Teleseismic P Wave Tomography in the Southeast Margin of the Tibetan Plateau

In this paper, we collected 111718 P-wave traveltimes of 888 tele-earthquakes recorded by 516 temporary and permanent seismic stations in the study area. Using the highest density of seismic station distribution up to now, we got the fine P-wave velocity structure deep to 670 km of the southeast of the Tibetan Plateau with application of FMTT technique. The result shows that high-velocity anomaly exists in the lithosphere of Sichuan Basin, and low-velocity anomaly in the east of the Tibetan Plateau. We educe this phenomenon is caused by the downward material flow from the asthenosphere of the Tibetan Plateau eroding the base of Sichuan Basin lithosphere. There is a continuous high-velocity anomaly dipping south in the south of the Sichuan Basin, which may be caused by the detachment of the lithosphere base. The detachment of the lithosphere brings about the upwelling of upper-mantle hot material, which decreases the mechanical strength of crust and together with the eastward intrusion of the Tibetan Plateau material gives rise to the steep topography and high seismic activity. The P-wave velocity is higher in Panzhihua than the surrounding area above the depth of 50 km. According to the geological setting of this place, we conclude that it is caused by the intrusion of mafic and ultramafic magmas during the Permain-Triassic magmatism activity which created the Emeishan Large Igneous Province.