- Ground-motion model is: where Z is in g, b1 = 0.237, b2 = 0.229, b3 = 0, b5 = -1.052, b6 = 0.174, h = 7.27km and σlog Z = 0.203
(see Spudich and Boore (2005) for correct value of σ3 for use in calculating σ for randomly-orientated
- Use two site classes:
Γ = 0
- Rock: sites with soil depths of < 5m.
Γ = 1
- Use data of Spudich et al. (1999).
- Correct equations of Spudich et al. (1999) for 20% overprediction of motions for rock sites, which was
due either to underestimation of shear-wave velocities for rock sites for extensional regimes (believed to
be more likely) or an overestimation of shear-wave velocities at soil sites. Correction based on adjusting b1
and b6 to eliminate bias in rock estimates but leave soil estimates unchanged.
- Verify that adjustment reduces bias in rock estimates.
- Do not change σlog Z because changes to b1 and b6 have a negligible influence on σlog Z w.r.t. errors in
determining σlog Z.