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, Vandemeulebrouck, Jean, Sigmundsson, Freysteinn, Árnason, Knútur, Ricci, Tullio, Deldicque, Damien, Roger, M, Gibert, B., Labazuy, Philippe
• Other Authors: #PLACEHOLDER_PARENT_METADATA_VALUE#, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione Roma1, Roma, Italia
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: 04.08. Volcanology; Krafla; Iceland
• Online Access: http://hdl.handle.net/2122/13411; https://doi.org/10.1093/gji/ggz240

This article has been accepted for publication in Geophysical Journal International ©: 2019, Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Interaction of H2S and basaltic rocks in volcanic geothermal areas can originate from natural up-flow of magmatic fluids or H2S 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 − 106 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 ...