Chiou and Youngs PEER-NGA Empirical Ground Motion Model for ...

In making such adjustments, we would stress the need for the user to obtain estimates of Q
for the two regions that are based on consistent geometric spreading models. The site
response portion of the ground motion model was constructed to force all ground motions to
be the same for VS30 greater than 1130 m/s. As the rock velocity increases we expect the
shallow crustal damping (i.e. “kappa”) to decrease, resulting in increases in high frequency
motions. Data for such sites are not present in the PEER-NGA data base and this effect is
not captured in our model. The model was developed using recordings from earthquakes
with a maximum depth to top of rupture of 15 km and a maximum hypocentral depth of 19
km. The model predicts a linear increase in ln(psa) with increasing ZTOR over this range.
Application of the model in regions with very thick crust (e.g. >> 20 km) is an extrapolation
outside of the range of data used to develop the model parameters.
C&Y2006 Page 67