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  • 251.
    Chouliaras, Gerassimos
    et al.
    Department of Seismology, University of Uppsala.
    Rasmussen, Thorkild Maack
    Department of Solid Earth Physics, University of Uppsala.
    The application of the magnetotelluric impedance tensor to earthquake prediction research in Greece1988In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 152, no 1-2, p. 119-135Article in journal (Refereed)
    Abstract [en]

    Continuous short period (0.1-3600 s) measurements of the magnetotelluric field components were conducted simultaneously at two sites in Greece for a period of 5 weeks. The estimation of the impedance tensor elements from 8-hr windows of recorded data, at each station, is found to describe the local electromagnetic induction with great accuracy. The computation of the residual electric field, obtained as the difference between the observed and estimated inductive part of the electric fields, clearly improves the detection of any local electric field anomaly. This method was used in an attempt to detect precursory Sci smic electrical signals (SES) that have been reported to precede earthquakes in Greece. The results indicate the success of this method in resolving ambiguities about the nature of the reported SES, i.e. whether it has an external or internal source. Although during the recording period no large earthquake occurred, five with a magnitude of between ML = 4.0 and ML = 4.3 occurred within a radius of 150 km from one of the stations. The magnetotelluric recordings and the computed residual electric fields for the time intervals reported to contain the SES precursors to these events were analysed in some detail. In two of the cases it was found that the sources could not be related to earthquake processes. In the other three cases the nature of the source of the suspected SES, although electric, could not be established with certainty. These results indicate that for earthquakes of small magnitude (ML ≤ 4.3) or of large epicentral distance (r ≥ 100 km), the detection of a SES is extremely difficult.

  • 252. Cory, N.
    et al.
    Andrén, Cecilia M
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Bishop, K.
    Modelling inorganic Aluminium with WHAM in environmental monitoring2007In: APPLIED GEOCHEMISTRY, ISSN 0883-2927, Vol. 22, p. 1196-1201Article in journal (Refereed)
    Abstract [en]

    Due to the varying toxicity of different Al species, information about Al concentration and speciation is important when assessing water quality. Modelling Al speciation can support operational monitoring programmes where Al speciation is not measured directly. Modelling also makes it possible to retroactively speciate older samples where laboratory fractionation was not undertaken. Organic-rich waters are a particular challenge for both laboratory analysis and models. This paper presents the modelling of Al speciation in Swedish surface waters using the Windermere Humic Acid Model (WHAM). The model was calibrated with data from operational monitoring, the Swedish national survey of lakes and rivers, and covers a broad spectrum of physical and chemical conditions. Calibration was undertaken by varying the amount of DOC active in binding Al. A sensitivity analysis identified the minimum parameters required as model input variables primarily to be total Al, organic C, pH, F-, and secondly Fe, Ca and Mg. The observed and modelled Ali had no significant differences (Spearman rank, p < 0.01), however, lake samples modelled better than rivers. Samples were placed in the correct toxicological category in 89-95% of the cases. The importance of the size of the calibration data set was assessed, and reducing the calibration data set resulted in poorer correlations, but had little impact on the toxicological placement. Overall, the modelling gave satisfactory results from samples covering a broad spectrum of physical and chemical conditions. This indicates the potential value of WHAM as a tool in operational monitoring of surface waters.

  • 253.
    Cunningham, Laura
    et al.
    Umeå University, Faculty of Science and Technology. Climate Impacts Research Centre (CIRC), Umeå University, 98107 Abisko, Sweden.
    Vogel, Hendrik
    Nowaczyk, Norbert
    Wennrich, Volker
    Juschus, Olaf
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rosen, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Climate Impacts Research Centre (CIRC), Umeå University, 98107 Abisko, Sweden.
    Climatic variability during the last interglacial inferred from geochemical proxies in the Lake El'gygytgyn sediment record2013In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 386, p. 408-414Article in journal (Refereed)
    Abstract [en]

    The Last Interglacial Period (LIP) is often regarded as a good analogue for potential climatic conditions under predicted global warming scenarios. Despite this, there is still debate over the nature, duration and frequency of climatic changes during this period. One particularly contentious issue has been the apparent evidence of climatic instability identified in many marine cores but seemingly lacking from many terrestrial archives, especially within the Arctic, a key region for global climate change research. In this paper, geochemical records from Lake El'gygytgyn, north-eastern Russia, are used to infer past climatic changes during the LIP from within the high Arctic. With a sampling resolution of similar to 20-similar to 90 years, these records offer the potential for detailed, high-resolution palaeoclimate reconstruction. This study shows that the LIP commenced in central Chukotka similar to 129 thousand years ago (ka), with the warmest climatic conditions occurring between similar to 128 and 127 ka before being interrupted by a short-lived cold reversal. Mild climatic conditions then persisted until similar to 122 ka when a marked reduction in the sedimentation rate suggests a decrease in precipitation. A further climatic deterioration at similar to 118 ka marks the return to glacial conditions. This study highlights the value of incorporating several geochemical proxies when inferring past climatic conditions, thus providing the potential to identify signals related to environmental change within the catchment. We also demonstrate the importance of considering how changes in sedimentation rate influence proxy records, in order to develop robust palaeoenvironmental reconstructions. (C) 2013 Elsevier B.V. All rights reserved.

  • 254.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Statistical Formulation of Generalized Tracer Retention in Fractured Rock2017In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 53, no 11, p. 8736-8759Article in journal (Refereed)
    Abstract [en]

    We study tracer retention in fractured rock by combing Lagrangian and time domain random walk frameworks, as well as a statistical representation of the retention process. Mass transfer is quantified by the retention time distribution that follows from a Lagrangian coupling between advective transport and mass exchange processes, applicable for advection-dominated transport. A unifying parametrization is presented for generalized diffusion using two rates denoted by k(1) and k(2) where k(1) is a forward rate and k(2) a reverse rate, plus an exponent as an additional parameter. For the Fickian diffusion model, k(1) and k(2) are related to measurable retention properties of the fracture-matrix by the method of moments, whereas for the non-Fickian case dimensional analysis is used. The derived retention time distributions are exemplified for interpreting tracer tests as well as for predictive modeling of expected tracer breakthrough. We show that non-Fickian effects can be notable when transport is upscaled based on a non-Fickian interpretation of a tracer test for which deviations from Fickianity are relatively small. The statistical representation of retention clearly shows the significance of the forward rate k(1) which depends on the active specific surface area and is the most difficult parameter to characterize in the field.

  • 255. Cyprych, Daria
    et al.
    Piazolo, Sandra
    Almqvist, Bjarne
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Seismic anisotropy from compositional banding in granulites from the deep magmatic arc of Fiordland, New Zealand2017In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 477, p. 156-167Article in journal (Refereed)
    Abstract [en]

    We present calculated seismic velocities and anisotropies of mafic granulites and eclogites from the Cretaceous deep lower crust (similar to 40-65 km) of Fiordland, New Zealand. Both rock types show a distinct foliation defined by cm-scale compositional banding. Seismic properties are estimated using the Asymptotic Expansion Homogenisation - Finite Element (AEH-FE) method that, unlike the commonly used Voigt-Reuss-Hill homogenisation, incorporates the phase boundary network into calculations. The predicted mean P- and S-wave velocities are consistent with previously published data for similar lithologies from other locations (e.g., Kohistan Arc), although we find higher than expected anisotropies (AV(P) similar to 5.0-8.0%, AV(S) similar to 3.0-6.5%) and substantial S-wave splitting along foliation planes in granulites. This seismic signature of granulites results from a density and elasticity contrast between cm-scale pyroxene +/- garnet stringers and, plagioclase matrix rather than from crystallographic orientations alone. Banded eclogites do not show elevated anisotropies as the contrast in density and elastic constants of garnet and pyroxene is too small. The origin of compositional banding in Fiordland granulites is primarily magmatic and structures described here are expected to be typical for the base of present day magmatic arcs. Hence, we identify a new potential source of anisotropy within this geotectonic setting.

