Assessment of the ground motion amplification factor at sites in mainland China

The seismic design spectrum is usually given for a reference site condition. For sites with soil conditions that differ from the reference site condition, soil amplification factors are employed to scale the seismic design spectrum. The fifth-generation Chinese seismic hazard maps (CSHM5) were provided in terms of the peak ground acceleration (PGA); the values of the soil amplification factor that depends on the value of PGA were suggested, although it is known that such a factor could depend on the natural vibration period. In the present study, we assessed the soil amplification factor by adopting the multi-level delineated seismic source model employed to develop CSHM5 and a set of newly developed ground motion prediction equations. We showed that the soil amplification factor at a site is relatively insensitive to the considered exceedance probability of the annual maximum PGA or spectral acceleration (SA) if the exceedance probability ranges from 63 % to 2 % in 50 years. However, they are significantly affected by the typical shear wave velocity value assigned to each site class, the natural vibration period, and the PGA value. We developed maps of the soil amplification factor for sites in mainland China. These developed maps by considering different site classes. The map of the soil amplification factor that is developed based on PGA could be directly used in conjunction with the design spectrum recommended in the current Chinese seismic design code. It is also suggested that the soil amplification factor that is developed based on SA be considered for future seismic design code-making.