大地电磁法三维反演计算模型分辨率分析

Analysis for Model Spatial Resolution in MT 3DInversion

设计了3个简单三维电性结构模型,通过模型三维正反演计算来对大地电磁法三维反演计算空间分辨率进行数值模拟,模拟结果表明:大地电磁法对低阻体反应灵敏,对高阻体反应相对薄弱,可以较好地应用于探测浅部、深部低阻异常体;大地电磁测深响应数据具有三维体效应属性,除了反应测点下方电阻分布情况之外,同时也包含测点周边电阻率分布信息,可较好地应用于区域电性结构调查;对于浅部异常体,尤其是低阻异常体,在测点控制区域范围内大地电磁三维反演计算具有较好的三维空间分辨率;对于深部异常体,仅在异常体具有足够尺度情况下,大地电磁三维反演计算才具有较好的三维空间分辨率;无论是浅部异常体还是深部异常体,在异常体具有足够尺度的情况下,即异常体的响应曲线在横向空间域和纵向频率域上具有一定的识别度,大地电磁三维反演计算可以较好地构建出异常体的结构形态,对于尺度不足够大的异常体,大地电磁三维反演计算可以较好地重建地下介质的宏观电性特征。

In this paper, 3 simple three-dimensional electrical structure models are designed, and the three-dimensional spatial resolution of magnetotelluric method is simulated and analyzed by the forward and inverse modeling method. Simulation results show that： The magnetotelluric method is sensitive to the low resistance body, and it can be used in the detection of shallow and deep low resistivity anomaly.Magnetotelluric sounding data has the attributes of three-dimensional effect, in addition to containing the resistance distribution below the observation station, but also includes surrounding resistivity distribution information, it can be better applied to the regional electrical structure survey.For the shallow anomaly, especially the low resistivity anomaly, the 3D inversion calculation of the magnetotelluric method has a better three-dimensional spatial resolution in the control region of the observation stations.For the deep anomalies, only in the case of abnormal body with sufficient size, the three-dimensional inversion calculation of the earth＇s electromagnetic has a better three-dimensional spatial resolution.Both shallow anomaly or deep anomaly, anomalous body with enough scale, response of abnormal body in the transverse space domain and the longitudinal frequency domain has a certain degree of recognition and three dimensional magnetotelluric inversion calculation can be better used tobuild the structure form of abnormal body, for abnormal body scale is not big enough, the 3D inversion of magnetotelluric inversion calculation can better reconstruction of underground medium macro electrical characteristics.