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  • 201.
    Dorostkar, Ali
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Lukarski, Dimitar
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computational Science.
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Neytcheva, Maya
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Notay, Yvan
    Schmidt, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Parallel performance study of block-preconditioned iterative methods on multicore computer systems2014Report (Other academic)
  • 202.
    Dorostkar, Ali
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Neytcheva, Maya
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Numerical and computational aspects of some block-preconditioners for saddle point systems2015In: Parallel Computing, ISSN 0167-8191, E-ISSN 1872-7336, Vol. 49, p. 164-178Article in journal (Refereed)
  • 203.
    Dorostkar, Ali
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Neytcheva, Maya
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    On some block-preconditioners for saddle point systems and their CPU–GPU performance2015Report (Other academic)
  • 204.
    Doughty, Christine
    et al.
    Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Rosberg, Jan-Erik
    Lund Univ, Lund, Sweden..
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Dobson, Patrick F.
    Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Birkholzer, Jens T.
    Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Flowing fluid electrical conductivity logging of a deep borehole during and following drilling: estimation of transmissivity, water salinity and hydraulic head of conductive zones2017In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 25, no 2, p. 501-517Article in journal (Refereed)
    Abstract [en]

    Flowing fluid electrical conductivity (FFEC) logging is a hydrogeologic testing method that is usually conducted in an existing borehole. However, for the 2,500-m deep COSC-1 borehole, drilled at re, central Sweden, it was done within the drilling period during a scheduled 1-day break, thus having a negligible impact on the drilling schedule, yet providing important information on depths of hydraulically conductive zones and their transmissivities and salinities. This paper presents a reanalysis of this set of data together with a new FFEC logging data set obtained soon after drilling was completed, also over a period of 1 day, but with a different pumping rate and water-level drawdown. Their joint analysis not only results in better estimates of transmissivity and salinity in the conducting fractures intercepted by the borehole, but also yields the hydraulic head values of these fractures, an important piece of information for the understanding of hydraulic structure of the subsurface. Two additional FFEC logging tests were done about 1 year later, and are used to confirm and refine this analysis. Results show that from 250 to 2,000 m depths, there are seven distinct hydraulically conductive zones with different hydraulic heads and low transmissivity values. For the final test, conducted with a much smaller water-level drawdown, inflow ceased from some of the conductive zones, confirming that their hydraulic heads are below the hydraulic head measured in the wellbore under non-pumped conditions. The challenges accompanying 1-day FFEC logging are summarized, along with lessons learned in addressing them.

  • 205.
    Duan, Chaoran
    et al.
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China..
    Zhang, Fengjiao
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China.
    Han, Liguo
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China..
    Chang, Ao
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China..
    Yang, Xiaochun
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China..
    Huang, Fei
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    COMPRESSED FWI INVERSION WITH NON-MONOTONE LINE SEARCH LBFGS2017In: Journal of Seismic Exploration, ISSN 0963-0651, Vol. 26, no 6, p. 561-586Article in journal (Refereed)
    Abstract [en]

    Full waveform inversion (FWI) is a high quality seismic imaging method. It is a nonlinear inversion problem which usually needs the monotone line search method to be solved. However, the speed of convergence for such a simple search technique is relatively slow. In this paper, we combine the non-monotone line search technique with the LBFGS method and apply them to the frequency-domain FWI. We test this new method on a two-dimensional Marmousi model. The results show that the method is robust. Comparing with the monotone line search method, the new method could improve the convergence rate of FWI. We also test the new method with a two-dimensional conventional streamer data set and the results show some improvements compared with the conventional FWI method.

  • 206. Dörr, N.
    et al.
    Lisker, F.
    Clift, P. D.
    Carter, A.
    Gee, David G.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tebenkov, A. M.
    Spiegel, C.
    Late Mesozoic-Cenozoic exhumation history of northern Svalbard and its regional significance: Constraints from apatite fission track analysis2012In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 514, p. 81-92Article in journal (Refereed)
    Abstract [en]

    The late Mesozoic-Cenozoic was a time of profound tectonic activity in the Arctic, with incipient spreading in the Arctic Ocean, Baffin Bay-Labrador Sea and North Atlantic, as well as the northward movement of the Greenland microplate leading to collision and deformation in Greenland, Arctic Canada and Svalbard (Eurekan Orogeny). It is, however, still unclear, how northern Svalbard, situated at the northwestern edge of the Barents Shelf, was affected by these processes. Furthermore, northern Svalbard has been proposed to have been a Cretaceous-Cenozoic sediment source to surrounding regions because it lacks a post-Devonian sedimentary cover. When erosion took place and how that related to the tectonic history of the Arctic, is yet unresolved. In order to reconstruct the erosion history of northern Svalbard, we constrained its thermal evolution using apatite fission track (AFT) thermochronology. Our data reveal AFT ages between 62 +/- 5 and 214 +/- 10 Ma, recording late Mesozoic-early Paleogene exhumation. Our data show that northern Svalbard was emergent and experienced erosion from the Early Jurassic and presumably through the Cenozoic, although total exhumation was restricted to similar to 6 km. Pronounced exhumation took place during Jurassic-Cretaceous time, probably linked to the extensional tectonics during the opening of the Amerasian Basin (Arctic Ocean). In contrast, Cenozoic ocean basin formation and the Eurekan deformation did not cause significant erosion of northem Svalbard. Nonetheless, AFT data show that Late Cretaceous-Early Paleocene fault-related exhumation affected some parts of northern Svalbard. Fault zones were reactivated due to the reorganization of Arctic landmasses during an early phase of the Eurekan deformation, which implies that this episode commenced similar to 20 m.y. earlier in Svalbard than previously understood.

  • 207.
    Ehsan, Siddique Akhtar
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Re-processing and Interpretation of 2D Seismic Line in the Kristineberg Mining Area, Northern Sweden2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Skellefte district, 1.90 to 1.80 Ga, is one of the most important base metal mining districts of Sweden with over 85 volcanic-hosted massive sulfide (VHMS) deposits. The study area focuses on the western part of the Skellefte district which contains volcanic, metasedimentary and intrusive rocks. In 2003, seismic data acquisition was carried out in the western part of the Skellefte district in the vicinity of the Kristineberg mine. Two parallel seismic lines were acquired about 8 km apart from each other. Profile 1 is about 22 km long and selected for the re-processing and interpretation in this thesis. The acquisition geometry, low fold coverage, the complex tectonic history and fewer outcrops in the area make the data processing and interpretation quite challenging and required a careful processing design to obtain interpretable seismic image. The re-processed Profile 1 is correlated with two other newly acquired seismic lines in the area for the purpose of possible 3D visualization and interpretation. The re-processing work includes a careful velocity analysis along with a series of iterations in residual statics, poststack and prestack migrations and cross dip analysis. The re-processed seismic section clearly shows a north dipping reflector which truncates against the Revsund Granites at depth. The possible interpretation for this reflector is a structural basement to the Skellefte Group constituting Bothnian Basin or a fault zone within the Viterliden intrusion. The Kristineberg mine is situated on the northern limb of a synform structure with prominent southwards dipping reflections. The major lithological contacts between different rock units are series of latest thrust faults. The prominent reflectivity within and at the contact with the Viterliden intrusion may suggest deep seated mineralized horizons. The cross dip analysis helps finding the eastward dipping component for the shallow horizons. The re-processed image is also compared with the previous processed seismic section and improvements in reflectors are evident.

  • 208. Ehsan, Siddique Akhtar
    et al.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Dehghannejad, Mandieh
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Re-processing and interpretation of 2D seismic data from the Kristineberg mining area, northern Sweden2012In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 80, p. 43-55Article in journal (Refereed)
    Abstract [en]

    The Kristineberg mining area in the western part of the Skellefte ore district, northern Sweden, contains the largest massive sulphide deposit in the district. In 2003, two parallel seismic lines, Profiles 1 and 5, each about 25 km long and about 8 km apart were acquired in the Kristineberg area. The initial processing results were successful in imaging the large-scale structures of the area down to 12 km of the crust, but resulted in relatively poor seismic image near the mine. In this paper, we re-processed the seismic data along Profile 1 that crosses the mine. The main objective was to improve the seismic section near the mine for further correlation with new seismic data recently acquired in the area. The crooked-line acquisition geometry, very low fold coverage of less than 17, complex geology and sparse outcrops in the area made the data re-processing and interpretation challenging. Despite these challenges, significant improvement is observed in the seismic data, in terms of event continuity and resolution. Refraction static corrections allowed high frequencies to be retained, which improved the seismic section. The refraction static solution was manually checked and adjusted at every iteration to avoid unstable solutions. 3D visualization of the re-processed data with other seismic profiles recently acquired in the area allowed the seismic reflections to be correlated. The majority of the reflections are interpreted to originate from either fault zones or lithological contacts. A very shallow reflection correlates well with the location of the Kristineberg mineralized horizon.

