Sorting out Geologic structures using electrical resistivity Surveys

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Geoelectric methods of prospection are by far the most developed and most frequently used method of prospection. Geoelectric methods can be divided in two main groups AC and DC. While in these groups there are those that involve the actual insertion of current others involve the use of current naturally occurring on earth like the magnetotelluric method. Over time, geoelectric tools have been developed by different companies and gone through, (in accordance to their use) different upgrades to make them more sensible, more resistant to adverse condition, more portable and to allow the collection of large data readings in a shorter period of time. The area in question (where the resistivity survey was carried out) has been subjected to numerous studies with two main objectives to evaluate the geothermic resources and to find new hydro-mineral clusters. The method applied in this dissertation is one of the method used for both the evaluation of geothermic resources and identification of hydro-mineral clusters and hence will enable the identification of subsurface aquifers, points of anomaly and geoelectric zones with higher probability of being mineral water reservoirs. Electro resistivity which is the inverse of conductivity is a type of geoelectric method of prospection currently used mostly for the prospection of mineral water, the location of possible aquifers, and the distribution on the earth surface of resistivity. However, the used of this method for knowledge of the subsurface and possible characterisation and identification of geologic features is but a recent activity in the geophysics area. This dissertation seeks to aid in geological characterisation of an area by geoelectric methods more precisely the electro resistivity method and for that this work was divided in to 4 main topics: introduction, data acquisition, data processing and discussion of results. The introduction, where definition of the objectives is carried out is the first and most important of all the steps it required us to identify targets based on other previous works around the area that include maps, publications, and scientific journals. Use the targets identified to determine the area where the resistivity sections will be carried out in order to obtain as much information as possible and determine the amount of sections that will be carried out in that particular area. Data acquisition is the process of collecting raw data of electro resistivity and is the second part of this dissertation in this process the equipment used is of extreme importance since it needs to be highly sensible as to be able to detect electro resistivity variation from point to point. The equipment choose for this work is the one made available by the university and it is the ABEM Terrameter SAS 300C connected to a booster. Data processing is the step that follows data acquisition and this step is carried out with the aid of software packages like RES2DINV, Excel, and ArcGIS. After data processing follows the discussion of results obtained and subsequent conclusions, having the care to constrain them with as much information as available, in an integrated manner.
Dissertação de Mestrado em Geociências Aplicadas