Boat-towed RMT Measurements on the Water Surface over the Äspö Hard Rock Tunnel in Sweden
2016 (English)Conference paper, Abstract (Refereed)
We carried out 3 km of radio magnetotelluric measurements in three hours on the water surface using a new boat-towed platform at the Borholm Fjord over the Äspö Tunnel in Sweden. The new platform was stable and use of DGPS receiver at the location of electromagnetic sensors facilitated faster data acquisition. The data were inverted in 2D and the resulting resistivity models revealed detailed information about the geological structures below the water. The estimated water depths were compared to the on-site echo sounder data that were collected simultaneously. We observed very close match between the two. The very low resistivity overburden (< 1 Ohmm) thickens towards the south-eastern part of the area with thicknesses > 10 m. After incorporating the RMT data that were acquired on the land at the northern part of the area a low resistivity zone that dips towards the northwest was resolved in the resistivity model. We interpret this zone as a major weak/fracture zone that is observed at depth inside the Äspö Tunnel. The low resistivity of water and overburden has strongly limited the depth penetration of the method and we suggest use of methods with deeper penetration such as controlled source magnetotelluric.
Place, publisher, year, edition, pages
IdentifiersURN: urn:nbn:se:uu:diva-303365DOI: 10.3997/2214-4609.201602172OAI: oai:DiVA.org:uu-303365DiVA: diva2:971657
Near Surface Geoscience 2016 - Second Applied Shallow Marine Geophysics Conference
FunderSwedish Research Council Formas