STUDY ON JURA-TYPE STRUCTURE IN SOUTHEASTERN SICHUAN AND INVESTIGATION OF TECTONIC ACTIVITY IN LUXIAN AREA
On September 16,2019,a magnitude 6.0 earthquake struck Lu County,Sichuan Province,marking the most powerful earthquake ever recorded in the region.The earthquake epicenter was located within the northeast-trending Yujiasi syncline in the Yibin area,situated in the southern part of the Huay-ingshan Fault Belt.The syncline is flanked by the northeast-trending Luoguanshan-Tiziya anticline and the Haichao anticline.This study investigates the surface fault activity and deep tectonic deformation charac-teristics of the Luxian Ms6.0 earthquake using a combination of field geological survey,remote sensing image interpretation,seismic reflection profile analysis,fault lithography,and electron spin resonance dat-ing methods.These methodologies provide insights into the seismic activity and structural changes associ-ated with the earthquake event.The investigation revealed no discernible surface fault in the Yujiasi syn-cline,the epicenter location of the earthquake.Surrounding faults such as the Huangniya and Duijinwan faults exhibit characteristics of right-lateral strike-slip and compressional kinematics.There is no conclu-sive evidence of fault truncation in Quaternary sediments.However,active signs of faults are evidenced by tectonic geomorphology,drainage anomalies,and local hot springs along these faults.Micromorphological analysis of quartz particles from fault gouge samples of the Huangniya fault indicates dominant subconch-oidal features,suggesting late Pleistocene faulting activity.Electron Spin Resonance(ESR)dating result of 85±22 ka also supports late Pleistocene activity of this fault.Interpretation of seismic reflection sec-tions in the study area reveals a typical Jura-type thin-skinned structure.Surface faults and concealed faults collectively form counterthrust structures with chevron or"λ"shaped patterns in profiles.These ac-tive faults predominantly extend into the weak paste salt layer detachment zone at the base of the Middle and Upper Cambrian series.Structural analysis of fault striations indicates maximum horizontal compres-sive stress in the late Pleistocene oriented between 230° to 316°,likely influenced by tectonic activities within the Sichuan-Yunnan Block and the Longmenshan Mountains.
active faultMs6.0 earthquakequartz morphologyElectron Spin ResonanceLu County
万方数据
维普
