SIMULATION AND INVERSION OF THE LUDING Ms6.8 EARTHQUAKE FAULT MOVEMENT IN SICHUAN
The southern-eastern segment of the Xianshui River Fault,the southwestern segment of the Longmenshan Houshan Fault,and the Anning River Fault together constitute a typical"Y"-shaped tectonic structure on the southeastern margin of the Qinghai-Xizang Plateau.The intense tectonic activity within this structural system leads to frequent seismic events in the affected area(29°00′～30°00′N,101° 30′～103°00′E),particularly in the vicinity of Moxi Town,Luding County,located at the intersection of the"Y"shape,where several moderate to strong earthquakes with magnitudes above Ms6.0 have occurred.The recent Moxi Ms6.8 earthquake on September 5,2022,which took place along the southern-eastern segment of the Xianshui River Fault in Moxi Town,represents the latest manifestation of strong seismic activity.This earthquake resulted in over a hundred casualties and has garnered significant attention as one of the most notable earthquakes in the southeastern margin of the Qinghai-Xizang Plateau in recent years.However,the geological structure in this region is highly complex,and traditional geological research methods face challenges in rapidly and effectively analyzing seismic fault movements and stress changes.In this study,we employed the finite element contact interface method to numerically simulate the main fault movement during seismic events,and conducted inversion analysis of the displacement vector field and Coulomb stress changes in the pre-and post-seismic regions.The numerical simulation results indicate that by applying a southeastward lateral force to the left boundary of the model and a southward lateral force to the northwestern corner of the upper boundary,while keeping the Yangtze block fixed,a high degree of numerical convergence is achieved when imposing counterclockwise rotation on the lower crust of the Sichuan-Yunnan block and clockwise rotation on the lower crust of the Sichuan-Qinghai block.Prior to the earthquake,Moxi Town experienced both tensile and compressive stresses,with stress concentration observed in Yanzi Gou,Moxi Town,and Xinmin Township,located along the southern-eastern segment of the Xianshui River Fault.The main earthquake occurred at a depth of approximately 13 km below the surface,with the maximum slip displacement observed in the Yanzi Gou-Moxi Town segment,exhibiting a left-lateral slip of 1.5～2.0 m during the seismic event.The observed vector direction of displacement points changed pre-and post-earthquake,influenced by the effect of fracture convergence and post-seismic physical rebound deformation of the blocks.The post-seismic shear strain increment of the Sichuan-Yunnan block(averaging 10x10-5)was higher than that of the Yangtze block(averaging 5 × 10-5),indicating that the Sichuan-Yunnan block still plays a dominant role in regional block movements,and there is a clear southeastward transfer trend of shear stress along the main fault zone.This study provides new insights into the crustal deformation characteristics of the southeastern margin of the Qinghai-Xizang Plateau,offering valuable scientific and practical information for understanding the mechanisms of strong earthquake generation,seismic hazard analysis,and economic development in the region.
the Luding Ms6.8 earthquakeseismic motion characteristicsdisplacement vectorCoulomb stress field
万方数据
