- Based on Sadigh et al. (1997), see Section 2.87.
- Ground-motion model is:
where PGA is in g, for M < 6.5 C4 = 1.29649 and C5 = 0.25 and for M ≥ 6.5 C4 = -0.48451 and
C5 = 0.524. For rock sites: C3 = -2.100, for strike-slip mechanism and M < 6.5 C1 = -0.949 and
C2 = 1.05, for strike-slip mechanism and M ≥ 6.5 C1 = -1.274 and C2 = 1.10, for reverse-slip and
M < 6.5 C1 = 0.276 and C2 = 0.90 and for reverse-slip and M ≥ 6.5 C1 = -1.024 and C2 = 1.10.
For soil sites: C3 = -1.75, for strike-slip mechanism and M < 6.5 C1 = -1.1100 and C2 = 0.875,
for strike-slip mechanism and M ≥ 6.5 C1 = -1.3830 and C2 = 0.917, for reverse-slip mechanism and
M < 6.5 C1 = -0.0895 and C2 = 0.750 and for reverse-slip mechanism and M ≥ 6.5 C1 = -1.175 and
C2 = 0.917 (σ not given).
- Use two site categories:
- Rock: bedrock within about a metre of surface. Note that many such sites are soft rock with
V s ≤ 750m∕s and a strong velocity gradient because of near-surface weathering and fracturing, 274
- Deep soil: greater than 20m of soil over bedrock. Exclude data from very soft soil sites such as those
from San Francisco bay mud, 690 records.
- Define crustal earthquakes as those that occur on faults within upper 20 to 25km of continental crust.
- Consider source mechanism: RV=reverse (26+2) and SS=strike-slip (and some normal) (89+0). Classified
as RV if rake> 45∘ and SS if rake< 45∘. Find peak motions from small number of normal faulting
earthquakes not to be significantly different than peak motions from strike-slip events so include in SS
- Separate equations for Mw < 6.5 and Mw ≥ 6.5 to account for near-field saturation effects, for rock and
deep soil sites and reverse and strike-slip earthquakes.
- Records from instruments in instrument shelters near ground surface or in ground floor of small, light
- 4 foreign records (1 from Gazli and 3 from Tabas) supplement Californian records.