7. Slope Motion Response and Failure Under Strong Earthquakes: Recording, Monitoring and Modeling

About 56 thousand landslides were induced by the Ms 8.0 Wenchuan earthquake on May 12, 2008. Field survey revealed that a majority of the landslides occurred in the transition parts from the middle to upper portions of deep valley slopes, on the thin ridges and especially parts of prominent terrains. Those positions have evident topographic amplification effects to seismic loading. An analysis of the spatial distribution of PGAs demonstrates that the directivity effect and the hanging wall effect in the near-fault ground motion occurred in this earthquake. Monitoring of the aftershocks has shown that the micro-relief is one of the key factors for topographic amplification and site conditions have an important effect on slope ground motion response. Large scale shaking table test was used to analyze the ground motion response of the slopes with different lithologies and structures. Both dip slopes and anti-dip slopes have significant PGA amplifications at the upper top region. Results of numerical simulation and fracture mechanics based calculation show that failure development parts of the dip slopes and anti-dip slopes are different.