}= -(1 + b_{1}(T))∕(2b_{6}(T)). For M < M_{min}use M only in first term of equation and M_{min}elsewhere and for M > M_{max}using M_{max}everywhere. - Screen data to minimize possible bias in the model, which could result from uneven distribution of data among the different magnitude ranges and site conditions, or from excessive contribution to the database from several abundantly recorded earthquakes.
- Originally include a term linear in Δ, i.e. b
_{4}(T)Δ∕100, but find that b_{4}(T) is insignificant for most periods so deleted it. - Use method of Trifunac and Anderson (1977) for residuals, see Section 4.4.