  • 256.
    Czymzik, Markus
    et al.
    Lund Univ, Dept Geol, Quaternary Sci, S-22362 Lund, Sweden..
    Adolphi, Florian
    Lund Univ, Dept Geol, Quaternary Sci, S-22362 Lund, Sweden..
    Muscheler, Raimund
    Lund Univ, Dept Geol, Quaternary Sci, S-22362 Lund, Sweden..
    Mekhaldi, Florian
    Lund Univ, Dept Geol, Quaternary Sci, S-22362 Lund, Sweden..
    Martin-Puertas, Celia
    GEZ German Res Ctr Geosci, Sect Climate Dynam & Landscape Evolut 5 2, D-14473 Potsdam, Germany..
    Aldahan, Ala
    United Arab Emirates Univ, Dept Geol, Al Ain 15551, U Arab Emirates..
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Tandem Laboratory.
    Brauer, Achim
    GEZ German Res Ctr Geosci, Sect Climate Dynam & Landscape Evolut 5 2, D-14473 Potsdam, Germany..
    A varved lake sediment record of the Be-10 solar activity proxy for the Lateglacial-Holocene transition2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 153, p. 31-39Article in journal (Refereed)
    Abstract [en]

    Solar modulated variations in cosmogenic radionuclide production provide both information on past changes in the activity of the Sun and a global synchronization tool. However, to date the use of cosmogenic radionuclides for these applications is almost exclusively based on Be-10 records from ice cores and C-14 time-series from tree rings, all including archive-specific limitations. We present the first Be-10 record from annually laminated (varved) lake sediments for the Lateglacial-Holocene transition from Meerfelder Maar. We quantify environmental influences on the catchment and, consequently, Be-10 deposition using a new approach based on regression analyses between our Be-10 record and environmental proxy time-series from the same archive. Our analyses suggest that environmental influences contribute to up to 37% of the variability in our Be-10 record, but cannot be the main explanation for major Be-10 excursions. Corrected for these environmental influences, our Be-10 record is interpreted to dominantly reflect changes in solar modulated cosmogenic radionuclide production. The preservation of a solar production signal in Be-10 from varved lake sediments highlights the largely unexplored potential of these archives for solar activity reconstruction, as global synchronization tool and, thus, for more robust paleoclimate studies.

  • 257.
    Cáceres Calix, Diego José
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Earthquake Sources and Hazard in northern Central America2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Northern Central America is a tectonically complex zone defined by its borders with Cocos and North America plates. The Middle America subduction zone and the strike-slip motion along the North America-Caribbean plate boundary, in that order, control most of its deformation. The interaction between the different elements of the studied area is evident from the high seismicity in the region, especially along plate boundaries. Also in the interior of the region, seismicity shows that deformation takes place, though in lesser degree. In a time window of 30 years, three earthquakes with moment magnitude larger than 7 struck northern Central America evincing the need to estimate the seismic hazard for the zone. To tackle the problem, we compiled a catalogue of hypocenters commencing in 1964, defined seismogenic sources and described the evolution of earthquake activity through a Poisson model. Probabilistic seismic hazard (PSH) calculations for the next 50 years were performed. The highest estimate of seismic hazard was obtained for the zone adjacent to the subduction zone. Because of the fundamental importance of demarcating seismogenic sources in the PSH analysis, i.e. defining the seismotectonic model, we extended the catalogue to cover 102 years for the whole northern Central America. We have studied the North America-Caribbean plate boundary in order to refine the fault representation. Different techniques were used, like that of body-waveform modeling, allowing us to limit the extent of depth of faulting to 20 km. The seismic moment tensor was used to estimate the deformation velocities on known tectonic structures, including those of the Honduras depression and borderland faults. Finally, we made use of the Coulomb stress criterion to determine the relation between earthquake occurrence and static stress changes following major earthquakes.

  • 258. D´Agrella-Filho, Mabuel S.
    et al.
    Pacca, Igor I. P.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Teixeira, Wilson
    Bettencourt, Jorge Silva
    Geraldes, M.C.
    Preliminary paleomagnetic results from metabasic and sedimentary rocks from the Amazonian craton: tectonic implications for the Rodinia supercontinent2001In: Workshop on Geology of the SW Amazonian Craton: State-of- the-art. Abstracts, Instituto de Geociências-USP , 2001, p. 155-158Conference paper (Other academic)
  • 259.
    D'Agrella-Filho, Manoel S.
    et al.
    Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Tohver, Eric
    School of Earth and Geographical Sciences, University of Western Australia, Crawley.
    Santos, João O.S.
    Redstone Resources Limited, Perth.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Trinidade, Ricardo I.F.
    Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Pacca, Igor I.G.
    Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Geraldes, Mauro C.
    Faculdade de Geologia, Universidade do Estado do Rio de Janeiro.
    Direct dating of paleomagnetic results from Precambrian sediments in the Amazon craton: Evidence for Grenvillian emplacement of exotic crust in SE Appalachians of North America2008In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 267, no 1-2, p. 188-199Article in journal (Refereed)
    Abstract [en]

    We apply a new diagenetic dating technique to determine the age of magnetization for Precambrian sedimentary rocks in the SW Amazon craton. Two new palcomagnetic poles are reported from the rocks of the Aguapei Gp.: red beds of the Fortuna Fm. (P-lat = 59.8 degrees N, P-lon = 155.9 degrees E, A(95)=9.5, K= 14, 18 sites, N/n 128/115, Q=5) and the reverse-polarity mudstones of the overlying Vale da Promissao Formation (P-lat=49.5 degrees N, P-lon = 89.3 degrees E, A(95) = 12.5, K=30, 6 sites, N/n=94/80, Q=4). The Fortuna Fm. magnetization is hosted by massive, interstitial hematite cement and constitutes a post-depositional remanence. The age of diagenesis of the red beds is well-constrained by the 1149 +/- 7 Ma U-Pb age of authigenic xenotime rims on detrital zircons determined by SHRIMP analysis. The magnetite-hosted remanence of the Vale da Promissao Fm. may be detrital in origin, but the age of deposition is poorly constrained. The reliable and precisely-dated Fortuna Fun. pateomagnetic pole fixes the paleogeographic position of the Amazon craton near the SE Appalachians portion of North America at 1.15 Ga. These data demonstrate a mobile Grenvillian link between these two cratons, and support the recent identification of Amazon crust in the Blue Ridge province region of North America

  • 260.
    D'Agrella-Filho, Manoel S.
    et al.
    Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Trindade, Ricardo I.F.
    Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Teixeira, Wilson
    Instituto de Geociências, Universidade de São Paulo.
    Yokoyama, Elder
    Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Tohver, Eric
    School of Earth and Geographical Sciences, University of Western Australia, Crawley.
    Geraldes, Mauro C.
    Faculdade de Geologia, Universidade do Estado do Rio de Janeiro.
    Pacca, Igor I.G.
    Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Barros, Marcia A.S.
    Instituto de Ciências Exatas e da Terra, Departamento de Geologia, Universidade Federal de Mato Grosso.
    Ruiz, Amarildo S.
    Instituto de Ciências Exatas e da Terra, Departamento de Geologia, Universidade Federal de Mato Grosso.
    The 1420 Ma Indiavaí Mafic Intrusion (SW Amazonian Craton): Paleomagnetic results and implications for the Columbia supercontinent2012In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 22, no 3-4, p. 956-973Article in journal (Refereed)
    Abstract [en]

    The configuration and the timing of assembly and break-up of Columbia are still matter of debate. In order to improve our knowledge about the Mesoproterozoic evolution of Columbia, a paleomagnetic study was carried out on the 1420 Ma Indiavaí mafic intrusive rocks that crosscut the polycyclic Proterozoic basement of the SW Amazonian Craton, in southwestern Mato Grosso State (Brazil). Alternating field and thermal demagnetization revealed south/southwest ChRM directions with downward inclinations for sixteen analyzed sites. These directions are probably carried by SD/PSD magnetite with high coercivities and high unblocking temperatures as indicated by additional rock magnetic tests, including thermomagnetic data, hysteresis data and the progressive acquisition of isothermal remanent magnetization. Different stable magnetization components isolated in host rocks from the basement 10 km NW away to the Indiavaí intrusion, further support the primary origin of the ChRM. A mean of the site mean directions was calculated at Dm = 209.8°, Im = 50.7° (α95 = 8.0°, K = 22.1), which yielded a paleomagnetic pole located at 249.7°E, -57.0°N (A95 = 8.6°). The similarity of this pole with the recently published 1420 Ma pole from the Nova Guarita dykes in northern Mato Grosso State suggests a similar tectonic framework for these two sites located 600 km apart, implying the bulk rigidity of the Rondonian-San Ignacio crust at that time. Furthermore these data provide new insights on the tectonic significance of the 1100-1000 Ma Nova Brasilândia belt –a major EW feature that cuts across the basement rocks of this province, which can now be interpreted as intracratonic, in contrast to previous interpretation. From a global perspective, a new Mesoproterozoic paleogeography of Columbia has been proposed based on comparison of these 1420 Ma poles and a 1780 Ma pole from Amazonia with other paleomagnetic poles of similar age from Baltica and Laurentia, a reconstruction in agreement with geological correlations.

