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Sökning: WFRF:(Korja T.)

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  • Autio, U.A., et al. (författare)
  • Magnetotelluric array in the central Finnish Lapland II : 3-D inversion and tectonic implications
  • 2020
  • Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 794
  • Tidskriftsartikel (refereegranskat)abstract
    • The northern part of the Fennoscandian shield records several Palaeoproterozoic phases of rifting, crustal shortening, metamorphism and structural reactivation. The geologic history has left behind a complex crustal geoelectric structure as evidenced by magnetotelluric (MT) data from the central Finnish Lapland acquired in the context of the MaSca-project in 2014. The data are characterized by strong 3-D effects such as high phase tensor skew values and anomalous induction vectors. Interestingly, however, at the same time a dominant E-W principal direction from the phase tensor data can be inferred. 3-D conductivity models derived using the ModEM code display, high crustal conductance (> 10,000 S) in the vicinity of the Central Lapland Greenstone Belt, the Peräpohja Belt and the Kuusamo Belt. Conductors in the northern and southern part of the study area are separated by a resistor coinciding with the Central Lapland Granitoid Complex. A remarkable feature is an arc-shaped conductor inside the northern part of the Central Lapland Granitoid Complex, which continues into the Central Lapland Greenstone Belt in the north. The conductor is associated with a major induction vector anomaly and also coincides with extreme responses (negative phase tensor principal values), which are discussed in an accompanying paper. The conductive structures in the models are interpreted as deeply buried graphite and sulphide bearing metasedimentary rocks or as reactivated Archaean shear zones. The revealed geoelectric structures also partly correlate with seismic reflection and other geophysical data from the area. A possible explanation for the observed pervasive E-W principal direction of the phase tensor data could be the aulacogen (failed rift) suggested in recent tectonic evolution models.
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  • Bock G., Roberts R.G., Kissling E., Achauer A., Alingahi J., Bruneton M., Friedrich W., Grad M. Guterch A., Hjelt S-E., Hyvönen T., Ikonen J-P., Komminaho K., Korja A, Heikkinen P., Kozolovaskaya E., Nevsky M.V., Pavlenkova N., Pedersen H., Plomerova J. (författare)
  • Seismic probing of Archean and Proterozoic Lithosphere in Fennoscandia.
  • 2001
  • Ingår i: EOS Transactions American Geophysical Union. - : American Geophysical Union. ; 82, s. 621,628-629
  • Tidskriftsartikel (refereegranskat)
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  • Cherevatova, M., et al. (författare)
  • Crustal structure beneath southern Norway imaged by magnetotellurics
  • 2014
  • Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 628, s. 55-70
  • Tidskriftsartikel (refereegranskat)abstract
    • We use data from two magnetotelluric profiles, ToSca10 and ToSca'09, over the Scandinavian Mountains to study the crustal structure in southern Norway. The profiles cross the major tectonic structures of the Caledonian orogen as well as the western margin of the Precambrian Baltica. Dimensionality and strike analyses indicate generally 3-D behavior of the data. However, the majority of the used data distinguishes a preferable strike direction, which is supported by the geology of the region. Hence, we employ 2-D inversion and choose to invert the determinant of the impedance tensor to mitigate 3-D effects in the data on our 2-D models. Magnetotelluric data from both profiles are inverted using a damped least squares solution based on a singular value decomposition. We improved the solution by defining the inverse model covariance matrix through gradient or Laplacian smoothing operators. The two-dimensional inversion models of the ToSca'09 and ToSca'10 field data from southern Norway derived from the damped least squares scheme with the Laplacian inverse model covariance matrix are presented. Resistive rocks, extending to the surface, image the autochthonous Southwest Scandinavian Domain and the allochthonous Western Gneiss Region. Near-surface conductors, which are located between the resistive Caledonian nappes and Precambrian basement, delineate highly conductive shallow-sea sediments, so called alum shales. They exhibit a decollement along which the Caledonian nappes were overthrust. A deeper, upper to midcrustal conducting layer in the Southwest Scandinavian Domain may depict the remnants of closed ocean basins formed during the accretions and collisions of various Sveconorwegian terranes. In ToSca'10, the Caledonian nappes, the conducting alum shales and the deeper conductor are terminated in the west by the Faltungsgraben shear complex which represents a crustal scale boundary between the Western Gneiss Region in the west and the Southwest Scandinavian Domain in the east.  
