Abstract

A total of 72 free-field accelerograms recorded at rupture distances of less than 200 km during the Wenchuan earthquake were used to compare the Wenchuan earthquake ground motions with those predicted by the recent Next Generation Attenuation (NGA) ground-motion models developed using global data from shallow crustal earthquakes, but few have recordings from earthquakes with magnitudes as large as 7.9. Overall, the Wenchuan earthquake produced smaller than expected long-period (T>1 s) ground motions, but higher than expected short-period (T<0.5 s) ground motions compared with the predicted motions by the NGA models. This general trend is observed at all distances, but it is stronger at distances greater than 50 km. The scaling with VS30 from the Wenchuan earthquake is not consistent with the scaling from the NGA models: the Wenchuan data show a much stronger VS30 dependence at short spectral periods and a weaker VS30 dependence at long spectral periods. The short-period hanging wall effects on rock sites are consistent with the NGA hanging wall scaling, but the short-period ground motions on soil sites on the footwall are greater than those predicted by the NGA models.

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