INVERSION OF THE UPPER CRUSTAL VELOCITY STRUCTURE IN CAPITAL AREA WITH PG WAVE

The velocity structure in the upper crust of Capital Area is inversed with the Pg wave travel time data, which is the seismic sounding data with densest explosion distance and high resolution from Tianjin-Beijing-Chicheng DSS profile.The results show that the profile can be divided into North China Basin and Yanshan Uplift, and the former can be also divided into Huanghua depression, Cangxian upheaval, Jizhong depression and so on.Dachang depression, Tongxian upheaval, Beijing depression and Jingxi uplift belong to the front edge of Yanshan Uplift.It is mainly lower velocity depression in North China plain area, with lower surface velocity, deeper basement, thicker cover strata and high gradient vertical velocity.Whereas in Yanshan Uplift, it is mainly higher velocity upheaval, with high surface velocity, shallower basement, thinner cover strata and lower gradient vertical velocity.The basement undulates greatly, which reaches 6km at deep region, but can not get 1km at shallow area.