Research On The Relationship Between The Activity Of The Middle Part Of The Jiali Fault (Niwu-Guxiang) And The Strong Uplift Of The Northern Part Of The Eastern Tectonic Section

The interaction and relationship between tectonics,climate and geomorphology is one of the frontier hotspots in geomorphology research,and topography,as an important vehicle for the joint action of tectonics and climate,is also a hotspot of concern in tectonics and geomorphology.The East Himalayan Tectonic Junction is the southern margin of the collision and convergence of the Eurasian and Indian Ocean plates,with strong tectonic uplift and complex geological and deformation evolution.The Jiali Fault is a very important regulating fault for the eastward transport of the uplifting blocks of the Tibetan Plateau and the extrusion and uplift of the eastern tectonic junction.However,due to the harsh natural environment and inaccessibility,no reliable evidence of Quaternary activity has been found in the middle section of the Jiali Fault(Niwu-Guxiang),and the exact spreading of the fault,the nature of its activity and the latest activity era are more controversial.The study area is the southeast Tibetan region north of the Eastern Tectonic Junction,where the surface of the northern side of the Eastern Tectonic Junction of the Tibetan Plateau is strongly uplifted and rivers are undercut to form a typical alpine valley landscape,located along the Jiali Fault in the Yigonzangbu-Palungzangbu basin.In tectonically active orogenic belts,rivers usually record a wealth of information on tectonic activity and geomorphological evolution,and the extraction of such information from river longitudinal sections in particular has become an important research element in orogenic belt studies.Therefore,this paper focuses on the activity characteristics and topographic relationships of the middle section of the Jiali Fault(Niwu-Guxiang)since the Quaternary,and uses SRTM high-precision digital elevation model(DEM)data to carry out a quantitative study of the structure,geomorphology and tectonic activity of these water systems.It provides an in-depth analysis of the history of the formation and evolution of the watershed geomorphology and its theoretical understanding of its response to tectonic activity and climate change,and combines the results of field fracture investigations to determine the nature and age of fracture activity in this section,and discusses the regional tectonic deformation mechanism and regional seismic hazard analysis.In this paper,based on DEM data,a macro geomorphological analysis was carried out in the study area of the Egonzangbo-Palungzangbo watershed(Niwu-Guxiang)using ArcGIS environment,and a series of geomorphological parameters including topographic slope,topographic relief,five strip profiles,55 tributary basin areaelevation integral HI values and 43 tributary valley aspect ratio indices were extracted,A series of geomorphological parameters including slope,local relief,five swath profiles,55 tributary basin area-elevation integral HI values and 43 tributary valley width-to-height indices were extracted to obtain the regional geomorphological characteristics.Based on the geomorphological analysis,435 rivers originating in the study area were selected,and longitudinal profiles of 53 rivers in the upper reaches,42 rivers in the northern and 27 rivers in the southern reaches of the Niwu-Guxiang section were extracted using Matlab script files,from which standardised channel steepness indices(ksn),concavity indices and kinckpoints were obtained for the study area.A series of parameters including standardised river steepness index(ksn),concavity index and kinckpoint were used to characterise the morphology of the longitudinal profiles.A study of the relationship between the geomorphology of the watershed and the activity of the Niwu-Guxiang section of the Jiali Fault was carried out in conjunction with field investigations;the spatial variation in activity in the middle section of this fault zone was analysed and the following conclusions were obtained:(1)The extraction of longitudinal profiles and standardized steepness indices(Ksn),Valley floor width-to-height ratio(VF),and Hypsometric Index(HI)of tributaries in the Palungzangbu and Yigongzangbu basins show that the middle section of the Jiali Fault(Niwu-Guxiang section)is significantly different from other regions,and all indices indicate that this section of the Fault is in a state of rapid uplift and denudation.(2)By comparing the HI and VF values of the tributaries on both sides of the main stream,it is revealed that the neotectonic activities of the tributaries on the south side of the basin may be more active than those on the north side.The extraction results of the river rift points show that the tributaries on the south side of the main stream are more developed with two levels of rift points,while the north side has only one level of rift points.(3)The results of the field geological survey,the two Quaternary fluvial sediment middle sections in Niwu Township and Tongmai indicate that the middle section of the Jiali Fault shows strong extrusion in addition to the right-slip activity,which is consistent with the results of the geomorphological index.It is assumed that this is due to the fact that the middle section is located directly north of the eastern tectonic junction of the Tibetan Plateau,and that the right-slip movement of the fault is a result of the eastward transport of the Qiangtang block,while the recoil is a reflection of the continued northward pushing of the eastern tectonic junction.