  • 209.
    Eken, Tuna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Isotropic and Anisotropic P and S Velocities of the Baltic Shield Mantle: Results from Analyses of Teleseismic Body Waves2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The upper mantle structure of Swedish part of Baltic Shield with its isotropic and anisotropic seismic velocity characteristics is investigated using telesesismic body waves (i.e. P waves and shear waves) recorded by the Swedish National Seismological Network (SNSN).

    Nonlinear high-resolution P and SV and SH wave isotropic tomographic inversions reveal velocity perturbations of ± 3 % down to at least 470 km below the network. Separate SV and SV models indicate several consistent major features, many of which are also consistent with P-wave results. A direct cell by cell comparison of SH and SV models reveals velocity differences of up to 4%. Numerical tests show that differences in the two S-wave models can only be partially caused by noise and limited resolution, and some features are attributed to the effect of large scale anisotropy.

    Shear-wave splitting and P-travel time residual analyses also detect anisotropic mantle structure. Distinct back-azimuth dependence of SKS splitting excludes single-layer anisotropy models with horizontal symmetry axes for the whole region. Joint inversion using both the P and S data reveals 3D self-consistent anisotropic models with well-defined mantle lithospheric domains. These domains of differently oriented anisotropy most probably retain fossil fabric since the domains' origin, supporting the idea of the existence of an early form of plate tectonics during formation of continental cratons already in the Archean.

    The possible disturbing effects of anisotropy on seismic tomography studies are investigated, and found to be potentially significant. P-wave arrival times were adjusted based on the estimates of mantle anisotropy, and re-inverted. The general pattern of the velocity-perturbation images was similar but changed significantly in some places, including the disappearance of a slab-like structure identified in the inversion with the original data. Thus the analysis demonstrates that anisotropy of quite plausible magnitude can have a significant effect on the tomographic images, and should not be ignored. If, as we believe, our estimates of anisotropy are reasonably correct, then the model based on the adjusted data should give a more robust and correct image of the mantle structure.

  • 210.
    Eken, Tuna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Plomerova, Jaroslova
    GFU, Prague.
    Vecsey, Ludek
    GFU, Prague.
    Babuska, Vladislav
    GFU, Prague.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shomali, Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bödvarsson, Reynir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Effects of seismic anisotropy on P-velocity tomography of the Baltic Shield2012In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 188, no 2, p. 600-612Article in journal (Refereed)
    Abstract [en]

    We investigate possible effects of neglecting seismic anisotropy on standard isotropic P-velocity tomographic images of the upper mantle beneath the Baltic shield. Isotropic inversions of teleseismic P- and S-wave traveltimes exhibit alternating high- and low-velocity heterogeneities down to depths of over 400 km. Differences in tomographic inversions of SV- and SH-wave traveltimes are distinct down to depths of about 200 km and are associated with anisotropy of the lithospheric mantle. Anisotropic structures of the upper mantle affect both the P and S traveltimes, shear-wave splitting as well as the P polarization directions. Joint inversion for isotropic and anisotropic velocity perturbations is not feasible due to the limited 3-D ray coverage of available data. Therefore, we correct the input traveltimes for anisotropic contributions derived from independent analyses and then perform standard isotropic inversions. These corrections are derived either directly from directional deviations of P-wave propagation or are calculated in anisotropic models retrieved by joint inversions of body-wave anisotropic parameters (P-residual spheres and shear-wave splitting). These anisotropic models are also used to fit backazimuth variations of P-wave polarization directions. General features of tomographic images calculated from the original and the anisotropy-corrected data are similar. Amplitudes of the velocity perturbations decrease below similar to 200 km depth, that is in the sub-lithospheric mantle. In general, large-scale anisotropy related to the fabrics of the continental mantle lithosphere can contaminate tomographic images in some parts of models and should not be ignored.

  • 211.
    Eken, Tuna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Plomerová, Jaroslava
    Geophysical Institute, Czech Acad. Sci..
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Vecsey, Ludek
    Geophysical Institute, Czech Acad. Sci..
    Babuška, Vladislav
    Geophysical Institute, Czech Acad. Sci..
    Shomali, Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bodvarsson, Reynir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Seismic anisotropy of the mantle lithosphere beneath the Swedish National Seismological Network (SNSN)2010In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 480, no 1-4, p. 241-258Article in journal (Refereed)
    Abstract [en]

    Body-wave analysis – shear-wave splitting and P-travel time residuals - detect anisotropic structure of the upper mantle beneath the Swedish part of Fennoscandia. Geographic variations of both the splitting measurements and the P-residual spheres map regions of different fabrics of the mantle lithosphere. The fabric of individual mantle domains is internally consistent, usually with sudden changes at their boundaries. Distinct back-azimuth dependence of SKS splitting excludes single-layer anisotropy models with horizontal symmetry axes for the whole region. Based upon joint inversion of body-wave anisotropic parameters we instead propose 3D self-consistent anisotropic models of well-defined mantle lithosphere domains with differently oriented fabrics approximated by hexagonal aggregates with plunging symmetry axes. The domain-like structure of the Precambrian mantle lithosphere, most probably retaining fossil fabric since the domains’ origin, supports the idea of the existence of an early form of plate tectonics during formation of continental cratons already in the Archean. Similarly to different geochemical and geological constraints, the 3D anisotropy modelling and mapping of fabrics of the lithosphere domains contribute to tracking plate tectonics regimes back in time.

  • 212.
    Eken, Tuna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shomali, Z. Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Bödvarsson, Reynir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Upper-mantle structure of the Baltic Shield below the Swedish National Seismological Network (SNSN) resolved by teleseismic tomography2007In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 169, no 2, p. 617-630Article in journal (Refereed)
    Abstract [en]

    Upper-mantle structure under the Baltic Shield is studied using non-linear high resolution teleseismic P-phase tomography. Observed relative arrival-time residuals from 52 teleseismic earthquakes recorded by the Swedish National Seismological Network (SNSN) are inverted to delineate the structure of the upper mantle. The network consists of 47 (currently working) three-component broad-band stations located in an area about 450 km wide and 1450 km long. In order to reduce complications due to possible significant three-dimensionality of Earth structure, events chosen for this study lay close to in-line with the long-axis of the array  (±30°) . Results indicate P-wave velocity perturbations of ±3 per cent down to at least 470 km below the network. The size of the array allows inversion for structures even at greater depths, and lateral variations of velocity at depths of up to 680 km appear to be resolved. Below the central part of the array (60°–64° N), where ray coverage is best, the data reveals a large region of relatively low velocity at depths of over about 300 km. At depths less than about 250–300 km, the models include a number of features, including an apparent slab-like structure dipping gently towards the north.

  • 213.
    Eken, Tuna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hieronymus, Christoph F.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bödvarsson, Reynir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    S and P velocity heterogeneities within the upper mantle below the Baltic Shield2008In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 462, no 1-4, p. 109-124Article in journal (Refereed)
    Abstract [en]

    Upper mantle structure beneath the Baltic (Fennoscandian) Shield is investigated using non-linear tomographic inversion of relative arrival-time residuals. 52 selected teleseismic earthquakes recorded by 45 broadband stations of the Swedish National Seismological Network (SNSN) provide 1532 good quality S-wave relative arrival times. SV and SH arrival-time residuals were initially analyzed independently, providing two separate models. These reveal several consistent major features, many of which are also consistent with P-wave results. Lateral velocity variations of ± 3–4% are observed to depths of at least 470 km. The correlation between the SH and SV models is investigated and shows a pattern of minor but significant differences down to around 150–200 km depth, below which the models are essentially similar. Direct cell by cell comparison of the model velocities reveals a similar pattern, with velocity differences between the models of up to 4%. Numerical tests show that differences in the two S-wave models can only be partially attributed to noise and limited resolution, and some features are attributed to the effect of large scale anisotropy. One of the significant and sharp discrepancies between the S models coincides with a presumed boundary between Archean and Proterozic domains, suggesting different anisotropic characteristics in the two regions.

