| 1. |
- Sopher, Daniel
(författare)
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Characterization of the structure, stratigraphy and CO2 storage potential of the Swedish sector of the Baltic and Hanö Bay basins using seismic reflection methods
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An extensive multi-channel seismic dataset acquired between 1970 and 1990 by Oljeprospektering AB (OPAB) has recently been made available by the Geological Survey of Sweden (SGU). This thesis summarizes four papers, which utilize this largely unpublished dataset to improve our understanding of the geology and CO2 storage capacity of the Baltic and Hanö Bay basins in southern Sweden.A range of new processing workflows were developed, which typically provide an improvement in the final stacked seismic image, when compared to the result obtained with the original processing. A method was developed to convert scanned images of seismic sections into SEGY files, which allows large amounts of the OPAB dataset to be imported and interpreted using modern software. A new method for joint imaging of multiples and primaries was developed, which is shown to provide an improvement in signal to noise for some of the seismic lines within the OPAB dataset. For the first time, five interpreted regional seismic profiles detailing the entire sedimentary sequence within these basins, are presented. Depth structure maps detailing the Outer Hanö Bay area and the deeper parts of the Baltic Basin were also generated. Although the overall structure and stratigraphy of the basins inferred from the reprocessed OPAB dataset are consistent with previous studies, some new observations have been made, which improve the understanding of the tectonic history of these basins and provide insight into how the depositional environments have changed throughout time. The effective CO2 storage potential within structural and stratigraphic traps is assessed for the Cambrian Viklau, När and Faludden sandstone reservoirs. A probabilistic methodology is utilized, which allows a robust assessment of the storage capacity as well as the associated uncertainty. The most favourable storage option in the Swedish sector of the Baltic Basin is assessed to be the Faludden stratigraphic trap, which is estimated to have a mid case (P50) storage capacity of 3390 Mt in the deeper part of the basin, where CO2 can be stored in a supercritical phase.
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| 2. |
- Salas Romero, Silvia
(författare)
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Multidisciplinary Near-Surface Investigation of a Quick-Clay Landslide Prone Area in Southwest Sweden
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quick-clay landslides are considered one of the most important geohazards in Sweden, Norway, and Canada. The deposits involved are glacial and postglacial clays and silty clays, which are very sensitive to increased stress that may collapse their structure and cause liquefaction.A multidisciplinary approach was adopted in this study of quick clays in an area of southwest Sweden that is prone to landslides. It was mainly based on geophysical methods, but was complemented and validated with geotechnical, geological, and hydrological data. Downhole geophysics, land and river reflection seismics, radio magnetotellurics, P-wave refraction tomography, magnetics, and multichannel analysis of surface waves comprised the main geophysical methods used in this research. Laboratory measurements of core samples, such as grain size analysis, mineral magnetic properties, fossil content, X-ray fluorescence, cation exchange capacity, X-ray powder diffraction, electrical conductivity, and pH were also taken. Hydrological modelling was used to obtain information on the properties of groundwater within a coarse-grained layer, given the importance of this information in the formation of quick clays.The evaluation of the physico-chemical properties of the coarse-grained layer revealed high values of magnetic susceptibility, probably as a result of fluvial sorting, which tends to accumulate denser minerals such as magnetite. Potential quick clays were visually observed above this layer, and their presence was also confirmed by geotechnical data acquired in previous studies. Marine fossils identified within the coarse-grained layer confirmed the glaciomarine origin of the clays. Geophysical results revealed the presence of large-scale structures, an undulating fractured bedrock and a coarse-grained layer sandwiched between clay deposits, with leached sediments on top and unleached sediments below. This layer, important for the development of quick clays in the area, was 3D modelled in a regional context. Magnetic data also revealed that the coarse-grained layer together with quick clays, have the potential to act as a sliding prone layer. Multichannel analysis of surface waves helped to geotechnically characterize the area. Although the results could not reach the deeper layers, it did yield information about the shallower layers of clay, silt and sand. The VS30 values indicated the presence of soft soils, as well as soft clays/silts with high plasticity index and high water content.This PhD is expected to improve the current knowledge of quick-clay landslides and how they are preconditioned. Climate change will probably affect the study area in the near future, most likely increasing landslide risk, therefore, research should continue and advance to new levels. Application of other geophysical methods such as borehole or geophysical monitoring, and induced polarization, could provide more information about the formation of quick clays and associated landslides.
