Abrahamson & Silva (2008)

Description: 

This Attenuation Relationship is one of the PEER NGA Models. The OpenSHA implementation has been verified using Ken Campbell's NGA test files.

Reference: 

Abrahamson, N. A., and W. J. Silva (2008), Summary of the Abrahamson & Silva NGA Ground-Motion Relations, Earthquake Spectra, 24(1), 67-97.

Supported Intensity Measure Types (IMTs): 
SA damping (5%) at the following periods:
  • 0.01
  • 0.02
  • 0.03
  • 0.05
  • 0.075
  • 0.1
  • 0.2
  • 0.25
  • 0.3
  • 0.4
  • 0.5
  • 0.75
  • 1.0
  • 1.5
  • 2.0
  • 3.0
  • 4.0
  • 5.0
  • 7.5
  • 10.0
Required Parameters: 
Earthquake Rupture
Site
  • Vs30 (applicable range is 180 to 1500 m/sec)
  • Vs30 Type [Measured, Inferred] (only influences std. dev.)
  • Depth 1.0 km/sec (if unknown, value is computed; see model details below)
Propagation-Effect
Other
Parameter values are numeric unless otherwise indicated with options. If only one option is presented, the value is fixed for this attenuation relationship.
Model Details: 

Distance notes: The OpenSHA implementation of this NGA model uses the (distRup - distJB) / distRup parameter in place of DistanceJB, and (distRup - distX) / distRup in place of DistanceX. The reason is that in some applications (e.g. Attenuation Relationship Plotter), where one can plot intensity-measure levels as a function of one parameter while holding others constant, it is illogical to hold DistanceJB (or DistanceX) constant while allowing DistanceRup to vary. This modification, however, does not change how hazard is computed using this model.

Aftershock notes: The aftershock parameter is set to false when parameters are set from an Earthquake Rupture (because the latter does not yet have a flag indicating whether it is an aftershock).

Depth 1.0 km/sec notes: If unkown, the value is computed according to the equations:

exp(6.745) if Vs30 < 180 m/s
Depth (m) = exp(6.745-1.35*ln(Vs30/180)) if 180 ≤ Vs30 ≤ 500 m/s
exp(5.394-4.48*ln(Vs30/500)) if Vs30 > 500 m/s

Computed values follow the red line: