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采用 Gaver-Stehfest( G-S)方法模拟水平电偶极源在不同介质模型中地表面的负阶跃波电磁场响应 ,然后引入逆时序偏移的观点 ,把这些电磁场响应作为实际观测值 ,利用 Stratton-Chu积分公式将其向下偏移 ,对偏移后的电磁场值进行归一化处理并对场值求偏导数 ,重建地下拟地震深度剖面图 ,实现时间域电磁场的偏移成像。选用了均匀介质、含良导和高阻薄层水平均匀层状介质模型以及高阻柱体、断层等模型分别进行计算 ,成像的结果表明能够得到较高质量的地下地电构造图 ,从重建的深度剖面图中可以识别出地下反射界面的位置 ,该图比时间剖面直观。
The Gaver-Stehfest (GS) method is used to simulate the negative step-wave electromagnetic field response of the horizontal dipole on the ground surface in different media models. Then, the viewpoints of inverse time series shift are introduced, and these electromagnetic field responses are taken as the actual observations. Stratton- Chu integral formula to down-shift the electromagnetic field value after the offset normalized and the partial derivative of the field values, reconstruction of the quasi-seismic depth profile of the underground, the realization of time-domain electromagnetic field migration imaging. The homogeneous medium, the horizontal uniform layered medium model with good conductivity and high resistivity thin layer, the model of high resistivity column and fault are selected for calculation respectively. The imaging results show that the high quality underground structure can be obtained, The depth profile can identify the location of the subsurface reflection interface, which is more intuitive than the time profile.