3-D Tomographic Determination of Uppermost Crust Using Pg Diving Wave

In this paper a method, reconstructing three dimensional local velocity distribution of uppermost crust using Pg diving wave generated by explosions, is proposed.The forward problem is calculated using least-square iteration technique to obtain model parameters with vertical velocity gradient and travel-time residuals.The inverse problem is solved based on Least-squares criteria in functional space.It is not necessary to parameterize velocity model ahead in our method.The velocity at any point in model space cna be estimated.In this paper the observed Pg data in Luanxian seismic region have been treated and the 3-D velocity distribution of the uppermost crust in this region has also been reconstructed.