Inversion of strong motion data for source parametersof Wenchuan aftershocks, attenuation functionand average site effect

The average shear-wave velocity profile for shallow soil sites at a depth of 20 m is derived from the drilling data of strong motion stations in Sichuan and Gansu provinces. Combined with the profile of California and the crust model used inearthquake prediction study for Sichuan Province, the average shear-wave velocity profile is extended to 40 km. The site amplification factor for shallow soil sites is generated by using the quarter wave-length method. Then, the quality factors of different zones, the effective stress drop and kappa value at shallow soil sites are deduced from the Fourier amplitude spectra of 13 aftershocks of the Wenchuan earthquake. Due to different site effects, the strong motion data at deep soil sites show a large bias from the inverted model. According to the bias, the site amplification factor for deep soil sites is derived from revision of the site amplification factor for shallow soil sites.