Empirical model for basin effects accounts for basin depth and source location

Empirical relationships are developed to predict amplification factors for 5% damped response spectral acceleration that incorporate basin response effects. The parameters considered are depth to the 1.5 km/sec shear-wave isosurface (z (sub 1.5) ) as well as the location of the source beneath or outside the perimeter of the basin in which the site is located. Sites located in a basin overlying the source are denoted as having coincident source and site basin locations (CBL) and are differentiated from distinct source and site basin locations (DBL). Amplification factors for CBL and DBL sites are evaluated from simulated data (developed by others) and strong-motion data. Amplification factors derived from strong-motion recordings are taken as residuals of rock attenuation relations coupled with amplification factors for shallow-site conditions. Models relating amplification to z (sub 1.5) were developed separately for the CBL and DBL data groups. The results indicate that the use of basin models is generally worthwhile for periods T> or =0.75 sec. At those long periods, residuals are significantly sensitive to z (sub 1.5) for CBL but not for DBL. The standard deviation is also reduced for long periods to an extent that the standard deviations for long and short periods are similar.