  • 261.
    D’Agrella-Filho, Manoel S.
    et al.
    Universidade de São Paulo.
    Trindade, Ricardo I.F.
    Universidade de São Paulo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Yokoyama, Eder
    Universidade de São Paulo.
    Bispo-Santos, Franklin
    Universidade de São Paulo.
    A new 1.42 GA paleomagnetic pole from the Amazonian craton: implications for the Columbia supercontinent configuration2011In: Proceedings of Second Biennial Meeting of Latinmag: Tandil Argentina, November 2011, 2011Conference paper (Other academic)
    Abstract [en]

    Paleomagnetic studies carried out on the 1.42 Ga Indiavaí mafic intrusive rocks, that crop out in the SW Mato Grosso State provides a great opportunity to test the proposed paleogeographic models for Columbia. Paleomagnetic AF and thermal treatment revealed south/southwest magnetic directions with downward inclinations for sixteen analyzed sites. These directions are probably carried by SD/PSD magnetite with high coercivities and high unblocking temperatures as indicated by additional magnetic tests, including thermomagnetic curves, hysteresis loops and the IRM acquisition curves. A different magnetization obtained for host mafic rocks from the basement ca. 10 km NW away from the Indiavaí intrusive, further attests to the primary origin of the characteristic magnetic component. A mean site direction was calculated at Dm=209.8°, Im=50.7° (α95=8.0°, K=22.1), which yielded a paleomagnetic pole located at 249.7°E, -57.0°N (A95=8.6°). Comparison of this pole with other paleomagnetic poles of similar age from Baltica and Laurentia provides evidence for a link of north-northeastern Amazonian craton, southwestern Baltica and Laurentia, as previously suggested from the similar Mesoproterozoic geological evolution of their margins.

  • 262.
    D'Agrella-Filho, Manoel Souza
    et al.
    Sao Paulo University.
    Trindade, Ricardo I. Ferreira
    Sao Paulo University.
    Tohver, Eric
    University of Western Australia.
    Bispo-Santos, Franklin
    Sao Paulo University.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pacca, Igor I. Gil
    Sao Paulo University.
    Proterozoic paleogeographic evolution of South American cratons2008Conference paper (Other academic)
    Abstract [en]

    The South American platform is composed of four major cratons (Amazonian, São Francisco, Rio de la Plata and São Luis) and other smaller continental blocks and terrains that may have taken part in supercontinental assemblages. Here, paleogeographic configurations from the Paleoproterozoic up to the Cambrian are tested by means of an updated paleomagnetic and geochronologic record of South America, including new high-quality poles from the Amazonian and São Francisco cratons. These poles are compared to those of other cratons thought to have interacted with South American units in the Proterozoic, such as Baltica and Laurentia. The oldest assemblage of continents to be addressed is the Paleoproterozoic Columbia (~1800 Ma), for which our data support a configuration aligning Laurentia, Baltica, North China and Amazonia through their Paleo-Mesoproterozoic belts. For Neoproterozoic times (~1200-1000 Ma) a connection between Laurentia and the Amazonian craton in an evolving configuration (with relative movement between the two units) is supported by a pole-to-pole comparison. In contrast, striking differences in Laurentia's drift history compared to São Francisco, São Luis (=West Africa) and Kalahari rule-out the effective participation of these cratons in Rodinia. The assembly of Gondwana has probably occurred in different steps, comprising first (~630 Ma) the connection between Sao Francisco, Rio de la Plata, other minor blocks and the African cratons, followed by the collision of these central Gondwanan blocks with the Amazonian craton and adjoining blocks by mid-Cambrian times (~530 Ma), after the opening of the Iapetus ocean basin between Laurentia and the Amazonian craton. In this scenario, the West Gondwana was not a coherent tectonic unit before the end of Precambrian times.

  • 263.
    d'Agrella-Filho, M.S.
    et al.
    University of Sao Paolo.
    Pacca, I I G
    University of Sao Paolo.
    Sigueira, R.
    University of Sao Paolo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Teixeira, W.
    University of Sao Paolo.
    Bettencourt, J.S.
    Geraldes, M.C.
    Amazonian Proterozoic poles: implications to Rodinia paleogeography2001In: From basins to mountains: Rodinia at the turn of the century / Chris Powell Memorial Symposium / [ed] K.N. Sircombe; Z.X. Li, University of Western Australia , 2001, p. 27-30Conference paper (Other academic)
  • 264.
    D'Agrella-Filho, M.S.
    et al.
    University of Sao Paolo.
    Pacca, Igor Gal
    University of Sao Paolo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Trinidade, R.I.F.
    University of Sao Paolo.
    Paleomagnetic evidence for oblique collision between Amazonia and Laurentia at about 1.1 Ga2004In: International Geological Congress, Abstracts: 32nd international geological congress, Florence, Italy, Aug. 20-28, 2004, 2004, p. 1089-Conference paper (Other academic)
    Abstract [en]

    The connection between Amazonia and Laurentia at late Meso- proterozoic times through the Grenville/Sunsas-Aguapei collisional belts is a key feature of Rodinia paleogeography.However, at least three different geometries are proposed for such connection, mainly due to the paucity of paleomagnetic data for Amazonia.Connections along Greenland and Labrador were initially proposed based on the fit of geological provinces and scarse virtual geomagnetic poles.More recently, a connection through the Llano belt in Texas was proposed based on a single well dated 1.2 Ga paleopole obtained in mafic rocks from the Nova Floresta Formation. We present a series of poles obtained on sedimentary rocks of the Aguapei Group (western Matto Grosso State-Amazonian Craton) and intrusive mafic rocks, whose evolution is related to the Meso-Neoproterozoic Aguapei-Sunsas orogeny (1.3-0.9 Ga).Together with the 1.2 Ga Nova Floresta pole, they define a straight apparent polar wander path which matches the Laurentia APWP by 1.1 Ga for a connection along the (present day) Labrador region. The pole's trajectories imply a high degree of obliquity for such a collision in agreement with tectonic models put forward for the southwestern margin of Amazonia, the southeastern margin of Laurentia and the southwestern margin of Baltica.

  • 265. Dahlgren, H.
    et al.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lanchester, B. S.
    Monoenergetic high-energy electron precipitation in thin auroral filaments2012In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, no 20, p. L20101-Article in journal (Refereed)
    Abstract [en]

    The energy distribution of the electron precipitation responsible for extremely narrow (70 m) and dynamic auroral filaments is found to be sharply peaked at around 8 keV. The events were captured with high resolution low-light optical imagers located near Tromso, Norway. The method uses imaging in two emissions which have different energy dependent responses to auroral electron precipitation. The key feature of the events was that no difference in the altitude of the two emissions was detected, nor any time-of-flight dispersion, thus leading to the conclusion that the filaments were caused by monoenergetic precipitation. Comparisons with an electron transport and ion chemistry model show that the high energy filaments were embedded in a region of lower energy precipitation of about 4 keV. There is currently no consistent theory to explain the characteristics of the observed auroral structures.

