[S07-1] Amplification of ground motions and GMPEs

[S07-1-01] Source parameters, path attenuation, and site effects from strong-motion recordings of the Wenchuan aftershocks (2008-2013) using nonparametric generalized inversion technique

^○Yefei Ren, Ruizhi Wen, Hongwei Wang, Dongwang Tao (Institute of Engineering Mechanics, China Earthquake Administration, Harbin, China)

S-wave amplitude spectra from 928 strong-motion recordings, which were obtained at 43 permanent and temporary strong-motion stations in 132 Ms 3.2-6.5 earthquakes occurred in the vicinity of the fault plane of the 2008 Wenchuan earthquake from May 12, 2008 to December 31, 2013, are collected for determining the source spectra, path attenuation, and site responses using a nonparametric generalized inversion technique (GIT). Some source parameters are determined by the grid-searching method. Seismic moment (M0) and corner frequency (fc) vary from 2.0*10^21 to 1.7*10^25 dyne*cm and from 0.1 to 3.1 Hz, respectively. Stress drop mainly ranges from 0.1 to 1.0 MPa, significantly lower than the globally averaged level. S-wave energy-to-moment ratio is approximately 1.32*10^-12. The source scaling properties are studied by analyzing these parameters. It shows that the moment magnitude (Mw) is universally lower than the surface-wave magnitude (Ms) or local magnitude (ML) measured by China Earthquake Network Center (CENC). M0 is proportional to fc^-3, and stress drop has no significant dependence on the size of earthquake, which implies self-similarity for earthquakes in this study. It shows that larger stress drop of aftershocks generates at the areas where smaller slip occurs in the main shock. The inverted path attenuations show that geometrical spreading in region of the Wenchuan earthquake sequence is weak and significantly depends on the frequency. The frequency-dependent S-wave quality factor (Qs) is regressed to be 143.9f^0.97 at frequencies from 0.5 to 20 Hz. The inverted site responses are compared with those given by the previous study (Ren et al. 2013), showing that both studies provide compatible results for most of stations. The site responses are obviously different at different stations of a terrain array, higher at the hilltop and lower at the hill foot, which indicates ground motion is significantly affected by the local topography.