The Numerical Simulations And The Comparison Of Responses Of Seismic Wave Field And Magnetotelluric Field Based On Two-dimensional Model

In geophysical numerical simulation stage,the finite element method and the finite difference method are widely used effective solutions of partial differential equations.In this essay, the finite difference method and the finite element method are separately applied in two-dimensional acoustic wave equation forward and the simulation of magnetotelluric response. After migration, we compare the seismic records with the MT responses caused by similar abnormalities.First, according to the acoustic wave equation in the homogeneous medium, we gained the discrete expressions of the finite difference scheme, which is fourth order in space second-order in time, and the expression of Reynolds discrete absorbing boundary. And then, after iterations in time direction, we added the discrete values of the source wavelet to the two latter. Not only get the snapshots of the wave field, we also received shot gathers and zero offset section. At last, we adopt to Delphi and Fortran mixed programming in order to make parameters input simple and easy to view. Based on layered model, the vertical fault model and stratigraphic pinch-out model we get the migration sections, which illustrate the status of underground media.Similar models are applied to magnetotelluric numerical simulation using the finite element method. Apparent resistivity and phase curves of TM and TE mode are generated. Among them, the apparent resistivity contour maps of TE mode indicate the distribution of resistivity anomalies.Comparing the two simulations of two geophysical fields, we could draw a conclusion that, the results of the acoustic field forward is more accurate than the magnetotelluric forward in terms of the simulation of the complex morphology. In theory, the finite element method should perform better than the finite difference method. Regard to the execution efficiency, that the finite difference one is faster for the reason that the finite element mesh is less fine than the the finite difference mesh, result in a large amount of calculation. Besides, several processing steps are necessary to get migration sections, whereas we could get the apparent resistivity contour maps of TE mode directly and rapidly. It shows that the accuracy and efficiency of the numerical simulations depends on the difference of the geophysical field.