  • 266.
    Dahlgren, Hanna
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. University of Southampton, United Kingdom.
    Lanchester, B. S.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Whiter, D. K.
    Electrodynamics and energy characteristics of aurora at high resolution by optical methods2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 6, p. 5966-5974Article in journal (Refereed)
    Abstract [en]

    Technological advances leading to improved sensitivity of optical detectors have revealed that aurora contains a richness of dynamic and thin filamentary structures, but the source of the structured emissions is not fully understood. In addition, high-resolution radar data have indicated that thin auroral arcs can be correlated with highly varying and large electric fields, but the detailed picture of the electrodynamics of auroral filaments is yet incomplete. The Auroral Structure and Kinetics (ASK) instrument is a state-of-the-art ground-based instrument designed to investigate these smallest auroral features at very high spatial and temporal resolution, by using three electron multiplying CCDs in parallel for three different narrow spectral regions. ASK is specifically designed to utilize a new optical technique to determine the ionospheric electric fields. By imaging the long-lived O+ line at 732 nm, the plasma flow in the region can be traced, and since the plasma motion is controlled by the electric field, the field strength and direction can be estimated at unprecedented resolution. The method is a powerful tool to investigate the detailed electrodynamics and current systems around the thin auroral filaments. The two other ASK cameras provide information on the precipitation by imaging prompt emissions, and the emission brightness ratio of the two emissions, together with ion chemistry modeling, is used to give information on the energy and energy flux of the precipitating electrons. In this paper, we discuss these measuring techniques and give a few examples of how they are used to reveal the nature and source of fine-scale structuring in the aurora.

  • 267. Daras, I.
    et al.
    Fan, Huaan
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Papazissi, K.
    Fairhead, J. D.
    Determination of a Gravimetric Geoid Model of Greece Using the Method of KTH2010In: Gravity, Geoid And Earth Observation, Springer Berlin/Heidelberg, 2010, p. 407-413Conference paper (Refereed)
    Abstract [en]

    The main purpose of this study is to compute a gravimetric geoid model of Greece using the least squares modification method developed at KTH. In regional gravimetric geoid determination, the modified Stokes' formula that combines local terrestrial data with a global geopotential model is often used nowadays. In this study, the optimum modification of Stokes' formula, introduced by Sjöberg (2003), is employed so that the expected mean square error (MSE) of the combined geoid height is minimized. According to this stochastic method, the geoid height is first computed from modified Stokes' formula using surface gravity data and a global geopotential model (GGM). The precise geoid height is then obtained by adding the topographic, downward continuation, atmospheric and ellipsoidal corrections to the approximate geoid height. In this study the downward continuation correction was not considered for the precise geoid height computations due to a limited DEM. The dataset used for the computations, consisted of terrestrial gravimetric measurements, a DEM model and GPS/Levelling data for the Greek region. Three global geopotential models (EGM96, EIGEN-GRACE02S, EIGEN-GL04C) were tested for choosing the best GGM to be combined into the final solution. Regarding the evaluation and refinement of the terrestrial gravity measurements, the cross-validation technique has been used for detection of outliers. The new Greek gravimetric geoid model was evaluated with 18 GPS/Levelling points of the Greek geodetic network. After using a 7-parameter model to fit the geoid model to the GPS/Levelling data, the agreement between the absolute geoid heights derived from the gravimetric method and the GPS/Levelling data, was estimated to 27 cm while the agreement for the relative geoid heights after the fitting, to 0.9 ppm. In an optimal case study, considering the accuracies of the ellipsoidal and orthometric heights as σh≈±10 cm and σH≈±20 cm respectively, the RMS fit of the model with the GPS/Levelling data was estimated to σN≈±15 cm. The geoid model computed in this study was also compared with some previous Greek geoid models, yielding better external accuracy than them.

  • 268.
    Darwesh, Ali K.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maack Rasmussen, Thorkild
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Kicks controlling techniques efficiency in term of time2017In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, no 5, p. 482-492Article in journal (Refereed)
    Abstract [en]

    Kicks are the result of under balance drilling operation. Time consumed to control the kicks will be different in depending on the controlling technique. Drilling fluid considered as a first barrier to control formation pressure and well kicks. Any advance in drilling fluids leads to more controlled operation in term of time. This paper will follow the general increasing profile of pressure before entering the reservoir. Both methods of well controlling technique; circulating techniques and non-circulating have been implemented in many oil blocks. The process of designing and casing selection, setting depth and many other issues is predominately dependent on the utilization of accurate values of formation pressure. Formation pressures used to design safe mud weights to overcome fracturing the formation and prevent well kicks. Hence the emphasis has been placed on the practical utilization of kicks pressure near the reservoir. The presented relationships will help the engineer to better understand lithological columns and reduce potential hole problems during the kick appearance. Selecting the best well controlling practical method can lead to not harming the reservoir and more production later. Changes in some drilling fluid properties have been proposed with increasing the depth without damaging the reservoir. Suggestions in relation to the casing setting point of the intermediate section are also proposed. Standard equations with proper modification for gases and safety margin have been proposed for the future drilling operation in oil fields above the reservoir.

  • 269.
    Darwesh, Ali K.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Time Optimizing near the Pay Zone2017In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, no 10, p. 848-858Article in journal (Refereed)
    Abstract [en]

    Well control techniques are used in oil and gas drilling operations to control bottom hole pressure and avoid any fluid influx from formation to the well. These techniques are highly important near the pay zone in term of time. Controlling formation fluid pressure and thereby the formations behavior in a predictable fashion will help toward more optimized environmental friendly drilling operation. Time consumed to control the formation fluid pressure will range between few hours to many days. This paper discusses hydrostatic pressure distribution and changes near the pay zone for one oil blocks in Kur- distan, in the northern part of Iraq. Obtaining homogeneous increase in some drilling fluid properties will help the engineer to better interpret sampling of the lithological columns and reduce potential hole problems and operationtime.

  • 270.
    Darwesh, Ali K.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Wiper Trips Effect on Wellbore Instability Using Net Rising Velocity Methods2018In: Open Petroleum Engineering Journal, ISSN 1874-8341, Vol. 11, p. 14-28Article in journal (Refereed)
    Abstract [en]

    Background: This paper discusses the wiper trip effects on well instability in shale formations.Objectives: Problematic shale interval sections have been studied for the time spent on the wiper trip operations. Lifting efficiency and well wall instability change with the time analyzed. Detailed drilling operation, formation heterogeneity, rheological and filtration characteristics of polymer water-based mud are discussed. Physical and chemical properties of the drilled formation and drilling fluid are also studied.Materials and Methods: Wiper trips are analyzed using a typical drawing program to find the relations between the most controllable parameters. For that, two calculation models have been implemented to find the net rising cutting particles velocity in the annular. The relation between the net rising velocity and wiper trips is analyzed. Laboratory works have been done to support the findings of field work.Results: Strong relations have been found between the wiper trip impacts and lithology types of the penetrated shale.Conclusion: A modified drilling program is proposed in relation to changes in casing setting depth and drilling fluid properties that make the operations more efficient in cost and time.

  • 271.
    Darwesh, Ali
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Evaluation of Limestone Interval in the Drilled Surface Section of Bn-1 Oil Well2016In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 8, no 8, p. 515-524Article in journal (Refereed)
    Abstract [en]

    The first exploration oil well in any oil block consumes in general more time and cost than the other wells in the same block. Evaluating the drilled wells serves to improve the future operations. This paper evaluates the drilled surface section through real field data for the first exploration oil well drilled in one of the oil blocks, in Kurdistan north of Iraq. The surface section of the well was drilled with the conventional method to penetrate many different geological formations with tight intervals. Drilling efficiency and the difficulties encountered are discussed and explained using various data sources. All daily drilling reports concerning a specific interval were studied. This includes weight on bit, string rotation, mud pump flow and penetration rate. Evaluation was carried out by analyzing the used controllable drilling parameters with the formations features. Penetration of the Pila Spi formation (Middle Eocene) was the most difficult formation in the drilled section. Microsoft Office 365 Pro Plus used in making graphs and Excel tables. Evaluations showed that the conventional technology used left many negative effects, like increase in None Productive Time NPT, cost and ground water pollution. Simultaneous Casing Drilling method proposed as an alternative method for the future campaign.