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  • Cherevatova, M., et al. (författare)
  • Electrical conductivity structure of north-west Fennoscandia from three-dimensional inversion of magnetotelluric data
  • 2015
  • Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 653, s. 20-32
  • Tidskriftsartikel (refereegranskat)abstract
    • New magnetotelluric (MT) data in north-west Fennoscandia were acquired within the framework of the project "Magnetotellurics in the Scandes" (MaSca). The project focuses on the investigation of the crustal and upper mantle lithospheric structure in the transition zone from stable Precambrian cratonic interior to passive continental margin beneath the Caledonian orogen and the Scandinavian Mountains in western Fennoscandia. An array of 59 simultaneous long period and 220 broad-band MT sites were occupied in the summers of 2011 to 2013. The 3-D inversion of the MaSca data was obtained using the ModEM 3-D code. The full impedance and tipper data were used for the inversion. The rocks of Archaean and Proterozoic basement towards east and the Caledonian nappes towards west are modelled as resistive structures. In the central and southern parts, the whole crust is resistive and reflects the Trans-Scandinavian Igneous Belt granitoids. The middle to lower crust of the Svecofennian province is conductive. An uppermost crustal conductor is revealed in the Skelleftea Ore District. The south end of the Kittila Greenstone Belt is seen in the models as a strong upper to middle crustal conductor. In the Caledonides, the highly conductive alum shales are observed along the Caledonian Thrust Front. A map of the crustal conductance for the north-west Fennoscandian Shield is presented.
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  • Cherevatova, M., et al. (författare)
  • Magnetotelluric array data analysis from north-west Fennoscandia
  • 2015
  • Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 653, s. 1-19
  • Tidskriftsartikel (refereegranskat)abstract
    • New magnetotelluric (MT) data in north-west Fennoscandia were acquired within the framework of the project "Magnetotellurics in the Scandes" (MaSca). The project focuses on the investigation of the crustal and upper mantle lithospheric structure in the transition zone from stable Precambrian cratonic interior to passive continental margin beneath the Caledonian orogen and the Scandinavian Mountains in western Fennoscandia. An array of 59 synchronous long period and 220 broad-band MT sites was occupied in the summers of 2011 to 2013. We estimated MT transfer functions in the period range from 0.003 to 10(5) s. The Q-function multi-site multi-frequency analysis and the phase tensor were used to estimate strike and dimensionality of MT data. Dimensionality and strike analyses indicate generally 2-D behaviour of the data with 3-D effects at some sites and period bands. In this paper we present 2-D inversion of the data, 3-D inversion models are shown in the parallel paper. We choose to invert the determinant of the impedance tensor to mitigate 3-D effects in the data on our 2-D models. Seven crustal-scale and four lithospheric-scale 2-D models are presented. The resistive regions are images of the Archaean and Proterozoic basement in the east and thin Caledonian nappes in the west. The middle and lower crust of the Svecofennian province is conductive. The southern end of the Kittila Greenstone Belt is seen in the models as a strong upper to middle crustal conductor. In the Caledonides, the highly conductive alum shales are observed along the Caledonian Thrust Front. The thickest lithosphere is in the Palaeoproterozioc Svecofennian Domain, not in the Archaean. The thickness of the lithosphere is around 200 km in the north and 300 km in the south-west.
