Mechanism of rock avalanche induced by earthquake - Insight from the discontinuous numerical modeling approach

The Ms 8.0 Wenchuan earthquake occurred on 12 May, 2008 triggered over 56,000 landslides in the affected area, especially many large-scale rock avalanches distributed along the coseismic surface rupture. These rock avalanches were usually thought to be caused by the ground vibration during earthquake. Based on the evidences identified during our field investigation on many rock avalanches, it is found that rock avalanches distributed along the surface rupture may be generated by the seismogenic fault activity directly instead of ground motion. During the earthquake, rock masses of the mountain slopes fractured along the slip zone of seismogenic fault, firstly by the fault movement, which triggered rock avalanches. The ground vibration played a minor role in the causative mechanism of rock avalanches. In this paper, the Discontinuous Deformation Analysis (DDA) is adopted to verify the mechanism of rock avalanche induced by the Wenchuan earthquake. Two initial causative factors are considered in the numerical model to compare and verify the effect on the formation of rock avalanche, namely, ground motion and displacement along the seismogenic fault. According to the criterion put forward by the authors, here we show an agreement on the mechanism between the numerical results and observations during field investigation.