3-D magnetotelluric inversion of 2-D profiles: Application to land and marine data for shallow crustal investigation

Abstract

The 3-D magnetotelluric (MT) inversion has a great potential for providing useful information on the geological background needed in petroleum and mining exploration. We developed a simple and robust full tensor 3D MT data inversion scheme that was tested on several real data sets. The technique allows to provide a detailed 3-D image of complicated geological contexts such as rift basins beneath thick basaltic screen covers. However, for practical reasons, 2-D profiles are still carried out to investigate geological questions. In such cases, tensor decomposition helps to obtain a local or regional strike which enable 2-D inversion but static distortion and effects of local and regional 3-D structures may affect the data. Ad hoc static shift techniques and heavy smoothing techniques are often used to obtain a reasonable solution but they may induce possible bias in the result. Here, we propose a 3-D inversion approach to interpret 2-D data without any decomposition technique or static correction required. The 3-D inversion uses the full MT tensor information in order to recover structures on either side of the 2-D profile. We present results from a synthetic test and applications to land and marine real data sets. Comparison between a standard 2-D approach and our local 3-D inversion provides clues about the bias induced by 2-D inversion of 3-D structures.