Seismicity Of The Yarlung Tsangpo Grand Canyon Region, China

Yarlung Tsangpo Grand Canyon is located in the eastern Himalayas,is the core parts of the eastern Himalayas structures,which is formed by Indian plate moved northward and collided with Eurasian plate,the crust structure is complex,the tectonic movements are intensive,the earthquakes are frequent,the natural disasters are serious.However,the Grand Canyon area as a result of environment and transport facilities,the core of it is scientific investigation and research gaps,where the capacity of the seismic monitoring is lower,seismic activity has not been specialized analyzed and researched,here is an ideal site to explore the seismic activity and the relationship between deep and shallow structures.The author integrated the phenomenon and problems which were discovered in the process of geological survey,seismic array construction,data acquisition,data processing and information explanation,formed a basic research idea of this paper: proceeding earthquake locations and focal mechanism solutions,by history devastating earthquakes information,modern small earthquakes information and the temporary seismic array data of the Grand Canyon region,combined with the characteristics of deep and shallow structures,to analyze the seismic active regularity and the characteristics of tectonic stress field of Yarlung Tsangpo Grand Canyon region,preliminary study the relationship between deep and shallow structures with Eastern Himalayas(Namjagbarwa)structure.The Paper includes the following specific contents:seismic array construction, operation and data acquisition;seismic data processing(crust velocity model building, seismic waveform data processing,earthquake locations,focal mechanism solutions); seismic activity and the characteristics of tectonic stress field analysis;the relationship between earthquake activities and the deep-shallow structures and discussing the conditions of the structure of earthquake preparation area.The paper realized the grasp of geological survey,sites choice,array building,data acquisition, data processing,data analysis and results discussion.The paper from the application point of view of geophysics,contacted with geological structure,studied the analytical techniques and research methods of seismic activity more systematic,the research results to some extent,explained the Yarlung Tsangpo Grand Canyon region seismic activity,the characteristics of tectonic stress field and the relationship between deep and shallow structures,filled the gaps in relevant research area. The papers research theory is close connected with reality,by the following major findings,conclusions and understanding of:①The seismic activity of Yarlung Tsangpo Grand Canyon is strong,there are 157 destructive earthquakes in history which M_s≥4.7,including 21 earthquakes which M_s≥6.0,the largest earthquake is Zay-Moto earthquake which M_s=8.6 and occurred in 1950.②Phase I of the temporary seismic array(2007.8-2008.8) recorded 203 earthquakes,the smallest magnitude is 0.6,the maximum magnitude is 4.6,the information of the earthquakes which M_L≥1.8 is complete.③Seismic activity is closely related to tectonic movement strength and divisional and fracture structure,time and space show that heterogeneity,is mainly distributed in the forward of the Grand Canyon region(5-6 magnitude),the Moto fault zone and Appalachian Long fault zone(8.6 magnitude),Bangong-Nujiang fault zone and Jiali fault zone(6-7 magnitude) and internal of the eastern Himalayas.④The earthquakes in the region are mostly shallow,maximum depth of the earthquake is in the north and the east,strong earthquakes are in the deep of 40-60km (deepened from south to north,turn shallow from Namjagbarwa structure to the east and west sides).⑤The distribution characteristics of earthquakes reflect the crust structure, show Indian plate northward subduction,Namjagbarwa structure northward and eastward subduction.⑥Strong earthquakes occur in the blocks surrounding where is the deep fault zone and its vicinity,and over seven magnitude earthquakes are related to the faults in north east direction and northwest direction,in particular closely related to the fault zones of the larger and strong activity of Holocene epoch.Of these,eight magnitude earthquakes occur in the faults in west northwest direction with strike-slip component larger;but mainly dip-slip,a single fracture no scale,the largest magnitude is about 7.⑦Strong earthquakes often occur in parts of the complex geometry or a convergence of directions of fracture zones.⑧Over seven magnitude earthquakes occur in the crust thickness changes with the steep,gradient zones of gravity anomaly belt,over seven magnitude earthquakes occur in the anomaly with the shape distortion between the different activities of the different pieces of gravity and magnetic anomalies district boundary. ⑨The tectonic stress field of Yarlung Tsangpo Grand Canyon region is ne-nne to nearly the level of extrusion,prone to strike-slip,thrust and strike-slip thrust faults.