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

Solid Earth ◽  
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.

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

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.

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

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. B97-B107 ◽  
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.

scholarly journals High resolution reflection seismic profiling over the Tjellefonna fault in the Møre-Trøndelag Fault Complex, Norway

Solid Earth ◽  
2012 ◽  
Vol 3 (1) ◽  
pp. 175-188 ◽  
Author(s):  
E. Lundberg ◽  
C. Juhlin ◽  
A. Nasuti
Keyword(s):  
Large Scale ◽  
P Wave ◽  
Seismic Profiles ◽  
Surface Geometry ◽  
Southeastern Part ◽  
Near Surface ◽  
Reflection Seismic ◽  
Reflection Data ◽  
Time Modeling ◽  
The Individual

Abstract. The Møre-Trøndelag Fault Complex (MTFC) is one of the most prominent fault zones of Norway, both onshore and offshore. In spite of its importance, very little is known of the deeper structure of the individual fault segments comprising the fault complex. Most seismic lines have been recorded offshore or focused on deeper structures. This paper presents results from two reflection seismic profiles, located on each side of the Tingvollfjord, acquired over the Tjellefonna fault in the southeastern part of the MTFC. Possible kilometer scale vertical offsets, reflecting large scale northwest-dipping normal faulting, separating the high topography to the southeast from lower topography to the northwest have been proposed for the Tjellefonna fault or the Baeverdalen lineament. In this study, however, the Tjellefonna fault is interpreted to dip approximately 50–60° towards the southeast to depths of at least 1.3 km. Travel-time modeling of reflections associated with the fault was used to establish the geometry of the fault structure at depth, while detailed analysis of first P-wave arrivals in shot gathers, together with resistivity profiles, were used to define the near surface geometry of the fault zone. A continuation of the structure on the northeastern side of the Tingvollfjord is suggested by correlation of an in strike direction P-S converted reflection (generated by a fracture zone) seen on the reflection data from that side of the Tingvollfjord. The reflection seismic data correlate well with resistivity profiles and recently published near surface geophysical data. A highly reflective package forming a gentle antiform structure was also identified on both seismic profiles. This structure could be related to the folded amphibolite lenses seen on the surface or possibly by an important boundary within the gneissic basement rocks of the Western Gneiss Region. The fold hinge line of the structure is parallel with the Tjellefonna fault trace suggesting that the folding and faulting may have been related.

Two-dimensional elastic pseudo-spectral modeling of wide-aperture seismic array data with application to the Wichita Uplift-Anadarko Basin region of southwestern Oklahoma

1990 ◽  
Vol 80 (6A) ◽  
pp. 1677-1695 ◽  
Author(s):  
Ik Bum Kang ◽  
George A. McMechan
Keyword(s):  
Large Scale ◽  
Deep Structure ◽  
Sedimentary Basins ◽  
P Wave ◽  
Two Dimensional ◽  
Anadarko Basin ◽  
Near Surface ◽  
University Of Texas ◽  
Wide Aperture ◽  
The University

Abstract Full wave field modeling of wide-aperture data is performed with a pseudospectral implementation of the elastic wave equation. This approach naturally produces three-component stress and two-component particle displacement, velocity, and acceleration seismograms for compressional, shear, and Rayleigh waves. It also has distinct advantages in terms of computational requirements over finite-differencing when data from large-scale structures are to be modeled at high frequencies. The algorithm is applied to iterative two-dimensional modeling of seismograms from a survey performed in 1985 by The University of Texas at El Paso and The University of Texas at Dallas across the Anadarko basin and the Wichita Mountains in southwestern Oklahoma. The results provide an independent look at details of near-surface structure and reflector configurations. Near-surface (<3 km deep) structure and scattering effects account for a large percentage (>70 per cent) of the energy in the observed seismograms. The interpretation of the data is consistent with the results of previous studies of these data, but provides considerably more detail. Overall, the P-wave velocities in the Wichita Uplift are more typical of the middle crust than the upper crust (5.3 to 7.1 km/sec). At the surface, the uplift is either exposed as weathered outcrop (5.0 to 5.3 km/sec) or is overlain with sediments of up to 0.4 km in thickness, ranging in velocity from 2.7 to 3.4 km/sec, generally increasing with depth. The core of the uplift is relatively seismically transparent. A very clear, coherent reflection is observed from the Mountain View fault, which dips at ≈40° to the southwest, to at least 12 km depth. Velocities in the Anadarko Basin are typical of sedimentary basins; there is a general increase from ≈2.7 km/sec at the surface to ≈5.9 km/sec at ≈16 km depth, with discontinuous reflections at depths of ≈8, 10, 12, and 16 km.

