Ground-motion models are (if define site in terms of local geological site classification):
or (if define site in terms of depth of sediment):
S0= S0(T) represents the coherence radius of the source and can be approximated by S0~ CsT∕2, Cs 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
s = 2
Sites on basement rock.
Depth of sediments from surface to geological basement rock beneath site, h.
Response parameter is pseudo-velocity for 0, 2, 5, 10 and 20% damping.
Equations only apply in range Mmin≤ M ≤ Mmax where Mmin= -b1(T)∕(2b6(T)) and Mmax=-(1 + b1(T))∕(2b6(T)). For M < Mmin use M only in first term of equation and Mmin elsewhere and for
M > Mmax using Mmax 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. b4(T)Δ∕100, but find that b4(T) is insignificant for most periods
so deleted it.