Three-dimensional seismic velocity tomography of the upper crust in Tengchong volcanic area, Yunnan Province

Based on data collected by deep seismic sounding carried out in 1999, a three-dimensional P wave velocity structure is determined with tomographic inversion. The tomographic result shows that there is a P wave low velocity zone (LVZ) in the upper crust beneath the Tengchong volcanic area. The LVZ is in the depth of 7~8 km and may be a small magma chamber or a partial melting body. The result also shows that the LVZ is in the northeastern side of the Rehai hydrothermal field, which is located in another LVZ near the surface. The shallow LVZ may represent a well-developed fracture zone. The strong hydrothermal activity in Rehai area can attribute to the existence of fractures between two LVZs. These fractures are the channels for going upwards of the deep hot fluid.