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Boat-towed radio-magnetotellurics; a new technique and case study from the city of Stockholm

Mehrdad Bastani, Lena Persson, Suman Mehta and Alireza Malehmir
Boat-towed radio-magnetotellurics; a new technique and case study from the city of Stockholm
Geophysics (November 2015) 80 (6): B193-B202

Abstract

We have developed a new data acquisition system and technique to measure the radio magnetotelluric (RMT) signals from distant radio transmitters with the objective of mapping and modeling electric resistivity structures below a river or lake. The acquisition system is towed by a boat; therefore, we call the technique boat-towed RMT. The data acquisition is fast with a production rate of approximately 1 km/hr using a nominal sampling spacing of 10-15 m. Given the ample number of radio transmitters available in most parts of the world, the method can be used for near-surface studies of various targets. We have developed boat-towed RMT measurements on Lake Maelaren near the city of Stockholm in Sweden to determine the feasibility of the method. Approximately 15 km of RMT data were collected during three days above a planned 60-m-deep bypass tunnel with the goal of providing information on the bedrock depth and possible weak zones within the bedrock. The measured resistivity and phase data were of high quality with errors on the order of a few percent. The resistivity models from 2D inversion of the data showed a good correlation with available geologic data in resolving bedrock depth and also resistivity layering within the lake. Resistivity maps derived from the dense 2D models suggested a northeast-southwest-striking low-resistivity zone at less than a 30-m depth. The zone likely represents fractured crystalline bedrock. The boat-towed RMT technique is well suited for water bodies with moderate electric resistivity such as in brackish and freshwater environments.


ISSN: 0016-8033
EISSN: 1942-2156
Coden: GPYSA7
Serial Title: Geophysics
Serial Volume: 80
Serial Issue: 6
Title: Boat-towed radio-magnetotellurics; a new technique and case study from the city of Stockholm
Affiliation: Geological Survey of Sweden, Uppsala, Sweden
Pages: B193-B202
Published: 201511
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 43
Accession Number: 2016-007345
Categories: Applied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch map
N59°19'60" - N59°19'60", E18°04'00" - E18°04'00"
Secondary Affiliation: Uppsala University, SWE, Sweden
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 201604
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