The role of blind fault in soil liquefaction during strong earthquake: A case study of the 2008 Wenchuan Mw7.9 earthquake

Strong ground shaking during the 2008 Wenchuan Mw7.9 earthquake caused widespread seismic hazard phenomena, such as sand liquefaction and water ejection, in the foothills of the Longmen Mountain in southwestern China. The results of field investi-gation after the earthquake showed that the majority of liquefaction sites occurred along major alluvial fan-building rivers, where the water table was a few meters below the surface and the earthquake was characterized by widespread gravely sand liquefaction, with ~58% of liquefaction sites located 20~35km from the Beichuan fault. The authors recorded the water ejection height and the process of water ejection for the first time, and there was no clear correlation between water ejection height and peak ground acceleration, and clusters of sites with anomalously high (>2m) water ejections were located near the surface projection of the piedmont fault system. The fact that the positions of anomalously high water ejections and gravely sand liquefaction during the Wenchuan earthquake were in line with the piedmont fault system indicates that the geological structure in a sedimentary basin is likely to play a role in augmenting liquefaction intensity and shaking-related seismic hazards, and hence in similar geological and hydrological environments, researchers should consider the geological structure playing an important role in seismic hazard evaluation and earthquake resistance design of buildings in addition to the primary earthquake-producing fault.