CSRMT Survey on Frozen Lake - A New Technique with an Example from the Stockholm Bypass Tunnel
S. Mehta, M. Bastani, A. Malehmir and L.B. Pedersen
Event name: 23rd European Meeting of Environmental and Engineering Geophysics
Session: Geophysics for Engineering Geology and Geotechnical Investigations I
Publication date: 03 September 2017
Info: Extended abstract, PDF ( 2.18Mb )
Price: € 20
More than 7% of the Scandinavian landmass is covered with fresh-water bodies in the form of lakes and rivers. This poses a unique challenge to carry out electromagnetic survey on shallow-water bodies for various purposes for example geotechnical investigations. Recently boat-towed RMT (radio-magnetotelluric) technique was introduced and used for measurements over the Lake Mälaren in Stockholm, Sweden. The RMT covers a wide range of frequencies (10-250 kHz) and provides good resolution for shallow subsurface studies although it lacks resolution at greater depths. Using controlled-source frequencies in the range of 1-10 kHz sufficient penetration depths can be achieved for most of the near surface targets. In this study, we present the results from the combined use of controlled-source and RMT (CSRMT) data that were obtained over frozen Lake Mälaren. The objective of this study was to map bedrock surface and fractures in the middle of the profile where using only RMT data these were not adequate. We demonstrate a new technique where CSRMT surveys were carried out over frozen-shallow-water bodies and we expect the idea to be used in the near future for other applications where moderately-resistive water bodies are present.