The site classifications and soil amplification factors proposed in the NEHRP Provisions for the seismic rehabilitation of buildings (FEMA, 1997) are widely used both in the United States and elsewhere.
2000) describe the derivation of the NEHRP amplification factors, which originate from a combination of empirical data (response spectral ratios of soil to rock sites from the 1989 Loma Prieta earthquake) and numerical site response analyses.
The use of site classification schemes such as the NEHRP one is well suited to regional hazard studies, since the zoning can be undertaken using a manageable level of input data and the amplification factors may be applied to the bedrock spectra using simple algorithms in database or GIS environments.
The results of the PSHA are presented in terms of uniform hazard bedrock response spectra, where bedrock was defined as NEHRP Site Class A (FEMA, 1997) or 'Hard Rock', with a shear wave velocity of 1500 m/s, in accordance with measured data from Hong Kong.
The subsoil conditions in Hong Kong have been categorized according to the NEHRP Site Classes A to E, as presented by Pappin et al.
In this case, the NEHRP system was adopted, and the uncertainty and variability related site amplification, including the deep geology, was incorporated into the site amplification factors, as described below.
Table 1 compares the seismicity, in terms of spectral accelerations, used in the NEHRP guidelines with that of Hong Kong presented by Free et al.
Rather than use the NEHRP factors, a number of 1-dimensional site response analyses have been undertaken for a range of typical soil profiles and input parameters for each site class.
Figure 1 compares the average computed site amplification factors to those presented in the NEHRP guidelines.
In many regional seismic loss estimations, site amplification is represented using the NEHRP classifications and factors.