Mapping of thin sandy aquifers by using high resolution reflection seismics and 2-D electrical tomography

Abstract

Electrical tomography, which gives good results even in fairly complex geological environments, has given a new lease of life to electrical methods in hydrogeological surveys. Nevertheless, a rapid decline in resolution with increasing depth remains the main problem of the electrical methods. In the Pannonian basin in Croatia, at a test area, combining both electrical tomography and seismic reflection methods provides data that better constrain the lithological and hydrogeological model of the subsurface.Electrical tomography revealed a rather thick packet of sediments with increased resistivity at depths of 40-100 m. Using the electrical forward modelling, the existence of two different hydrogeological models was shown. The first model presupposes a reasonably homogeneous packet of sandy clays or clayey sands, and the other model presupposes the alternation between layers of clays and sands. From the hydrogeological point of view, the second model is perspective, but unfortunately, the use of electrical tomography alone does not allow the ambiguity to be resolved. The separation of these two models became possible using seismic reflection. Three seismic environments were isolated from the seismic profile treated, and the strongest reflections were discovered in the first seismic environment, which covers the depths from 40 to 100 m. It was determined that the second model is more acceptable, because these reflections are caused by lithological changes, that is, the alternations of sands and clays. The interpretation is consistent with exploratory borehole data. The conclusion is that electrical tomography gives data concerning the sediment lithology up to depths of 40 m, but at greater depths combined interpretation of electrical and seismic data constrains the subsurface model better. D

Joint application of ground penetrating radar and electrical resistivity imaging to investigate volcanic materials and structures in Tenerife (Canary Islands, Spain)

“…The principal applications of this technique include (see for example Telford et al, 1990;Reynolds, 1997;Šumanovac, 2006) definition of aquifer boundary units, such as aquitards, bedrock, faults and fractures, the detection of voids in karstic regions, the mapping of saltwater intrusions into coastal aquifers, the identification of contaminated groundwater plumes, the detection of mineralized zones, and the exploration of sand and gravel resources among others.…”

Electrical Tomography Applied to the Detection of Subsurface Cavities

“…This technique has numerous possible applications when one is faced with various problems in different geological settings (Caputo et al, 2003;Colella et al, 2004). It is increasingly used in environmental studies, hydrogeology (Maillet et al 2005;Š umanovac, 2006;Martínez et al, 2009), and geotechnics (Naudet et al, 2008), among other fields. This technique has also been used for detection of natural crevice-type caves (van Schoor, 2002;Gutiérrez et al, 2009;Pá nek et al, 2010;Gambetta et al, 2011) and in some cases, to locate manmade mining cavities (Maillol et al, 1999;Martínez-Ló pez et al, 2007).…”

Identification of the gravitational boundary in weathered gneiss by geophysical survey: La Clapière landslide (France)

“…) or the application of other geophysical methods (seismic reflection and refraction, gravity) to validate the results obtained. Some recent works have shown that the application of resistivity methods can reveal very important details of the weathered zones, the hydrological system, and geological structure (Robain et al, 1996;Lebourg et al, 1999;Ritz et al, 1999;Jongmans et al, 2000;Sumanovac and Weisser, 2001;Lebourg and Frappa, 2001;Godio and Bottino, 2001;Wise et al, 2003;Perrone et al, 2004;Lebourg et al, 2005;Rey et al, 2006;Godio et al, 2006;Sumanovac, 2006). However, this method has been rarely used on deep seated landslides because of logistical difficulties with using resistivity equipment in steep and unstable terrain.…”