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  • Korja, T, et al. (författare)
  • Structure of the Central Scandinavian Caledonides and the underlying Precambrian basement, new constraints from magnetotellurics
  • 2008
  • Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 175:1, s. 55-69
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the structure of the accretionary wedge of the Caledonian orogen, the underlying autochthonous/parautochthonous carbonaceous alum shales and the Precambrian basement. We have conducted 60 broad-band magnetotelluric soundings along a 180 km long profile in JAmtland, Sweden, across the eastern section of the Central Scandinavian Caledonides. Dimensionality analysis and regional strike estimates indicate that the conductivity structure can be approximated by a 2-D model having a N40 degrees E strike direction, consistent with the dominant geological strike. The determinant average of the impedance tensor, together with the tipper transfer function from the best 34 sites, were inverted by the REBOCC 2-D inversion code. An electrically highly conducting layer beneath the Caledonides images alum shales, the autochthonous Cambrian carbon-bearing black shales on top of the Precambrian basement. Based on the comparison of electrical conductivity and seismic reflectivity models, we suggest that the Caledonian accretionary wedge thickens in a step-wise manner from ca. 1 to 5-6 km towards the west. In the east, the wedge is composed of the lower allochthon. In the west, the wedge reaches the thickness of 15 km and is composed of the lower allochthon at the bottom, the middle/upper allochthons at the top and resistive allochthonous basement slices. The upper crust of the autochthonous Precambrian basement is homogeneous and resistive from surface down to 15 km and can be associated with the Revsund and RAtan granites. The border between the eastern Revsund- and western RAtan-type granites coincides in the JAmtland region, with the boundary between the northern Central Svecofennian Province and the southern Svecofennian volcanic belt and is marked by a subvertical conductor associated with a steeply dipping band of reflectors. The lower crust and uppermost mantle in the easternmost part of the profile are very resistive, whereas in west, they are 2-3 orders of magnitude more conductive. The increase of average crustal conductivity is related to the Caledonian processes or later opening of the Atlantic Ocean that have affected also the lower crust.
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  • Pulli, E. P., et al. (författare)
  • Prenatal exposures and infant brain: Review of magnetic resonance imaging studies and a population description analysis
  • 2019
  • Ingår i: Human Brain Mapping. - : Wiley. - 1065-9471 .- 1097-0193. ; 40:6, s. 1987-2000
  • Tidskriftsartikel (refereegranskat)abstract
    • Brain development is most rapid during the fetal period and the first years of life. This process can be affected by many in utero factors, such as chemical exposures and maternal health characteristics. The goal of this review is twofold: to review the most recent findings on the effects of these prenatal factors on the developing brain and to qualitatively assess how those factors were generally reported in studies on infants up to 2 years of age. To capture the latest findings in the field, we searched articles from PubMed 2012 onward with search terms referring to magnetic resonance imaging (MRI), brain development, and infancy. We identified 19 MRI studies focusing on the effects of prenatal environment and summarized them to highlight the recent advances in the field. We assessed population descriptions in a representative sample of 67 studies and conclude that prenatal factors that have been shown to affect brain metrics are not generally reported comprehensively. Based on our findings, we propose some improvements for population descriptions to account for plausible confounders and in time enable reliable meta-analyses to be performed. This could help the pediatric neuroimaging field move toward more reliable identification of biomarkers for developmental outcomes and to better decipher the nuances of normal and abnormal brain development.
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  • Raj, R, et al. (författare)
  • Dynamic prediction of mortality after traumatic brain injury using a machine learning algorithm
  • 2022
  • Ingår i: NPJ digital medicine. - : Springer Science and Business Media LLC. - 2398-6352. ; 5:1, s. 96-
  • Tidskriftsartikel (refereegranskat)abstract
    • Intensive care for patients with traumatic brain injury (TBI) aims to optimize intracranial pressure (ICP) and cerebral perfusion pressure (CPP). The transformation of ICP and CPP time-series data into a dynamic prediction model could aid clinicians to make more data-driven treatment decisions. We retrained and externally validated a machine learning model to dynamically predict the risk of mortality in patients with TBI. Retraining was done in 686 patients with 62,000 h of data and validation was done in two international cohorts including 638 patients with 60,000 h of data. The area under the receiver operating characteristic curve increased with time to 0.79 and 0.73 and the precision recall curve increased with time to 0.57 and 0.64 in the Swedish and American validation cohorts, respectively. The rate of false positives decreased to ≤2.5%. The algorithm provides dynamic mortality predictions during intensive care that improved with increasing data and may have a role as a clinical decision support tool.
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  • SVEKALAPKO Seismic Tomography Working Group (SSTWG): G. Bock, U. Achauer, A. Alinaghi, J. Ansorge, M. Bruneton, W. Friederich, M. Grad, A. Guterch, S.-E. Hjelt, T. Hyvönen, J.-P. Ikonen, E. Kissling, K. Komminaho, A. Korja, P. Heikkinen, E. Kozlovskaya, M (författare)
  • Seismic probing of Fennoscandian Lithosphere
  • 2002
  • Ingår i: EOS, Trans. Am. geophys. Un.. ; 82:621, s. 628-629
  • Tidskriftsartikel (refereegranskat)
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  • Resultat 1-24 av 24

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