The lithospheric structure beneath southeast Tibet revealed by P and S receiver functions

Abstract

Yunnan is located at the margin of southeast Tibet, where dramatic tectonic activities occur. In this study, we calculated the P and S receiver functions by the deconvolution of three-component seismic data from 48 permanent broad-band stations deployed in Yunnan region. In order to improve signal-noise ratios of the receiver functions, we move-out corrected receiver functions to a reference epicentral distance of 67°, and then stacked them to one trace for each station. Finally, the stacked traces were converted to the depth domain to obtain the crustal and lithospheric thicknesses beneath each station. In southwestern Yunnan (at the west side of the Jinshajiang-Red River Fault), the crustal thicknesses from the P-wave receiver functions (PRFs) and from the S-wave receiver functions (SRFs) are in the ranges of 30–36km, and of 33–39km, respectively. But in northwestern Yunnan, the crustal thicknesses from PRFs and SRFs are from 66 to 69km and from 63 to 66km, respectively. Our results show that the crustal thicknesses in Yunnan from PRFs and SRFs are consistent, with a maximum deviation of 3km; and increase gradually from ∼30km in the south to ∼68km in the northwest. Besides, the lithospheric thickness from PRFs is also similar to that from SRFs, with the largest difference of 15–20km in southeastern Yunnan. At the west side of the Jinshajiang-Red River Fault in western Yunnan, it is only about 80–100km, and increases to 140–150km regionally in northern and southeastern Yunnan. The thinned lithosphere extends eastward from western Yunnan to eastern Yunnan. We attribute the thinned lithosphere to the upwelling of hot upper mantle materials associated with the eastward subduction of the Indian plate.