Reflection seismic imaging of buried shallow salt structures – examples from ongoing case studies in Northern Germany

2021 ◽  
Author(s):  
Ulrich Polom ◽  
Rebekka Mecking ◽  
Phillip Leineweber ◽  
Andreas Omlin
Keyword(s):  
High Resolution ◽  
Water Resources ◽  
Industrial Development ◽  
Geophysical Methods ◽  
Hydrocarbon Exploration ◽  
P Wave ◽  
Depth Range ◽  
Reflection Seismic ◽  
Wide Range ◽  
Cap Rock

<p>In the North German Basin salt tectonics generated a wide range of evaporite structures since the Upper Triassic, resulting in e.g. extended salt walls, salt diapirs, and salt pillows in the depth range up to 8 km. Due to their trap and seal properties these structures were in the focus of hydrocarbon exploration over many decades, leading to an excellent mapping of their geometries below 300 m in depth. During salt rise Rotliegend formations were partly involved as a constituent. Some structures penetrated the salt table, some also the former surface. Dissolution (subrosion) and erosion of the salt cap rock by meteoric water took place, combined with several glacial and intraglacial overprints. Finally the salt structures were covered by pleistocene and holocene sediments. This situation partly resulted in proneness for ongoing karstification of the salt cap rock, leading to e.g. local subsidence and sinkhole occurrence at the surface. The geometry, structure and internal lithology of these shallow salt cap rocks are widely unknown. Expanding urban and industrial development, water resources management and increasing climate change effects enhance the demands for shallow mapping and characterization of these structures regarding save building grounds and sustainable water resources.</p><p>Results of shallow drilling investigations of the salt cap rock and the overburden show unexpectedly heterogenous subsurface conditions, yielding to limited success towards mapping and characterization. Thus, shallow high-resolution geophysical methods are in demand to close the gaps with preferred focus of applicability in urban and industrial environments. Method evaluations starting in 2010 geared towards shallow high-resolution reflection seismic to meet the requirements of both depth penetration and structure resolution. Since 2017 a combination of S-wave and P-wave seismic methods including depth calibrations by Vertical Seismic Profiling (VSP) enabled 2.5D subsurface imaging starting few meters below the surface up to several hundred meters depth in 0.5-5 m resolution range, respectively. The resulting profiles image strong variations along the boundaries and on top of the salt cap rock. Beside improved mapping capabilities, aim of research is the development of characteristic data features to differentiate save and non-save areas.</p>

scholarly journals Finite-difference modelling to evaluate seismic P-wave and shear-wave field data

Solid Earth ◽  
2015 ◽  
Vol 6 (1) ◽  
pp. 33-47 ◽  
Author(s):  
T. Burschil ◽  
T. Beilecke ◽  
C. M. Krawczyk
Keyword(s):  
Wave Field ◽  
Shear Wave ◽  
Field Data ◽  
P Wave ◽  
Sh Wave ◽  
Surface Shear ◽  
Near Surface ◽  
Reflection Seismic ◽  
Surface Shear Wave ◽  
Seismic Measurements

Abstract. High-resolution reflection seismic methods are an established non-destructive tool for engineering tasks. In the near surface, shear-wave reflection seismic measurements usually offer a higher spatial resolution in the same effective signal frequency spectrum than P-wave data, but data quality varies more strongly. To discuss the causes of these differences, we investigated a P-wave and a SH-wave seismic reflection profile measured at the same location on the island of Föhr, Germany and applied seismic reflection processing to the field data as well as finite-difference modelling of the seismic wave field. The simulations calculated were adapted to the acquisition field geometry, comprising 2 m receiver distance (1 m for SH wave) and 4 m shot distance along the 1.5 km long P-wave and 800 m long SH-wave profiles. A Ricker wavelet and the use of absorbing frames were first-order model parameters. The petrophysical parameters to populate the structural models down to 400 m depth were taken from borehole data, VSP (vertical seismic profile) measurements and cross-plot relations. The simulation of the P-wave wave-field was based on interpretation of the P-wave depth section that included a priori information from boreholes and airborne electromagnetics. Velocities for 14 layers in the model were derived from the analysis of five nearby VSPs (vP =1600–2300 m s-1). Synthetic shot data were compared with the field data and seismic sections were created. Major features like direct wave and reflections are imaged. We reproduce the mayor reflectors in the depth section of the field data, e.g. a prominent till layer and several deep reflectors. The SH-wave model was adapted accordingly but only led to minor correlation with the field data and produced a higher signal-to-noise ratio. Therefore, we suggest to consider for future simulations additional features like intrinsic damping, thin layering, or a near-surface weathering layer. These may lead to a better understanding of key parameters determining the data quality of near-surface shear-wave seismic measurements.

