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  • 151.
    Lyngsie, Stig B.
    et al.
    Geological Institute, University of Copenhagen.
    Thybo, H.
    Geological Institute, University of Copenhagen.
    Rasmussen, Thorkild Maack
    bGeological Survey of Denmark and Greenland.
    Regional geological and tectonic structures of the North Sea area from potential field modelling2006In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 413, no 3-4, p. 147-170Article in journal (Refereed)
    Abstract [en]

    The spatial distribution of large-scale crustal domains and their boundaries are investigated in the North Sea area by combining gravity, magnetic and seismic data. The North Sea is situated on the plates of three continents, Avalonia, Laurentia and Baltica, which collided during the Caledonian orogeny in the middle Palaeozoic. The location and continuation of the collisional sutures are debated. We apply filters and transformations to potential field data to focus on the crystalline crust and uppermost mantle on a regional scale in order to extract new information on continental sutures. The transformations reveal intrinsic features of crustal transitions between the Caledonian plates and their relation to later extensional structures. The transformations include the Hough Transform applied to the gravity field, calculation of fractional derivatives and integrals of the gravity and magnetic fields, the pseudogravity field and the horizontal gradient field as well as upward continuation. The results indicate a fundamental difference between the lithosphere of Avalonia, Laurentia and Baltica. The location of the Mesozoic rift system (the Central Graben and Viking Graben), may have been partly determined by the presence of the sutures between these three plate, indicative of extensional reactivation of compressional structures. A significant lineament across the entire North Sea between Scotland and North Germany indicates that the lower crust of Baltica provenance may extend as far south-westward as to this lineament. Comparison of the power spectra of the gravity field in five selected areas shows significant differences in the long wavelength components between the areas north and south of the lineament corresponding to differences in crustal properties. This lineament could represent the suture between lithosphere of Caledonian origin (Avalonia) versus lithosphere of Precambrian origin (Baltica) in the lower crust and upper mantle. If this is the case, the lineament is the missing link in the reconstruction of the triple plate collision

  • 152.
    Mainali, Ganesh
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Thunehed, Hans
    Monitoring of the tailings dam at Kiruna, northern Sweden using self-potential method2005In: Asian Regional Conference on Engineering Geology for Major Infrastructure Development and Natural Hazards Mitigation, Nepal Geological Society , 2005, p. 14-Conference paper (Other academic)
  • 153.
    Martinsson, Jesper
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science. Department of Mining Technology, Luossavaara-Kiirunavaara AB, 98381 Malmberget.
    Jonsson, Adam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    A New Model for the Distribution of Observable Earthquake Magnitudes and Applications to b-Value Estimation2018In: IEEE Geoscience and Remote Sensing Letters, ISSN 1545-598X, E-ISSN 1558-0571, Vol. 15, no 6, p. 833-837Article in journal (Refereed)
    Abstract [en]

    The b-value in the Gutenberg–Richter (GR) law contains information that is essential for evaluating earthquake hazard and predicting the occurrence of large earthquakes. Estimates of b are often based on seismic events whose magnitude exceed a certain threshold, the so-called magnitude of completeness. Such estimates are sensitive to the choice of threshold and often ignore a substantial portion of available data. We present a general model for the distribution of observable earthquake magnitudes and an estimation procedure that takes all measurements into account. The model is obtained by generalizing previous probabilistic descriptions of sensor network limitations and using a generalization of the GR law. We show that our model is flexible enough to handle spatio-temporal variations in the seismic environment and captures valuable information about sensor network coverage. We also show that the model leads to significantly improved b-value estimates compared with established methods relying on the magnitude of completeness.

