The Influence of Thrust Fault Structure on Cross-fault Short-leveling Survey  

作　　者：YUE Chong QU Chunyan YAN Wei ZHAO Jing SU Qin 

机构地区：[1]Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China [2]China Earthquake Networks Center,Beijing 100045,China [3]Survey Engineering Institute,Sichuan Earthquake Agency,Ya'an 625000,Sichuan,China

出　　处：《Earthquake Research in China》2019年第3期489-502,共14页中国地震研究（英文版）

基　　金：supported by the Youth Science and Technology Fund of China Earthquake Networks Center(QNJJ201801);the National Key R&D Programof China(2018YFC0807000)

摘　　要：Aiming at different variation patterns of cross-fault short-leveling before earthquakes,the paper establishes the 2-D finite-element models with different crustal stratification and fault occurrence perpendicular to Longmenshan fault zone. By contact analysis and viscoelastic finite element method,the influence of fault structure on cross-fault short-leveling is obtained under the same constraint conditions,the results show that:with the increase of the horizontal projection distance of fault,the cumulative displacements of surface increase gradually in the models with fixed dip angles of the fault plane(model 1). However,when the horizontal projection distance exceeds 20 km,the influence of fault?s dip angle on the cumulative displacements of surface short-leveling will decrease significantly,and the cumulative displacements are maintained at about 1. 5 m. However,in the listric fault models(model 2),when the projection distance is less than 20 km,the listric fault structure impedes the sliding of fault. The short-leveling variation rate is only half of model 1;as a result,the ability to reflect the regional stress enhancement by cross-fault short-leveling is further weakened. But when the horizontal projection distance exceeds25 km,the cumulative displacements significantly increase,with the maximum displacement reaching 1. 75 m. The results of equivalent stress show that the listric fault structure causes a sudden increasement in equivalent stress when the horizontal projection distance is 10 km,higher equivalent stress values are accumulated between the projection distance of 5-20 km,and then high-low stress difference zones are formed at the bottom of the fault plane and near the transition zone of low-high dip angle.Aiming at different variation patterns of cross-fault short-leveling before earthquakes,the paper establishes the 2-D finite-element models with different crustal stratification and fault occurrence perpendicular to Longmenshan fault zone. By contact analysis and viscoelastic finite element method,the influence of fault structure on cross-fault short-leveling is obtained under the same constraint conditions,the results show that:with the increase of the horizontal projection distance of fault,the cumulative displacements of surface increase gradually in the models with fixed dip angles of the fault plane(model 1). However,when the horizontal projection distance exceeds 20 km,the influence of fault?s dip angle on the cumulative displacements of surface short-leveling will decrease significantly,and the cumulative displacements are maintained at about 1. 5 m. However,in the listric fault models(model 2),when the projection distance is less than 20 km,the listric fault structure impedes the sliding of fault. The short-leveling variation rate is only half of model 1;as a result,the ability to reflect the regional stress enhancement by cross-fault short-leveling is further weakened. But when the horizontal projection distance exceeds25 km,the cumulative displacements significantly increase,with the maximum displacement reaching 1. 75 m. The results of equivalent stress show that the listric fault structure causes a sudden increasement in equivalent stress when the horizontal projection distance is 10 km,higher equivalent stress values are accumulated between the projection distance of 5-20 km,and then high-low stress difference zones are formed at the bottom of the fault plane and near the transition zone of low-high dip angle.

关 键 词：CROSS-FAULT short-leveling FINITE element Listric FAULT STRUCTURE EQUIVALENT stress 

分 类 号：P31[天文地球—固体地球物理学]