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| 3. |
- Hlousek, Felix, et al.
(författare)
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Three-dimensional reflection seismic imaging of the iron oxide deposits in the Ludvika mining area, Sweden, using Fresnel volume migration
- 2022
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Ingår i: Solid Earth. - : Copernicus Publications. - 1869-9510 .- 1869-9529. ; 13:5, s. 917-934
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Tidskriftsartikel (refereegranskat)abstract
- We present pre-stack depth-imaging results for a case study of 3D reflection seismic exploration at the Blotberget iron oxide mining site belonging to the Bergslagen mineral district in central Sweden. The goal of the study is to directly image the ore-bearing horizons and to delineate their possible depth extension below depths known from existing boreholes. For this purpose, we applied a tailored pre-processing workflow and two different seismic imaging approaches, Kirchhoff pre-stack depth migration (KPSDM) and Fresnel volume migration (FVM). Both imaging techniques deliver a well-resolved 3D image of the deposit and its host rock, where the FVM image yields a significantly better image quality compared to the KPSDM image. We were able to unravel distinct horizons, which are linked to known mineralization and provide insights on their possible lateral and depth extent. Comparison of the known mineralization with the final FVM reflection volume suggests a good agreement of the position and the shape of the imaged reflectors caused by the mineralization. Furthermore, the images show additional reflectors below the mineralization and reflectors with opposite dips. One of these reflectors is interpreted to be a fault intersecting the mineralization, which can be traced to the surface and linked to a fault trace in the geological map. The depth-imaging results can serve as the basis for further investigations, drilling, and follow-up mine planning at the Blotberget mining site.
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| 4. |
- Shan, Chunling, 1986-, et al.
(författare)
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Integration of controlled-source and radio-magnetotellurics, electrical resistivity tomography and reflection seismics to delineate 3D structures of a quick-clay landslide site in southwest Sweden
- 2016
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Ingår i: Geophysics. - 0016-8033 .- 1942-2156. ; 81:1, s. B13-B29
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Three-dimensional radio magnetotelluric (RMT), controlled-source radio magnetotelluric (CSRMT), electrical resistivity tomography (ERT), and high-resolution reflection seismic data were acquired at a quick-clay landslide site close to the Göta River in southwest Sweden. These data were collected with the main objectives of evaluating the performance of each method and delineating different subsurface materials down to the bedrock, which in turn control a peculiar and hazardous retrogressive-type landslide. These materials consist of mainly marine clays, quick clays, sand to gravel and the crystalline bedrock. The RMT, CSRMT and ERT data were inverted separately using 3D inversion schemes and the independent results from 3D processing of reflection seismic data together with the existing geotechnical data were used for their interpretations. The 3D CSRMT resistivity model shows the highest depth penetration and well resolves the geometry of the bedrock. The RMT and ERT models, however, show better resolution closer to the surface because of their denser data coverage compared with the CSRMT data. Considerable correlations in resolving a coarse-grained layer and the bedrock were observed between the CSRMT model and the 3D reflection seismic data. Because an Occam-type regularization was used in the inversion, the lateral and depth extent of the quick clays cannot accurately be determined just by using the resistivity models. The depth to the top of the resistive crystalline bedrock is to some extent uncertain. Comparisons with the borehole data suggest that the resistivity models are poor in resolving the sharp boundary between the quick clays and their underlying more resistive coarse-grained materials. The upper boundary of the more conductive marine clays underlain by the coarse-grain materials was well modeled by the CSRMT data. This study illustrates the potentials of 3D geophysical data especially when different types are collected and particularly for better site characterizations.
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| 5. |
- Andersson, Magnus, et al.
(författare)
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Carbonatite ring-complexes explained by caldera-style volcanism
- 2013
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- Carbonatites are rare, carbonate-rich magmatic rocks that make up a minute portion of the crust only, yet they are of great relevance for our understanding of crustal and mantle processes. Although they occur in all continents and from Archaean to present, the deeper plumbing system of carbonatite ring-complexes is usually poorly constrained. Here, we show that carbonatite ring-complexes can be explained by caldera-style volcanism. Our geophysical investigation of the Alnö carbonatite ring-complex in central Sweden identifies a solidified saucer-shaped magma chamber at ∼3 km depth that links to surface exposures through a ring fault system. Caldera subsidence during final stages of activity caused carbonatite eruptions north of the main complex, providing the crucial element to connect plutonic and eruptive features of carbonatite magmatism. The way carbonatite magmas are stored, transported and erupt at the surface is thus comparable to known emplacement styles from silicic calderas.