  • 154.
    Mattsson, Håkan
    Luleå tekniska universitet.
    Magnetic fabrics and paleomagnetism of the Storsjön-Edsbyn deformation zone, central Sweden1999Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Anisotropy of magnetic susceptibility (AMS) and paleomagnetic data from the Storsjön-Edsbyn Deformation Zone (SEDZ) in central Sweden are presented. The SEDZ is a regional shear zone c. 200km in length that cuts through 1.7-1.9 Ga old rocks in the central part of the Fennoscandian shield. The AMS analyses support a tectonic model suggesting that the SEDZ is a pureshear dominated transpression zone. The width of the zone in its southern part is defined to c. 10-12km and in the northern part it is c. 20-25km. A dolerite sill that truncates the plastic deformation pattern of the SEDZ postdates its activity to c. 1250 Ma, but paleomagnetic data from a dolerite dike indicates that the zone may be older than c. 1.6 Ga.

  • 155.
    Mattsson, Håkan
    et al.
    Luleå tekniska universitet.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A magnetic study of deformed rocks in the Fennoscandian Shield1999In: Vol. 4, no 1, p. 626-Article in journal (Other academic)
    Abstract [en]

    In the central parts of the Fennoscandian shield a regional shearzone (The Storsjön Edsbyn Deformation Zone, SEDZ) cuts through three 1.70-1.85 Ga old granite-granodiorite bodies. During the emplacement of a c. 1.85 Ga old granodiorite it suffered from a regional high-grade metamorphosis that gave rise to a subhorizontal E-W striking foliation (SGU, 1992). This pattern rotates to N-S strike with a vertical dip approaching the SEDZ. Different generations of dolerite sills and dikes cut, and are cut, by the zone. AMS (Anisotropy of Magnetic Susceptibility) and susceptibility versus temperature measurements, together with AF and thermal demagnetisation, were performed on samples along three trajectories across the zone. Thin sections of selected samples were analysed. The AMS directions correlate well with tectonic fabrics and major structures interpreted from areomagnetic data, with the minimum AMS axis being parallel to the pole of tectonic foliation. In mylonites the AMS axes are tightly grouped with subvertical maximum axes and in less deformed rocks the maximum and intermediate axes form a girdle pattern. In deformed rocks most often only a soft remanence component can be established, which generally lies parallel to the maximum AMS axis. Samples from a metamorphic rock outside of the shearzone-area carry a stable remanence in AF-fields up to 160 mT, and after a correction by use of the AMS tensor, the mean remanence direction better fits the expected paleo-latitude and longitude defined by the APWP for the Fennoscandian shield. A dolerite dike that is cut by a brittle shearzone has a paleomagnetic age of c. 1.6 Ga, indicating that the SEDZ was active after the dikes emplacement, and a dolerite sill that cuts the shearzone-fabric has a paleomagnetic age of c. 1.25 Ga, an age which post dates its movements. Magnetite is generally the main magnetic carrier, but biotite dominates the magnetic properties in one of the granites. Hematite and amphiboles are also present. Examples of good correlation between mean susceptibility and the degree of AMS shows that the degree of AMS cannot be used as a measure of the magnitude of tectonic strain in these rocks.

  • 156.
    Mattsson, Håkan
    et al.
    Luleå tekniska universitet.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A rock magnetic study of a regional deformation zone in the Fennoscandian Shield1998In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 16, no Suppl. 1, p. 200-Article in journal (Other academic)
  • 157.
    Mattsson, Håkan
    et al.
    Luleå tekniska universitet.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magma flow directions of post Jotnian dolerite sills in central-east Sweden: a magnetic fabric and paleomagnetic survey2003In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 125, no 1, p. 7-16Article in journal (Refereed)
    Abstract [en]

    An anisotropy of magnetic susceptibility (AMS) and paleomagnetic study has been performed on post-Jotnian basic sills of the Ulvö complex, of the Central Scandinavian Dolerite Group (CSDG). The CSDG intruded some 1.27 Ga ago in the central part of the Fennoscandian Shield and extends over an area of c. 150 000 km2. Previously presented AMS data of the CSDG sills from southcentral and northern Sweden indicated a NW or SE directed magma flow. In this study new measurements of the AMS reveal a fairly uniform pattern of NW-SE lineation directions also for the dolerites of the Ulvö complex. While the magma is flowing in a dyke or a sill, elongated particles become imbricated against the chilled margins, and the AMS can be used to determine not only the lineation but also the true direction of the magma flow. An imbrication pattern defined for one of the sills suggests that the magma propagated from the present NW towards SE. The established paleomagnetic pole position (Plat=-3° and Plon=157°) is in very good agreement with other paleomagnetic data from the Ulvö complex and from other parts of the CSDG. The new AMS data from the Ulvö complex presented in this study fit well in to the magnetic fabric pattern previously presented for the CSDG sills and support a plate tectonic model suggesting that the CSDG is a related to the break up of Baltica from Laurentia at c. 1.27 Ga ago.