  • 214.
    Eklöf, Sara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Högdahl, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Jonsson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Sveriges Geologiska Undersökning.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Michael, Setter
    Nordic Iron Ore.
    Towards a structural framework for apatite-iron oxide deposits in the Grängesberg-Blötberget area, Bergslagen, Sweden2016Conference paper (Refereed)
  • 215.
    Ershova, Victoria B.
    et al.
    All Russian Geol Inst, Sredniy Prospect 74, St Petersburg 199106, Russia.; St Petersburg State Univ, Inst Earth Sci, Univ Skaya Nab 7-9 St, St Petersburg 199034, Russia.
    Lorenz, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Prokopiev, Andrei V.
    Russian Acad Sci, Siberian Branch, Diamond & Precious Met Geol Inst, Lenin Prospect 39, Yakutsk 677980, Russia.
    Sobolev, Nikolay N.
    All Russian Geol Inst, Sredniy Prospect 74, St Petersburg 199106, Russia.
    Khudoley, Andrei K.
    All Russian Geol Inst, Sredniy Prospect 74, St Petersburg 199106, Russia.; St Petersburg State Univ, Inst Earth Sci, Univ Skaya Nab 7-9 St, St Petersburg 199034, Russia.
    Petrov, Eugeny O.
    All Russian Geol Inst, Sredniy Prospect 74, St Petersburg 199106, Russia.
    Estrada, Solveig
    Fed Inst Geosci & Nat Resources BGR, Stilleweg 2, D-30655 Hannover, Germany.
    Sergeev, Sergey
    All Russian Geol Inst, Sredniy Prospect 74, St Petersburg 199106, Russia.; St Petersburg State Univ, Inst Earth Sci, Univ Skaya Nab 7-9 St, St Petersburg 199034, Russia.
    Larionov, Alexander N.
    All Russian Geol Inst, Sredniy Prospect 74, St Petersburg 199106, Russia.
    Thomsen, Tonny B.
    Geol Survey Denmark & Greenland GEUS, Dept Petr & Econ Geol, Oster Voldgade 10, DK-1350 Copenhagen, Denmark.
    The De Long Islands: A missing link in unraveling the Paleozoic paleogeography of the Arctic2016In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 35, p. 305-322Article in journal (Refereed)
    Abstract [en]

    The vast Laptev and East Siberian shelves in the eastern Russian Arctic, largely covered by a shallow sea and buried beneath sea ice for 9 months of the year, remain one of the least studied parts of continental crust of the Earth and represent a big unknown when performing pre-Cenozoic geodynamic reconstructions of the Arctic. The De Long islands provide a vitally important window into the geology of this area and are a key for [1] understanding  the Early Paleozoic history of the Amerasian Arctic. Four of them (Jeanette, Henrietta, Bennett and Zhokhov islands) were studied using structural data, petrographic and geochemical analyses and U-Pb zircon age dating to offer the following new constraints for the Early Paleozoic paleogeography of the Arctic realm. The basement beneath the De Long Islands is of Late Neoproterozoic to earliest Cambrian age, about 670-535 Ma. In the Early Paleozoic, the De Long Islands were located along the broad Timanian margin of Baltica, with a clastic sediment provenance from the Timanian, Grenville-Sveconorwegian, and Baltic Shield domains. The Cambro-Ordovician volcaniclastic successions on Jeannette and Henrietta islands formed part of a continental margin volcanic arc with a corresponding back-arc basin located to the south (in present co-ordinates). On the continent-ward side of the back-arc basin, shallow marine shelf clastic and carbonate rocks were deposited, which are exposed today on Bennett Island in the south-west of the archipelago (in modern coordinates). The De Long Islands together with other continental blocks, such as Severnaya Zemlya, Arctic Alaska-Chukotka, and the Alexander Terrane, formed the contiguous active continental margin of Baltica during the Early Paleozoic. Today however, these terranes are spread out over a distance of 5000 km across the Arctic and eastern Pacific margins due to the subsequent opening of a series of Late Paleozoic, Mesozoic and Cenozoic oceanic basins.

  • 216.
    Fei, Huang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Christopher, Juhlin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Monika, Ivandic
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Fengjiao, Zhang
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    DMO processing on the Ketzin 3D seismic data2014Conference paper (Refereed)
    Abstract [en]

    The Dip-moveout (DMO) correction is a process which attempts to make the finite offset data closer to zero offset data after the normal-moveout (NMO) correction. The NMO correction is then dip independent and reflections with different dips will stack coherently. DMO plays a critical role in seismic processing by enhancing the final image quality of the seismic data. In this study, we apply 3D Squeezing DMO (Hale and Artley, 1993) to seismic data from the Ketzin pilot CO2 site after NMO to study the impact of DMO on time-lapse seismic imaging and to investigate if it enhances the CO2 seismic monitoring technique. This 3D DMO method is based on an integral approach and incorporates Hale and Artley’s (1993) modifications for variable velocity with time. A constant velocity algorithm is used with a gamma correction function which depends on the velocity function. An anti-alias velocity of 3000 m/s is used for the DMO. After DMO the data are stacked and F-XY deconvolution is applied. Finally, 3D finite-difference migration using the final smoothed NMO velocities is performed for each data set.We then apply a time-lapse analysis to the 3D seismic data sets and compare the results with and without DMO processing. The most important aspect of the DMO processing is determining the velocity field for the NMO step. This is done by using the initial smoothed velocity field obtained from the conventional velocity analysis before DMO as a first estimate. The data are input into the DMO process and then inverse NMO is applied. These data are then subjected to a new velocity analysis and the velocity field is updated and used as input for the NMO process. A number of iterations are generally required until the velocity field does not need further updating. In this study velocities were picked at every 20th CDP in the inline and crossline directions. Compared to the velocity spectrum without DMO processing, the velocity trend is improved and the ambiguity in the velocity picks is eliminated after DMO correction. The improved accuracy of velocity picking makes it easier to interpret the velocity spectrum and obtain correct interval velocities. Considering the stacked section, DMO suppresses the random noise to a greater extent and thus the signal-to-noise ratio is enhanced. From the comparison of the amplitude difference horizon at the reservoir level, the shape of the anomaly observed in the data with DMO processing is similar to that observed in the data without DMO processing. However, the amplitude anomalies of the former are stronger than those of the latter, especially close to the injection well. In addition, one stronger amplitude anomaly in the DMO time-lapse horizon indicates a preferred trend of the CO2 migration in WNW direction due to the reservoir heterogeneity.

  • 217.
    Fei, Huang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Christopher, Juhlin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Thomas, Kempka
    GFZ German Research Centre for Geosciences.
    Ben, Norden
    GFZ German Research Centre for Geosciences.
    Integration of Reservoir Simulation with 3D Reflection Seismic Time-lapse Data at Ketzin2014Conference paper (Refereed)
    Abstract [en]

    In this study we integrate reservoir simulation with 3D reflection seismic time-lapse data from the Ketzin CO2 storage pilot site using density and velocity models, a porosity model and a fluid flow simulation model. To simulate the seismic response corresponding to the real data, detailed density and velocity models are properly generated from the stratigraphic model and available borehole logging data. The reservoir simulation model providing the spatial CO2 saturation in the reservoir based on numerical simulations history-matched to the site monitoring data is used to calculate the bulk densities and compressional wave velocities of the rock after CO2 injection using a fluid substitution method. 3D synthetic seismic data are generated by convolving the density and velocity models with two different sources to study the change in seismic response after CO2 injection and to investigate the impact of the different source types on CO2 monitoring. Our results provide estimates of the time-lapse anomalies caused by CO2 injection and demonstrate that the choice of source type is a critical factor for time-lapse seismic monitoring to assess the distribution of injected CO2. The same source type should be used in the baseline and repeat surveys for site operation.

  • 218.
    Ferdinand, Richard Wambura
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Inverstigations of Crustal Structure Structure and Seismo-Tectonics in the Western Branch of the East African Rift System2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The most seismically active part of the East African rift system (EARS) is the western branch. Understanding the crustal structure and its evolution is important in order to obtain accurate locations and mechanisms of earthquakes, hence to deduce the nature of the neotectonics. This thesis uses information from earthquakes to investigate the crustal structure and active tectonics in the western branch of the EARS, centred on the Rukwa rift. An average 1-D crustal structure characterised by longitudinal and shear wave velocities, plus the quality factor, QLg, has been determined, using arrival times of body waves and maximum displacement amplitudes of Lg waves. This structure is used to determine the body-wave magnitude scale (mbLg) for the region and to establish the earthquake detection threshold for stations of the Mbeya seismic network located within the Rukwa rift.

