With the demands of engineers and scientists, the spectral inversion method was used in present study to estimate simultaneously the site response, source parameters and S-wave attenuation (Q value) for the aftershocks of the Great 2008 Wenchuan Earthquake. In this regard, 602 recordings from 96 earthquakes associated at 28 stations were selected as a database.
After getting the inversion results, we compared the site response with the one calculated by the HVSR method and 1-D theory computation, and regressed the relationship between the site amplification and Vs20 (the average uppermost-20m shear wave velocity) for different frequency bands. In addition, the inversed site response was used to identify the soil nonlinearity during strong motion. In present study, a new distance measure called the asperity distance DAspt was proposed for reasonably characterizing the source-to-site distance in large earthquake.
Furthermore, the term of S-wave attenuation, Q factor was obtained as a frequency- dependent function, Q( f ) = 100.6f 1.1. The source parameters for each earthquake including the seismic moment (M0), corner frequency (f0), stress drop (Δσ) and source radius (r) were estimated by fitting a ω-2 model with the source spectrum from the inversion. A regression analysis yielded the valuable relationship between M0 and f0, logM0 and Ms and between Mw and Ms, respectively.