### 2.160 Sadigh and Egan (1998)

• 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:
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.
• 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 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 structures.
• 4 foreign records (1 from Gazli and 3 from Tabas) supplement Californian records.