Mapping geological structures in bedrock via large‐scale direct current resistivity and time‐domain induced polarization tomography

Abstract

An investigation of geological conditions is always a key point for planning infrastructure constructions. Bedrock surface and rock quality must be estimated carefully in the designing process of infrastructures. A large direct-current resistivity and time-domain induced-polarization survey has been performed in Dalby, Lund Municipality, southern Sweden, with the aim of mapping lithological variations in bedrock. The geology at the site is characterised by Precambrian granitic gneisses and amphibolites, which are intensely deformed, fractured, and partly weathered. In addition, there are northwest-trending Permian dolerite dykes that are less deformed.Four 2D direct-current resistivity and time-domain induced-polarization profiles of about 1-km length have been carefully pre-processed to retrieve time-domain induced polarization responses and inverted to obtain the direct-current resistivity distribution of the subsoil and the phase of the complex conductivity using a constant-phase angle model. The joint interpretation of electrical resistivity and induced-polarization models leads to a better understanding of complex three-dimensional subsoil geometries. The results have been validated by lithological descriptions from several drillings. In addition, direct-current resistivity and time-domain induced-polarization logging has been carried out in two different boreholes, showing a good match with the results of the surface direct-current resistivity and time-domain induced-polarization profiles.The direct-current resistivity and time-domain induced-polarization methodology proved to be a suitable technique for extensively mapping weathered zones with poor geotechnical characteristics and tectonic structures, which can lead to severe problems for infrastructure construction and/or constitute risk zones for aquifer contamination.In order to provide spatially resolved variation of rock quality, the electrical resistivity tomography (ERT) method has been successfully employed in many field cases. During the construction of the Hallandsås Tunnel in southern Sweden, for example, the ERT profiles could predict challenging zones with highly fractured waterbearing or weathered unstable rock (Dahlin, Bjelm and Svensson 1999;Danielsen and Dahlin 2009). Similarly, fractured zones in bedrock have been detected with ERT in several other field cases, e.g., tunnel projects in Italy (Cavinato et al. 2006) and Norway (Ganerød et al. 2006;Rønning et al. 2014). A large-scale application of ERT to investigate bedrock geology is shown by Storz, Storz and Jacobs (2000), where the authors detected electrically conductive fault zones in the metamorphic crystalline basement.

Cross-borehole tomography with full-decay spectral time-domain induced polarization for mapping of potential contaminant flow-paths

“…Gazoty et al 2012a, Johansson et al 2015, Wemegah et al 2017, geological discrimination (e.g. Gazoty et al 2012b, Rossi et al 2017), permeability estimation (e.g. Fiandaca et al 2018b, time-lapse monitoring of CO2 injection (e.g.…”

Investigating the applicability of induced polarization method in ore modelling and drilling optimization: a case study from Abassabad, Iran

“…IP and ER methods are among the most applicable geophysical methods used in subsurface studies notably for selection of the best drilling points for exploration purposes (Bishop and Emerson 1999;Wynn and Grosz 2000;Ferdows and Ramazi 2015b;Hope and Andersson 2016). Some examples of their increased usage include copper exploration using 3D IP modelling in NSW, Australia (Whaite et al 2001), using combination of ER and IP in polymetal deposit in China (Yang, Liu and Wang 2008), gold exploration at the eastern desert of Egypt by IP measurement (Taha et al 2018), combination of ER, IP and microgravity to detect buried caves in Spain (Martínez-Moreno et al 2013), copper exploration using IP and ER in Iran (Ramazi and Jalali 2014), gold-silver deposit exploration by IP method in Russia (Gurin et al 2015), detection of the uranium mineralization zone in India (Biswas and Sharma 2016), integration of geophysical methods including IP and ER methods for massive sulphide exploration in Sweden (Tavakoli et al 2016), bitumen mineralization exploration in the west of Iran (Mashhadi, Mostafaei and Ramazi 2017), gold deposit exploration by 3D-induced polarization modelling in Indonesia (Halim et al 2017), 3D tomography of induced polarization and its application in polymetallic mine (Jun-Lu et al 2017), copper mineral exploration using 3D model of IP and resistivity in Brazil (Morriera et al 2018), investigation of a rock glacier by 3D tomography of IP and ER in France (Duvillard et al 2018) and urban area investigation by 3D IP and ER in Stockholm (Pazzi et al 2018;Rossi et al 2017Rossi et al , 2018.…”

Detection and characterization of fracture zones in bedrock in marine environment: possibilities and limitations

“…; Rossi et al . ). The theoretical response of such structures to ERT measurements in a Nordic environment, where low‐resistivity overburden transits to highly resistive bedrock quite abruptly, has been studied and tested by Reiser et al .…”