  • 272. Das, U.C.
    et al.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Resistivity and induced polarization responses of arbitarily shaped 3-D bodies in a two-layered Earth1987In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 35, no 1, p. 98-109Article in journal (Refereed)
  • 273.
    Dehghannejad, A.
    et al.
    Uppsala University.
    Juhlin, C.
    Uppsala University.
    Malehmir, A.
    Uppsala University.
    Weihed, Pär
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Luleå tekniska universitet.
    High-resolution reflection seismic imaging in the Kristineberg mining area, Northern Sweden2010In: 72nd European Association of Geoscientists and Engineers conference and exhibition 2010: Barcelona, 14 - 17 June 2010, Curran Associates, Inc. , 2010, p. 5368-5371Conference paper (Refereed)
    Abstract [en]

    The Kristineberg mining area is located in the western part of the Skellefte Ore District, one of the most important mining districts in Europe. As a part of a 4D geologic modeling project, two new reflection seismic profiles were acquired. Although the structural geology is complex, the processed seismic data reveal a series of steeply dipping to sub-horizontal reflections, some of which reach the surface and allow correlation with surface geology. Reflection modeling was carried out to obtain the 3D orientation of the main reflections and to provide insight into the possible contribution of out-of-the-plane reflections. The new reflection seismic profiles have improved our understanding of shallow geological structures in the area and in conjunction with recently acquired potential field data, magnetotelluric data and geological observations will help to refine previous 3D geologic modeling interpretations that were aimed at larger scale structures.

  • 274.
    Dehghannejad, M.
    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.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Weihed, P.
    Luleå University of Technology.
    High-resolution reflection seismic imaging in the Kristineberg mining area, Northern Sweden2010In: Society of Petroleum Engineers - 72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010 - Incorporating SPE EUROPEC 2010, Barcelona: Curran Associates, Inc., 2010, Vol. 7, p. 5368-5371Conference paper (Refereed)
    Abstract [en]

    The Kristineberg mining area is located in the western part of the Skellefte Ore District, one of the most important mining districts in Europe. As a part of a 4D geologic modeling project, two new reflection seismic profiles were acquired. Although the structural geology is complex, the processed seismic data reveal a series of steeply dipping to sub-horizontal reflections, some of which reach the surface and allow correlation with surface geology. Reflection modeling was carried out to obtain the 3D orientation of the main reflections and to provide insight into the possible contribution of out-of-the-plane reflections. The new reflection seismic profiles have improved our understanding of shallow geological structures in the area and in conjunction with recently acquired potential field data, magnetotelluric data and geological observations will help to refine previous 3D geologic modeling interpretations that were aimed at larger scale structures.

  • 275.
    Dehghannejad, Mahdieh
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Reflection seismic investigation in the Skellefte ore district: A basis for 3D/4D geological modeling2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Skellefte ore district in northern Sweden is a Palaeoproterozoic volcanic arc and one of the most important ones hosting volcanogenic massive sulfide (VMS) deposits, producing mainly base metals and orogenic gold deposits. Due to high metal prices and increased difficulties in finding shallow deposits, the exploration for and exploitation of mineral resources is quickly being moved to greater depths. For this reason, a better understanding of the geological structures in 3D down to a few kilometers depth is required as a tool for ore targeting. As exploration and mining go deeper, it becomes more and more evident why a good understanding of geology in 3D at exploration depths, and even greater, is important to optimize both exploration and mining.

    Following a successful pilot 3D geological modeling project in the western part of the district, the Kristineberg mining area, a new project "VINNOVA 4D modeling of the Skellefte district" was launched in 2008, with the aim of improving the existing models, especially at shallow depth and extending the models to the central district. More than 100 km of reflection seismic (crooked) profiles were acquired, processed and interpreted in conjunction with geological observations and potential field data. Results were used to constrain the 3D geological model of the study area and provided new insights about the geology and mineral potential at depth.

    Results along the seismic profiles in the Kristineberg mining area proved the capability of the method for imaging reflections associated with mineralization zones in the area, and we could suggest that the Kristineberg mineralization and associated structures dip to the south down to at least a depth of about 2 km. In the central Skellefte area, we were able to correlate main reflections and diffractions with the major faults and shear zones. Cross-dip analysis, reflection modeling, pre-stack time migration, swath 3D processing and finite-difference seismic modeling allowed insights about the origin of some of the observed reflections and in defining the imaging challenges in the associated geological environments.

  • 276.
    Dehghannejad, Mahdieh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bauer, Tobias E.
    Division of Geosciences, Luleå University of Technology, Sweden.
    Malehmir, Alireza
    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.
    Weihed, Pär
    Division of Geosciences, Luleå University of Technology, Sweden.
    Crustal geometry of the central Skellefte district, northern Sweden – constraints from reflection seismic investigations2012In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 524, p. 87-99Article in journal (Refereed)
    Abstract [en]

    The Palaeoproterozoic Skellefte mining district in Sweden is one of the most important mining districts in Europe. As a part of a 4D geologic modeling project, three new sub-parallel reflection seismic profiles, with a total length of about 95 km, were acquired in the central part of the district. Processed seismic data reveal a series of gentle- to steeply- dipping reflections and a series of diffraction packages. The majority of reflections that extend to the surface can be correlated with geological features either observed in the field or interpreted from the aeromagnetic map. A set of south-dipping reflections represent inferred syn-extensional listric extensional faults that were inverted during subsequent crustal-shortening. Cross-cutting northdipping reflections are correlated to late-compressional break-back faults. Flat-lying reflections in the central parts of the study area could represent lithological contacts within the Skellefte Group, or the contact between Skellefte Group rocks and their unknown basement. Flat-lying reflections occurring further north are inferred to originate from the top of the Jörn intrusive complex or an intrusive contact within it. So far unknown south- and north-dipping faults have been identified in the vicinity of the Maurliden deposit. Based on the seismic results, a preliminary 3D-model has been created in order to visualize the fault pattern and to provide a base for future 3D/4D modeling in the Skellefte district.

  • 277.
    Dehghannejad, Mahdieh
    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.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    García Juanatey, María de los Ángeles
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Skytta, Pietari
    Bauer, Tobias E
    Weihed, Par
    Reflection seismic imaging in the Skellefte ore district, northern Sweden2013In: Mineral depostits for a high-tech world: Proceedings of the 12th SGA Biennial Meeting 2013, Uppsala: Sveriges Geologiska Undersökning , 2013, p. 126-129Conference paper (Refereed)
  • 278.
    Dehghannejad, Mahdieh
    et al.
    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.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Skytta, Pietari
    Division of Ore Geology, Luleå University of Technology, Luleå, Sweden.
    3D constraints and finite-difference modeling of massive sulfide deposits: The Kristineberg seismic lines revisited, northern Sweden2012In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 77, no 5, p. WC69-WC79Article in journal (Refereed)
    Abstract [en]

    The Kristineberg mining area in the western part of the Skellefte ore district is the largest base metal producer in northern Sweden and currently the subject of extensive geophysical and geologic studies aimed at constructing 3D geologic models. Seismic reflection data form the backbone of the geologic modeling in the study area. A geologic cross section close to the Kristineberg mine was used to generate synthetic seismic data using acoustic and elastic finite-difference algorithms to provide further insight about the nature of reflections and processing challenges when attempting to image the steeply dipping structures within the study area. Synthetic data suggest processing artifacts manifested themselves in the final 2D images as steeply dipping events that could be confused with reflections. Fewer artifacts are observed when the data are processed using prestack time migration. Prestack time migration also was performed on high-resolution seismic data recently collected near the Kristineberg mine and helped to image a high-amplitude, gently dipping reflection occurring stratigraphically above the extension of the deepest Kristineberg deposit. Swath 3D processing was applied to two crossing seismic lines, west of the Kristineberg mine, to provide information on the 3D geometry of an apparently flat-lying reflection observed in both of the profiles. The processing indicated that the reflection dips about 30 degrees to the southwest and is generated at the contact between metasedimentary and metavolcanic rocks, the upper part of the latter unit being the most typical stratigraphic level for the massive sulfide deposits in the Skellefte district.

