Study On The Tectono-geomorphic Response To Late Quaternary Active Deformation Along The Maqin-Maqu Segment Based On Multiple Remote Sensing Data

The East Kunlun fault zone(EKLF),as a large-scale left-lateral strike-slip fault zone in the northern Tibetan Plateau,is extending about 1600 km.It is an ideal natural laboratory to study Cenozoic tectono-geomorphic evolution and the geometry,kinematics and seismic rupture mechanism of active strike-slip fault zone in Tibetan Plateau.During the past 100 years,seven large seismic events with a magnitude ≥ 7.0have occurred along entire EKLF,which had produced over 1200-km-long co-seismic surface ruptures.However,the Xidatan-Dongdatan segment and Maqin-Maqu segment(MMS)have not experienced large seismic events in the past 660-1000 years,which are defined as the most dangerous seismic gaps with high seismic risks in the future.Previous studies indicated that the late Quaternary left-lateral slip rate along the major fault of MMS shows an eastward gradient decreasing.But the geodynamic mechanism to explain this gradient decreasing of slip rate remains controversial.Meanwhile,there are a series of cities and towns with relatively high population like the Maqin and Maqu County and many national mega-projects along MMS.It is critical for assessing the potential disaster risk of future large seismic events in this region.Therefore,accurate analysis of the geometric and kinematic characteristics of the major fault zone and branch faults of MMS can deepen understanding of the tectonic transformation mechanism,and provide important technical supports for its seismic risk assessment and earthquake prevention.In this thesis,I will focus on analyzing the geometric patterns of MMS and the geodynamic mechanism of slip rate gradient decreasing.Firstly,the geometric characteristics and late Quaternary tectonic activity of MMS will be documented based on the detailed tectono-geomorphic interpretations of high-resolution satellite sensing images,cm-level unmanned aerial vehicle(UAV)photogrammetric data and highprecision DEM data,combined with field investigations and 14 C dating.Then,the 30 m AW3D30 data will be used to extract systematically the geomorphic indices of 69 drainage basins along MMS and adjacent area using the GIS spatial analysis technology,which can quantitatively describe and discuss the tectono-geomorphic features in response to regional tectonic activity intensity.Main research results and conclusions obtained from this study are as follows:(1)Analyses of the geometric patterns and activity characteristics show that the major fault zone of MMS,extending about 330 km,is an active left-lateral strike-slip fault zone,together with the Awancang fault(AWCF)and Gahai fault(GHF),which are making up a typical horsetail-shaped fault system.Among them,AWCF extends about 200 km with a strike of NW,and dominates left-lateral strike-slip with thrust faulting component,which is composed of three segments by sequence from NW to SE,namely Abudala,Jiaozongzamar-Wote and Wote-Cairima sub-segments.The NEEtrending GHF with a length of 160 km,is characterized by the thrust faulting with a left-lateral strike-slip component,which can be divided into 3 sub-segments in space,each namely Duosong,Halatang-Hrangqu and Gahai sub-segments.(2)Late Quaternary slip rates of MMS indicate that the slip rates on MaqinOulasuma and Oulasuma-Gongma sub-segments of the major fault zone are yielded to be 8.16±1.23 mm/a and 5.35±0.30 mm/a.And the slip rates are estimated to be2.70±0.01 mm/a,3.07±0.09 mm/a for the northwestern and middle sub-segments of AWCF,respectively.In the east of Dagongka,the slip rates along the major fault zone of MMS are rapidly going down by 4 mm/a,decreasing from west(9 mm/a)to east(5mm/a),which is almost equal to the slip rate of 3 mm/a on AWCF.Therefore,it is inferred that branch faults play a key role on the tectonic transformation of MMS,absorbing the slip-rate decrease along the major fault zone.(3)Quantitative analyses of tectono-geomorphic features display that the values of HI indices,TR indices,Hack profiles and SLK indices along the major fault zone and branch faults of MMS display a continuous eastward decreasing,which is similar with the variations of the late Quaternary long-term slip rate gradients along the major fault zone of MMS.It demonstrates that quantitative geomorphic analysis is of great indicative function on reflecting the regional activity intensity.And the HI and TR indicate that a turning point of tectonic activity intensity of MMS is near the Oulasuma.(4)Synthetic study of geodynamic mechanism reveals that the major fault zone of MMS together with AWCF and GHF are displaying a horsetail-shaped fault system on the plane and a typical flower structure in the deep geophysical profile,respectively.Therefore,this study proposed that the attenuation of slip rate along the major fault zone of MMS might be absorbed and adjusted by the left-lateral strike-slip motion and thrust faulting of AWCF and GHF.It further revealed that tectonic transformation and dispersion deformation among the major fault zone and branch faults plays an important role on the partitioning of slip rates and pinching out of fault trace at end of the largescale strike-slip fault system.