- Ground-motion model is:
where PGA is in g, for horizontal PGA, rock sites and strike-slip faulting C

_{3}= 0 and C_{4}= -2.100, for M ≤ 6.5 C_{1}= -0.624, C_{2}= 1.0, C_{5}= 1.29649 and C_{6}= 0.250 and for M > 6.5, C_{1}= -1.274, C_{2}= 1.1, C_{5}= -0.48451 and C_{6}= 0.524. For reverse and thrust earthquakes multiply strike-slip prediction by 1.2. σ = 1.39 - 0.14M for M < 7.21 and σ = 0.38 for M ≥ 7.21. For horizontal PGA and deep soil C_{2}= 1.0, C_{3}= 1.70 and C_{6}= 0, for strike-slip faulting C_{1}= -2.17 and for reverse or thrust faulting C_{1}= -1.92, for M ≤ 6.5 C_{4}= 2.1863 and C_{5}= 0.32 and for M > 6.5 C_{4}= 0.3825 and C_{5}= 0.5882. σ = 1.52 - 0.16M for M ≤ 7 and σ = 0.40 for M = 7.For vertical PGA, rock sites and strike-slip faulting C

_{3}= 0 and C_{4}= -2.300, for M ≤ 6.5 C_{1}= -0.430, C_{2}= 1.0, C_{5}= 1.2726 and C_{6}= 0.228 and for M > 6.5, C_{1}= -1.080, C_{2}= 1.1, C_{5}= -0.3524 and C_{6}= 0.478. For reverse and thrust earthquakes multiply strike-slip prediction by 1.1 and for oblique faulting multiply by 1.048. σ = 0.48 for M ≥ 6.5, σ = 3.08 - 0.40M for 6 < M < 6.5 and σ = 0.68 for M ≤ 6. - Use two site categories (for horizontal motion):
- 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.

Vertical equations only for rock sites.

- Crustal earthquakes defined as those that occur on faults within upper 20 to 25km of continental crust.
- Use source mechanism: RV=reverse (26+2) ⇒ Z
_{T }= 1 and SS=strike-slip (and some normal) (89+0) ⇒ Z_{T }= 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 were including in SS category. - 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.
- Separate equations for M
_{w}< 6.5 and M_{w}≥ 6.5 to account for near-field saturation effects and for rock and deep soil sites.