Swave velocity structure in southwest China from surface wave tomography and receiver functions

Abstract

Using the surface wave records of 504 teleseismic events at 50 temporary and 92 permanent seismic stations in southwest China, we obtain phase velocity maps at 10, 15, 25, 40, 60, and 75 s at a grid spacing of 0.5°× 0.5°from the interstation correlation method and surface wave tomography. We also obtain the S wave velocity structures beneath three profiles using the joint inversion of receiver functions and surface waves. At short periods (10 and 15 s), high-velocity zones (HVZs) are found in the Panzhihua-Emeishan region, the Sichuan basin and the Weixi-Lijiang region surrounding the low-velocity zones (LVZs) from Songpan-Ganzi block to the east of Lijiang, where the elevations are significantly higher. At long periods (40, 60, and 75 s), HVZs are found in the Weixi-Lijiang region, the Panzhihua-Chuxiong basin,and the Kunming-Tonghai region, which form a belt in the center part of the study area. The fast polarization directions on both sides of the belt defined by the shear wave splitting of teleseismic SKS waves vary significantly and indicate that the flow of material from the plateau is blocked in two different depth intervals and leads to different horizontal extents. The long-period maps and the structures along the three profiles show that LVZs are present in the upper mantle beneath rapidly slipping fault zones, such as the Anninghe-Zemuhe-Xiaojiang fault zone, the Red River fault zone, and the Xiaojinhe fault zone, implying that these faults penetrate deep into the mantle.

Crustal thickness and Poisson's ratio in southwest China based on data from dense seismic arrays

“…Combined with the high heat flow (76 mW/m 2 ), low resistivity, and low S wave velocity in the SE Tibetan Plateau [ Hu et al , ; Wei et al ., ; Sun et al , ; Yao et al , ; Wang et al , ], partial melt may also exist in the region. The young Konga Shan granite (~10 Ma) in the Xianshuihe fault zone is considered to result from the partial melt of the continental crust [ Roger et al , ].…”

“…It is also important to carry out a detailed study of crustal structure to evaluate the lower crust flow model. Although intermediate Poisson's ratios are found near the Longmenshan fault, there may be no low‐velocity zone in the lower crust [ Wang et al , , ]. Therefore, there should be no lower crustal flow beneath this fault.…”

Geodetic imaging of potential seismogenic asperities on the Xianshuihe‐Anninghe‐Zemuhe fault system, southwest China, with a new 3‐D viscoelastic interseismic coupling model

“…Many studies have investigated the crustal structure of the Sichuan basin and eastern Tibetan Plateau [e.g., Hu et al ., ; Li et al ., ; Liu et al ., ; Sun et al ., ; Wang et al ., , , Y. Wang et al , ; Wang et al , ; Xu et al ., ; Yang et al ., ; Zhang et al ., ; Xu and Song , ; Zhou et al ., ]. The results from S and P wave receiver function analysis as well as ambient noise surface wave and P wave tomography show that the crustal thickness of the Ahba subblock ranges from 50 km to 60 km northwestward.…”

“…In addition, there is a lower‐velocity zone (LVZ) in the middle lower crust of the eastern Tibetan Plateau detected by seismic observations [e.g., Fu et al ., ; Li et al ., ; Wang et al ., , , Y. Wang et al , ; Wang et al , ; Xu and Song , ; Yang et al ., ; Yao et al ., ; Zhang et al ., ] as well as magnetotelluric data [ Bai et al ., ]. The LVZ probably indicates localized and limited partial melting crustal flow.…”

Reliable workflow for inversion of seismic receiver function and surface wave dispersion data: a “13 BB Star” case study

“…Even in this case however, there may remain a certain ambiguity that should be taken into careful consideration throughout the inversion. A single model obtained by minimization of the data misfit function cannot be regarded as a full solution of the inverse problem (Gubbins 2004), which is often the case in linearized inversion (Julià et al 2003;Horspool et al 2006;Wang et al 2014;Sosa et al 2014;Bao et al 2015;Li et al 2016). One needs to probe the whole space of physically plausible solutions, by drawing inferences from an ensemble (Sambridge and Mosegaard 2002).…”