网格剖分对电阻率曲线的影响

Influence of Grid Subdivision on the Resistivity Curve

有限元法作为一种高效的数值模拟方法,广泛用于地球物理的正演计算。网格剖分的合适与否是有限元求解的先决条件。在满足剖分区域大小一致,且满足边界条件,进行稀疏与加密网格比较的前提下,讨论了二维介质理想模型的网格剖分对大地电磁正演精度的影响。研究表明,在低频阶段,TE和TM两种极化模式从整体上看,粗网格比细网格模拟精度高,但是在近地表开始阶段,TM模式下,粗网格模拟精度不及细网格;整体变化幅度粗网格比细网格缓和,曲线尾部粗网格与细网格波动幅度都较大,脱离了正常值。结果表明,正确的网格剖分能有效地提高电磁有限元正演的精度,且对后续反演同样有意义。

As a highly efficient numerical simulation method, finite element method is widely used in geophysical forward calculation. Whether grid subdivision is suitable or not is the prerequisite for finite element solution. From the aspect of ideal two- dimensional medium model, this paper discusses the effect of grid subdivision on magnetotelluric forward modeling precision, under the conditions that the subdivision areas have the same size, the boundary conditions are satisfied, and the sparse and dense mesh are compared. In low frequency phase, two polarization modes were taken as a whole, the coarse grid has higher simulation accuracy than the fine grid, but at the beginning of the near-surface phase under TM mode, the simulation accuracy of the coarse grid is not as high as that of the fine grid. Overall, the coarse grid has more moderate change than the fine grid, and the fluctuation amplitude of the coarse grid and fine grid is higher in the tail of the curve, both of which deviate from the normal value. The results show that proper grid subdivision can effectively improve the accuracy of electromagnetic finite element forward modeling, amt it is significant for the subsequent inversion as well.