| The modern high topography of the Tianshan resulted from the reactivation of a Paleozoic orogenic belt by the India/Asia collision.It has become a natural test site for studying intracontinental deformation,intracontinental strong earthquake observation,continental dynamics and Cenozoic tectonic geology.Exploring the geodynamic problems of the Tianshan Mountains,studying the deformation modes of the Tianshan Mountains,and studying the spatial and temporal deformation rate distribution of the Tianshan Mountains plays an important role in understanding the deformation of the intracontinental orogenic belt.Combined with previous studies,to determine the strike-slip rate of giant strike-slip faults in Tianshan,what is the distribution of these strike-slip rates at different tempor and in different spaces? What kind of regulation effect does the different faults play under the compression of the Tianshan Mountains? Why does the strike-slip fault' rate change in different region? How does the strike –slip fault affect the adjacent landform unit? What is the recurrence feature of the giant strike-slip fault?This thesis highlights the Jinghe section of Bolokenu-Aqikekuduk.Combining satellite remote sensing imagery,unmanned aerial photography,cosmogenic nuclides(TCN),optical luminescence(OSL)dating and field observations,we study the geometry,kinematics,and deformation pattern of Bo-A.We study the activity habits of earthquakes through excavation trenches.The conclusions of this thesis are stated below.1.the alluvial fans in the study area were divided into six stages based on the surface characteristics,altitudes,development features of alluvial fans,and drainage.The abandoned ages of Fan2 b,Fan3a and Fan3 b are 98.47±6.09 ka,74.01±6.14 ka,12.33±1.90 ka,formed during the transition from glacial to interglacial.Through the abandoned ages of the alluvial fans and terraces obtained in other parts of the Tianshan Mountains,we can confirm that the abandonment of the alluvial fan is controlled by the paleoclimate cycle.The abandonment of the river terrace is not only controlled by the paleoclimatic cycle,but also by other factors such as tectonic movement.2.Geomorphic offset measurements from the field and high-resolution DEM along 10 km across the alluvial fan and along 10 km of the fault,range from6.5 to 29.5 m,with distinct clusters at 15.5m,23.5m.The cluster of the smallest offsets around 7.5 m distributed over a minimumlength,is attributed to the last largest surface rupturing event that testifies of the occurrence of a magnitude Mw 7.4or M7.7earthquake along the Jinghe section of Bo-A fault.3.By calculating the dislocation distance of the single geomorphological flag and the abandoned age of the alluvial fan,it is concluded that the strike-slip rate of the Fan2 b,Fan3a,Fan3 b and site 1 is 2.16±0.18mm/a,1.24±0.13mm/ a,3.74±0.68mm/a and 1.42±0.24mm/a,respectively.The average strike-slip rate Jinghe section of the Bo-A fault in the 100 ka time scale can be obtained.It is 1.96+0.19/-0.16mm/a.4.Four earthquakes are identified based on event evidence in the form of open fissures,unconformities,and upward fault terminations,with ages of E1(21.9-18.8)ka,E2(18.9-16.3)ka,E3(11.1-7.4)ka,E4(6.8-5.9)ka.The mean recurrence interval is 4.7±2.8 ka with a coefficient of variation(COV)of 0.67,indicating that earthquake recurrence is not periodic,with individual intervals ranging from as short as 2.8 ka to as long as 8.3 ka.5.The average strike-slip rate of the 100 ka of the Jinghe section of B-A fault is 1.96+0.19/-0.16mm/a.This value is similar to the strike slip rate of ~2.2 mm/a obtained by Campbell et al(2013)near Alashankou.The N-S crustal shortening rate caused by the active structure inside the Tianshan Mountains is ~4.94 mm/a,accounting for 47% of the total shortening rate of the N-S crust in the Tianshan Mountains. |
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