    This thesis also develops a new approach for modelling full waveform, high frequency siesmograms to obtain fault plane solutions for micro-earthquakes in local inhomogeneous media. As it is possible to model low frequency data using a homogeneous medium, modelling high frequency seismic waves in inhomogeneous media requires characterisation of the media along different propagation paths between the source and stations. After checking that this approach produces reliable fault plane solutions for three micro-earthquakes, it was applied to micro-earthquakes along the Rukwa rift. Together with solutions for large earthquakes previously determined by other investigators, fault plane solutions for micro-earthquakes were used to constrain the kinematics of the Rukwa rift. It has been found that the T- (tension) axis is oriented NE along the Ufipa plateau that forms the western boundary to the Rukwa rift, and NW in the Songwe basin within the rift. This difference is attributed to differences in gravitational forces induced by differences in topography: the Ufipa plateau is about 1 km higher than the Songwe basin, the later being at the same level as the East African plateau.

  • 219. Foerster, A.
    et al.
    Giese, R.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Norden, B.
    Springer, N.
    The Geology of the CO2SINK Site: From Regional Scale to Laboratory Scale2009In: GREENHOUSE GAS CONTROL TECHNOLOGIES 9, 2009, Vol. 1, p. 2911-2918Conference paper (Other academic)
    Abstract [en]

    Here we report on the framework of geological site exploration, which encompassed investigations at different scales prior to and after the drilling of the three CO2SINK boreholes. Past and new exploration data are integrated to delineate at regional scale (1) the geological structure of CO2 storage formation and its overburden, including fault systems as potential fluid pathways and (2) the shallow hydrogeology and the groundwater flow directions for an assessment of effects in case of CO2 leakage and migration. The poro-perm facies and mineralogical composition of the CO2 reservoir rock and the top seal formation were studied by routine and special core analyses, including the measurement of porosity, gas and brine permeability, and by XRD analysis. (C) 2009 Elsevier Ltd. All rights reserved.

  • 220.
    Frenje, L
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Scattering attenuation: 2-D and 3-D finite difference simulations vs. theory2000In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 44, no 1, p. 33-46Article in journal (Refereed)
    Abstract [en]

    Scattering of seismic waves is studied by producing synthetic vertical seismic profiling (VSP) seismograms with 2-D and 3-D finite difference modelling in random media. The random models used are Gaussian and band-limited self-similar, or fractal random media. The modelling is performed acoustically, but we believe that, considering the geometry of this study, the results obtained will hold for the elastic case as well.

    Properties of the random media are discussed, in particular the difference between discrete and continuous media, and the importance of this difference. We show that when using the band-limited Von Karman correlation function when generating the random medium, the size of the model should be greater than 2πa, where a is the correlation distance, and the grid spacing should be less then a. If not, the medium will not have the proper characteristics.

    Analytical expressions for scattering attenuation, derived from single scattering theory, can be used to estimate scattering Q from borehole velocity logs, if it is known what minimum scattering angle, θmin, to use. θmin, the minimum angle energy, must be scattered to be regarded as not contributing to the propagating wave. We estimate θmin by comparing Q values estimated from our synthetic VSP seismograms with the analytical expressions. The comparison also shows when the assumption of single scattering is valid. Previous studies in 2-D give a θmin of ∼30°. In this paper, we make a comparison for both the 2-D and 3-D cases, and show that the Q estimate is highly sensitive to how the analysis is done. We show that single scattering theory agrees well with finite difference simulations for self-similar media with low Hurst numbers, but with a somewhat lower θmin of 10–20°. This holds for a range of correlation lengths, a, including the case of infinite, or absence of, a. For Gaussian and exponential media, simulations and theory agree as well with θmin of 10–20°, but only for ka<5, where k is the wave number of the source. For ka>5, simulations and theory diverge, and single scattering theory cannot explain the amplitude attenuation observed in the scattering simulations for these types of media, indicating that it may be difficult to estimate the fractal properties of a medium from seismic data alone.

    With the difficulties of characterizing the scattering medium, and to estimate the scattering attenuation in the simple case of synthetic data with pure scattering, we conclude that it may be difficult to separate scattering and intrinsic attenuation from real data.

  • 221.
    Friberg, M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Green, AG
    Horstmeyer, H
    Roth, J
    Rybalka, A
    Bliznetsov, M
    Europrobe seismic reflection profiling across the eastern Middle Urals and West Siberian Basin2001In: Terra Nova, ISSN 0954-4879, E-ISSN 1365-3121, ISSN 0954-4879, Vol. 12, no 6, p. 252-257Article in journal (Refereed)
    Abstract [en]

    New deep seismic reflection data provide images of the crust and uppermost mantle underlying the eastern Middle Urals and adjacent West Siberian Basin. Distinct truncations of reflections delineate the late-orogenic strike-slip Sisert Fault extending vertically to ∼28 km depth, and two gently E-dipping reflection zones, traceable to 15–18 km depth, probably represent normal faults associated with the opening of the West Siberian Basin. A possible remnant Palaeozoic subduction zone in the lower crust under the West Siberian Basin is visible as a gently SW-dipping zone of pronounced reflectivity truncated by the Moho. Continuity of shallow to intermediate-depth reflections suggest that Palaeozoic accreted island-arc terranes and overlying molasse sequences exposed in the hinterland of the Urals form the basement for Triassic and younger deposits in the West Siberian Basin. A highly reflective lower crust overlies a transparent mantle at about 43 km depth along the entire 100 km long seismic reflection section, suggesting that the lower crust and Moho below the eastern Middle Urals and West Siberian Basin have the same origin.

  • 222.
    Fridlund, Julia
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Analysis of Multicomponent Data to Study Esker Structures, Turku-Finland2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Eskers are long winding ridges that originate from gravel that has travelled in meltwater streams in glaciers. At the study site, Virttaankangas plane in southwest Finland, there are esker structures covered by sediments. One reason why it is important to study eskers is because they are used for purifying drinking water. The data used in the study were collected during a seismic survey in July 2014. During the survey a controlled source created seismic waves that travelled down through the earth and then reflected back up again. By detecting the travel time of the waves and estimating the velocity of the geologic layers, the depth to the reflecting structures could be calculated. There are two types of waves that travel through the body of the earth, pressure waves (P-waves) and shear waves (S-waves). In a previous study (Maries et al., 2017) P-wave data from the same survey have been analyzed, so this work focuses on S-wave data but also compares the result from the two. Some structures related to eskers were identifiable, such as fractures in the bedrock from the pressure of the main esker core. By comparing S- and P-wave results it was possible to see hints of the arched esker cores and esker fan lobes. Overall the result confirmed the model that was achieved of the profile in the previous study. The location of the bedrock both matched with the previous study, and added information about its orientation. An additional goal was to demonstrate the insensitivity of S-waves to water content by showing that if there was a water table reflection in the P-wave data, this reflection was missing in the S-wave data. The results showed water table reflections in the P-wave data, but there were no distinguishable water table reflections with appropriate velocity for S-waves in the S-wave data.

  • 223.
    Fridlund, Julia
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Processing of Noisy Controlled Source Audio Magnetotelluric (CSAMT) Data2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Controlled Source Audio Magnetotellurics (CSAMT) is a geophysical method for characterizing the resistivity of the subsurface with the help of electromagnetic waves. The method is used for various purposes, such as geothermal- and hydrocarbon exploration, mineral prospecting and for investigation of groundwater resources. Electromagnetic fields are created by running an alternating current in a grounded electric dipole and by varying the frequency, different depths can be targeted. Orthogonal components of the electromagnetic fields are measured at receiver stations a few kilometers away from the source. From these field components, so called magnetotellurics transfer functions are estimated, which can be used to invert for the resistivity of the subsurface.

    The data used in this project is from a survey conducted in 2014 and 2016 in Kiruna by Uppsala University and the mining company LKAB. Measurements were made at 31 stations along two orthogonal profiles. The data have been processed earlier, but due to noise, especially in the lower frequencies, a significant part of the data set could not be inverted. The aim of this project was to improve the results by analyzing the data and testing different methods to remove noise.

    First, robust regression was used to account for possible non-Gaussian noise in the estimation of the magnetotelluric transfer functions. Except for one station on profile 1, the robust method did not improve the results, which suggests that the noise is mostly Gaussian.

    Then modified versions of least squares, each affected by a different bias, were used to estimate the transfer functions. Where there is more noise, the estimates should differ more due to their different biases. The estimates differed most for low frequencies and especially on the part of profile 2 that was measured in 2014.

