Velocity Structure And Dynamics Mechanism In Crust Beneath Yunnan Province

In this article, we select and analyze159teleseismics seismogram from50stations which are located in Yunnan Province. The zone of stations lies between97°E-107°E and21°N-29°N. In the beginning, we compute every P wave receive function from every station, the number is2211. Then we obtain their velocity structures by choosing a simple initial model and managing to do the double-inversion. After carrying on a kind of bootstrap statistics to all the teleseismic velocity structures in one station, the particular velocity structures of it will be estimated. We analyze the Mohorovicic discountinuity (Moho), which separates Earth’s crust from the underlying mantle in this region. These questions will be also asked:Is there any low velocity zone in this crust and where are they? With the help of S wave velocity structures, a lot of figures and forms will be determined. We combine all the stations into an overall field in the last and characterize the features of it. These features can help to illuminate crust structures of Tibet Plateau or Yunnan Province, so as to the dynamic mechanism between Eurasian Plate and India Plate.Main conclusions in this article:1. After theoretical number simulation experiment and the calculation with real data, we make sure that the method of bootstrap statistics is feasible when we calculate a particular velocity structure under one certain station with kinds of observed results. And it is even more reliable than the method that superposing wave forms before the inversion. Besides, there will be less dependence in inversion results by choosing initial model twice and computing receives functions with different Gaussian parameter.2. The thickness of crust in this area increases from south to north and variation extends from32km to68km, which reveals an upraising of Tibet Plateau. Some tongue shape embossments are observed near the Dianzhong block in Moho isoline images. It tells fact that the range-abilities of Moho thickness are variational in different direction, which lead to a heterogeneity of Moho distribution.3. Illuvial horizons widely distributes within study area2km depth underground. S velocity changes to3.0km/s under this layer. There are low velocity structures below part of the station. These stations are located near deep fault, volcanism zone or in Dianzhong block. There are few low velocity structures in regions where lithosphere is relatively stable, such as Sichuan Basin, Baoshan Block and Orchid-Simao block. 4. According to the calculation results, our study in this paper supports the method that crustal movement of material flow mode of the Tibetan Plateau, i.e. material matter in lower crust has been extruded out of the Tibetan Plateau and become some flows. They are limited by Sichuan Basin and Eastern Himalayan Syntaxis, and then they flow into Yunnan province mainly along the deep fault. Besides, flowing crustal matter has already move through the Lijiang fault, they get into and concentrate within Ddianzhong fault.