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García Juanatey, M. d., Hübert, J., Tryggvason, A., Juhlin, C., Pedersen, L. B., Bauer, T. E. & Dehghannejad, M. (2019). 2D and 3D MT in the central Skellefte Ore District, northern Sweden. Tectonophysics, 764, 124-138
Open this publication in new window or tab >>2D and 3D MT in the central Skellefte Ore District, northern Sweden
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2019 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 764, p. 124-138Article in journal (Refereed) Published
Abstract [en]

New broadband magnetotelluric (MT) data have been acquired along two parallel profiles in the central part of the metallogenic Skellefte district in northern Sweden. The data were recorded as part of the Swedish 4D modelling of mineral belts project and cover an area with several economical and sub-economical deposits. The dimensionality and quality of the data were carefully analyzed and new error floors were systematically determined prior to inverse modelling in 2D and 3D. The algorithms used were EMILIA and WSINV3DMT. For the 2D inversion, only the determinant of the impedance tensor was used, while for the 3D inversion all elements were considered. The obtained models fit the inverted data, and image the main regional features. A detailed comparison reveals the superiority of the 3D model, both in model structures and data fit. After assessing the main features in the model, an interpretation is proposed and refined with the support of previous geophysical studies. The most interesting features are large and medium-sized conductors associated with crustal-scale shear zones and faults within the Skellefte Group rocks. These may be depicting a network of fossil pathways for hydrothermal fluid transport and as such, provide new insight into past processes in the area.

Keywords
Magnetotellurics, 3D inversion, Deep exploration, Brownfield, Shear zones, Mineral systems
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-178057 (URN)10.1016/j.tecto.2019.04.003 (DOI)000472697900008 ()
Projects
VINNOVA 4D modeling of mineral belts
Funder
Vinnova
Available from: 2012-07-26 Created: 2012-07-26 Last updated: 2019-08-16Bibliographically approved
Simon, H., Buske, S., Hedin, P., Juhlin, C., Krauss, F. & Giese, R. (2019). Anisotropic Kirchhoff pre-stack depth migration at the COSC-1 borehole, central Sweden. Geophysical Journal International, 219(1), 66-79
Open this publication in new window or tab >>Anisotropic Kirchhoff pre-stack depth migration at the COSC-1 borehole, central Sweden
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2019 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 219, no 1, p. 66-79Article in journal (Refereed) Published
Abstract [en]

A remarkably well preserved representation of a deeply eroded Palaeozoic orogen is found in the Scandinavian Caledonides, formed by the collision of the two palaeocontinents Baltica and Laurentia. Today, after 400 Ma of erosion along with uplift and extension during the opening of the North Atlantic Ocean, the geological structures in central western Sweden comprise far transported allochthonous units, the underlying Precambrian crystalline basement, and a shallow west-dipping decollement that separates the two and is associated with a thin layer of Cambrian black shales. These structures, in particular the Seve Nappes (upper part of the Middle Allochthons), the Lower Allochthons and the highly reflective basement are the target of the two approximately 2.5 km deep fully cored scientific boreholes in central Sweden that are part of the project COSC (Collisional Orogeny in the Scandinavian Caledonides). Thus, a continuous 5 km tectonostratigraphic profile through the Caledonian nappes into Baltica's basement will be recovered. The first borehole, COSC-1, was successfully drilled in 2014 and revealed a thick section of the seismically highly reflective Lower Seve Nappe. The Seve Nappe Complex, mainly consisting of felsic gneisses and mafic amphibolites, appears to be highly anisotropic. To allow for extrapolation of findings from core analysis and downhole logging to the structures around the borehole, several surface and borehole seismic experiments were conducted. Here, we use three long offset surface seismic profiles that are centred on the borehole COSC-1 to image the structures in the vicinity of the borehole and below it. We applied Kirchhoff pre-stack depth migration, taking into account the seismic anisotropy in the Seve Nappe Complex. We calculated Green's functions using an anisotropic eikonal solver for a VTI (transversely isotropic with vertical axis of symmetry) velocity model, which was previously derived by the analysis of VSP (Vertical Seismic Profile) and surface seismic data. We show, that the anisotropic results are superior to the corresponding isotropic depth migration. The reflections appear significantly more continuous and better focused. The depth imaging of the long offset profiles provides a link between a high-resolution 3-D data set and the regional scale 2-D COSC Seismic Profile and complements these data sets, especially in the deeper parts below the borehole. However, many of the reflective structures can be observed in the different data sets. Most of the dominant reflections imaged originate below the bottom of the borehole and are situated within the Precambrian basement or at the transition zones between Middle and Lower Allochthons and the basement. The origin of the deeper reflections remains enigmatic, possibly representing dolerite intrusions or deformation zones of Caledonian or pre-Caledonian age.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2019
Keywords
Composition and structure of the continental crust, Controlled source seismology, Crustal imaging, Seismic anisotropy, Crustal structure
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-394185 (URN)10.1093/gji/ggz286 (DOI)000484124800004 ()
Funder
German Research Foundation (DFG), BU1364/10-1German Research Foundation (DFG), GI982/2-1
Available from: 2019-10-09 Created: 2019-10-09 Last updated: 2019-10-09Bibliographically approved
Place, J., Draganov, D., Malehmir, A., Juhlin, C. & Wijns, C. (2019). Crosscoherence-based interferometry for the retrieval of first arrivals and subsequent tomographic imaging of differential weathering. Geophysics, 84(4), Q37-Q48
Open this publication in new window or tab >>Crosscoherence-based interferometry for the retrieval of first arrivals and subsequent tomographic imaging of differential weathering
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2019 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 84, no 4, p. Q37-Q48Article in journal (Refereed) Published
Abstract [en]