    It was investigated whether the railway network could explain part of the low frequency noise. Measures were taken to reduce spectral leakage from the railway signal at 16 ⅔ Hz to the closest transmitter frequencies 14 Hz and 20 Hz, but no clear improvement was seen and more detailed studies need to be conducted to determine this matter.

    Finally, a method based on comparing the ratio of short-term and long-term averages was tested to remove transients in the measured time series of the electromagnetic field components. This proved difficult to implement due to the variability of the time series’ behavior between different stations, frequencies and field components. However, the method showed some potential for stations 9 and 10 on profile 1, and could probably be developed further to remove transients more efficiently and thus improve the data.

  • 224.
    Fälth, Billy
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Clay Technology AB.
    Simulating Earthquake Rupture and Near-Fault Fracture Response2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Sweden is presently a low seismicity area where most earthquakes are small and pose no serious threat to constructions. For the long-term perspectives of safety assessments of geological repositories for spent nuclear fuel, however, the effects of large earthquakes have to be considered. For the Swedish nuclear waste storage concept, seismically induced secondary fracture shear displacements across waste canister positions could pose a long-term seismic risk to the repository.

    In this thesis, I present earthquake simulations with which I study the potential for near-fault secondary fracture shear displacements. As a measure I use the Coulomb Failure Stress (CFS), but also calculate explicit fracture displacements. I account for both the dynamic and quasi-static stress perturbations generated during the earthquake. As numerical tool I use the 3DEC code, whose performance I validate using Stokes closed-form solution and the Compsyn code as benchmarks. In a model of a Mw 6.4 earthquake, I investigate how fault roughness, the fault rupture propagation model and rupture velocity may impact the near-fault CFS evolution. I find that fault roughness can reduce the amount of fault slip by tens of percent, but also increase the near-fault CFS with similar amounts locally. Furthermore, different fault rupture models generate similar CFS levels. I also find that the secondary stresses scale with rupture velocity.

    In a model based on data from the Forsmark nuclear waste repository site, and assuming stress conditions prevailing at the end of a glaciation, I simulate several high stress drop ~Mw 5.6 earthquake scenarios on the gently dipping fault zone ZFMA2 and calculate secondary fracture displacements on 300 m diameter planar fractures. Less than 1% of the fractures at the shortest distance from ZFMA2 generate displacements exceeding the 50 mm criterion established by the Swedish Nuclear Fuel and Waste Management Co. Given the high stress drops and the assumption of fracture planarity, I consider the calculated displacements to represent upper bound estimates of possible secondary displacements at Forsmark. Hence, the results should strengthen the confidence in the safety assessment of the nuclear waste repository at the Forsmark site.

  • 225.
    Fälth, Billy
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hökmark, Harald
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Simulation of co-seismic secondary fracture displacements for different earthquake rupture scenarios at the proposed nuclear waste repository site in Forsmark2016In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 84, p. 142-158Article in journal (Refereed)
  • 226.
    Fälth, Billy
    et al.
    Clay Technology AB, Lund, Sweden.
    Hökmark, Harald
    ClayTech AB, Lund, Sverige.
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Mai, Martin
    King Abdullah University of Science and Technology, Saudi Arabia.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Munier, Raymond
    Svensk kärnbränslehantering AB.
    Simulating earthquake rupture and off-fault fracture response: Application to the safety assessment of the Swedish nuclear waste repository2015In: Bulletin of The Seismological Society of America (BSSA), ISSN 0037-1106, E-ISSN 1943-3573, Vol. 105, no 1, p. 134-151Article in journal (Refereed)
    Abstract [en]

    To assess the long‐term safety of a deep repository of spent nuclear fuel, upper bound estimates of seismically induced secondary fracture shear displacements are needed. For this purpose, we analyze a model including an earthquake fault, which is surrounded by a number of smaller discontinuities representing fractures on which secondary displacements may be induced. Initial stresses are applied and a rupture is initiated at a predefined hypocenter and propagated at a specified rupture speed. During rupture we monitor shear displacements taking place on the nearby fracture planes in response to static as well as dynamic effects. As a numerical tool, we use the 3Dimensional Distinct Element Code (3DEC) because it has the capability to handle numerous discontinuities with different orientations and at different locations simultaneously. In tests performed to benchmark the capability of our method to generate and propagate seismic waves, 3DEC generates results in good agreement with results from both Stokes solution and the Compsyn code package. In a preliminary application of our method to the nuclear waste repository site at Forsmark, southern Sweden, we assume end‐glacial stress conditions and rupture on a shallow, gently dipping, highly prestressed fault with low residual strength. The rupture generates nearly complete stress drop and an Mw 5.6 event on the 12  km2 rupture area. Of the 1584 secondary fractures (150 m radius), with a wide range of orientations and locations relative to the fault, a majority move less than 5 mm. The maximum shear displacement is some tens of millimeters at 200 m fault‐fracture distance.

  • 227.
    Fälth, Billy
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Clay Technology AB.
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hökmark, Harald
    Clay Technology AB.
    How does the Fault Rupture Model affect Simulated Co-Seismic Near-Fault Stress Evolution?Manuscript (preprint) (Other academic)
    Abstract [en]

    The dynamic and static stress perturbations generated in an earthquake affect the stability of faults and fractures in the vicinity of the rupture. Estimates of co-seismic near-fault stress effects can be made using numerical simulations. Here, we study the co-seismic stress evolution close to an earthquake using two different models to simulate the rupture. One model is the linear slip-weakening (SW) model, where a spontaneous earthquake rupture is simulated. We compare this to a constant rupture velocity time-weakening (TW) model, which we implement in four different instances of rupture velocity Vr and strength reduction time interval Δtred. We evaluate the near-fault stress effects using the Coulomb Failure Stress (CFS), which we calculate from the stress evolution at various positions relative to the rupture plane. The results show that the TW method is capable of generating similar secondary effects as those generated by the SW model. However, the assumption of constant values of Δtred and Vr implies that there will always be locations on the rupture plane where these values are incompatible. We also see that variationsin Δtred and Vr have a significant impact on the results. Particularly, Vr is important for how the stresses around the rupture front are superimposed, and is thus important for the temporal evolution and spatial distribution of CFS around the fault. Lower Vr tends to generate a gentler near-fault stress evolution and lower peak CFS values. The results also indicate that not only the momentary value of Vr is important for the secondary stress effects at a near-fault position passed by the rupture, but also the integrated Vr-history up to that position.

  • 228.
    Fälth, Billy
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Clay Technology AB.
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hökmark, Harald
    Clay Technology AB.
    Influence of Fault Roughness on Co-Seismic Near-Fault Stress EvolutionManuscript (preprint) (Other academic)
    Abstract [en]

    Co-seismic displacements on fractures and faults close to large earthquakes may not contribute significantly to the shaking hazard for surface infrastructures. However, for deep geological nuclear waste repositories, such secondary displacements could, if large enough, damage intersected waste containers and constitute a significant long-term safety concern. To study how the potential for such displacements may depend on the earthquake rupture evolution, we simulate dynamic earthquake ruptures, and calculate the co-seismic evolution of Coulomb Failure Stress (CFS) on hypothetical fracture planes in the near-fault continuum. Poroelastic coupling is accounted for via Skempton’s coefficient B. We study three cases: (1) A planar fault with homogeneous properties. (2) A planar fault where the dynamic friction increases gradually along the fault edge to obtain a gentler rupture arrest. (3) An undulated fault with fractal properties. For Case 3, we consider ten different fault surface realizations. Since the undulations reduce fault slip, we also run models with adjusted dynamic friction coefficients, such that they generate seismic moments on par with that of Case 1. We observe the following: (i) The initial stress field, rather than the co-seismic stress effects, is the dominating influence on the fracture orientations that obtain the highest CFS values. (ii) Lower slip gradients and less fault slip in Case 2 reduce the maximum CFS by 10-15% relative to the reference case. (iii) Fault roughness may increase CFS locally by tens of percent. (iv) Given our reference value of B=0.5, B-value variations of ±0.5 would give CFS variations of ±20%, at most.