  • 158.
    Mattsson, Håkan
    et al.
    Luleå tekniska universitet.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnetic fabrics and paleomagnetism of the Storsjön-Edsbyn deformation zone, central Sweden2001In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 107, no 3-4, p. 265-281Article in journal (Refereed)
    Abstract [en]

    A regional deformation zone, separating tectonomagmatic blocks in the central part of the Fennoscandian Shield, has been studied using anisotropy of magnetic susceptibility and paleomagnetism in order to define the tectonic character and age of the zone and to put the deformation into a plate tectonic context. The deformation zone (the Storsjön-Edsbyn Deformation Zone; SEDZ) separates the Rätan granite of the Trans Scandinavian Igneous Belt (TIB) and the southern Svecofennian subprovince in the southwest from older Svecofennian granitoids of the central Svecofennian subprovince in the northeast. The SEDZ is the most prominent deformation zone in a regional pattern of NW-SE trending shear zones. On basis of AMS data the width of the zone, which cuts through 1.7-1.9 Ga old rocks, is estimated at 10-12 km in its central-southern part and 20-25 km in its northern part. The orientations of the susceptibility axes vary systematically across the zone, in a way that suggests that the SEDZ is a pure shear dominated transpression zone caused by a compressive stress from the present SSW. Paleomagnetic data from a dolerite sill (Plat=10°, Plon=166°) and from a dyke (Plat=25°, Plon=190°) that cut the SEDZ indicate that no plastic deformation has occurred along the zone during the past 1.25 Ga, and probably not for the past 1.5-1.6 Ga. AMS data do not point to any deformation of the 1.70 Ga old Rätan granite, which further limits the time span of deformation. The main phase of deformation most likely took place between ≈1.80 and 1.70 Ga ago. The geological evolution of this part of the Fennoscandian Shield at the time between 1.80 and 1.70 Ga ago is very complex and in part still enigmatic. This time period involves magmatism of the TIB, which is related to eastward subduction. It also comprises the beginning of the Gothian orogeny and the development of a regional system of transpressive deformation zones. The compressive stress field from the present SSW indicated in this study is interpreted to be related to an initial stage of plate collision between the southwestern Scandinavian subprovince and older parts of the Fennoscandian Shield. This collision resulted in a system of regional NW-SE trending intra-plate deformation zones, one of which is the SEDZ

