Attenuation Relationship

Abrahamson (2000) Attenuation Relationship

This Attenuation Relationship was published by Abrahamson (2000, Proc. of 6th Int. Conf. on Seismic Zonation, Palm Springs, Earthq. Eng. Res. Inst.).

Supported Intensity Measure Types (IMTs):

Peak Ground Acceleration (PGA)
Spectral Acceleration (SA) - 5% damped at the following periods: 0.0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.075, 0.09, 0.1, 0.12, 0.15, 0.17, 0.2, 0.24, 0.3, 0.36, 0.4, 0.46, 0.5, 0.6, 0.75, 0.85, 1.0, 1.5, 2.0, 3.0, 4.0, and 5.0.

Earthquake Rupture Related Parameters:

Magnitude
Fault Type (Reverse, Reverse-Oblique, or Other)

Site Related Parameters:

Site Type (Rock/Shallow-Soil or Deep Soil)

Propagation-Effect Related Parameters:

DistanceRup
On Hanging Wall? (true or false)
X (length-ratio directivity parameter)
Theta (angle between fault and ray path directivity parameter)

Other Parameters:

Component (Average Horizontal)
Standard Deviation Type (Total or Zero)
Sigma Truncation (and Sigma Truncation Level)

Model Details:

If the Earthquake Rupture related parameters are set from an Earthquake Rupture object, the Hypocenter of the latter much have been set (otherwise directivity parameters cannot be computed). This model works only for strike-slip earthquakes (even though Somerville et al. (1997) handles all types), and is implemented only for the average horizontal component. One can easily add fault normal and fault parallel components too, but the specs would have to be obtained from Norm (the necessary info is not contained in the paper). SA periods down to 0 are included even though the directivity effects are zero below 0.6 sec (PGA is not an option for this reason). See the above referenced publication for more information.