  • 229. Förster, A
    et al.
    Norden, B
    Zinck-Jørgensen, K
    Frykman, P
    Kulenkampff, J
    Spangenberg, E
    Erzinger, J
    Zimmer, M
    Kopp, J
    Borm, G
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Cosma, C
    Hurter, S
    Baseline characterization of the CO2SINK geological storage site at Ketzin, Germany2006In: Environmental Geosciences, ISSN 1075-9565, E-ISSN 1526-0984, Vol. 13, no 3, p. 145-161Article in journal (Refereed)
    Abstract [en]

    Since April 2004, preparatory work prior to CO2injection hasbeen conducted in the CO2SINK Project, the European Union’sfirst research and development activity on the in-situ testing ofgeological storage of CO2near the town of Ketzin, Germany.Carbon dioxide will be injected into a saline aquifer of the TriassicStuttgart Formation in an anticlinal structure of the northeastGerman Basin. The drilling of one injection and two observationwells will commence at the end of 2006. The predrilling phasefocuses on the baseline geological parameters of the anticline. TheStuttgart Formation is lithologically heterogeneous; it consists ofsandy channel-(string)-facies rocks, with good reservoir propertiesalternating with muddy flood-plain-facies rocks of poor reservoirquality. Playa-type rocks form the immediate cap rock above theCO2SINK reservoir. A geostatistical approach has been applied todescribe the reservoir architecture between and beyond well con-trol. This model forms the basis for the generation of reservoir-dynamic models of CO2injection that assist in the planning ofinjection operations and in the understanding of CO2plume evo-lution. A verification of the geometry of the reservoir and thestructural situation of its overburden is expected from a three-dimensional baseline seismic survey that was conducted in theautumn of 2005. Laboratory experiments under simulated in-situconditions were performed to evaluate the geophysical signatureof rocks saturated with CO2. The chemical composition of thegroundwater and the CO2flux in the soil were analyzed across theKetzin anticline, providing the baseline for a monitoring programduring and after injection of CO2, targeted at the detection ofpotential CO2leakage from the storage reservoir.

  • 230.
    Garcia Juanatey, Maria de los Angeles
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hübert, Juliane
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tryggavson, Ari
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Integrated MagnetoTelluric and seismic reflection study: Skellefte Ore District, northern Sweden2011Conference paper (Refereed)
    Abstract [en]

    The Skellefte District is a very rich mining area in northern Sweden. The main deposits consist of volcanic-hosted massive sulphides VHMS rich in zinc, copper, lead, gold and silver. Since the area has been mined and explored for over a century, today's challenge is to locate deeper deposits. The VINNOVA 4D modeling project aims to address this challenge by understanding the regional setting of the district and its evolution over time. © 2011 Society of Exploration Geophysicists.

  • 231.
    García Juanatey, María de los Angeles
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hübert, Juliane
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tryggvason, Ari
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bauer, Tobias E.
    Luleå University of Technology.
    Dehghannejad, Mahdieh
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    2D and 3D MT in the central Skellefte Ore District, northern Sweden2019In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 764, p. 124-138Article in journal (Refereed)
    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.

    The full text will be freely available from 2021-04-13 15:31
  • 232.
    García Juanatey, María de los Ángeles
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Inversión conjunta de datos eléctricos de corriente continua y radiomagnetotelúricos bajo un esquema TSVD2007Student thesis
    Abstract [es]

    Varios estudios han demostrado que los métodos eléctricos y electromagnéticos, a pesar de responder a la misma propiedad física de las rocas, lo hacen de manera distinta, por lo que su combinación siempre conlleva a mejores resultados (Vozoff y Jupp, 1975). Considerando esto, se plantea en el presente trabajo la inversión conjunta de datos eléctricos de corriente continua (CC) y datos radiomagnetotelúricos (RMT). Para ello se adapta el programa REBOCC (Siripunvaraporn y Egbert, 2000) para invertir datos CC y RMT de manera independiente y conjunta, utilizando el esquema TSVD.

    Luego se configura un modelo de resistividades para generar datos sintéticos CC y RMT con el fin de realizar inversiones simples y una inversión conjunta, que permitan estudiar el comportamiento de cada método y su combinación. Adicionalmente, se realiza un análisis de resolución y varianza no lineal (Kalscheuer y Pedersen, 2007) para comprobar la fiabilidad de cada modelo estimado.

    Los resultados permiten concluir que el modelo estimado de la inversión conjunta se asemeja más al modelo verdadero, que los modelos estimados a partir de las inversiones simples. Particularmente presenta un buen desempeño recuperando el ancho y la forma de las estructuras involucradas, así como la resistividad del medio en el cual se encuentran sumergidas. Cabe destacar que esta inversión logra reducir notablemente la aparición de artefactos resistivos poco profundos, presentes en el modelo estimado CC.

  • 233.
    García Juanatey, María de los Ángeles
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Seismics, 2D and 3D Inversion of Magnetotellurics: Jigsaw pieces in understanding the Skellefte Ore District2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Skellefte District (SD) is one of the richest metallogenic mining areas in Sweden. The main deposits consist of volcanic-hosted massive sulphides (VHMS) rich in zinc, copper, lead, gold and silver, that have been explored and mined for more than a century. Considering that technological advancements allow deeper mining, and that today new discoveries rarely occur, renewed efforts are now directed at locating targets at greater depths.  

    Thus, current exploration strategies need to be adapted, and a better understanding of regional scale structures is necessary. To address these questions the project VINNOVA 4D modeling of the Skellefte District was launched. Its main purpose is to unravel the regional structures and tectonic setting of the SD. To accomplish this, new geological and geophysical data have been acquired in two key localities.

    This thesis presents the contribution from 2D and 3D inversion of magnetotelluric (MT) data and seismic reflection data. The main findings include: conductive hydrothermally altered zones within the otherwise resistive rocks of the Skellefte Group, the depth extension of early and postorogenic intrusions, prominent shear zones in the central part of the district, and enhanced reflectivity and conductivity at the base of the Skellefte Group throughout the SD.

    Even though the application of these methods is challenged by the complex geological setting of the SD, it is shown that after a careful processing and analysis of the data, they are able to provide a robust image of the deep subsurface. Additionally, the combination of reflection seismics and MT has proved to be a powerful tool for hypothesis testing and to develop the general understanding of the configuration and history of the SD.

    Furthermore, two 3D inversion models of MT data are presented and compared with the results of standard 2D determinant inversions. The 3D procedure shows significant improvements in data fit and is able to constrain better the observed model features. Although 3D inversion of MT data is not yet a run of the mill scheme and issues like model assessment and galvanic distortion effects need to be further addressed, results from complex environments with areal coverage, are already superior to those from 2D inversions.

  • 234.
    García Juanatey, María de los Ángeles
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hübert, Juliane
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tryggavson, Ari
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust B
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Dehghannejad, Mahdieh
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bauer, Tobias E
    Weihed, Par
    Skytta, Pietari
    Magnetotelluric measurements in the Skellefte ore district, northern Sweden2013Conference paper (Refereed)
    Abstract
  • 235.
    García Juanatey, María de los Ángeles
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hübert, Juliane
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tryggavson, Ari
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust B
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Imaging the Kristineberg mining area with two perpendicular magnetotelluric profiles in the Skellefte Ore District, northern Sweden2013In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 61, no 1, p. 200-219Article in journal (Refereed)
    Abstract [en]

    New magnetotelluric (MT) data from two perpendicular profiles in the Kristineberg area, northern Sweden, were analysed and modelled. In the Skellefte Ore District, the Kristineberg volcanic hosted massive sulphide (VHMS) deposit mine is one of the largest and deepest (1250 m). Seventeen broadband magnetotelluric stations were installed along two existing seismic reflection lines. The profiles were 6 and 12 km long with 500 m and 1 km site spacing, respectively. The obtained MT transfer functions in the period range of 0.0015–200 s are of fairly good quality. Detailed strike and dimensionality analysis reveal consistent but period dependent, strike directions, indicating a change in the geoelectrical strike with depth. From the two-dimensional inversion of the determinant of the impedance tensor, two stable conductivity models with good data fit were obtained. The addition of seismic reflection information from the co-located survey, improved the data fit of one of them. Extensive sensitivity analyses helped to delineate the well resolved regions of the models and to determine the position of pronounced boundaries. The results are in good agreement with previous studies, especially regarding the presence of a deep conductor interpreted as a structural basement to the district. They also reveal with more detail the configuration of the main geological units of the Skellefte Ore District, especially of the ore bearing volcanic rocks and the embedded alteration zones.

