- Based on Sadigh et al. (1997), see Section 2.87.
- Ground-motion model is:
where PGA is in g, for M < 6.5 C

_{4}= 1.29649 and C_{5}= 0.25 and for M ≥ 6.5 C_{4}= -0.48451 and C_{5}= 0.524. For rock sites: C_{3}= -2.100, for strike-slip mechanism and M < 6.5 C_{1}= -0.949 and C_{2}= 1.05, for strike-slip mechanism and M ≥ 6.5 C_{1}= -1.274 and C_{2}= 1.10, for reverse-slip and M < 6.5 C_{1}= 0.276 and C_{2}= 0.90 and for reverse-slip and M ≥ 6.5 C_{1}= -1.024 and C_{2}= 1.10. For soil sites: C_{3}= -1.75, for strike-slip mechanism and M < 6.5 C_{1}= -1.1100 and C_{2}= 0.875, for strike-slip mechanism and M ≥ 6.5 C_{1}= -1.3830 and C_{2}= 0.917, for reverse-slip mechanism and M < 6.5 C_{1}= -0.0895 and C_{2}= 0.750 and for reverse-slip mechanism and M ≥ 6.5 C_{1}= -1.175 and C_{2}= 0.917 (σ not given). - Use two site categories:
- 1.
- 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 records. - 2.
- 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 category. - Separate equations for M
_{w}< 6.5 and M_{w}≥ 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 structures.
- 4 foreign records (1 from Gazli and 3 from Tabas) supplement Californian records.