三维大地电磁数据的二维反演解释

Using 2-D inversion for interpretation of 3-D MT data.

鉴于现今三维电磁反演方法尚不成熟,探讨提高二维反演方法解释三维大地电磁数据仍有必要。文中给出3D/1D和3D/2D两种模型的二维反演结果,通过对三维棱柱导体地质模型与二维长方形导体地质模型的大地电磁视电阻率与相位响应的比较发现,二维TM模式的响应与对应的三维YX模式响应很接近,且可通过单一TM模式反演确定导体赋存位置,但反演的电阻率值要比真实值偏大;二维TE模式的响应与对应的三维XY模式响应在低频时相差较大,TE模式的反演结果能够反映导体的电阻率值,但是在垂直方向上有拉伸导体的现象。而TE和TM联合反演结果则结合了TE与TM模式反演的优点,可以较好地反演出导体的赋存位置及电阻率值。随着三维良导体埋深的增大,二维反演结果很难反映真实三维构造,若增大三维异常体的走向长度和尺度,使用二维反演仍可以有效地反映三维异常体的存在.

In view ot premature inversion method for 3-D MT data,it is necessary to probe improving the method using 2-D inversion method for interpretation of 3-D MT data. The paper gave the 2-D inverted results of two models:3D/1D and 3D/2D. It is discovered through the comparing the responses of MT apparent resistivity and phase of 3-D geologic prism conductor model with 2-D geologic rectangle conductor model that the response of 2-D TM mode is close to that of 3-D YX mode and the existed position of conductor could be determined by the inversion of single TM mode but inverted the resistivity is greater than the real value;the response of 2-D TE mode is large different to that of 3-D XY mode at low frequency and the resistivity of conductor could be reflected by the inversion of TE mode but the phenomenon of stretched conductor exists in vertical direction. The results of joint inversion of TE and TM combine the advantages of inversion of TE with TM mode, which can better invert the existed position and resistivity. The results of 2-D inversion are difficult in reflection of real 3-D structure along with the increasing buried depth of good conductor; using 2-D inversion can still effectively reflect the exist of 3 D anomalous body if increasing the oriental length and scale of 3-D anomalous body.