Exhumation of crust exposes rocks to weathering agents that weaken the rocks' mechanical strength. Weakened rocks will have lower seismic velocity than intact rocks and can therefore be mapped using seismic methods. However, if the rocks are heavily weathered, they will attenuate controlled-source seismic waves to such a degree that the recorded wavefield would become dominated by ambient noise and/or surface waves. Therefore, we have examined the structure of differential weathering by first-break traveltime tomography over a seismic profile extending approximately 3.5 km and acquired at a mining site in Zambia using explosive sources and a source based on the swept-impact seismic technique (SIST). Seismic interferometry has been tested for the retrieval of supervirtual first arrivals masked by uncorrelated noise. However, use of crosscorrelation in the retrieval process makes the method vulnerable to changes in the source signal (explosives and SIST). Thus, we have developed a crosscoherence-based seismic-interferometry method to tackle this shortcoming. We investigate the method's efficiency in retrieving first arrivals and, simultaneously, correctly handling variations in the source signal. Our results illustrate the superiority of the cross-coherence-over cross-correlation-based method for retrieval of the first arrivals, especially in alleviating spurious ringyness and in terms of the signal-to-noise ratio. These benefits are observable in the greater penetration depth and the improved resolution of the tomography sections. The tomographic images indicate isolated bodies of higher velocities, which may be interpreted as fresh rocks embedded into a heavily weathered regolith, providing a conspicuous example of differential weathering. Our study advances the potential of seismic methods for providing better images of the near surface (the critical zone).

Place, publisher, year, edition, pages
SOC EXPLORATION GEOPHYSICISTS, 2019
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-393753 (URN)10.1190/GEO2018-0405.1 (DOI)000480678900034 ()
Funder
EU, European Research Council, 775971
Available from: 2019-10-16 Created: 2019-10-16 Last updated: 2019-10-16Bibliographically approved
Buntin, S., Malehmir, A., Koyi, H., Högdahl, K., Malinowski, M., Larsson, S. A., . . . Gorszczyk, A. (2019). Emplacement and 3D geometry of crustal-scale saucer-shaped intrusions in the Fennoscandian Shield. Scientific Reports, 9, Article ID 10498.
Open this publication in new window or tab >>Emplacement and 3D geometry of crustal-scale saucer-shaped intrusions in the Fennoscandian Shield
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 10498Article in journal (Refereed) Published
Abstract [en]

