Study On Fault Activity And Tectonic Geomorphology Of The West-Northern Segment Of Ganzi-Yushu Fault

Ganzi-Yushu fault as a large strike-slip boundary fault between Bayan Har block active block and Chuandian active block, which has occurred many large earthquakes recorded in the history. In addition, as the south-eastern margin of Tibetan plateau is an important part of the main boundary faults. Ganzi-Yushu fault activity characteristics and genetic mechanism for further constraint dynamics in eastern Tibetan plateau has great significance. Many scholars at home and abroad focus on its geometric characteristics and activity habits.According to previous studies on Ganzi-Yushu fault, the paper taking the west-northern segment of Ganzi-Yushu fault as the research object. The author use the Arcgis10.1 software analyzed the DEM data of the study region, extracted typical parameters of tectonic geomorphology, such as amplitude of landforms, the maximum elevation, the minimum elevation, the mean elevation, stream density and stream direction, the fault activated can be indicated by the parameters. In addition, the paper also carried out the details survival fault survey, make full use of differential range finder measuring instrument conduct the fault geomorphology such as dislocation river, fault scarp, pressure ridge, analysis the geometric characteristic of the fault, and choose the typical fault zone to mapped and trench and obtain abundant sample which is used to calculated the average slip rate and the Paleo-earthquake sequence, in order to gain the late quaternary activity of the fault. At last according the geometrical structure and activated characteristics of the west-northernern segment of Ganzi-Yushu fault to analyze its kinematics characteristics and genetic mechanism. Author gets the preliminary insights:(1)The development and evolution of the landscape areas around the west-northern segment of Ganzi-Yushu fault is controlled by the fault: from landform morphological characteristics, the terrain is whole step and high plateau border flinched unceasingly, drainage area expands unceasingly, the upper mountain with multistage planation surface, mainly planation surface in the 5000 m or so, topography slope, amplitude of landforms, the maximum elevation, the minimum elevation and the mean elevation were all controlled by the fault. From view of river morphology, drainage crosscutting by fault performance for S type, the density of water is NW towards with the same of fault towards.(2)The west-northern segment of Ganzi-Yushu fault can be divided into four segments, which is Dangjiang fault, Yushu fault, Batang fault, Dengke-Xianggu fault from north to south. Yushu fault and Batang fault located in the middle, performance for “?”, fault as a whole performance for “Z”; Yushu fault zone as a typical tensile strike-slip duplex structure, acrossing the Yushu fault zone of vertical segment of a typical negative flower structure and sag area gradually narrowed from west-northern to east-south. There are many associated structure of strike-slip fault development along the west-northern segment of Ganzi-Yushu fault,such as pull-apart basin, negative flower structure, ladder structure, horsetail structure.(3)Drainage deflection caused by faulting have the characteristic of time and space. In addition, according to the distance of fault and time data, we can get those results: from late quaternary Dengke-Xianggu fault the average slip velocity is 6.67~8.86mm/a; Batang fault The average vertical slip rate is 0.39~0.69mm/a and the average slip velocity is 2.21~3.04mm/a. Combining previous study of the slip rate of west-northern segment of Ganzi-Yushu fault, the author indicate the horizontal slip rate gradually increased from west-northern to east-south of the fault. Through the organization and analysis of paleoearthquake trench of Ganzi-Yushu fault, it concludes that average recurrence interval of earthquake of Ganzi-Yushu fault in Dengke segment is 420 years stronger than the southeast segment of Yushu fault which is about 1500 years.(4)According to the geometrical structure and kinematic characteristics of the west-northern segment of Ganzi-Yushu fault, author pointed out that the material of Tibetan plateau expand to east, which resulted that Qiangtang block in continuous sliding clockwise, and relative to Bayan Har block movement to the south. Ganzi-Yushu late quaternary left strike-slip fault formed in this context.