多层界面的H-κ扫描方法获取的拉萨深部结构特征

Characteristics of deep structure beneath Lhasa from multi-layer H-κstacking method

对不同深度莫霍面正演模拟的每条接收函数进行H-κ扫描,将得到的H和κ投影到平面图,发现同深度莫霍面的投影点能够拟合成一条曲线,进而通过该曲线能够分离不同深度界面对应的接收函数。在此基础上,再利用H-κ-θ方法计算估计倾斜界面的倾角和倾向。最终实现倾斜界面和“双莫霍”现象的辨识。利用此流程处理了拉萨固定台站(LSA)记录的大量接收函数,获得了拉萨台下方的地壳厚度约为70 km,地壳平均波速比约为1.67,莫霍面倾向北东,倾角为24°,而莫霍面下俯冲的印度板块界面深度约为106 km,倾向正北,倾角约为40°,其上方地幔楔内部的平均波速比约为1.69。正演模型计算结果和实际观测数据检验综合表明该方法能较好地区分不同界面对应的接收函数,藉此获取其界面的构造变化特征,有助于获得更加精细的壳幔结构特征。

The Moho discontinuity,marking the boundary between the Earth’s crust and mantle,carries abundant information about the structure and evolution of the crust-mantle system.The“doublet Moho”phenomenon observed beneath the Tibetan Plateau complicates the investigation of Moho structure.The H-κstacking of teleseismic receiver functions is a widely employed technique for determining Moho depth and crustal vP/vS ratios of horizontal layered crustal structure.The H-κstacking was performed on each receiver function for different depth of the Moho from synthetic model.And,the obtained values of H andκis projected onto a planar map,which reveals that the projected points corresponding to the same depth Moho interface align along a curve.Thus,the separated receiver functions is easily associated with distinct interface depths.Then,one can determine the dip direction of a tilted interface by analyzing the crustal thickness projection map.Subsequent processing can be targeted at each layer of receiver functions individually.Utilizing a large dataset of seismic recordings from LSA station of China Digital Seismograph Network,we follow the above-mentioned steps to separate the receiver functions of LSA and identify two key interfaces.Finally,employing the H-κ-θmethod independently for each interface,we derived the following characteristics of the two interfaces:①the crustal thickness beneath the Lhasa station is approximately 70 km with an average vP/vS ratio of about 1.67,and the Moho interface dips at an angle of 24°;②the subducting Indian Plate interface lies at a depth of about 106 km with a dip angle of 40°.Above this interface of 106 km depth,the average vP/vS ratio within the mantle wedge between the two interfaces is approximately 1.69.Our results demonstrate the effectiveness of this method in distinguishing receiver functions corresponding to different interfaces.By integrating this approach with other techniques,more accurate subsurface structures can be elucidated,providing valuable insights into the geologic structure beneath the Qinghai-Xizang Plateau.This work contributes to a better understanding of the complex tectonic processes in this seismically active region.