Integration of controlled-source and radio magnetotellurics, electric resistivity tomography, and reflection seismics to delineate 3D structures of a quick-clay landslide site in southwest of Sweden

Quick clay, which is the main cause of landslides that occur in the northern countries, liquefies easily, and its presence implies an increased risk of landslide. Geophysical methods have been increasingly used in landslide investigations. Three-dimensional electric resistivity tomography, radio magnetotelluric (RMT), controlled-source RMT (CSRMT), and high-resolution reflection seismic data were acquired at a quick-clay landslide site in the southwest of Sweden. The main objectives were to evaluate the capability of each method in delineating different subsurface geologic structures that controlled a peculiar and hazardous retrogressive-type landslide in the study area. A 3D resistivity model from the inversion of CSRMT data showed the best correlation with the reflection seismic data and borehole information, thanks to the broad frequency range of the data set. It better imaged the resistive crystalline bedrock underlying the marine conductive clays and showed considerable correlations with the 3D reflection seismic data in resolving a coarse-grained layer that was interpreted to act as a conduit directing freshwater into the clays under a confined pressure, leaching their salt and forming quick clays. The 3D CSRMT resistivity model and 3D reflection seismic data showed that the coarse-grained layer has a varying thickness. At some locations, it was too thin to be resolved by the methods used here. Combination of the CSRMT model, reflection seismic data, and the borehole data suggested that a layer with thickness of approximately 5 m and resistivity between [Formula: see text] was potentially quick clay, which probably extended laterally in the entire study area. These observations suggested that future developments should focus on joint inversion of such 3D data sets incorporating sharp boundaries as constraints in the inversion and particularly when quick clays were studied.

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Integrated 2D modeling and interpretation of geophysical and geotechnical data to delineate quick clays at a landslide site in southwest Sweden

Geophysics ◽

10.1190/geo2013-0201.1 ◽

2014 ◽

Vol 79 (4) ◽

pp. EN61-EN75 ◽

Cited By ~ 25

Author(s):

Chunling Shan ◽

Mehrdad Bastani ◽

Alireza Malehmir ◽

Lena Persson ◽

Mats Engdahl

Keyword(s):

Electrical Resistivity ◽

Seismic Data ◽

Coarse Grained ◽

Data Set ◽

Resistivity Tomography ◽

Geotechnical Data ◽

Reflection Seismic ◽

Quick Clay ◽

2D Resistivity ◽

Marine Clays

Radio magnetotellurics (RMT), electrical resistivity tomography (ERT), and high-resolution reflection seismic data were collected along four lines to characterize the geometry and physical properties of geologic structures at a quick-clay landslide site in southwest Sweden. The site is situated in the Göta River valley where the normally consolidated materials mainly consist of glacial and postglacial sediments. Geotechnical data suggest the presence of quick clays above coarse-grained layers. These layers play a key role in the formation of quick clays and landslide triggering. The RMT and ERT data were individually and jointly inverted in 2D to study the resolution of resulting models for each data set. The resistivity models from the joint inversions demonstrate superior resolution and accuracy compared with individual ones. The geometry and location of shallower structures resolved in the 2D resistivity models from joint RMT&ERT inversions correlated well with those imaged in the reflection seismic data and observed in the existing geotechnical boreholes. The models were poor in resolving deeper resistive bedrock at locations where the thickness of the conductive overburden exceeds a certain limit. However, information from the reflection seismic data could be used to estimate the depth to the top of the bedrock along all the four lines. Comparison between the geotechnical data and the resistivity models suggested that quick clays overlying the coarse-grained layer have higher electrical resistivity than the marine clays. We further validated and refined the obtained results by performing synthetic tests. We showed that integration of ERT and RMT data with reflection seismic data is ideal for quick-clay landslide studies especially when the clay materials are thick.