  • 279.
    Dehghannejad, Mahdieh
    et al.
    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.
    Lundberg, Emil
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Möller, Henrik
    Tyréns.
    Svensson, Mats
    Tyréns.
    High-resolution Reflection Imaging for the Planning of a Double Train-track Tunnel in the City of Varberg, Sweden2016Conference paper (Refereed)
    Abstract [en]

    A newly developed broadband MEMs-based seismic landstreamer system was employed for the planning of a double train-track tunnel in the city of Varberg, southwest Sweden. In addition to the refraction analysis and velocity tomographic modeling, reflection processing of the data was considered given the good quality of the data and realization of reflections in some raw shot gathers. Bedrock is strongly reflective in most cases and only at occasions when reaches near the surface it disappears in the reflection section. Bedrock undulation is clearly noticeable in most reflection sections and at one occasion it appears to be strongly diffractive. The diffraction signature is now known to be associated with a buried water tank used in fire emergency situations. Reflection seismic data greatly complements tomographic models and may support a deep bedrock at where the tunnel is planned to be excavated in the downtown Varberg.  

  • 280.
    Dehghannejad, Mahdieh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    Svensson, Mats
    Tyrens AB, Malmö, Sweden..
    Linden, Mattias
    Tyrens AB, Malmö, Sweden..
    Möller, Henrik
    Geokonsult AB, Malmö, Sweden..
    High-resolution reflection seismic imaging for the planning of a double-train-track tunnel in the city of Varberg, southwest Sweden2017In: Near Surface Geophysics, ISSN 1569-4445, E-ISSN 1873-0604, Vol. 15, no 3, p. 226-240Article in journal (Refereed)
    Abstract [en]

    A newly developed broadband digital-based seismic landstreamer system was employed for the planning of a double-train-track tunnel in the city of Varberg, southwest Sweden. Twenty-five seismic profiles, totalling more than 7.5 km of data, were acquired using a 2-to 4-m receiver and source spacing. At places where it was not possible to move the streamer such as road crossings, wireless recorders connected to 28-Hz geophones were used. In addition to the earlier refraction data analysis and first-break traveltime tomographic modelling, reflection processing of the data was considered in this study, given the realisation of reflections in raw shot gathers and their good quality. Bedrock is strongly reflective in most cases but is not evident in the sections when it gets near the surface. Bedrock undulation is noticeable in most reflection sections, and at one occasion, strong diffraction is observed in the bedrock or near to it. The diffraction is originated, not known during the survey, from a 400-m3 cylindrical (of about 3-m-height and 13-m-diameter) concrete-made fire-protection water tank situated in the bedrock and used in emergency situations. Reflection seismic data greatly complement the tomographic models and support deep bedrock where the excavation of the tunnel is planned in downtown Varberg. This interpretation implies different reinforcements and tunnel construction methods (e.g., roofed concrete) at this section of the tunnel. In addition, weakness zones associated with fracture systems are inferred from the reflection characteristics and in conjunction with the velocity models requiring verification by additional boreholes.

  • 281.
    Dehkordi, Seyed Emad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. University of Western Ontario, Canada.
    Olofsson, Bo
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Schincariol, Robert A.
    Effect of groundwater flow in vertical and horizontal fractures on borehole heat exchanger temperatures2015In: Bulletin of Engineering Geology and the Environment, ISSN 1435-9529, E-ISSN 1435-9537, Vol. 74, no 2, p. 479-491Article in journal (Refereed)
    Abstract [en]

    Vertical closed loop systems, also known as borehole heat exchangers (BHEs), are a popular way of extracting the ground source heat energy. Primary factors affecting the performance of BHEs are the thermal and hydrogeological properties of the subsurface. Groundwater flow is known to potentially influence heat transport and system performance. The effect of groundwater movement is more commonly studied under homogeneous conditions. However, in heterogeneous fractured rocks, BHEs are more common than horizontal or open loops due to lack of sufficient soil layers and productive aquifers. The finite-element modelling shows that fractures can play an important role in BHE functioning. Especially, vertical open fractures (≥1 mm) near the borehole (≤10 m) can have a considerable impact. Although increase in fracture aperture continuously affects the subsurface and BHE temperatures, the increase in its effect progressively lessens. Depending on the distance and aperture, one major fracture influencing the BHE operation performance can be identified; yet a larger number of fractures may govern heat transport (thermal plume outline) and thermal recovery. Individually, horizontal fractures may have less influence than vertical fractures. However, as the density of horizontal fractures increases, their impact can be major, exceeding that of fracture aperture. In particular, we propose that measurements of rock thermal properties be combined with fracture mapping, to better analyse the thermal response testing results and integrate the configuration of fractures in design and layout of the BHE(s). This is particularly valid for (vertical) fractures not intersecting with the borehole.

  • 282.
    Dehkordi, Seyed Emad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Schincariol, Robert A.
    Olofsson, Bo
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Impact of Groundwater Flow and Energy Load on Multiple Borehole Heat Exchangers2014In: Ground Water, ISSN 0017-467X, E-ISSN 1745-6584Article in journal (Refereed)
    Abstract [en]

    The effect of array configuration, that is, number, layout, and spacing, on the performance of multiple borehole heat exchangers (BHEs) is generally known under the assumption of fully conductive transport. The effect of groundwater flow on BHE performance is also well established, but most commonly for single BHEs. In multiple-BHE systems the effect of groundwater advection can be more complicated due to the induced thermal interference between the boreholes. To ascertain the influence of groundwater flow and borehole arrangement, this study investigates single- and multi-BHE systems of various configurations. Moreover, the influence of energy load balance is also examined. The results from corresponding cases with and without groundwater flow as well as balanced and unbalanced energy loads are cross-compared. The groundwater flux value, 10−7 m/s, is chosen based on the findings of previous studies on groundwater flow interaction with BHEs and thermal response tests. It is observed that multi-BHE systems with balanced loads are less sensitive to array configuration attributes and groundwater flow, in the long-term. Conversely, multi-BHE systems with unbalanced loads are influenced by borehole array configuration as well as groundwater flow; these effects become more pronounced with time, unlike when the load is balanced. Groundwater flow has more influence on stabilizing loop temperatures, compared to array characteristics. Although borehole thermal energy storage (BTES) systems have a balanced energy load function, preliminary investigation on their efficiency shows a negative impact by groundwater which is due to their dependency on high temperature gradients between the boreholes and surroundings.

  • 283. Delle Piane, Claudio
    et al.
    Almqvist, Bjarne
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    MacRae, Colin
    Torpy, Aaron
    Mory, Arthur
    Dewhurst, David
    Texture and diagenesis of Ordovician shale from the Canning Basin, Western Australia: implications for elastic anisotropy and geomechanical properties2015In: Marine and Petroleum Geology, ISSN 0264-8172, E-ISSN 1873-4073, Vol. 59, p. 56-71Article in journal (Refereed)
  • 284.
    Deng, Juan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment.
    Ban, Yifang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Liu, Jinshuo
    Li, Li
    Niu, Xin
    Zou, Bin
    Hierarchical Segmentation of Multitemporal RADARSAT-2 SAR Data Using Stationary Wavelet Transform and Algebraic Multigrid Method2014In: IEEE Transactions on Geoscience and Remote Sensing, ISSN 0196-2892, E-ISSN 1558-0644, Vol. 52, no 7, p. 4353-4363Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to develop a new effective method for hierarchical segmentation of multitemporal ultrafine-beam synthetic aperture radar (SAR) data in urban areas. Multitemporal RADARSAT-2 ultrafine-beam high-resolution horizontal transmit and horizontal receive-Synthetic Aperture Radar (HH-SAR) images acquired in the rural-urban fringe of the Greater Toronto Area during the summer of 2008 are selected for this research. Stationary wavelet transform (SWT) and algebraic multigrid (AMG) method are proposed for segmentation of SAR data. SWT is applied for decomposition of multitemporal SAR images in image preprocessing. The hierarchical and matrix-based AMG method is applied for segmentation. A pyramid of fine-to-coarse grids is constructed by iteration of selecting representative pixels and calculating the interpolation matrix between a fine-level grid and a coarse-level grid. When the pyramid is completed, segments are determined by a top-down scanning based on the interpolation matrices. The AMG techniques provide a complete hierarchical segmentation of SAR data. The experimental results show that our method produces higher accuracy than eCognition.

