### 2.87 Geomatrix Consultants (1991), Sadigh et al. (1993) & Sadigh et al. (1997)

• Ground-motion model is:

where PGA is in g, for horizontal PGA, rock sites and strike-slip faulting C3 = 0 and C4 = -2.100, for M 6.5 C1 = -0.624, C2 = 1.0, C5 = 1.29649 and C6 = 0.250 and for M > 6.5, C1 = -1.274, C2 = 1.1, C5 = -0.48451 and C6 = 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 C2 = 1.0, C3 = 1.70 and C6 = 0, for strike-slip faulting C1 = -2.17 and for reverse or thrust faulting C1 = -1.92, for M 6.5 C4 = 2.1863 and C5 = 0.32 and for M > 6.5 C4 = 0.3825 and C5 = 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 C3 = 0 and C4 = -2.300, for M 6.5 C1 = -0.430, C2 = 1.0, C5 = 1.2726 and C6 = 0.228 and for M > 6.5, C1 = -1.080, C2 = 1.1, C5 = -0.3524 and C6 = 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 750ms 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) ZT = 1 and SS=strike-slip (and some normal) (89+0) ZT = 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 Mw < 6.5 and Mw 6.5 to account for near-field saturation effects and for rock and deep soil sites.