Combining Electrical Resistivity Tomography and Ground Penetrating Radar to study geological structuring of karst Unsaturated Zone |
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| Institution: | 1. UAPV, UMR 1114 EMMAH, 84000 Avignon, France;2. UPPA FR 2952 IPRA, 64000 Pau, France;1. Departamento de Ciencias de la Tierra, Universidad de Zaragoza, Edificio Geológicas, C/. Pedro Cerbuna 12, 50009 Zaragoza, Spain;2. Departamento de Geología, Universidad Autónoma de Barcelona, Barcelona, Spain;3. Àrea de Geodinàmica Externa i Geomorfologia, Universitat de Girona, Girona, Spain;4. Geo-Haz Consulting Inc., CO, USA;5. Universidad Estatal de Bolivar, Guaranda, Ecuador;1. Department of Mining Exploitation and Prospecting, School of Mining Engineering (University of Oviedo), C/ Independencia 13, 33004, Oviedo, Spain;2. Hydro-Geophysics and NDT Modelling Unit, Polytechnical School of Mieres (University of Oviedo), C/ Gonzalo Gutiérrez Quirós S/N, 33600, Mieres, Spain;3. Department of Geography, Prehistory and Archaeology, Faculty of Arts, University of the Basque Country, C/ Tomás y Valiente s/n, 01006-Vitoria-Gasteiz, Spain;1. Institute of Bio and Geosciences 3, Forschungszentrum Jülich, Jülich, Germany;2. Applied Geophysics Unit, Faculty of Applied Sciences, University of Liège, Liège, Belgium;3. Research Group Geophysics, Department of Geodesy and Geoinformation, TU-Wien, Vienna, Austria;1. Departamento de Geodinámica, Universidad de Granada, 18071 Granada, Spain;2. Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, 18071 Granada, Spain;3. Instituto Andaluz de Geofísica y Prevención de Desastres Sísmicos, Universidad de Granada, 18001 Granada, Spain;4. Instituto Geológico y Minero de España, Ríos Rosas 23, 28003 Madrid, Spain |
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| Abstract: | This paper highlights the efficiency and complementarity of a light package of geophysical techniques to study the structure of karst Unsaturated Zone (UZ) in typical Mediterranean environment where soil cover is thin or absent. Both selected techniques, 2D Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT), are widely used in environmental studies and their application is accessible for a lot of scientists/engineers. However, GPR or ERT alone is not able to provide an enhanced characterization of geological features in karst media. In the present study, GPR results supply a near surface high resolution imaging and thus can provide relevant geological information such as stratifications and fractures. Despite the quality of the results GPR's investigation depth remains limited to around 12 m. Apparent and inverted resistivity provided by ERT surveys shows strong lateral and vertical variations. These variations can inform about general geological structuring and feature orientation. ERT is able to prospect down to 40 m but it's a low resolution integrative technique. In the study area the investigated limestone is a commonly electrical resistive formation (more than 2000 Ω.m). However deeper than 5–7 m, the ERT profiles reveal several zones of moderate resistivity (around 900 Ω.m). In these zones a stratification change corresponding to slanted bedding is clearly identified by GPR results. The combination of both GPR and ERT results can allow a well-established geological interpretation. These moderate resistivity zones with slanted beddings can explain the presence of a perennial water flow point 35 m below the surface of the studied site within the underground gallery of the Low-Noise Underground Laboratory (LSBB). |
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