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

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-κ stacking of teleseismic receiver functions is a widely employed technique for determining Moho depth and crustal v_P/v_S ratios of horizontal layered crustal structure. The H-κ stacking was performed on each receiver function for different depth of the Moho from synthetic model. And, the obtained values of H and κ is 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-θ method independently for each interface, we derived the following characteristics of the two interfaces: ① the crustal thickness beneath the Lhasa station is approximately 70 km with an average v_P/v_S ratio of about 1.67, and the Moho interface dips at an angle of 24°; ② the 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 v_P/v_S 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.