Shallow to very shallow, high‐resolution reflection seismic using a portable vibrator system

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1295-1309 ◽  
Author(s):  
Ranajit Ghose ◽  
Vincent Nijhof ◽  
Jan Brouwer ◽  
Yoshikazu Matsubara ◽  
Yasuhiro Kaida ◽  
...  
Keyword(s):  
High Resolution ◽  
High Frequency ◽  
Seismic Waves ◽  
Soft Soil ◽  
Geophysical Methods ◽  
Seismic Source ◽  
P Wave ◽  
Nondestructive Technique ◽  
Buried Objects ◽  
Reflection Seismic

In shallow engineering‐geophysical applications, there is a lack of controlled, nondestructive, high‐resolution mapping tools, particularly for the target depth that ground‐penetrating radar cannot reach but which is too shallow for other conventional geophysical methods. For soft soil, this corresponds to a depth of 2 to 30 m. We have developed a portable, high‐frequency P-wave vibrator system that is capable of bridging this gap. As far as the important contribution of the seismic source is concerned, penetration and resolution can be individually controlled through easy modulation of the sweep signal generated by this electromagnetic vibrator. The feasibility of this system has been tested in shallow (10–50 m) to very shallow (0–10 m) applications. Seven field data sets representing varying geology, site conditions, and exploration targets are presented to illustrate the applicability. The first three examples show the potential of this portable vibrator source in shallow applications. Under favorable situations, a maximum resolution of about 20 cm for events located at 15–30 m depth could be achieved. Because high‐frequency seismic waves suffer from severe attenuation in the dry, unsaturated weathered zone, the penetration is relatively limited when the water table is deeper than 4–5 m. The fourth to seventh field examples illustrate very shallow applications at noisy, asphalt‐paved urban sites that are often encountered in civil, geotechnical, and environmental engineering projects. The prospecting targets were thin soil layers or small buried objects. On asphalt, the vibrator can produce high‐frequency energy easily. The fourth example shows high‐resolution delineation of very shallow soil structures. The last three examples present successful location of buried bodies—often small and closely spaced—in soft soil at depths of 0.5 to 5 m. We observe well‐defined reflection events of frequency exceeding 200 Hz. These results suggest that high‐frequency seismic reflection imaging using the portable vibrator system can indeed serve as a powerful, nondestructive technique for shallow to very shallow underground prospecting.

scholarly journals Landslide investigations using the geoelectrical scanning method and ground penetrating radar: Case studies

Tehnika ◽  
2021 ◽  
Vol 76 (4) ◽  
pp. 419-425
Author(s):  
Filip Arnaut ◽  
Branislav Sretenović
Keyword(s):  
Ground Penetrating Radar ◽  
Geophysical Methods ◽  
Relevant Information ◽  
Electromagnetic Signal ◽  
Near Surface ◽  
Scanning Method ◽  
Low Resistivity ◽  
Geotechnical Investigations ◽  
Landslide Body ◽  
Ground Penetrating

Geotechnical investigations of landslides for future mitigation are a complex task. To obtain relevant information, various geophysical methods are used, with varying degrees of success. The geoelectrical scanning method, also known as Electrical Resistivity Tomography (ERT) has been successfully applied in several locations in Serbia in the las three decades. The geoelectrical scanning method was used during investigations of landslides: Umka, Lukovska banja, Tara, and Trandžament, while both geoelectrical scanning and Ground Penetrating Radar (GPR) were utilized at the Trandžament landslide. The achieved results from both methods are mutually correlated at the Trandžament landslide. Correlation of GPR data with geoelectrical scanning data was only possible since there were no nearsurface low resistivity zones in the Trandžament landslide body. Otherwise, electromagnetic signal attenuation would be high in the presence of near-surface low resistivity zones, and a quality signal would be impossible to detect at the receiving antenna.

Challenges in geophysical mapping of glaciotectonic structures

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. B287-B303 ◽  
Author(s):  
Anne-Sophie Høyer ◽  
Ingelise Møller ◽  
Flemming Jørgensen
Keyword(s):  
Large Scale ◽  
Structural Information ◽  
Geophysical Methods ◽  
Small Scale ◽  
Reflection Seismic ◽  
Electromagnetic Data ◽  
Transient Electromagnetic ◽  
Scale Structures ◽  
Geologic Setting ◽  
Types Of Information

Glaciotectonic complexes have been recognized worldwide — traditionally described on the basis of outcrops or geomorphological observations. In the past few decades, geophysics has become an integral part of geologic mapping, which enables the mapping of buried glaciotectonic complexes. The geophysical methods provide different types of information and degrees of resolution and thus, a different ability to resolve the glaciotectonic structures. We evaluated these abilities on the basis of an integrated application of four commonly used geophysical methods: airborne transient electromagnetics, high-resolution reflection seismic, geoelectrical, and ground-penetrating radar (GPR). We covered an area of [Formula: see text] in a formerly glaciated region in the western part of Denmark. The geologic setting was highly heterogeneous with glaciotectonic deformation observed in the form of large-scale structures in the seismic and airborne transient electromagnetic data to small-scale structures seen in the GPR and geoelectrical data. The seismic and GPR data provided detailed structural information, whereas the geoelectrical and electromagnetic data provided indirect lithological information through resistivities. A combination of methods with a wide span in resolution capabilities can therefore be recommendable to characterize and understand the geologic setting. The sequence of application of the different methods is primarily determined by the gross expenditure required for acquisition and processing, e.g., per kilometer of the surveys. Our experience suggested that airborne electromagnetic data should be acquired initially to obtain a 3D impression of the geologic setting. Based on these data, areas can be selected for further investigation with the more detailed but also more expensive and time-consuming methods.

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