Saucer-shaped intrusions of tens of meters to tens of kilometres across have been observed both from surface geological mapping and geophysical observations. However, there is only one location where they have been reported to extend c. 100 km laterally, and emplaced both in a sedimentary basin and the crystalline basement down to 12 km depth. The legacy BABEL offshore seismic data, acquired over the central Fennoscandian Shield in 1989, have been recovered and reprocessed with the main goal of focusing on this series of globally unique crustal-scale saucer-shaped intrusions present onshore and offshore below the Bothnian Sea. The intrusions (c. 1.25 Ga), emplaced in an extensional setting, are observed within both sedimentary rocks (<1.5 Ga) and in the crystalline basement (>1.5 Ga). They have oval shapes with diameters ranging 30-100 km. The reprocessed seismic data provide evidence of up-doming of the lower crust (representing the melt reservoir) below the intrusions that, in turn, are observed at different depths in addition to a steep seismically transparent zone interpreted to be a discordant feeder dyke system. Relative age constraints and correlation with onshore saucer-shaped intrusions of different size suggest that they are internally connected and fed by each other from deeper to shallower levels. We argue for a nested emplacement mechanism and against a controlling role by the overlying sedimentary basin as the saucer-shaped intrusions are emplaced in both the sedimentary rocks as well as in the underlying crystalline basement. The interplay between magma pressure and overburden pressure, as well as the, at the time, ambient stress regime, are responsible for their extensive extent and rather constant thicknesses (c. 100-300 m). Saucer-shaped intrusions may therefore be present elsewhere in the crystalline basement to the same extent as observed in this study some of which are a significant source of raw materials.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2019
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-391379 (URN)10.1038/s41598-019-46837-x (DOI)000476468700026 ()31324841 (PubMedID)
Funder
Swedish Research Council, 2015-05177
Available from: 2019-09-03 Created: 2019-09-03 Last updated: 2019-09-03Bibliographically approved
Sopher, D., Juhlin, C., Levendal, T., Erlstrom, M., Nilsson, K. & Da Silva Soares, J. P. (2019). Evaluation of the subsurface compressed air energy storage (CAES) potential on Gotland, Sweden. Environmental Earth Sciences, 78(6), Article ID 197.
Open this publication in new window or tab >>Evaluation of the subsurface compressed air energy storage (CAES) potential on Gotland, Sweden
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2019 (English)In: Environmental Earth Sciences, ISSN 1866-6280, E-ISSN 1866-6299, Vol. 78, no 6, article id 197Article in journal (Refereed) Published
Abstract [en]

Wind energy is an important field of development for the island of Gotland, Sweden, especially since the island has set targets to generate 100% of its energy from renewable sources by 2025. Due to the variability of wind conditions, energy storage will be an important technology to facilitate the continued development of wind energy on Gotland and ensure a stable and secure supply of electricity. In this study, the feasibility of utilizing the Middle Cambrian Faludden sandstone reservoir on Gotland for Compressed Air Energy Storage (CAES) is assessed. Firstly, a characterization of the sandstone beneath Gotland is presented, which includes detailed maps of reservoir thickness and top reservoir structure. Analysis of this information shows that the properties of the Faludden sandstone and associated cap rock appear favorable for the application of CAES. Seven structural closures are identified below the eastern and southern parts of Gotland, which could potentially be utilized for CAES. Scoping estimates of the energy storage capacity and flow rate for these closures within the Faludden sandstone show that industrial scale CAES could be possible on Gotland.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Faludden reservoir, OPAB data set, Gas storage, Baltic Basin, Baltic Sea, Wind power
National Category
Other Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-380480 (URN)10.1007/s12665-019-8196-1 (DOI)000460829600006 ()
Funder
Swedish Research Council, 2010-3657
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-04-15Bibliographically approved
Levendal, T., Sopher, D., Juhlin, C. & Lehnert, O. (2019). Investigation of an Ordovician carbonate mound beneath Gotland, Sweden, using 3D seismic and well data. Journal of Applied Geophysics, 162, 22-34
Open this publication in new window or tab >>Investigation of an Ordovician carbonate mound beneath Gotland, Sweden, using 3D seismic and well data
2019 (English)In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 162, p. 22-34Article in journal (Refereed) Published
Abstract [en]

The Swedish island of Gotland is located within the Baltic Basin. During the Late Ordovician the region around Gotland was part of a shallow epicratonic basin in the southern subtropics. In these warm-water environments algae flourished, diverse reefs developed close to the coastline and further outboard carbonate mounds developed. These mounds formed rigid high relief structures surrounded by fine-grained siliciclastics and marls and can be detected on seismic images as isolated concave upwards features. The sedimentary succession beneath Gotland was intensely investigated in the 1970s and 1980s for its hydrocarbon potential, and subsequently, oil was commercially produced from reservoirs within Ordovician mounds. In 1981, a 3D seismic survey was conducted by Horizon Exploration Ltd. over the Fardume mound on northern Gotland. To date no results from these 3D data have been published in scientific literature.

The region of Gotland aims to produce 100% of its energy from renewable sources and currently much of Gotland's electricity is provided by wind turbines. Due to the intermittent nature of wind power, one solution to regulate the supply of electricity from wind energy is Compressed Air Energy Storage (CAES).

In this study, we convert the 3D seismic survey acquired over the Fardume mound from scanned TIFF images to SEGY format. These data are then utilized together with well data to gain a better knowledge of the geological structure of the mound and to examine its reservoir characteristics and potential for CAES. To date, carbonate mounds on Gotland have mainly been reported in the scientific literature using well data. This 3D seismic survey, therefore, provides a rare opportunity to better characterize and investigate the structure of one of the carbonate mounds on Gotland.

