2.270 Amiri et al. (2007a) & Amiri et al. (2007b)

• Ground-motion model is:

  where y is in cm∕s2, C₁ = 4.15, C₂ = 0.623, C₃ = -0.96 and σ = 0.478 for horizontal PGA, rock sites and Alborz and central Iran; C₁ = 3.46, C₂ = 0.635, C₃ = -0.996 and σ = 0.49 for vertical PGA, rock sites and Alborz and central Iran; C₁ = 3.65, C₂ = 0.678, C₂ = -0.95 and σ = 0.496 for horizontal PGA, soil sites and Alborz and central Iran; C₁ = 3.03, C₂ = 0.732, C₃ = -1.03 and σ = 0.53 for vertical PGA, soil sites and Alborz and central Iran; C₁ = 5.67, C₂ = 0.318, C₃ = -0.77, C₅ = -0.016 and σ = 0.52 for horizontal PGA, rock sites and Zagros; C₁ = 5.26, C₂ = 0.289, C₃ = -0.8, C₅ = -0.018 and σ = 0.468 for vertical PGA, rock sites and Zagros; C₁ = 5.51, C₂ = 0.55, C₃ = -1.31 and σ = 0.488 for horizontal PGA, soil sites and Zagros; and C₁ = 5.52, C₂ = 0.36, C₃ = -1.25 and σ = 0.474 for vertical PGA, soil sites and Zagros. Constrain C₄ to zero for better convergence even though σs are higher.

• Use two site categories (derive individual equations for each):

  Rock

  Roughly V _s ≥ 375m∕s.

  Soil

  Roughly V _s < 375m∕s.

• Divide Iran into two regions: Alborz and central Iran, and Zagros, based on tectonics and derive separate equations for each.
• Use S-P times to compute r_hypo for records for which it is unknown.
• Exclude data from earthquakes with M_s ≤ 4.5 to remove less accurate data and since larger earthquakes more important for seismic hazard assessment purposes.
• Most records from r_hypo > 50km.
• Exclude poor quality records.
• Instrument, baseline correct and bandpass filter records with cut-offs depending on instrument type and site class. For SSA-2 recommend: 0.15–0.2Hz and 30-33Hz for rock records and 0.07–0.2Hz and 30–33Hz for soil records. For SMA-1 recommend: 0.15–0.25Hz and 20–23Hz for rock records and 0.15–0.2Hz and 20–23Hz for soil records. Apply trial and error based on magnitude, distance and velocity time-history to select cut-off frequencies.
• Test a number of different functional forms.
• Often find a positive (non-physical) value of C₅. Therefore, remove this term. Try removing records with r_hypo > 100km but find little difference and poor convergence due to limited data.
• Do not include term for faulting mechanism because such information not available for Iranian events.