Resolution and sensitivity of boat-towed RMT data to delineate fracture zones – Example of the Stockholm bypass multi-lane tunnel
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Keywords:
Bedrock
Magnetotellurics
Coring
Electrical Resistivity Tomography
Seismic refraction
This works presents the results gained with classical geophysical methods (Electrical Resistivity Tomography and Seismic Refraction) for the characterization of water infiltration within fissured clays in a landside area. Measurements were repeated on a monthly basis. Time-lapse processing of the data showed that electrical resistivity tomography is efficient to image preferential infiltration paths. On an other hand, seismic refraction methods did not allow to detect variations. Other techniques, such as ambient noise cross-correlation, will be tested in the future.
Electrical Resistivity Tomography
Infiltration (HVAC)
Seismic refraction
Geophysical Imaging
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Geophysical subsurface investigations use the principles of physics to unravel intrinsic Earth’s subsurface features and nature of the underlying geology. Over the past two decades, the use of Seismic Refraction Tomography (SRT) and Electrical Resistivity Tomography (ERT) for subsurface investigations has greatly improved the quality of acquired data for two- and three-dimensional (2D and 3D) surveys. SRT employs more shotpoints and receivers than the conventional seismic refraction for its imaging technique. ERT uses automated multi-electrode array systems to improve the confidence of large and dense data collection. SRT and ERT techniques use powerful inversion algorithms to achieve high resolution subsurface inversion models for resolving subsurface characteristics and geological conditions over a complex and larger area that may be difficult with the use of their conventional methods. The 2D and 3D inversion models (tomograms) generated from the field data sets of these techniques efficiently ameliorate inaccurate subsurface boundaries and structural delineation with higher depth resolution, especially the 3D inversion models for areas of complex geology. These state-of-the-art techniques have extensively been used for groundwater, environmental, engineering and mining investigations among others. This study provides insight from theories to data inversion techniques for the known tomography techniques (SRT and ERT) in use for subsurface investigations.
Electrical Resistivity Tomography
Seismic refraction
Environmental geology
Seismic Tomography
Economic geology
Geophysical Imaging
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Electrical Resistivity Tomography
Seismic refraction
Geophysical survey
Exploration geophysics
Seismic Tomography
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Summary In many cases, the contact between the bedrock and alluvial materials are not clear, this cause unnecessary movement of materials to locate the resource for construction, and consequently damage the environment. For this reason, the geophysical methods as electrical resistivity tomography and seismic refraction tomography can be an excellent combination to delimit the variation of the materials laterally and with depth because the high contrast between the resistivity and seismic velocity of the materials.
Electrical Resistivity Tomography
Seismic refraction
Bedrock
Seismic Tomography
Geophysical Imaging
Seismic velocity
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Geophone
Electrical Resistivity Tomography
Seismic refraction
Marl
Seismic Tomography
Ranging
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ABSTRACT Underground constructions for public traffic purposes are becoming increasingly important for urban areas in order to use the limited space more efficiently. Several electric resistivity tomography and seismic refraction tomography measurements were performed crossing a water passage near Stockholm during the pre‐investigation phase of a tunnel building project. The objective was to determine the bedrock interface and qualitatively assess the rock quality. The scope of this study is to present a field case in an urban environment and show improvements of geophysical results due to additional model constraints by a joint inversion. Results of individual inversions show a large transition zone below the seabed from electric resistivity tomography. Some parts of the seismic refraction tomography have a low model resolution, due to gas‐bearing sediments with a low velocity together with a high noise level, which leads to insufficient investigation depth that makes it difficult to determine the bedrock interface. However, the bedrock interface could be reconstructed in the resistivity model by performing a joint inversion, using the seismic velocity model to constrain the electric resistivity tomography model and vice versa. Adjacent geotechnical soundings support the joint inversion results. A vertical low resistive zone could be identified as a dominant fracture zone in the southern part of the investigated area. In general, the joint inversion approach significantly improved the electric resistivity tomography results and provided a more reliable bedrock estimation.
Electrical Resistivity Tomography
Bedrock
Seismic refraction
Environmental geology
Seismic Tomography
Economic geology
Geophysical Imaging
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The subsurface characteristics of the archaeological site of Priniatikos Pyrgos at Istron, Eastern Crete were studied through the combined use of seismic and electrical tomography techniques. Twenty-nine seismic refraction profiles were applied to determine soil thickness and bedrock geometrical characteristics. First arrivals were picked and a 3D algorithm of seismic tomography was used to invert the travel times. To confirm the reliability of the final results a checkboard test was used. Part of the seismic area was overlapped with six electrical resistivity tomography sections. The ERT data were used to validate the resulted tomographic images. The integrated application of these tomographic methods enhanced the knowledge regarding the geological conditions and contributed in the archaeo-environmental reconstruction of Istron area by providing indications regarding the ancient harbour of the nearby settlement.
Electrical Resistivity Tomography
Seismic refraction
Seismic Tomography
Bedrock
Settlement (finance)
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Electrical Resistivity Tomography
Seismic refraction
Bedrock
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