隐伏断层在强震砂土液化中的作用——以2008年汶川Mw 7.9地震为例

2008年汶川Mw7.9地震的强地面震动在龙门山前地区造成大量的砂土液化、喷砂冒水等地震灾害现象。震后野外调查发现,砂土液化点主要分布于地下水位只有几米深的山前河流的低阶地处,以大面积砾性土液化为特征,约58%的液化点位于距北川断层20~35km的范围内。对喷水高度及喷水过程进行了详细记录,喷水高度与峰值加速度并没有明显的相关性,喷水高度异常点(2m)集中于山前断裂系统近地表投影处。汶川地震中喷水高度异常、砾性土液化的位置与山前断裂系统的吻合性说明,沉积盆地内的地质构造可能在砂土液化强度和与震动相关的地震灾害方面起到促进作用,所以在类似的地质和水文环境中,除主震的断层错动外,应考虑地质构造在地震危险性评估和建筑物抗震设计中的重要作用。

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.