  • 159.
    Mattsson, Håkan Johannes
    Luleå tekniska universitet.
    Magnetic anisotropy and paleomagnetism of precambrian rocks in the Fennoscandian shield2001Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents three applications of the anisotropy of magnetic susceptibility (AMS) technique, dealing with tectonic and magmatic flow fabrics of Proterozoic igneous rocks in the central and northern parts of the Fennoscandian Shield. Paleomagnetic measurements were performed in attempts to put the different rock units into a geological and plate tectonic context. The Storsjön-Edsbyn deformation zone (SEDZ) separates the Rätan granite of the Trans Scandinavian Igneous Belt (TIB) and the southern Svecofennian subprovince in the southwest, from the central Svecofennian subprovince in the northeast. The zone strikes NNW-SSE, it is c. 200 km long and 5 – 30 km wide. The study of the SEDZ was performed in order to define the tectonic character of the zone and to test a previously presented tectonic model. A close-up investigation of the Rätan granite was carried out in an attempt to test if the granite was emplaced in a tectonic regime governed by compression or extension. Large parts of the Rätan granite, and also the SEDZ, have been intruded by post-Jotnian dolerite sills belonging to the Central Scandinavian Dolerite Group (CSDG). The ancient magma flow directions in different parts of the CSDG sills were defined in attempts to locate the magma source. Paleomagnetism was used to look for eventual geographical differences in time of the intrusions and also to identify new areas in the shield intruded by the CSDG. On basis of AMS data the width of the Storsjön-Edsbyn deformation zone is estimated at 10 – 12km in its central-southern part and 20 – 25km in its northern part. The orientations of the susceptibility axes vary systematically across the zone, in a way that suggests that the SEDZ is a pure shear dominated transpression zone caused by a compressive stress from the present SSW. This supports a previously proposed tectonic model of the SEDZ. Paleomagnetic data from a post-Jotnian dolerite sill and from a dyke that cut the SEDZ indicate that no plastic deformation has occurred along the zone during the past 1.25 Ga, and probably not for the past 1.5 – 1.6 Ga. The compressive stress field from the present SSW indicated in this study could be related to an initial stage of plate collision between the southwestern Scandinavian subprovince and older parts of the Fennoscandian Shield. AMS data from the 1.70 Ga old Rätan granite indicate a primary magnetic/magmatic fabric. The Rätan granite seems to have been emplaced in a tectonic environment primarily governed by NW-SE directed extension and the pluton was most likely fed obliquely with a magma source situated to the present northwest. The CSDG dolerites were previously known in four complexes in central Sweden and Finland (Ulvö, Jämtland, Dalarna and Satakunta) and from the results of this paleomagnetic study another complex (the Västerbotten complex) has been identified in northern Sweden. These complexes cover an area of c. 150 000 km2 and the palaeomagnetic data suggest a small difference in time between the intrusion of the dolerites. The measurements of anisotropy of magnetic susceptibility reveal a magnetic fabric with almost horizontal foliation planes and lineations that indicate fairly uniform c. NW or SE directed magma flows. The dolerites of the CSDG are geochemically rather uniform and have compositions typical of mantle derived melts formed in continental tensional settings. In a paleomagnetic reconstruction of Baltica versus Laurentia at c. 1.27 Ga the two continents were joined with NE Greenland attached to NW Baltica. AMS and geological data from a few dolerites and a basalt in NE Greenland indicate magma flow directions that in the tectonic reconstruction is more or less parallel to the flow of the dolerites in Sweden. This may suggest a common magma source located in the reconstructed contact between Baltica and Laurentia. The tensional regime that is reflected by the huge sill complexes is in this interpretation related to the break up of Baltica from Laurentia at c. 1.27 Ga ago.

  • 160.
    Matzka, Jürgen
    et al.
    DTU Space.
    Rasmussen, Thorkild Maack
    GEUS.
    Olesen, Arne Vestergaard
    DTU Space, National Space Institute, Technical University of Denmark.
    Nielsen, Jens Emil
    DTU Space.
    Forsberg, René
    DTU Space.
    Olsen, Nils
    DTU Space.
    Halpenny, John F.
    Natural Resources Canada, Ottawa, ON.
    Verhoef, Jacob H.
    Natural Resources Canada, Ottawa, ON.
    A new aeromagnetic survey of the North Pole and the Arctic Ocean north of Greenland and Ellesmere Island2010In: Earth Planets and Space, ISSN 1343-8832, E-ISSN 1880-5981, Vol. 62, no 10, p. 829-832Article in journal (Refereed)
    Abstract [en]

    We present a preliminary analysis of more than 50,000 km of aeromagnetic survey lines flown in the Arctic Ocean, acquired in 2009 with an optically pumped scalar magnetometer as part of the airborne geophysical survey 'LOMGRAV'. From the observations we removed main and magnetospheric fields as given by the CHAOS-3 field model (Olsen et al., 2010) and remaining external fields as monitored by the Canadian magnetic observatory Alert. The reduced data were levelled based on cross-over differences at line intersections. Finally, a grid was computed, upward continued by 3500 m and compared with the EMAG2 grid (Maus et al., 2009), showing a good general agreement but also areas with systematic differences. The obtained data are expected to be part of the next version of the World Digital Magnetic Anomaly Map (WDMAM).