  • 285. Dickens, Gerald R.
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    A comment on "Pliocene climate change of the Southwest Pacific and the impact of ocean gateways" by C. Karas, D. Nurnberg, R. Tiedemann, D. Garbe Schonberg, EPSL 301, 117-124 (2011)2012In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 331, p. 364-365Article in journal (Other academic)
  • 286.
    Dineva, Savka
    et al.
    Queen's University.
    Drysdale, J
    Geological Survey of Canada.
    Peci, V
    Geological Survey of Canada.
    Steffen, Rebekka
    University of Calgary.
    Fay, Emily
    Queen's University.
    Weaver, B
    Queen's University.
    Solis, N
    Queen's University.
    Aftershock Study for the 2010 Val-des-Bois (Quebec) Earthquake2011Conference paper (Refereed)
  • 287.
    Dineva, Savka
    et al.
    Queen's University.
    Steffen, Rebekka
    University of Calgary.
    Drysdale, J
    Geological Survey of Canada.
    Peci, V
    Geological Survey of Canada.
    Fay, Emily
    Queen's University.
    McManus, M
    Queen's University.
    Development of the aftershock process of the 2010 Val-des-Bois (Quebec) Mw 5.0 Earthquake2011Conference paper (Refereed)
  • 288. Divin, A.
    et al.
    Khotyaintsev, Y. V.
    Vaivads, A.
    André, M.
    Toledo-Redondo, S.
    Markidis, Stefano
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Lapenta, G.
    Three-scale structure of diffusion region in the presence of cold ions2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 12, p. 12,001-12,013Article in journal (Refereed)
    Abstract [en]

    Kinetic simulations and spacecraft observations typically display the two-scale structure of collisionless diffusion region (DR), with electron and ion demagnetization scales governing the spatial extent of the DR. Recent in situ observations of the nightside magnetosphere, as well as investigation of magnetic reconnection events at the Earth's magnetopause, discovered the presence of a population of cold (tens of eV) ions of ionospheric origin. We present two-dimensional particle-in-cell simulations of collisionless magnetic reconnection in multicomponent plasma with ions consisting of hot and cold populations. We show that a new cold ion diffusion region scale is introduced in between that of hot ions and electrons. Demagnetization scale of cold ion population is several times (∼4–8) larger than the initial cold ion gyroradius. Cold ions are accelerated and thermalized during magnetic reconnection and form ion beams moving with velocities close to the Alfvén velocity.

  • 289.
    Donadini, Fabio
    et al.
    Scripps Institution of Oceanography, La Jolla, United States of America.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tauxe, Lisa
    Scripps Institution of Oceanography, La Jolla, United States of America.
    Paleointensity results from the 1.7 GA old hoting Gabbro, Sweden2009Conference paper (Other academic)
    Abstract [en]

    Complete text of publication follows. The Hoting Gabbro is located in the western part of the Central Svecofennian Subprovince, and dates about 1.786+-0.010 Ga. In the Hoting area, dykes intruded at around 1.6 Ga, and partly remagnetized the gabbros. Previous paleomagnetic and geochemical studies indicated that the stable characteristic remanent magnetization was acquired at about 1.7 Ga, when the slow cooling of the gabbro is taken into account. Preliminary palaeointensity studies from gabbros in the Hoting area suggested a very low field of about 5.8+-1.9 muT. Unfortunately, at that stage, only two sites out of nine yielded results. During 2008, we sampled seven sites from the Hoting area in order to perform new palaeointensity experiments. At Scripps, we applied the IZZI method on 60 specimens, and 39 yielded reliable results varying between 3 and 20 muT, and confirm the previous low results. Low field values have been associated with oxyexolution processes that might bias the palaeointensity result towards low values, and so we are currently investigating the mineralogy of the samples with SEM analyses. We will present the details of the palaeointensity and mineralogical results, and infer the evolution of the geomagnetic field during Precambrian.

  • 290.
    Donadini, Fabio
    et al.
    ETH Zürich.
    Elming, Sten-Åke
    Luleå Tekniska Universitet.
    Tauxe, Lisa
    University of California, La Jolla.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Paleointensity determination on a 1.786 Ga old gabbro from Hoting, Central Sweden2011In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 309, p. 234-248Article in journal (Refereed)
  • 291.
    Donadini, Fabio
    et al.
    Institut für Geophysik, ETH Zürich.
    Elming, Sten-Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tauxe, Lisa
    Scripps Institution of Oceanography, University of California, San Diego.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Mineralogy.
    Paleointensity determination on a 1.786 Ga old gabbro from Hoting, Central Sweden2011In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 309, no 3-4, p. 234-248Article in journal (Refereed)
    Abstract [en]

    Paleointensities from Precambrian rocks are rare and might be biased by remagnetization processes. Here we present new analyses of samples from a 1.786 Ga gabbro near Hoting, Central Sweden. Rock magnetic and mineralogical analyses indicate that one of the sites (site 5) may be pristine, whereas the others exhibit evidence of alteration. Characteristic remanent magnetization was determined using principal component analysis for each sample and was compared with results obtained in a previous study of Elming et al. (2009). Intensity measurements from site 5 show higher values compared to those of the other sites, suggesting that alteration processes may lead to underestimation of the field intensity. After cooling rate and anisotropy correction, the field moment at 1.786 Ga was estimated to be 25.6 ± 3.3 ZAm2 and 15.2 ± 6.1 ZAm2 from site 5 only and from all sites respectively. We consider the result from site 5 to be more accurate owing to the lack of evidence for alteration; our estimates agree well with the Proterozoic VDM values suggested by Biggin et al. (2009).

  • 292. Donohue, Shane
    et al.
    Long, Michael
    L'Heureux, Jean-Sébastien
    Solberg, Inger-Lise
    Sauvin, Guillaume
    Rømoen, Magnus
    Kalscheuer, Thomas
    ETH Zurich.
    Bastani, Mehrdad
    Persson, Lena
    Lecomte, Isabelle
    O'€™Connor, Peter
    The Use of Geophysics for Sensitive Clay Investigations2014In: Landslides in Sensitive Clays: From Geosciences to Risk Management / [ed] L’Heureux, Jean-Sébastien; Locat, Ariane; Leroueil, Serge; Demers, Denis; Locat, Jacques, Springer Netherlands , 2014, Vol. 36, p. 159-178Chapter in book (Other academic)
    Abstract [en]

    Marine clay deposits in coastal, post-submarine areas of Scandinavia and North America may be subjected to quick clay landslides and hence significant efforts are being taken to map their occurrence and extent. Recently, considerable efforts by a number of researchers have been made to investigate areas of sensitive clay using a range of geophysical techniques. Although the majority of this work has focussed on measurements of electrical resistivity, other electromagnetic and seismic geophysical techniques have also received attention in the literature. The purpose of this paper is to review recent research concerning the effectiveness of a number of geophysical techniques for investigating sensitive clays. In addition to discussing a number of case studies, this review will also consider recent work showing the correlation of geophysical measurements, and in particular electrical resistivity, with a range of relevant engineering properties.

