Engineering Analysis of Strong Motion Data from Recent Earthquakes in Sichuan, China

Abstract

Recent earthquakes in the Sichuan Province have contributed to significantly expand the existing ground-motion database for China with new, high-quality ground-motion records. This study investigated the compatibility of ground-motion prediction equations (GMPEs) established by the NGA-West2 project in the US and local GMPEs for China, with respect to magnitude scaling, distance scaling, and site scaling implied by recent Chinese strong-motion data. The NGA-West2 GMPEs for shallow crustal earthquakes in tectonically active regions are considerably more sophisticated than widely used previous models, particularly in China. Using a mixed-effects procedure, the study evaluated event terms (inter-event residuals) and intra-event residuals of Chinese data relative to the NGA-West2 GMPEs. Distance scaling was investigated by examining trends of intra-event residuals with source-to-site distance. Scaling with respect to site conditions was investigated by examining trends of intra-event residuals with soil type. The study also investigated other engineering characteristics of Chinese strong ground motions. In particular, the records were analyzed for evidence of pulse-like forward-directivity effects. The elastic median response spectra of the selected stations were compared to code-mandated design spectra for various mean return periods. Results showed that international and local GMPEs can be applied for seismic hazard analysis in Sichuan with minor modification of the regression coefficients related to the source-to-site distance and soil scaling. Specifically, the Chinese data attenuated faster than implied by the considered GMPEs and the differences were statistically significant in some cases. Near-source, pulse-like ground motions were identified at two recording stations for the 2008 Wenchuan earthquake, possibly implying rupture directivity. The median recorded spectra were consistent with the code-based spectra in terms of amplitude and shape. The new ground-motion data can be used to develop advanced ground-motion models for China and worldwide and, ultimately, for advancing probabilistic seismic hazard assessment (PSHA).