1.School of Materials Engineering, Changshu Institute of Technology;2.National Institute of Natural Hazards, Ministry of Emergency Management of China;3.The First Monitoring and Application Center, China Earthquake Administration;4.Institute of Geology, China Earthquake Administration
The Eastern Himalayan Syntaxis (EHS) and its vicinities, located in the tectonic front of the collision between India plate and Eurasia plate, is characterized by strong crustal shortening and tectonic rotation deformation. Based on the latest and large-scale GPS velocity data, we analyze horizontal differential crustal movement associated with the EHS and its vicinities. Furthermore, we use a ‘‘spline in tension’’ technique to get a continuous strain rate map of the EHS region. Combined with the previous research results, we focus on the present-day tectonic deformation and mechanism of the EHS and its vicinities, and try to discuss the continental internal dynamic mechanism reflected by the current tectonic deformation in this area. The following results are obtained: Under the background of continuous subduction of Indian plate beneath Eurasian plate at an angle of NE20°, the most remarkable crustal motion is the clockwise rotation of southeastern and eastern Tibetan Plateau around the Eastern Himalayan Syntaxis. The maximum rotation rates of (109.7~123.6) × 10-9 rad/a occurred to the east of the Syntaxis, around this area of Lancangjiang fault, Jinshajiang fault and Nujiang fault. High value region of tectonic strain rates in this area concentrate around the vicinity of Himalayan Main boundary thrust, Sagaing fault, Xianshuihe-Xiaojiang fault and other large strike-slip faults, as well as the ring areas of the Eastern Himalayan Syntaxis, whereas there are no significant strain anomalies in the area across Jiali fault and Red-River fault. Moreover, the maximum superficial compressive strain rates of 152.1×10-9/a is in the northeast areas of Assam sub-block, which indicates that the core position moves from the Namjagbarwa area towards its southeast to the northeast of Assam, where the Himalayan Main boundary thrust successively meets the inferred Northern Sagaing thrust. It is considered according to the research that, owing to the hyper-oblique subduction of the Indian plate, the Eastern Himalayan Syntaxis region is mainly characterized by crustal thickening, and the flow of the lower crust and upper mantle with viscoplastic characteristics in the deep drives the overall movement of the overlying brittle upper crust block.