The application of 2D AMT and MT method in basement exploration in Brazil

A 2-D Audio Frequency Magnetotelluric (AMT) and Magnetotelluric (MT) survey were successfully completed in area of São Francisco, Brazil last year. Totally 40 MT sites were designed to cover part of one seismic line in order to compare the data of two geophysical methods. The main objective of this project is to supply the resistivity profile and data comparison with seismic exploration to outline the depth of basement ranging from the surface to 4,000 meters. The optimal inversion method and interpretation strategy for this 2-D AMT/MT data was first selected through the comparison of different modeling and inversion tryout results using a variety of inversion methods and actual field 2-D AMT/MT data. Upon applying the optimal inversion method and interpretation strategy, the depth and distribution of the basement was estimated based on the 2-D AMT/MT inversion results. From the 2D inversion of different modes, one can see that the depth of basement of this area is roughly from surface to about 1.2 km depth and it was relatively flat with a little fluctuation, which is correlate well with the result of seismic data. The interpretation result of the 2-D AMT/MT surveys indicates that AMT/MT methods were proven to be the effective methods for prospecting deep structures which in many cases appear to correlate well with geological structures.