Attenuation Relationship

Campbell & Bozorgnia (2008) Attenuation Relationship

This Attenuation Relationship, which is one of the so-called NGA Models, is currently described in a pre-print of a forthcoming publication in Earthquake Spectra.

Supported Intensity Measure Types (IMTs):

Peak Ground Acceleration (PGA)
Peak Ground Velocity (PGV)
Peak Ground Displacement (PGD)
Spectral Acceleration (SA) - 5% damped at the following periods: 0.01, 0.02, 0.03, 0.05, 0.075, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, 0.75, 1, 1.5, 2, 3, 4, 5, 7.5, and 10 seconds.

Independent Parameters (used to compute exceedance probabilities):

Earthquake Rupture Related Parameters:

Magnitude
Fault Type - options are Reverse (30<Rake<150), Normal (-150<Rake<-30), and Strike-Slip (all other Rakes).
Rupture Top Depth
Dip

Site Related Parameters:

Vs30 - range of applicability is 180 to 1500 m/sec.
Depth 2.5 km/sec - if null (not available), this defaults to 2 km if Vs30<2500 m/sec, and 0 otherwise.

Propagation-Effect Related Parameters:

DistanceRup
(distRup-distJB)/distRup (see discussion below under more details)

Other Parameters:

Component (Average Horizontal (GMRotI50) or Random Horizontal)
Standard Deviation Type (Total, Inter Event, Intra Event, or Zero)
Sigma Truncation (and Sigma Truncation Level)

Model Details:

We use a (distRup-distJB)/distRup parameter rather than the DistanceJB parameter. The reason is for our Attenuation Relationship Plotter, where one can plot intensity-measure levels as a function of one parameter while holding the others constant (the classic attenuation relationship curve plot). It makes no sense to hold DistanceJB constant while allowing DistanceRup to vary, whereas it makes more sense to hold (distRup-distJB)/distRup constant in this situation. Rest assured, this does not change how the calculations are done.

We honor the following stipulation on page 11 of their report: for SA periods less than 0.2 seconds: if the median is less than that for PGA, then the value for PGA is applied.

More details can be found in their documentation.