  • 236.
    García Juanatey, María de los Ángeles
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tryggavson, Ari
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bergström, Ulf
    Geological Survey of Sweden.
    Hübert, Juliane
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust B
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    MT and reflection seismics in northwestern Skellefte Ore District, Sweden2013In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 78, no 2, p. B65-B76Article in journal (Refereed)
    Abstract [en]

    A seismic reflection and MT survey was carried out along a 27-km long transect in northwestern Skellefte District, as part of a bigger 3D modeling project. The main motivation for the data acquisition is to elucidate the geologic relationship between the known mineralizations in the Adak mining camp to the north and in the well studied Kristineberg area south of the transect. The seismic reflection data were acquired with a VIBSIST system, and show reflectivity down to 3 s. Apart from the conventional processing for crystalline environments, the seismic data was also subject to an azimuthal binning procedure and cross-dip analysis, allowing the orientation of planar reflectors in 3D. Regarding the MT data, it is primarily of good quality along the 17 installed sites. The inversion of the determinant of the impedance tensor yielded a stable 2D resistivity model, dominated by resistors corresponding to the postorogenic intrusions along the transect. Adding the location of the analyzed seismic reflectors in the MT inversion rendered an integrated model that facilitated a preliminary joint interpretation of the data sets. Overall, the results are in good agreement with surface observations and reveal a crude configuration of the geologic units below the transect. The most prominent outcomes are the lateral and depth extent of the large postorogenic intrusions in the area reaching to 5- or 6-km depth, the dimensions of the nearly vertical Brännäs gabbro extending to 6-km depth, and the presence of enhanced conductivities along the transect at about 10 km depth. The latter is probably related to the deep conductor previously identified in the district.

  • 237.
    Gee, David
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    Scandinavian Caledonides (with Greenland2005In: Elsevier: Encyclopedia of Geology, Vol. 2, p. 64-74Article in journal (Refereed)
  • 238.
    Gee, David
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    Timanides of Northern Russia2005In: Elsevier: Encyclopedia of Geology, Vol. 2, p. 49-56Article in journal (Refereed)
  • 239.
    Gee, David G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Andreasson, Per-Gunnar
    Lund Univ, Dept Geol, Lund, Sweden..
    Li, Yuan
    MLR Inst Geol, Beijing, Peoples R China..
    Krill, Allan
    Norwegian Univ Sci & Technol, Dept Geol & Mineral Resources, Trondheim, Norway..
    Baltoscandian margin, Sveconorwegian crust lost by subduction during Caledonian collisional orogeny2017In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 139, no 1, p. 36-51Article in journal (Refereed)
    Abstract [en]

    Underthrusting of Laurentia by the continental margin of Baltica during Caledonian orogeny resulted in the lateral emplacement of Iapetus Ocean-related terranes of the Upper Allochthon at least 500 km onto Baltica. The underlying Lower and Middle allochthons of the Baltoscandian margin mostly comprise Cryogenian, Ediacaran and Cambro-Silurian sedimentary successions; basement to these formations are present only as minor, isolated fragments, except at the base of the Middle Allochthon and within the underlying windows. The upper parts of the Middle Allochthon are notable for the presence of early Ediacaran dyke-swarms and other components of the Baltoscandian continent-ocean transition zone (COT). New data are presented here on the c. 610 Ma age of the COT-related dolerites in the Kalak Nappe Complex in Northern Norway and also on detrital zircons in the underlying Laksefjord and Gaissa nappes. The former confirms that the Baltoscandian COT has a similar age along the length of the orogen; the latter shows that the detrital zircon signatures in the Lower and Middle allochthons are comparable throughout the orogen. These sedimentary rocks have dominating populations of Mesoproterozoic to latest Palaeoproterozoic zircons similar to those from southern parts of the orogen, where Sveconorwegian complexes comprise the basement to the Caledonides. Thus, they help define the probable character and age of the crystalline basement that existed along this outer margin of Baltica during the Neoproterozoic, continental lower crust that was partly subducted during Ordovician continent-arc collision and subsequently lost beneath Laurentia during the 50 million years of Scandian collisional orogeny.

  • 240.
    Gee, David G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Andreasson, Per-Gunnar
    Lund Univ, Dept Geol, Lund, Sweden..
    Lorenz, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Frei, Dirk
    Univ Stellenbosch, Matieland, South Africa..
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, PL-30059 Krakow, Poland..
    Comments to "Detrital zircon signatures of the Baltoscandian margin along the Arctic Circle Caledonides in Sweden: The Sveconorwegian connection" by Gee et al. (2015) Reply to Ake Johansson (Precambrian Research)2016In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 276, p. 236-237Article in journal (Refereed)
  • 241.
    Gee, David G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Janák, Marian
    Geological Institute, Slovak Academy of Sciences, Bratislava Slovak Republic .
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Robinson, Peter
    Geological Survey of Norway, Leiv Eirikssons vei 39, 7040 Trondheim, Norway .
    van Roermund, Herman
    Structural Geology and Tectonics, Department of Earth Sciences, Utrecht University, The Netherlands .
    Subduction along and within the Baltoscandian margin during closing of the Iapetus Ocean and Baltica-Laurentia collision2013In: Lithosphere, ISSN 1941-8264, E-ISSN 1947-4253, Vol. 5, no 2, p. 169-178Article in journal (Refereed)
    Abstract [en]

    The recent discovery of ultrahigh-pressure (UHP) mineral parageneses in the far-transported (greater than 400 km) Seve Nappe Complex of the Swedish Caledonides sheds new light on the subduction system that dominated the contracting Baltoscandian margin of continental Baltica during the Ordovician and culminated in collision with Laurentia in the Silurian to Early Devonian. High-grade metamorphism of this Neoproterozoic to Cambrian rifted, extended, dike-intruded outer-margin assemblage started in the Early Ordovician and may have continued, perhaps episodically, until collision of the continents at the end of this period. The recent discovery of UHP kyanite eclogite in northern Jämtland (west-central Sweden) yields evidence of metamorphism at depths of 100 km. Although UHP rocks are only locally preserved from retrogression during the long-distance transport onto the Baltoscandian platform, these high-pressure parageneses indicate that deep subduction played an important role in the tectonothermal history of the complex. Based on existing isotopic age data, this UHP metamorphism occurred in the Late Ordovician, shortly before, or during, the initial collision between the continents (Scandian orogeny). In some central parts of the complex, migmatization and hot extrusion occurred in the Early Silurian, giving way to thrust emplacement across the Baltoscandian foreland basin and platform that continued into the Early Devonian. Identification of HP/UHP metamorphism at different levels within the Scandian allochthons, definition of their pressure-temperature-time paths, and recognition of their vast transport distances are essential for an understanding of the deeper structural levels of the orogen in the hinterland (e.g., the Western Gneiss Region), where the attenuated units were reworked together during the Early Devonian.

  • 242.
    Gee, David G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pascal, Christophe
    Geological Survey of Norway.
    Robinson, Peter
    Geological Survey of Norway.
    Collisional Orogeny in the Scandinavian Caledonides (COSC)2010In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 132, no 1, p. 29-44Article in journal (Refereed)
    Abstract [en]

    The COSC project is focused on the mid Paleozoic Caledonide Orogen in Scandinavia in order to better understand orogenic processes, both in the past and in today's active mountain belts. It relates to two of ICDP's main themes - the fundamental physics of plate tectonics and heat, mass and fluid transfer through Earth's crust, and on improving interpretation of geophysical data used to determine the structure and properties of the Earth's crust. Lateral transport of Caledonian allochthons over distances of several hundreds of kilometers in the Scandes, by a combination of thrusting and ductile extrusion, is comparable to that recognized in the Himalayas. The Caledonides in Scandinavia provide special opportunities for understanding Himalayan-type orogeny and the Himalayan Orogen itself, thanks to the deep level of erosion and the paucity of superimposed post-Paleozoic deformation. The surface geology in combination with the seismic, magnetotelluric, magnetic and gravity data provide control of the geometry of the Caledonian structure, both of the allochthon and the underlying parautochthon-autochthon, and define the locations for drilling. The latter will investigate both the high-grade, ductile Caledonian nappes and the underlying allochthons and basement, with two c. 2.5km deep boreholes, located near re and Jarpen in western Jamtland. The two boreholes will also provide unique information about other important aspects of the Scandinavian bedrock, including the heat flow and potential for geothermal energy, mineralization in the Seve nappes and alum shales, the uplift history of the Scandes, the Holocene paleoclimatological changes and the deep biosphere.

