Electrical resistivity tomography and time-domain induced polarization field investigations of geothermal areas at Krafla, Iceland: comparison to borehole and laboratory frequency-domain electrical observations

• Published in: Geophysical Journal International
• Main Authors: Lévy, L., Maurya, P.K., Byrdina, Svetlana, Vandemeulebrouk, J., Sigmundson, F., Arnason, K., Ricci, T., Deldicque, D, Roger, M., Gibert, Benoit, Labazuy, Philippe
• Other Authors: École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL), Aarhus University Aarhus, Institut des Sciences de la Terre (ISTerre), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement IRD : UR219-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes 2016-2019 (UGA 2016-2019 ), Nordic Volcanological Center Reykjavik, Institute of Earth Sciences Reykjavik, University of Iceland Reykjavik -University of Iceland Reykjavik, Istituto Nazionale di Geofisica e Vulcanologia - Sezione di Roma (INGV), Istituto Nazionale di Geofisica e Vulcanologia, Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: Hydrogeophysics; Hydrothermal Systems; Electrical Resistivity Tomography; [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; Krafla; Iceland
• Online Access: https://hal.umontpellier.fr/hal-02288892; https://hal.umontpellier.fr/hal-02288892/document; https://hal.umontpellier.fr/hal-02288892/file/ggz240.pdf; https://doi.org/10.1093/gji/ggz240

International audience Interaction of H 2 S and basaltic rocks in volcanic geothermal areas can originate from natural up-flow of magmatic fluids or H 2 S artificial re-injection in relation to geothermal exploitation, both causing pyrite mineralization. We study the possibility to track these processes with electrical impedance field measurements. Electrical Resistivity Tomography (ERT) and Time-Domain Induced Polarization (TDIP) measurements were performed along thirteen 1.24 km long profiles, at three different sites around the eastern caldera rim of the Krafla caldera: (i) a 'cold altered' site affected by past hydrothermal circulations, (ii) a hot active site and (iii) a 'cold un-altered' site, unaffected by hydrothermal circulations. We present 2-D inversions of direct current (DC) resistivity, maximum phase angle of the electrical impedance (MPA) and relaxation time. The maximum depth of investigation for the MPA is 200 m, obtained in zones of high resistivity, corresponding to fresh and recent unaltered basalt. At the hot and cold altered sites, the field resistivities are compared to in situ borehole logs and laboratory complex resistivity measurements on rock samples from the boreholes. The laboratory complex resistivity was measured at six different pore water conductivities, ranging from 0.02 to 5 S m −1 , and frequency in the range 10 −2 − 10 6 Hz. The time-range investigated in our field TDIP measurements was approximately 0.01-8 s. At the cold altered site, the inverted resistivity is consistent with both borehole observations and laboratory measurements. At the hot site, resistivity from field inversion and borehole logs are consistent. Comparing inversion results and borehole logs to laboratory resistivity measured on core samples at room temperature reveals that a correction coefficient for the effect of temperature on resistivity of 6 per cent per • C is appropriate at investigated depths. This exceptionally high temperature correction coefficient suggests a dominant influence of interface ...