Study On The Formation Mechanism Of Xiaoyudong Fault With Physical Model Test In Wenchuan Earthquake

Adopting the large physical model test with the Longmen faults zone as the researchbackground, three geomechanical models are built to discuss the evolution process and stressdistribution law of Longmen central fault，Qianshan fault and Xiaoyudong fracture, namely,(a)tectonic compression direction is perpendicular to imbricate thrust faults’ strike, there is noweak zone and buried fault located between those two faults;(b) tectonic compressiondirection is perpendicular to imbricate thrust faults’ strike, there exists a buried fault betweenthose two faults;(c) tectonic compression direction is skewed to imbricate thrust faults’ strike,there exists a buried fault between those two faults.Finally the genetic models and mechanicmechanism of Xiaoyudong fracture are deliberated and the conclusions drawn from this thesisare as follow:(1) The surface displacement and shallow crustal stress are accord to the deep stress inchange law, but all are lagging behind the deep stress.(2) The deformation of the imbricate thrusts are inclined along the upon fault zoneexcept partly inclined down of underlying fault footwall; the deep deformation is greater thanshallow surface at the same side of fault zone; The horizontal deformation is graduallydecreasing with the increase of the distance from the extrusion end, and accompanied byinstaneous jumping increase.(3) Combing displacement and crustal stress distribution law, we can summarize that thecrustal stress and displacement distribution are uniform, and there is no condition to generatenew fault in case(a);In case (b),although there appears rupture along the burid fault, but itdemonstrates only opening and closing, neither strike-slip nor thrusting; along with theimbricated faults moving in case (c),the buried fault (Xiaoyudong fracture)also occurredrupture with thrusting and levorotation.(4) The displacement observation shows that the Longmen central fault has obvioussegmentation from south west to north east, and changing from thrusting to thrusting withright-lateral component; Xiaoyudong fracture demonstrates left-lateral with thrustingcomponent; although there is slightly displacement appears around the Longmen Qianshanfault, but it also demonstrates thrusting with right-lateral component.(5) The initial rupture of Wenchuan earthquake is located in Xiaoyudong fractureintersected with the Longmen central fault, and then results in rupture along imbricated thrustfaults, meanwhile, the Xiaoyudong fracture occurs rupture and stress releasing from northwest to south east.