In this paper, according to the relationship of observation spectrum with source spectrum, travel-path attenuation factor and site effect, we use the digital seismic data of moderate-small earthquakes to invert the soft rock site effect and S wave inelastic attenuation under the constraint of site effect, and determine the parameters of path and site. The parameters obtained by this method exclude the topographic effect of seismic stations, and truly reflect the seismic effect of free soft rock sites and the S wave inelastic attenuation in the studied region. The average soft rock site effect is about 1.5 times in the frequency domain of 2-4 Hz and the S wave quality factor is obtained as Qs=278f0.346, which can be directly applied to the stochastic modeling of ground motions in the studied region.
In the paper, for the application of stochastic simulation of ground motion, we put forward a method to determine ″the combined effect of amplification and attenuation″ (combined effect for short) of soft rock site by using digital seismic data of moderate and small earthquakes. Our approach aims at solving the problem of the combined effect of soft rock site, which is difficult to determine in most regions of China because fewer measures were done for S-wave velocity structure. The combined effect of soft rock site can be determined by using the approach recom- mended by us. An example is given to discuss the practical application of the method.