Keywords
Sweden, Gotland, Carbonate mounds, Late Ordovician, OPAB dataset, Seismic interpretation, 3D seismic, CAES
National Category
Geophysics Geology
Identifiers
urn:nbn:se:uu:diva-383000 (URN)10.1016/j.jappgeo.2019.01.008 (DOI)000465056200003 ()
Funder
Swedish Research CouncilGerman Research Foundation (DFG), LE 867/8-1German Research Foundation (DFG), LE 867/8-2
Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2020-02-18Bibliographically approved
Levendal, T. C., Lehnert, O., Sopher, D., Erlström, M. & Juhlin, C. (2019). Ordovician carbonate mud mounds of the Baltoscandian Basin in time and space: a geophysical approach. Palaeogeography, Palaeoclimatology, Palaeoecology, 535, Article ID 109345.
Open this publication in new window or tab >>Ordovician carbonate mud mounds of the Baltoscandian Basin in time and space: a geophysical approach
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2019 (English)In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 535, article id 109345Article in journal (Refereed) Published
Abstract [en]

Carbonate mud mounds developed within the Baltoscandian Basin, an epicratonic basin on the Baltica palaeocontinent, during the Ordovician. In the Upper Ordovician succession of the Baltoscandian Basin, a large number of mud mounds are present at three stratigraphic levels namely, the Kullsbergs mounds (late Sandbian-early Katian), Nabala and Rakvere mounds (middle Katian), and the Boda mounds (late Katian). These formed in a subtropical-tropical carbonate platform environment, covered by a shallow epicontinental sea. The mud mounds at these stratigraphic levels beneath and around Gotland have been characterized using a comprehensive seismic and well dataset acquired during a period of hydrocarbon exploration and exploitation which began more than 30 years ago. Interpretation of the largely unpublished seismic data in this study provides details on the distribution of mound complexes in the basin and constraints on the geometry of the mounds. Detailed structure contour maps of the top and the base of the Ordovician succession beneath Gotland based on the seismic interpretation are presented. The results give a comprehensive characterization of carbonate mud mound generation on Gotland which may help in understanding the distribution patterns of similar mound complexes in other parts of the Ordovician world formed in similar environments.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Baltica, Carbonate mud mounds, Gotland, OPAB dataset, Seismic interpretation, Sweden
National Category
Earth and Related Environmental Sciences Geophysics
Identifiers
urn:nbn:se:uu:diva-393044 (URN)10.1016/j.palaeo.2019.109345 (DOI)000504786400002 ()
Funder
German Research Foundation (DFG), LE 867/8-1German Research Foundation (DFG), LE 867/8-2Swedish Research Council
Available from: 2019-09-17 Created: 2019-09-17 Last updated: 2020-01-28Bibliographically approved
Juhlin, C., Lueth, S., Ivandic, M. & Bergmann, P. (2019). Seismic and Electrical Resistivity Tomography 3D Monitoring at the Ketzin Pilot Storage Site in Germany. In: Thomas L. Davis, Martin Landrø, Malcolm Wilson (Ed.), Geophysics and Geosequestration: . Cambridge University Press
Open this publication in new window or tab >>Seismic and Electrical Resistivity Tomography 3D Monitoring at the Ketzin Pilot Storage Site in Germany
2019 (English)In: Geophysics and Geosequestration / [ed] Thomas L. Davis, Martin Landrø, Malcolm Wilson, Cambridge University Press, 2019Chapter in book (Refereed)
Abstract [en]

Geosequestration involves the deep geological storage of carbon dioxide from major industrial sources, providing a potential solution for reducing the rate of increase of atmospheric concentrations of carbon dioxide and mitigating climate change. This volume provides an overview of the major geophysical techniques and analysis methods for monitoring the movement and predictability of carbon dioxide plumes underground. Comprising chapters from eminent researchers, the book is illustrated with practical examples and case studies of active projects and government initiatives, and discusses their successes and remaining challenges. A key case study from Norway demonstrates how governments and other stake-holders could estimate storage capacity and design storage projects that meet the requirements of regulatory authorities. Presenting reasons for embracing geosequestration, technical best practice for carbon management, and outlooks for the future, this volume provides a key reference for academic researchers, industry practitioners and graduate students looking to gain insight into subsurface carbon management.

