| The northern margin of the Qaidam Basin is the basin-mountain transition zone between the Qilian Mountains and the Qaidam Basin.It develops the Delingha sag,the Olongbrook Mountain Uplift,the Southern Outer Depression,the Emnik Mountain Uplift,and the Hobson Sag.A concave structure between the concave phases.Since the new generation,the Qaidam-Qianlian area has been in the process of strong extrusion deformation.Some studies have pointed out that the extrusion deformation across the Qilian Mountains absorbs 20% of the deformation of the Indian-Eurasian plate,and the crustal shortening rate is 5-8mm/a.Since the 1960 s,a number of moderate-strong earthquake swarms have been recorded in the northern margin of the Qaidam Basin.In 1962,a magnitude 6.8 earthquake occurred on the south side of the Emni Mountain;In 1977,a magnitude 6.3 earthquake occurred in the south of the Xitieshan Mountain;In 2003,a 6.6-magnitude earthquake occurred in the north of Huaitoutara,and earthquakes of magnitude 6.3,6.6,and 6.1 occurred in Xiaochaidan Hubei in 2008 and 2009,respectively,which have high seismic risk.For a long time,there is a lack of research on the tectonic foundation of the northern margin of the Qaidam Basin.There are only a few field observations of the piedmont fault,and there is no comprehensive and reliable quantitative activity parameters and recurrence data of ancient earthquakes.The eastern part of the northern margin of the Qaidam is a depression-sinking depression zone.The predecessors carried out seismic exploration on the eastern Qaidam Basin and obtained some understanding of the fault structure,but there is no exact late Quaternary surface fault.As well as the report of the characteristics of the activity,in addition,the near-north-north tectonic belt of the Wulan BasinMaoniushan-Qaidam Basin is also an important component of the eastern part of the northern margin of the Qaidam Basin.The study of the active tectonic structure of this tectonic belt is the base of our understanding of the Qilian Mountains.The relationship between the edge and the East Qaidam area,which constrains the deformation of the crust in the northern margin of the Qaidam basin.Aiming at obtaining the geometry and movement characteristics of the TosuhuMaoniushan fault in the eastern part of the northern margin of the Qaidam margin,detailed geomorphological interpretation and field geological survey were carried out to investigate the fault geomorphology and geomorphology.The wrong landform measurement uses the drone photography method,and the regional geomorphological contrast constraint is used for the faulty dating:In the actual application process of high-resolution UAV photogrammetry,the phenomenon that the DEM cannot be correctly connected between different voyages appears,and the height difference of 4-5 appears in the vertical direction.Combined with the basic principle of photogrammetry,the airborne single-frequency GPS is considered.The positioning error is the reason that the DEM of different voyages cannot be connected.In the study,the high-difference translation method is used to eliminate the GPS positioning error,so that the DEM between the two voyages is accurately connected.On the other hand,the camera lens distortion has photogrammetry results.With a large impact,Photoscan software can be used to complete the entire process of the aerial data of the drone,and the camera lens can be corrected in advance.Therefore,the operation method of calibrating the lens with Photoscan is introduced.According to the distribution,relative height and surface characteristics of the alluvial fan,based on the previous studies,the typical pre-mountain alluvial landform in the northeastern part of the Qaidam Basin is selected,combined with the dating results of this and previous human illuminating samples,the flooding will be accumulated.The geomorphic area is divided into four stages.The highest a4 period is the residual alluvial fan in the piedmont.The a3 and a2 stage alluvial fans widely distributed between the flood plain and the piedmont residual alluvial fan are mainly formed in the last deglaciation period.Since its formation,the ages are 12-14 ka and 7-10 ka,which provides a good reference for determining the age of partial faultdistributed flood fan.Based on the geometrical distribution and discontinuous features of the TosuhuMaoniushan fault,it can be divided into three parts of the NWW trend.The study of the fault geomorphic features of several typical fault points shows that the fault has been in the late Quaternary since there is still some activity,and their active characteristics are different:1)The Tosuhu-Gahainanshan fault developed in the Delingha sag area and in front of the South-Gahai Mountain.It tends to N and controls the uplift of the northern part of Olongbrook and the southern part of the Gahai lake.The vertical sliding rate since the Late Quaternary is less than 0.15mm/a;2)The south-Maoniushan fault dipping toward south,and the broad alluvial fan in front of the mountain is faulted,resulting a Minimum vertical displacement of 10.6-5.7 m.The vertical sliding rate since the Late Quaternary is about(0.49-0.81)mm/a;3)The southern Alzto fault is exposed to the front of the mountain.The linear trough-like landforms and faulty steep ridges are widely developed.It should be caused by the continuous uplift of the Alzto Mountains,and the vertical sliding rate of the late Quaternary is about(0.19-0.51)mm/a.4)There is a NEE-trend active fault of about 5km in the southern margin of the Yak Mountain and the southern margin of the Alzto Mountain.Since 5.86 ka B.P,there have been earthquakes on the surface of the fault.In general,the thrust-overlying tectonic body at the northern margin of the Qaidam Basin has developed multiple active faults in the NWW trend,which together respond to regional squeeze shortening.The inner crust of the eastern sag of the northern margin of the Qaidam may be dominated by overall shortening;the vertical sliding rate of the southern Alzto fault is basically the same as that of the southern Zongwulong fault,despite seismic records lacked,it can be judged that there is a certain degree of seismic activity since the Late Quaternary in the eastern part of the northern margin of the Qaidam Basin.The eastern part of the Qaidam-Qilian Mountain Basin coupling system has potential seismic hazard. |
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