Rapid evaluation of multifrequency EMI data to characterize buried structures at a historical Jesuit Mission in Argentina

We present results from a geophysical prospection at a historical Jesuit Mission, located in San Ignacio (Misiones-Argentina), declared World Monument some years ago. We studied different sectors looking for buried structures; the total area under study covered 36 ha. In this work we will show the results obtained in a sector that at the time of the prospection was at imminent risk of being damaged by a wrong management of the historical resource. To optimize the data acquisition and the preliminary in-situ analysis of the results, we performed an electromagnetic survey using a multifrequency electromagnetic induction device (GEM-2) to have a first insight of the near surface electrical distribution. From 2D and 3D visualization of data, different targets were identified as possible historical structures. Around these anomalous zones, we performed different dipole–dipole profiles, forming high resolution grids for later 3D inversions. Further inversions of the electric and electromagnetic data completed the characterization of the anomalies. One of the main results of this work is that the 3D electric image obtained from 1D inversion of electromagnetic data coincides with the 3D images obtained from resistivity inversion, but at a much less time consuming cost.