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High-resolution 3D reflection seismic investigation over a quick-clay landslide scar in southwest Sweden

Geophysics ◽

10.1190/geo2013-0225.1 ◽

2014 ◽

Vol 79 (2) ◽

pp. B97-B107 ◽

Cited By ~ 14

Author(s):

Emil Lundberg ◽

Alireza Malehmir ◽

Christopher Juhlin ◽

Mehrdad Bastani ◽

Magnus Andersson

Keyword(s):

Seismic Data ◽

Pore Water Pressure ◽

Water Pressure ◽

Geophysical Methods ◽

Coarse Grained ◽

Reflection Seismic ◽

Site Investigations ◽

Quick Clay ◽

Triggering Mechanisms ◽

Landslide Development

Quick-clay landslides often occur in the northern hemisphere in areas that were covered by Pleistocene glaciations. They are particularly common along the shorelines of the Göta River in southwestern Sweden. Characterization of potential landslide areas and identification of features that indicate high risk are necessary to better understand the triggering mechanisms of these events. Therefore, an intensive characterization project was initiated at the Fråstad landslide in Sweden. Part of the characterization program included the acquisition of 3D reflection seismic data to image structures in the normally consolidated sediments, as well as the bedrock topography below the landslide scar. Two seismic horizons within the glacial and postglacial sediments were observed. The shallowest seismic horizon (here, referred to as S1) corresponds to a coarse-grained layer that was previously detected by eight geotechnical boreholes located within the 3D survey area. Discontinuities in S1, mapped by the 3D reflection seismic data, occur across a zone that correlates with the landslide scar boundary, suggesting that this zone may have played a role in triggering and/or in limiting the extension of the landslide. If S1 is truncated by or mixed with clays in this zone, then the outflow of water from the permeable S1 into the clays above may have increased the amount of quick clays above this zone. The increased outflow of water may also have caused a higher pore-water pressure south of the zone, which in turn could have acted as a trigger for the landslide. We evaluated the potential of using the 3D reflection seismic method as a complement to drilling and other geophysical methods when performing landslide site investigations. We also demonstrated the importance of further investigating the relationship between 3D subsurface geometries and landslide development.

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Subsurface characterization of a quick-clay vulnerable area using near-surface geophysics and hydrological modelling

Solid Earth ◽

10.5194/se-10-1685-2019 ◽

2019 ◽

Vol 10 (5) ◽

pp. 1685-1705

Author(s):

Silvia Salas-Romero ◽

Alireza Malehmir ◽

Ian Snowball ◽

Benoît Dessirier

Keyword(s):

Large Scale ◽

Geophysical Methods ◽

Hydrological Modelling ◽

P Wave ◽

Coarse Grained ◽

Near Surface ◽

Reflection Seismic ◽

Geotechnical Investigations ◽

Quick Clay ◽

Near Surface Geophysics

Abstract. Quick-clay landslides are common geohazards in Nordic countries and Canada. The presence of potential quick clays is confirmed using geotechnical investigations, but near-surface geophysical methods, such as seismic and resistivity surveys, can also help identify coarse-grained materials associated with the development of quick clays. We present the results of reflection seismic investigations on land and in part of the Göta River in Sweden, along which many quick-clay landslide scars exist. This is the first time that such a large-scale reflection seismic investigation has been carried out to study the subsurface structures associated with quick-clay landslides. The results also show a reasonable correlation with radio magnetotelluric and travel-time tomography models of the subsurface. Other ground geophysical data, such as high magnetic values, suggest a positive correlation with an increased thickness of the coarse-grained layer and shallower depths to the top of the bedrock and the top of the coarse-grained layer. The morphology of the river bottom and riverbanks, e.g. subaquatic landslide deposits, is shown by side-scan sonar and bathymetric data. Undulating bedrock, covered by subhorizontal sedimentary glacial and postglacial deposits, is clearly revealed. An extensive coarse-grained layer (P-wave velocity mostly between 1500 and 2500 m s−1 and resistivity from approximately 80 to 100 Ωm) exists within the sediments and is interpreted and modelled in a regional context. Several fracture zones are identified within the bedrock. Hydrological modelling of the coarse-grained layer confirms its potential for transporting fresh water infiltrated in fractures and nearby outcrops located in the central part of the study area. The modelled groundwater flow in this layer promotes the leaching of marine salts from the overlying clays by seasonal inflow–outflow cycles and/or diffusion, which contributes to the formation of potential quick clays.

