Study On Fault Activity And Tectonic Geomorphology Of Litang Fault Within The Chuandian Blocks

Litang fault is inside of Northwest Sichuan sub-block of Chuandian active block. The faults start from the northwestern of Shama townships of Bayu country in the eastern margin of Tibetan Plateau, extend to the southeastern, through Maoyaba Basin, Gaocheng Town of Litang, Jiawa, Dewu, Xisa Temple, until to Shawan region of Muli Country disappear, the full-length is about400km, which is an active fault with sinistral strike-slip in Holocene. Totally, the fault strike is NW and consist of series sub-faults, which is showing a characteristic with sinistral strike-slip movement. In Quaternary, this fault had a strong active, its southeastern segment occurred Ms7.3earthquake in1948, the geometric characteristic, activity habits of faults, kinematics characteristic and dynamics characteristic of this faults were focused by scholars at home and abroad. For a long time, the research center of researchers were concentrate on the Chuandian active block and the boundary main faults more than the internal active faults, so the researchers had a relative low understanding about the internal active faults. In addition that, together with the fact that the Litang fault located in the internal of Tibetan plateau with a hostile environment, which make the research more difficult.The paper relies on Litang-Yidun fault1:50000banded active faults survey, which is a sub topic of China earthquake active faults survey-middle and south of south to north earthquake zone. This paper studies on the Litang fault which is located internal of the Chuandian active block, the research priority focus on the geometric characteristic, new activity, Paleo-earthquake (and so on) of the fault. Base on the previous studies on this fault, the author use the Arcgis9.3software 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, then use the parameters to indicated that the fault activated. Beside, the paper also carried out the details survival fault survey, make full use of differential GPS measuring instrument conduct the fault geomorphology such as dislocation river, fault scarp, pressure ridge, sag-pond of the Litang fault, divided 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 new active with the fault. At last, through analyze the Kinematics characteristic of the fault to the internal active fault of Chuandian block, to analyze the dynamics characteristic of the internal Chuandian block. The author gets the preliminary insights:(1) The growth and evolution of the near Litang fault area geomorphology was controlled by the fault:From the view of geomorphological spatial morphology, 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, the river density and the river direction of Litang area were controlled by the fault. The Forth Grade Basin (Litang Basin), Maoya Dam Basin, Cuopu Lake Basin and Jiawa Basin of this area are all controlled by the Litang fault.(2)The Litang-Yidun faults can separate into Litang segment, Damaoya Dam segment, Cuopu Lake segment. Cuopo Gully segment since the Late Pleistocene, the slip rate is4.15±0.5mm/a, which shows a strong activity. The north of Litang-Damaoya Dam segment was preserved a clearly surface rupture zone, which is the product of an earthquake occurred in1890. Besides, nearly5000year, the north of Litang-Damaoya Dam occurred5times Paleo-earthquake, the mediuan of recurrence is1013±111a.(3) The material of Tibetan plateau expand to east, which resulted that Qiangtang block in continuous sliding eastward, which lead the Jinshajiang fault break out eastward, the dynamic continue transmit to western Sichuan block which compel the Chuandian active block move eastward. However, due to the countercheck of south china block, which caused the Chuandian active block done clockwise rotation, and this led that the Litang fault was conformed in this process.