Source parameters, path attenuation, and local site effects in China derived from the ground-motion spectral inversion analyses

The S-wave Fourier amplitude spectra from a total of 3232 ground-motion acceleration recordings obtained at 254 strong-motion stations during 400 earthquakes in seven regions (western Tianshan, northern Ningxia, Tianjin-Tangshan, Longmenshan fault region, northeastern Yunnan-southeastern Sichuan, northwestern Yunnan, and southeastern Yunnan) of China were selected and adopted for the spectral decomposition to separate simultaneously the path attenuation, source spectra, and site responses. The non-parametric path attenuation curves were empirically represented by the trilinear geometrical spreading model and the frequency-dependent anelastic attenuation expressed as the function of quality factor. The regional dependency of path attenuation was further discussed. The inverted source spectral were used to estimate the seismic moments, corner frequencies, and also stress drops based on the theoretical ω^-2 source model. The stress drops mainly varies in a range of 0.1-10 MPa. We discussed the dependence of stress drop both on region and on the type of fault. The spatiotemporal changes in stress drop values were further investigated to reveal the seismic self-similarity and seismic mechanism. The site responses at 211 stations were used to evaluate the effects of the local site conditions (e.g., V_S30, site class defined by Seismic Design Code for Buildings of China). We developed the empirical models for site responses related to either site class or V_S30. The regional-dependence of site response was also discussed in this study, and furthermore, empirical site responses for the same site class were suggested for various study regions. The comprehensive understanding on the path attenuation, source parameters, and site effects will play an important role on the reliable predictions on ground motions, especially considering their regional dependency.