The Combination of Static Shift Correction and 3D Inversion for Magnetotelluric Data and Its Application

Base on the previous studies on the static shift correction and nonlinear conjugate gradient inversion algorithms (NLCG) for magnentelluric data (MT), we improve the 3D inversion method, which is combined with a new static shift correction method.

The static shift correction method is proposed based on the 3D theory and real data. It can be detected by the quantitative analysis of apparent resistivity and impedance phase of MT in high frequency range, and completed correction in inversion process. The method is an automatic processing technology with 0 cost, and avoids the additional field work and human factors.

In addition, the 3D inversion algorithm is improved (Zhang et al., 2013) base on the NLCG method of Newman & Alumbaugh (2000) and Rodi & Mackie (2001). For the algorithm, we added the parallel structure and static shift correction, improved the computational efficiency, reduced the memory of computer and added the topographic and marine factors. So the 3D inversion could work in general PC with high efficiency and accuracy. And all the MT data of surface stations, seabed stations and underground stations can be used in the inversion algorithm. The method is applied in some deposits (hundreds km² for each one) and ore districts (thousands km² for each one).

One demo of the method application is shown in figure 1 for the data collected in southern NingWu volcanic basin and adjacent area (in the Middle-Lower Reaches of Yangtze River, eastern China). This basin is a typical iron ore district, and we find one local uplift in the southern area which is the key for copper deposits. That indicates one copper enrichment region existed on/to the south of NingWu basin, combining with the discovered copper deposits.

The demo shows the effectiveness of the combination method for MT data.