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Subsurface structures of a quick-clay sliding prone area revealed using land-river reflection seismic data and hydrogeological modelling

10.5194/se-2019-22 ◽

2019 ◽

Author(s):

Silvia Salas-Romero ◽

Alireza Malehmir ◽

Ian Snowball ◽

Benoît Dessirier

Keyword(s):

Large Scale ◽

Geophysical Methods ◽

Coarse Grained ◽

Magnetic Data ◽

Near Surface ◽

Side Scan Sonar ◽

Reflection Seismic ◽

Subsurface Structures ◽

Geotechnical Investigations ◽

Quick Clay

Abstract. Quick-clay landslides are common geohazards in Nordic countries and Canada. The presence of potential quick clays is confirmed using geotechnical investigations, but near-surface geophysical methods, such as seismic and resistivity surveys, can also help identifying coarse-grained materials associated to the development of quick clays. We present the results of reflection seismic investigations on land and in part of the Göta River in Sweden, along which many quick-clay landslide scars exist. This is the first time that such a large-scale reflection seismic investigation has been carried out to study the subsurface structures associated with quick-clay landslides. The results also show a reasonable correlation with the radio magnetotelluric and traveltime tomography models. The morphology of the river bottom and riverbanks, as e.g. subaquatic landslide deposits, is shown by side-scan sonar and bathymetric data. Undulating bedrock, covered by subhorizontal sedimentary glacial and postglacial deposits is clearly revealed. An extensive coarse-grained layer exists in the sedimentary sequence and is interpreted and modelled in a regional context. Individual fractures and fracture zones are identified within bedrock and sediments. Hydrological modelling of the coarse-grained layer confirms its potential for transporting fresh water infiltrated in fractures and nearby outcrops. The groundwater flow in the coarse-grained layer promotes leaching of marine salts from the overlying clays by slow infiltration and/or diffusion, which helps in the formation of potential quick clays. Magnetic data show coarse-grained materials at the landslide scar located in the study area, which may have acted as a sliding surface together with quick clays.

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Combined interpretation of marine controlled source electromagnetic and reflection seismic data in the German North Sea: a case study

Geophysical Journal International ◽

10.1093/gji/ggy408 ◽

2018 ◽

Vol 216 (1) ◽

pp. 218-230 ◽

Cited By ~ 4

Author(s):

Romina A S Gehrmann ◽

Claudia Schnabel ◽

Martin Engels ◽

Michael Schnabel ◽

Katrin Schwalenberg

Keyword(s):

North Sea ◽

Seismic Data ◽

Controlled Source ◽

Reflection Seismic

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Deep electrical resistivity tomography for the prospection of low- to medium-enthalpy geothermal resources

Geophysical Journal International ◽

10.1093/gji/ggz411 ◽

2019 ◽

Vol 219 (3) ◽

pp. 2056-2072

Author(s):

A Carrier ◽

F Fischanger ◽

J Gance ◽

G Cocchiararo ◽

G Morelli ◽

...

Keyword(s):

Electrical Potential ◽

Bouguer Anomaly ◽

Industrial Area ◽

Gravity Models ◽

Efficient Technology ◽

Geothermal Resources ◽

Reflection Seismic ◽

Resistivity Model ◽

Noise Data ◽

Geoelectrical Methods

SUMMARY The growth of the geothermal industry sector requires innovative methods to reduce exploration costs whilst minimizing uncertainty during subsurface exploration. Until now geoelectrical prospection had to trade between logistically complex cabled technologies reaching a few hundreds meters deep versus shallow-reaching prospecting methods commonly used in hydro-geophysical studies. We present a recent technology for geoelectrical prospection, and show how geoelectrical methods may allow the investigation of medium-enthalpy geothermal resources until about 1 km depth. The use of the new acquisition system, which is made of a distributed set of independent electrical potential recorders, enabled us to tackle logistics and noise data issues typical of urbanized areas. We acquired a 4.5-km-long 2-D geoelectrical survey in an industrial area to investigate the subsurface structure of a sedimentary sequence that was the target of a ∼700 m geothermal exploration well (Geo-01, Satigny) in the Greater Geneva Basin, Western Switzerland. To show the reliability of this new method we compared the acquired resistivity data against reflection seismic and gravimetric data and well logs. The processed resistivity model is consistent with the interpretation of the active-seismic data and density variations computed from the inversion of the residual Bouguer anomaly. The combination of the resistivity and gravity models suggest the presence of a low resistivity and low density body crossing Mesozoic geological units up to Palaeogene–Neogene units that can be used for medium-enthalpy geothermal exploitation. Our work points out how new geoelectrical methods may be used to identify thermal groundwater at depth. This new cost-efficient technology may become an effective and reliable exploration method for the imaging of shallow geothermal resources.

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