Place, publisher, year, edition, pages
Cambridge University Press, 2019
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-384285 (URN)10.1017/9781316480724 (DOI)9781316480724 (ISBN)
Available from: 2019-06-03 Created: 2019-06-03 Last updated: 2020-04-02Bibliographically approved
Beckel, R. A. & Juhlin, C. (2019). The cross-dip correction as a tool to improve imaging of crooked-line seismic data: a case study from the post-glacial Burtrask fault, Sweden. Solid Earth, 10(2), 581-598
Open this publication in new window or tab >>The cross-dip correction as a tool to improve imaging of crooked-line seismic data: a case study from the post-glacial Burtrask fault, Sweden
2019 (English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 10, no 2, p. 581-598Article in journal (Refereed) Published
Abstract [en]

Understanding the development of post-glacial faults and their associated seismic activity is crucial for risk assessment in Scandinavia. However, imaging these features and their geological environment is complicated due to special challenges of their hardrock setting, such as weak impedance contrasts, often high noise levels and crooked acquisition lines. A crooked-line geometry can cause time shifts that seriously de-focus and deform reflections containing a cross-dip component. Advanced processing methods like swath 3-D processing and 3-D pre-stack migration can, in principle, handle the crooked-line geometry but may fail when the noise level is too high. For these cases, the effects of reflector cross-dip can be compensated for by introducing a linear correction term into the standard processing flow. However, existing implementations of the cross-dip correction rely on a slant stack approach which can, for some geometries, lead to a duplication of reflections. Here, we present a module for the cross-dip correction that avoids the reflection duplication problem by shifting the reflections prior to stacking. Based on tests with synthetic data, we developed an iterative processing scheme where a sequence consisting of cross-dip correction, velocity analysis and dip-moveout (DMO) correction is repeated until the stacked image converges. Using our new module to reprocess a reflection seismic profile over the post-glacial Burtrask fault in northern Sweden increased the image quality significantly. Strike and dip information extracted from the cross-dip analysis helped to interpret a set of southeast-dipping reflections as shear zones belonging to the regional-scale Burtrask Shear Zone (BSZ), implying that the BSZ itself is not a vertical but a southeast-dipping feature. Our results demonstrate that the cross-dip correction is a highly useful alternative to more sophisticated processing methods for noisy datasets. This high-lights the often underestimated potential of rather simple but noise-tolerant methods in processing hardrock seismic data.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-383512 (URN)10.5194/se-10-581-2019 (DOI)000466424700001 ()
Available from: 2019-05-16 Created: 2019-05-16 Last updated: 2019-05-16Bibliographically approved
Ghosal, D. & Juhlin, C. (2018). Estimation of dispersion attributes at seismic frequency-a case study from the Frigg-Delta reservoir, North sea. Journal of Geophysics and Engineering, 15(5), 1799-1810
Open this publication in new window or tab >>Estimation of dispersion attributes at seismic frequency-a case study from the Frigg-Delta reservoir, North sea
2018 (English)In: Journal of Geophysics and Engineering, ISSN 1742-2132, E-ISSN 1742-2140, Vol. 15, no 5, p. 1799-1810Article in journal (Refereed) Published
Abstract [en]

Estimation of the reservoir physical parameters in hydrocarbon zones is important for seismic exploration. Frequency analysis has proven to provide useful information on the velocity dispersion and attenuation of seismic wave-fields propagating through porous media. In this study we have carried out a velocity and reflectivity dispersion analysis using borehole and post-stack angle dependent seismic datasets from the Frigg-Delta reservoir in the North Sea. Rock physics analysis using borehole datasets indicate that in the seismic frequency range (1-100 Hz) dispersion maxima appear at similar to 5 Hz frequency, assuming an oil saturation associated with the reservoir ranging between 40% and 60%, porosity as 30% and permeability as 1 Darcy. Moreover, the P-wave velocity (V-p) dispersion is estimated similar to 5 times less for the high oil saturation in the upper part of the reservoir compared to that for low oil saturation in the deeper part of the reservoir. Dispersion analysis on the angle dependent seismic migrated sections is carried out by inverting spectrally decomposed isofrequency sections using a least squares algorithm. The inverted results show that the top of the reservoir is more clearly demarcated at low frequency (similar to 7Hz) than at higher frequencies.

Keywords
velocity dispersion, WIFF, normal incidence, spectral decomposition, Frigg-Delta
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-357674 (URN)10.1088/1742-2140/aabb35 (DOI)000434383900001 ()
Available from: 2018-08-22 Created: 2018-08-22 Last updated: 2018-08-22Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2776-0846

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