  • 293.
    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.
    CPU and GPU performance of large scale numerical simulations in Geophysics2014In: Euro-Par 2014: Parallel Processing Workshops, Part I, Springer, 2014, p. 12-23Conference paper (Refereed)
  • 294. Dossow, Lisa
    1D and 2D Modelling of AMT and CSAMT Measurements from Swedish Lapland - A Case Study2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Audiomagnetotelluric measurements with (CSAMT) and without (AMT) a controlled source were performed near Gällivare and Kiruna in Swedish Lapland in order to retrieve representative conductivity models of the subsurfaces. Magnetotelluric transfer functions were gained from processed time series’ and subsequently inverted to generate the sought models successfully. Additionally, a strike angle analysis was performed to determine the dimension of the ground structures. That information was used to justify the approaches of 1D and 2D inversions of the data sets and to judge their applicability. In Kiruna, two profiles were installed. One profile is considered to be in line with the strike direction, the other profile was oriented rather orthogonal to the strike direction. In Gällivare, only one profile was installed orthogonally with respect to the strike direction. The strike analysis showed a preferentially 2-dimensional structure for Kiruna’s parallel profile. For the orthogonal oriented profiles from Kiruna and Gällivare, the analysis revealed a 2D (with distortions) to 3D dimension of the ground structures. For the AMT method, it was possible to generate 1-dimensional and 2-dimensional models. Regarding the CSAMT data, it was only possible to generate a 1D conductivitymodel for the subsurface. Due to a significant transmitter overprint, no undistorted start model for the 2-dimensional CSAMT data inversion could be produced. The models from Kiruna had a sufficient data quality and thus resulted in reliable 2D AMT resistivity models with, locally, 2 to 3 layers. However, in combination with the 1D models for AMT and CSAMT, a 3-layer structure was predicted, where a resistive layer is covered by a thin conductive layer and underlaid by a rather conductive basement. For Gällivare’s profile, the data quality was good such that for all inversion methods good results were achieved. The predicted 2-layer models were resolved for for depths between 10m and 10,000m and coincide with the at hand geological maps and cross sections.

  • 295. Dow, Christine F.
    et al.
    Kulessa, B.
    Rutt, I.C.
    Tsai, V. C.
    Pimentel, S.
    Doyle, S. H.
    van As, D.
    Lindbäck, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Jones, G. A.
    Hubbard, A.
    Modeling of subglacial hydrological development following rapid supraglacial lake drainage2015In: Journal of Geophysical Research - Earth Surface, ISSN 2169-9003, E-ISSN 2169-9011, Vol. 120, no 6, p. 1127-1147Article in journal (Refereed)
    Abstract [en]

    The rapid drainage of supraglacial lakes injects substantial volumes of water to the bed of the Greenland ice sheet over short timescales. The effect of these water pulses on the development of basal hydrological systems is largely unknown. To address this, we develop a lake drainage model incorporating both (1) a subglacial radial flux element driven by elastic hydraulic jacking and (2) downstream drainage through a linked channelized and distributed system. Here we present the model and examine whether substantial, efficient subglacial channels can form during or following lake drainage events and their effect on the water pressure in the surrounding distributed system. We force the model with field data from a lake drainage site, 70 km from the terminus of Russell Glacier in West Greenland. The model outputs suggest that efficient subglacial channels do not readily form in the vicinity of the lake during rapid drainage and instead water is evacuated primarily by a transient turbulent sheet and the distributed system. Following lake drainage, channels grow but are not large enough to reduce the water pressure in the surrounding distributed system, unless preexisting channels are present throughout the domain. Our results have implications for the analysis of subglacial hydrological systems in regions where rapid lake drainage provides the primary mechanism for surface-to-bed connections.

  • 296. Doyle, Sam H
    et al.
    Hubbard, Alun H
    Dow, Christine F
    Jones, Glenn A
    Fitzpatrick, Andrew
    Gusmeroli, Alessio
    Kulessa, Bernd
    Lindbäck, Katrin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Box, Jason E
    Ice tectonic deformation during the rapid in situ drainage of a supraglacial lake on the Greenland Ice Sheet2013In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 7, no 1, p. 129-140Article in journal (Refereed)
    Abstract [en]

    We present detailed records of lake discharge, ice motion and passive seismicity capturing the behaviour and processes preceding, during and following the rapid drainage of a 4 km2 supraglacial lake through 1.1-km-thick ice on the western margin of the Greenland Ice Sheet. Peak discharge of 3300 m3 s−1 coincident with maximal rates of vertical uplift indicates that surface water accessed the ice–bed interface causing widespread hydraulic separation and enhanced basal motion. The differential motion of four global positioning system (GPS) receivers located around the lake record the opening and closure of the fractures through which the lake drained. We hypothesise that the majority of discharge occurred through a 3-km-long fracture with a peak width averaged across its wetted length of 0.4 m. We argue that the fracture's kilometre-scale length allowed rapid discharge to be achieved by combining reasonable water velocities with sub-metre fracture widths. These observations add to the currently limited knowledge of in situ supraglacial lake drainage events, which rapidly deliver large volumes of water to the ice–bed interface.

  • 297. Dresen, G
    et al.
    Stephansson, Ove
    Zang, A
    Rock damage and fluid transport: part 12006In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 163, no 5-6, p. 915-916Article in journal (Refereed)
  • 298. DUBOULOZ, N
    et al.
    POTTELETTE, R
    MALINGRE, M
    HOLMGREN, G
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    DETAILED ANALYSIS OF BROAD-BAND ELECTROSTATIC NOISE IN THE DAYSIDE AURORAL-ZONE1991In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 96, no A3, p. 3565-3579Article in journal (Refereed)
    Abstract [en]

    The great number of bursts of broadband electrostatic noise (BEN) recorded during crossings of the dayside auroral zone by the Viking satellite enables their statistical study. The angular distribution of BEN with respect to the Earth's magnetic field is shown to be most likely isotropic, implying that it cannot consist of a unique linear plasma mode. Most of the bursts evidence a power law spectrum from the lower hybrid and ion plasma frequencies up to frequencies sometimes much higher than the electron plasma frequency, suggesting the presence of nonlinear effects. This is confirmed by their high intensity, and by the correlation between their amplitude and their frequency extension. BEN emissions are associated with ion conical distributions and with field-aligned electron beams. Although most of the power is concentrated at very low frequencies and around the lower hybrid and ion plasma frequencies, electron acoustic and beam mode waves may contribute to the high-frequency extension of BEN. The most intense BEN emissions are also correlated with sharp cold plasma density gradients and probably involve drift instabilities. Strong quasi-static perpendicular electric fields, which induce high-speed plasma flows, are also measured, so that the Doppler effect may contribute to the broadening of the BEN spectrum.

  • 299. Duffy, Brendan
    et al.
    Quigley, Mark
    Harris, Ron
    Ring, Uwe
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of Canterbury.
    Arc-parallel extrusion of the Timor sector of the Banda arc-continent collision2013In: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194, Vol. 32, no 3, p. 641-660Article in journal (Refereed)
    Abstract [en]

    Structural studies of synorogenic basins in Timor using field and remote sensing techniques provide new structural and geomorphic evidence for syn-collisional extension in the converging plate boundary zone between the Australian Plate and Banda Arc. Fault mapping and kinematic analysis at scales ranging from outcrop (<1m(2)) to the dimensions of the active orogen in East Timor (similar to 100km(2)) identify a predominance of NW-SE oriented dextral-normal faults and NE-SW oriented sinistral-normal faults that collectively bound large (5-20km(2)) bedrock massifs throughout the island. These fault systems intersect at non-Andersonian conjugate angles of approximately 120 degrees and accommodate an estimated 20km of NE-directed extension across the Timor orogen based on reconstructions of fault-dismembered massifs. Major orogen-parallel ENE-oriented faults on the northern and southern sides of Timor exhibit normal-sinistral and normal-dextral kinematics, respectively. The overall pattern of deformation is one of lateral crustal extrusion sub-parallel to the Banda Arc. Stratigraphic relationships suggest that extrusion began prior to 5.5Ma, before pronounced rapid uplift of the orogen. We link this to progressive coupling of the fore-arc to an underthrust plateau on the Australian Plate and subduction of its ocean crust. Our results enable us to track the structural evolution of the upper crust during dramatic plate-boundary reorganizations accompanying the transition from subduction to collision. The deformation structures that we document suggest that both upper and lower plate deformation during incipient island arc-continent collision was largely controlled by the geometry and topography of the lower plate.

  • 300.
    Dunkars, Mats
    KTH, Superseded Departments, Infrastructure.
    Multiple representation databases for topographic information2004Doctoral thesis, monograph (Other scientific)
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