  • 243.
    Gee, David G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Ladenberger, Anna
    Dahlqvist, Peter
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Be'eri-Shlevin, Yaron
    Frei, Dirk
    Thomsen, Tonny
    The Baltoscandian margin detrital zircon signatures of the central Scandes2014In: Geological Society, London, Special Publications, Vol. 390, p. 131-155Article in journal (Refereed)
    Abstract [en]

    In central parts of the Scandinavian Caledonides, detrital zircon signatures provide evidence of the change in character of the Baltoscandian crystalline basement, from the characteristic Late Palaeoproterozoic granites of the Transscandinavian Igneous Belt (TIB, c. 1650–1850 Ma) in the foreland Autochthon to the typical, mainly Mesoproterozoic-age profile (c. 950–1700 Ma) of the Sveconorwegian Orogen of southwestern Scandinavia in the hinterland. Late Ediacaran to Early Cambrian shallow-marine Vemdal quartzites of the Jämtlandian Nappes (Lower Allochthon) provide strong bimodal signatures with TIB (1700–1800 Ma) and Sveconorwegian, sensu stricto (900–1150 Ma) ages dominant. Mid-Ordovician turbidites (Norråker Formation) of the Lower Allochthon in Sweden, sourced from the west, have unimodal signatures dominated by Sveconorwegian ages with peaks at 1000–1100 Ma, but with subordinate components of older Mesoproterozoic zircons (1200–1650 Ma). Latest Ordovician shallow-marine quartzites also yield bimodal signatures, but are more dispersed than in the Vemdal quartzites. In the greenschist facies lower parts of the Middle Allochthon, the Fuda (Offerdal Nappe) and Särv Nappe signatures are either unimodal or bimodal (950–1100 and/or 1700–1850 Ma), with variable dominance of the younger or older group, and subordinate other Mesoproterozoic components. In the overlying, amphibolite to eclogite facies lower part of the Seve Nappe Complex, where the metasediments are dominated by feldspathic quartzites, calcsilicate-rich psammites and marbles, most units have bimodal signatures similar to the Särv Nappes, but more dispersed; one has a unimodal signature very similar to the Ordovician turbidites of the Jämtlandian Nappes. In the overlying Upper Allochthon, Lower Köli (Baltica-proximal, Virisen Terrane), Late Ordovician quartzites provide unimodal signatures dominated by Sveconorwegian ages (sensu stricto). Further north in the Scandes, previously published zircon signatures in quartzites of the Lower Allochthon are similar to the Vemdal quartzites in Jämtland. Data from the Kalak Nappes at 70°N are in no way exotic to the Sveconorwegian Baltoscandian margin. They do show a Timanian influence (ages of c. 560–610 Ma), as would be expected from the palinspastic reconstructions of the nappes. Thus the detrital zircon signatures reported here and published elsewhere provide supporting evidence for a continuation northwards of the Sveconorwegian Orogen in the Neoproterozoic, from type areas in the south, along the Baltoscandian margin of Baltica into the high Arctic.

  • 244.
    Gee, David G.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    Pease, V.L.
    The Neoproterozoic Timanide Orogen of eastern Baltica: introduction2004In: Geological Society London, Memoirs 30, p. 1-5Article in journal (Refereed)
  • 245.
    Gee, David G.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    Tebenkov, A.
    Svalbard: a fragment of the Laurentian margin2004In: Geological Society London, Memoirs 30, no 191-207Article in journal (Refereed)
  • 246.
    Gee, David Godfrey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Per-Gunnar, Andréasson
    Lund University.
    Lorenz, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Frei, Dirk
    Stellenbosch University.
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Detrital zircon signatures of the Baltoscandian margin along the Arctic Circle Caledonides in Sweden: The Sveconorwegian connection2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 265, p. 40-56Article in journal (Refereed)
    Abstract [en]

    New evidence is presented here that the Sveconorwegian Orogen continued northwards from type areas in southwestern Scandinavia along the Baltoscandian outer margin into the high Arctic. The Silver Road (Silvervägen) profile through the Scandinavian Caledonides, located in Sweden along the Arctic Circle at 66–67◦ N, provides a full section through the tectonostratigraphy of the Baltoscandian margin from the Autochthon, via the Lower Allochthon to the upperment parts of the Middle Allochthon. Metamorphic grade increases upwards through the nappes, being low greenschist facies at lowest levels and increas- ing to eclogite grade in the highest parts of the Seve Nappe Complex, the latter being related to early Ordovician subduction of the Baltoscandian outermost margin. The sedimentary rocks range in age from Neoproterozoic to Ordovician and provide evidence of the changes of environment from the Baltoscan- dian platform, westwards out over the Cryogenian rifted margin to the continent-ocean transition zone; also the Ordovician foreland basin. Twelve samples of psammites from the different tectonostratigraphic levels have yielded U/Pb detrital zircon age-signatures that reflect the changing character of their pro- venance. Autochthonous sandstones are derived from late Paleoproterozoic (1800–1950 Ma) crystalline rocks in the vicinity to the east of the thrust front. Ediacaran-early Cambrian quartzites of the Lower Allochthon also yield mainly late Paleoproterozoic zircon signatures, but with subordinate Mesopro- terozoic and late Archaean populations, whilst mid Ordovician, W-derived foreland basin turbidites are dominated by Sveconorwegian (950–1100 Ma) signatures, with subordinate older Mesoproterozoic to latest Paleoproterozoic populations. All samples from the lower parts of the Middle Allochthon (lacking dolerite dykes) have signatures that are dominated by latest Paleoproterozoic and early Mesoproterozoic ages, with subordinate populations down to Sveconorwegian ages; the latter dominate the overlying Särv nappes and also the Seve Nappe Complex, where c. 945 Ma rhyodacites have been previously reported. This evidence of Sveconorwegian source rocks in the hinterland, taken together with previously pub- lished detrital zircon data farther south and north of the Arctic Circle, clearly favours the interpretation that the Sveconorwegian Orogen, during the Neoproterozoic, extended along the entire Baltoscandian outer margin into the high Arctic.

  • 247.
    Gee, D.G.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    Bogolepova, O.K.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    Lorenz, H.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    A New Tectonic Map of the Arctic at 1:10 M2006In: 'The History of Convergent and Passive Margins in the Polar Realm: Sedimentary and Tectonic Processes, Transitions and Resources', 2006Conference paper (Other scientific)
  • 248.
    Gee, D.G.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    Lorenz, H.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Geophysics. Geofysik.
    Simonetti, A.
    Detrital zircon studies of the Vendian to Devonian successions of the Severnaya Zemlya Archipelago, North Kara Terrane: tectonic implications2006In: Bulletin of the Geological Society of Finland. Special Issue 1, 2006Conference paper (Other scientific)
  • 249. Gehring, Andreas
    et al.
    Riahi, Nima
    Kind, Jessica
    Almqvist, Bjarne
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Weidler, Peter
    The formation of the Namib Sand Sea inferred from the spatial pattern of magnetic rock fragments2014In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 395, p. 168-172Article in journal (Refereed)
  • 250.
    Geiger, Harri
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Mattsson, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Deegan, Frances
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Stockholm Univ, Dept Geol Sci, Stockholm, Sweden.
    Troll, Valentin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Burchardt, Steffi
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Gudmundsson, Ólafur
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tryggvason, Ari
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Krumbholz, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Harris, Chris
    Univ Cape Town, Dept Geol Sci, Rondebosch, South Africa.
    Magma plumbing for the 2014–2015 Holuhraun eruption, Iceland2016In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 17, no 8, p. 2953-2968Article in journal (Refereed)
    Abstract [en]

    The 2014–2015 Holuhraun eruption on Iceland was located within the Askja fissure swarm butwas accompanied by caldera subsidence in the Barðarbunga central volcano 45 km to the southwest. Geophysicalmonitoring of the eruption identified a seismic swarm that migrated from Barðarbunga to theHoluhraun eruption site over the course of two weeks. In order to better understand this lateral connectionbetween Barðarbunga and Holuhraun, we present mineral textures and compositions, mineral-meltequilibriumcalculations, whole rock and trace element data, and oxygen isotope ratios for selected Holuhraunsamples. The Holuhraun lavas are compositionally similar to recorded historical eruptions from theBarðarbunga volcanic system but are distinct from the historical eruption products of the nearby Askja system.Thermobarometry calculations indicate a polybaric magma plumbing system for the Holuhraun eruption,wherein clinopyroxene and plagioclase crystallized at average depths of 17 km and 5 km,respectively. Crystal resorption textures and oxygen isotope variations imply that this multilevel plumbingsystem facilitated magma mixing and assimilation of low-d18O Icelandic crust prior to eruption. In conjunctionwith the existing geophysical evidence for lateral migration, our results support a model of initial verticalmagma ascent within the Barðarbunga plumbing system followed by lateral transport of aggregatedmagma batches within the upper crust to the Holuhraun eruption site.

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