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| 6. |
- Cheraghi, Saeid, et al.
(författare)
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Crustal-scale reflection seismic investigations in the Bathurst Mining Camp, New Brunswick, Canada
- 2011
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 506:1-4, s. 55-72
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Tidskriftsartikel (refereegranskat)abstract
- The Bathurst Mining Camp, northern New Brunswick, Canada contains the super giant Brunswick No. 12 massive sulphide deposit and the smaller, now abandoned, Brunswick No. 6 deposit. Discoveries of additional base metal deposits in the camp require a better understanding of geological structures at depth. To this end, reflection seismic data in the Brunswick No. 6 area were acquired along three 2D profiles in 1999, with a total length of about 30 km. We have recovered, processed and interpreted these seismic data in conjunction with petrophysical and geological data from the study area. The seismic data and the borehole geophysical data allow a better understanding of both the shallow and deep structures (to 9 km depth) in the area. The seismic data show steeply dipping structures of the Brunswick No. 6 area, many of which reach the surface and allow for correlation with the surface and borehole geological information. Finite-difference modeling of major geological formations constrained with borehole petrophysical measurements indicates good correlation between the observed seismic and the synthetic data. A sequence of seismically reflective and transparent zones indicates a thrust stack in the Brunswick No. 6 area. The contact between the reflective and transparent zones is a series of faults bringing the two units over each other. A reflective package is observed in all three profiles and correlates well with the Brunswick horizon, the key mineralized zone in the study area. The Brunswick horizon extends down to depth greater than 3 km, increasing the hope for discovery of deeper base metal deposits. Two other sets of reflections are also observed in all three profiles in the depth range of about 5-8 km. We interpret them as two sets of thrusted sheets, which could be an indication that the Brunswick belt extends down to a maximum depth of 8 km.
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| 7. |
- Dehghannejad, Mahdieh, et al.
(författare)
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Reflection seismic imaging of the upper crust in the Kristineberg mining area, northern Sweden
- 2010
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Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 71:4, s. 125-136
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Tidskriftsartikel (refereegranskat)abstract
- The Kristineberg mining area is located in the western part of the Palaeoproterozoic Skellefte Ore District, one of the most important mining districts in Europe. As a part of a 3D geologic modeling project, two new reflection seismic profiles were acquired with a total length of about 20 km. One profile (HR), parallel to previous seismic profiles, was acquired using a 10 m receiver and source interval and crosses the steeply dipping structures of the Kristineberg mine. The other profile (Profile 2) runs perpendicular to all existing profiles in the area. Although the structural geology is complex, the processed seismic data reveal a series of steeply dipping to sub-horizontal reflections, some of which reach the surface and allow correlation with surface geology. Our general interpretation of the seismic images is that the Kristineberg mine and associated mineral horizon are located in the northern part of a series of steeply south dipping structures. Overall, main structures plunge to the west at about 30 degrees-40 degrees. Cross-dip analysis and reflection modeling were carried out to obtain the 3D orientation of the main reflections and to provide insight into the possible contribution of out-of-the-plane reflections. This helped, for example, to obtain the 3D geometry of a deep reflection that was previously interpreted as structural basement to volcanic rocks. The new reflection seismic profiles have improved our understanding of shallow geological structures in the area and in conjunction with recently acquired potential field data, magnetotelluric data and geological observations will help to refine previous 3D geologic modeling interpretations that were aimed at larger scale structures.
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| 8. |
- Hübert, Juliane, et al.
(författare)
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MT measurements in the western part of the Paleoproterozoic Skellefte Ore District, Northern Sweden : a contribution to an integrated geophysical study
- 2009
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Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 475:3-4, s. 493-502
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Tidskriftsartikel (refereegranskat)abstract
- A 2D conductivity model of the Kristineberg area in the Skellefte Ore District, Northern Sweden, has been derived from new magnetotelluric measurements. This complements an intensive geophysical and geological study of the area, including reflection seismics, gravity and aeromagnetic data modeling as well as geological field observations. In a pilot study, 20 broadband MT stations were installed in May 2007 along a 20 km long north–south profile. Dimensionality analysis shows that a 2D interpretation of the data is justified, although the presumed geoelectric strike direction of N75°E is not consistent over the whole profile. The new conductivity model of the upper crust agrees well with the results from the seismic studies. Interpreting both independent data sets confirms the major features from the previous model, such as the thickness of the Revsund granites in the south, the existence of a structural basement with metasedimentary origin, and gives new insight into the nature of the volcanic rocks and their possible mineral content.
