The Current Movement Characters Of Main Fault Zones Surrounding The Namcha Barwa Syntaxis

The Himalayan orogenic belt is the tetonic result of the collision between the Indian plate and the Eurasian plate.The rise of the Himalayas caused by the continental collision has attracted the attention from many scholars.In the Himalayas orogenic belt,the eastern and western ends of the mountain range and the direction of the water system have undergone a major turn of approximately 90°,which are named as the eastern tectonic knot and the western tectonic knot.The Himalayas East Tectonic Knot,the Namcha Barwa Syntaxis mentioned in this thesis,is located at the eastern side of the Himalayas orogenic belt.It is at the core of the continental collisions of the India,Myanmar and Qinghai-Tibet blocks.At the same time it is the region with the most dramatic topographic changes and the most complex structures in the southeastern margin of the Tibetan Plateau,where the Chayu Ms8.6 Earthquake occurred in 1950.It turns to be a natural laboratory for geodynamic studies.This paper mainly analyzes the characteristics in the movement of the major faults in this area.The main faults in the surrounding areas of the Namcha Barwa Syntaxis include the Medog fault zone,the Milin fault zone,the Jiali fault zone,the Apalong fault zone,and the Bianba-Damu new fault zone.The geological data reveals that the major faults around the Namcha Barwa Syntaxis are all Holocene active faults,and there are differences in the movement of faults with different strikes and structures.The movement characteristics of the Milin fault zone and the Medog fault zone,distributing at the North East direction are dominated by left-lateral strike-slip movements with some thrust movements.However,the rapid movement of the Milin fault zone located at the western side of the Namcha Barwa Syntaxis is significantly weaker than the Medog fault zone on the eastern side.For the NW-trending Jiali fault zone,Apalong fault zone and BianbaDamu new fault zone,they are all in dextral thrust movements.The movement gradually weakened from the Apalong fault zone at the top of the Assam structural junction to the Jiali fault zone in the north.Through the integration from GPS data in the research area,a high-precision and high-density GPS data was obtained under the unified Eurasian reference frame.By studying the cross-fault GPS profiles,the following research results are drawn.For the NE-trending Milin fault zone and the Medog fault zone,the movement of the Milin fault zone which is located on the western side of the Namcha Barwa Syntaxis is not obvious in present time,performing a weak right-lateral tensile movement.While,the movement of the Medog fault zone located on the east side of the Namcha Barwa Syntaxis displayed as an obvious left-lateral compression movement.The current movement of the Jiali fault zone in the NWW-extending is weak left-lateral tension,while the northwest direction of the Jiali fault zone is right-lateral compression.For the NW-trending Bianba-Damu new fault zone,the northwest section of the zone which located on the west of the Namcha Barwa Syntaxis shows a dextral strike-slip movement.For the middle section near the top of the Namcha Barwa Syntaxis is weak right-lateral compression,same as the Jiali fault zone.For the southeast segment located on the southeast of the Namcha Barwa Syntaxis shows a right-lateral compression movement.The right-lateral strike-slip speed on both sides is much greater than that near the top,indicating that the Bianba-Damu fault zone near the top of the Namcha Barwa Syntaxis may now be at an atresia stage.For Apalong fault zone,from the west side of the Assam to the east side,the right-lateral slip speed increases,and the extrusion rate decreases.It shows that the east of the Apalong fault zone may be affected by the strong right-lateral strike-slip of the Shijie fault.The fact that the Apalong fault zone has a low overall extrusion rate,indicating that the Apalong fault zone is not thecollision zone of the Assam structural junction,but a dextral strike-slip fault associated with the upper plate of the collision zone.The cross-fault GPS profile results show that the current movement of the major fault zones in the surrounding areas of the Namcha Barwa Syntaxis are controlled by the Assam Tectonic Knot,and the influence of the Namcha Barwa Syntaxis seems relatively weak.This article is based on the waveform data from 16 broadband seismographs in the surrounding area of the Namcha Barwa Syntaxis,through the relevant analysis of seismic events recorded by the seismic network,MSDP software was used to perform earthquake lcoations and the earthquake catalogs in the study area were compiled.The CAP method was used to obtain the focal mechanism of M3.0 evetns within 10 km from both sides of main faults in the study area,in order to analyze the current movement of major fault zones.The results show that seismic activity in the study area is mainly controlled by fractures.The current movement of the Medog fault zone is dominated by left-lateral strike-slip,combined with thrusting or normal fault movement The Milin fault zone is dominated by left-lateral strike-slip,and there is a positive fault movement,and the Jiali fault zone is dominated by right-handed thrusts,somewhere has normal fault movements.The movements of the Bianba-Damu new fault zone are relatively complicated,and the differences are not obvious in all movements,the overall performance is mainly right-lateral motion.The Apalong fault zone is dominated by the right-handed thrust,and in some area there has a normal fault motion,and the movement are basically consistent with the existing geology study and GPS data,indicating that the fault movement in the surrounding areas of the Namcha Barwa Syntaxis is mainly affected by the Assam structural knots.The research results on the current movement characteristics of the major fault zones in the surrounding areas of the Namcha Barwa Syntaxis are only preliminary,and more seismic observation data are still needed to conduct further research on some issues,such as what makes the movement characteristics of Jiali fault zone and the Bianba-damu diverse? The specific reasons for the diversity are the differences among the geological bodies and the deep structures or the fault structures,or other reasons.Perhaps further clarification of these issues will reveal the seismogenic environment and geodynamic settings of the surrounding area of Namcha barwa syntaxis.