Comparison of 2-D and 3-D Models of a Magnetotelluric Survey in Southern Portugal
We constructed 2-D and 3-D models for an areal magnetotelluric (MT) survey covering about 2500 km2 in southern Portugal. The geology is complex because the Messejana fault and the Ferreira-Ficalho overthrust intersect within the region, but it was possible to choose some profiles crossing areas that could be considered 2-D. Data from 34 measurement sites were processed and inverted for 1-D models (below each site); 2-D models were constructed from the 1-D models toward the boundary of the study area, where the geology appears to be 2-D. A 3-D electromagnetic model was constructed for the central region of the study area. Comparison of the 2-D and 3-D results shows that some of the geoelectric characteristics found in the 3-D model are not obvious, or even visible, in the 2-D results. The 2-D analysis does not give any indication of the 3-D nature of the nearby region. Furthermore, comparison between field data and the 3-D model results indicates that the main geoelectric characteristics of the region are evident in the response of the 3-D model, despite its simplicity. For this area of southern Portugal, 2-D MT profiles do not seem to present a good picture the region’s geoelectric structure.