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| 9. |
- Malehmir, Alireza, et al.
(författare)
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3D diffraction and mode-converted scattering signatures of base metal deposits, Bathurst Mining Camp, Canada
- 2010
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Ingår i: First Break. - : EAGE. - 0263-5046 .- 1365-2397. ; 28:12, s. 41-45
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Tidskriftsartikel (refereegranskat)abstract
- The localized and isolated nature of base-metal deposits can generate a complex scattered wavefield that may include P-P, P-S, S-P, and S-S events. Multi-component VSP data have previously confirmed the presence of several wave types scattered by a deep-seated base metal deposit at Halfmile Lake, Bathurst Mining Camp, Canada. However, mode-converted waves scattered from a massive sulphide deposit have not previously been recognized on surface seismic data. In this study, we used 3D surface seismic data acquired with an explosive source and vertical geophones to investigate the possible presence of P-P, P-S, S-P, and S-S events scattered at a base metal, lens-shaped body at about 1.2 km depth. We show that this body produces a diagnostic P-P diffraction and use finite-difference modelling to show it could produce mode-converted scattered signals. Results from a target-oriented azimuthal scattering analysis based on 3D prestack migration reveal amplitude anomalies at the location of the base metal lens for S-P waves and possibly P-S waves. The identification of these events confirms that mode-converted waves scattered from the deep sulphide lens were recorded on the 3D data. However, the real potential of these complementary wave modes for mineral exploration will only be realistically evaluated using P- and S-wave sources and multi-component receivers. © 2010 EAGE.
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| 10. |
- Malehmir, Alireza, et al.
(författare)
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Regional structural profiles in the western part of the Palaeoproterozoic Skellefte Ore District, northern Sweden
- 2007
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 159:1-2, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- The Kristineberg mining area is situated in the western part of the Palaeoproterozoic Skellefte Ore District, northern Sweden, and is well known for its VHMS base-metal and gold deposits. This paper presents five upper crustal geological cross sections that have been constructed and mainly constrained by seismic reflection data, potential field modeling as well as geological field observations. These profiles are visualized in 3D to highlight the three dimensionality and internal consistency of structures across the region. The resulting structural model for the Skellefte volcanics and overlying metasediments comprises two thrust-sheets that expose the Skellefte volcanics in the cores of hanging-wall anticlinal structures. A shear-zone is imaged as a band of seismic reflectivity terminated by the southern Revsund granite unit. Another shear-zone, possibly a continuation of the Skellefte Shear Zone (SSZ) runs through the centre of the region and accounts for some of the structural complexity and shearing observed between the two anticlinal exposures of the volcanics. Additional smaller scale shear-zones have been identified from geological and geophysical mapping within the main structural blocks of the Skellefte volcanics. The Mala volcanic rocks in the north are separated from the Skellefte volcanics by a fault that cuts discordant to the strike of the Mala volcanics. A structural basement has been proposed to the Skellefte volcanics, constrained by seismic reflection data. Exposures of Bothnian Basin rocks south of the Revsund granite outcrops, suggest that the domain beneath the north dipping reflectivity is associated with Bothnian Basin stratigraphy. The preferred interpretation for the contact between the Skellefte volcanics and the Bothnian Basin rocks is a thrust fault that brings the felsic volcanic rocks over the metasedimentary domain. The Revsund granites are divided into two major groups based on their present day thickness and shapes. Although parts of the Viterliden intrusion are almost undeformed, it is cut by a series of shear-zones, causing the magnetic lineations seen within these rocks. The structural profiles presented demonstrate that the Kristineberg ore is situated in the northern limb of a local synformal structure. The new crustal-scale structural model demonstrates the potential of integrating geophysical and geological data when modelling structures hosting mineralization in a complex region like the Skellefte District. The structural profiles presented in this paper, have greatly improved our understanding of the 3D tectonostratigraphy and architecture of the poly-deformed ca. 1.9 Ga the Skellefte Ore District.
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