Cause analysis of seismic wave-induced surface ruptures: a case study of Yushu Earthquake

Revealed by field investigations on four typical surface rupture observation spots in Yushu Earthquake, the surface ruptures can be divided into the following types: the co-seismic surface ruptures and gravity-induced ruptures formed after earthquake, such as the rear edge rupture of the landslide body and the rupture of the collapsed body on the river bank etc. Most co-seismic surface ruptures are triggered by fault dislocation and thus occur in seismogenic zone, whereas some surface ruptures does not coincide with the fault formations and thus are probably caused by other factors. As the relatively weak zone of the earth crest, the faults do not play the role of transferring energy so much as dissipating energy. The energy released by seismic source rupture is transmitted in the form of seismic waves through rather heterogeneous upper crust, undergoing the complex refraction and reflection when going through the faults, fissures, rock interfaces and folded surfaces of the earth crest. Subsequently, the seismic waves are superimposed and amplified in some weak sections to the extent and they eventually breakthrough the earth surface and release energy to cause co-seismic surface rupture. The process in which the seismic waves break through the earth surface and cause seismic ruptures can be defined as the formation of seismic wave-induced surface ruptures. Since the seismic waves carry the related information of seismogenic structures, the configuration of the seismic wave-induced surface ruptures is indicative to the basic features of seismogenic structures.