利用SsPmp震相相移约束青藏高原上地幔顶部地震波速度

印度与欧亚汇聚使青藏高原地壳增厚至正常地壳的两倍，因此有学者认为印度板块底垫在高原之下；也有研究认为岩石圈吸收块体间汇聚而缩短增厚使高原抬升。显然岩石圈变形对高原构造演化有重要指示，但因缺乏上地幔结构约束，对青藏高原岩石圈形态、印度俯冲角度等仍认识不足。上地幔顶部与地壳直接接触，其性质既受深部影响，也制约着浅部构造，是约束岩石圈变形及壳幔耦合状态的重要参数。Pn走时成像普遍用于探测上地幔速度，但其分辨率受到震中距和射线分布限制。30至50度间S波的壳内多次反射震相(SsPmp)在莫霍面产生相移，相移大小主要依赖于上地幔顶部P波速度。本申请拟搜集青藏高原远震波形数据，提取SsPmp相移获取青藏高原上地幔顶部速度结构，为青藏高原岩石圈变形和印度板片水平俯冲前缘提供约束；进而结合深部结构及浅层构造，分析上地幔顶部速度异常的成因并探讨青藏高原壳幔耦合状态，为理解高原生长和大陆俯冲提供地震学证据。

The continental collision and the subsequent convergence between the Indian and the Eurasian plates has thickened the crust of the Tibetan plateau to double of the normal crust. Thus, the Indian plate is suggested underlying beneath the Tibetan plateau horizontally. However, some other opinion aroused that which causes the raising of the Tibetan plateau is the shortening and thickening of the Tibetan lithosphere absorbing the amount of the convergence between the two plates. Obviously, the deformation of the Tibetan lithosphere is a key clue to understand the tectonic evolution of the Tibetan plateau. Due to the poor constrain from the structure of upper mantle, it is still controversial that the deformation of the Tibetan lithosphere and the subducting angle of the Indian slab. The seismic velocity of the upper most mantle is the significant parameter to constrain the deformation of the Tibetan lithosphere and the crust-mantle coupling. Pn-wave travel-time tomography is the most essential method to detect the upper mantle velocity structure at present, but resolution is limited by the epicenter distance, the frequency band of the signal, especially the coverage of the ray paths. The inter-crustal multiple reflective phase generated from the S-wave from the epicenter distances between 30° and 50° is total reflected at the Moho with high energy and producing a phase shift. The degree of the phase shift depends on the P-wave velocity at the upper most mantle. This application is intended to collect the tele-seismic waveform data recorded in and around the Tibetan plateau, extract P-wave velocity at the upper most mantle and constrain the lithospheric deformation. Comparing with the deep structure and shallow tectonic, to provide constraint for the range of the horizontally subducting Indian slab and discuss the reason causing the abnormal of the upper most mantle and the coupling state between the Tibetan crust and mantle.