- Ground-motion model is:
where PSA is in g, α1 = 7.0887, α2 = 0.2058, α3 = 0.0589, β1 = 2.9935, β2 = -0.2287, ξ = -0.854,
γ = -0.0027 and ϕ = 0.08 (for Mw ≤ 6.75) and α1 = 9.0138, α2 = -0.0794, α3 = 0.0589, β1 = 2.9935,
β2 = -0.2287, ξ = -0.854, γ = -0.0027 and ϕ = 0.08 (for Mw > 6.75). σ = 1.18 + 0.035ln(T) - 0.06M,
where for Mw < 5 use σ for Mw5, for Mw > 7.5 use σ for Mw7.5, for T < 0.05s use σ for T = 0.05s and
for T > 3s use σ for T = 3s.
- Uses V s,30 to characterise sites. Notes that V s,30 is not being used to account for nonlinearity but only
to better fit the observations. Presents coefficients for 450 ≤ V s,30 ≤ 2000m∕s. Only 34 records from
V s,30 > 1200m∕s hence for V s,30 > 1200m∕s recommends using V s,30 = 1200m∕s.
- Uses 2 mechanisms:
- Mechanisms 0 (strike-slip) and 1 (normal, only 39 records of all data from Mw ≥ 4.5) of Flatfile.
F = 0.
- Mechanisms 2 (reverse), 3 and 4 (reverse-oblique) of Flatfile. F = 1.
- Model update of Idriss (2008) (see Section 2.296).
- Model derived within NGA West 2 project, using the project database (Ancheta et al., 2014). Data
principally from: California (74 events) with some data from Idaho (1) and Nevada (1), Taiwan (5), China
(55), Japan (5), New Zealand (2) and other countries (Canada, Mexico, Italy, Turkey and Iran) (15).
- Uses PSA(0.01s) to approximate PGA rather than true PGA.
- Selects records with Mw ≥ 4.5, all the required independent and dependent parameters and at free-field
location. Because finds a significant change in decay of PGA (and spectral values) beyond rrup =
150–175km, excludes more distant records. Next excludes events with < 3 records and multiple records
from same earthquake at arrays (e.g. Taiwan SMART).
- Examines data binned into: soft soil sites (100–211m∕s), nonlinear soil sites (211–450m∕s) and quasi-linear
sites (≥ 450m∕s). Assesses rough shear strain using PGV/V s,30 for all records and plots against PGA.
Finds that for quasi-linear sites the behaviour of sites in 1999 Chi-Chi mainshock is significantly different
than remaining records and, hence, excludes these data. Estimates thresholds for nonlinear ranges based
on modulus reduction curves for each bin. Finds that ≤ 4% of records in quasi-linear bin could be in mildly
nonlinear range. Henceforth uses only data from this bin.
- Examine total residuals w.r.t. Mw, rrup and V s,30. Finds that model fits well in range 5.2–7.9 for PGA,
5.3–7.3 for T = 0.2s and 5.2–7.5 for T = 1s.
- Does not include depth to top of rupture (ZTOR) in model because finds, based on residuals, that this
parameter does not bias results for ZTOR < 13km.
- Does not include dip angle (δ) in model because finds, based on residuals, that this parameter does not
bias results for 24 < δ ≤ 90∘.
- Does not include distance to surface projection of top of rupture Rx or rjb because not independent distance
- Examines residual plots w.r.t. depth to 1.0km∕s and 2.5km∕s shear-wave horizons. Finds little dependence
and hence does not include these parameters.
- Insufficient data (95 records) on hanging wall to examine the effect of this parameter.