  • 161.
    Meissner, R.
    et al.
    Institut für Geophysik, Universität Kiel.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Deep seismic survey images crustal structure of Tornquist Zone beneath southern Baltic Sea1991In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 18, no 6, p. 1091-1094Article in journal (Refereed)
    Abstract [en]

    The Tornquist Zone is Europe's longest tectonic lineament and bisects the continent in a NW-SE direction from the North Sea (off NW Denmark) to the Black Sea. New deep seismic reflection and coincident refraction data have been collected across its 50 km wide, intensely faulted and inverted NW part. The marine reflection profile in the area north of Bornholm Island shows a tilted block structure in the rigid upper crust, whereas the lower crust seems to be more gently uplifted. A complex transition from the highly reflective lower crust to the mantle is indicated by mantle reflections and a curious wide-angle event recorded by a landstation on Bornholm Island. We suggest that deep-reaching inversion tectonics, induced by Alpine and Carpathian orogeny, were responsible for the development of the gross crust-mantle structure of the Tornquist Zone in our study area, which seems to be similar to that in Poland.

  • 162.
    Moakhar, Mohsen Oveisy
    Luleå tekniska universitet.
    Rapakivi granite and basic dykes in the Fennoscandian shield: a palaeomagnetic analysis1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Rapakivi rocks and basic dykes in the central part of Sweden have been subject to a palaeomagnetic study with the aim of putting the formation of these rocks into a plate tectonic context. Virtual geomagnetic poles were calculated and found to be distributed around the Jotnian Loop of the APWP of Fennoscandia. Paleolatitudes for the shield at the time of the intrusions were determied to a range from the equator to a 30 degrees North and a hot spot origin was tested as a model for the origin of the rapakivi rocks. Palaeomagnetic data from a basic dyke swarm in central Sweden suggest the dykes to be related to rapakivi intrusions, which means that this Neoproterozoic magmatism seems more widespread than was earlier suggested. From very detailed palaeomagnetic studies of basic dykes and the baked host rocks the ambient temperature of the rock at the time of intrusion of the dykes was determined at 376 degrees Celsius. A palaeothermal gradient was estimated and the depth of burial of the present erosion surface at 1.5 Ga ago was determined at 12 km.

  • 163.
    Moakhar, Mohsen Oveisy
    et al.
    Luleå University of Technology.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A palaeomagnetic analysis of rapakivi intrusions and related dykes in the Fennoscandian Shield2000In: Physics and chemistry of the earth. Part A: Solid earth and geodesy, ISSN 1464-1895, E-ISSN 1873-4642, Vol. 25, no 5, p. 489-94Article in journal (Refereed)
    Abstract [en]

    In the Fennoscandian Shield (Baltica) there are seven major rapakivi plutons and fifteen minor ones ranging in age from ca 1.66 to 1.50 Ga. These plutons are distributed in a broad WNW zone and if the most eastern pluton is excluded there is a westward trend of decreasing age of the intrusions. A palaeomagnetic study has been performed on 4 minor plutons (Rödö, Mårdsjö, Norsjö and Mullnäset) and associated dykes in central Sweden. The results were combined with palaeomagnetic data from other rapakivi complexes in Fennoscandia in order to test if a stationary hot spot may be the origin of these anorogenic intrusions. Plotting the pole positions of this study together with poles of other complexes, poles calculated from rapakivi rocks and related dykes in Finland are located at somewhat lower latitudes and more eastern longitudes than poles of corresponding rocks in Sweden, probably reflecting an APW related to the general age differences between the plutons. The palaeolatitudes for the Fennoscandian Shield at the time of the rapakivi intrusions are restricted to a latitudinal range between ca 16° south and 27° north and there is a weak trend of increasing palaeolatitude with decreasing age of the rocks. A trend of gradually changing palaeolatitudinal positions has also been observed for the intrusion of Proterozoic anorthosite-rapakivi plutons in the Ukranian Shield. Such differences in palaeolatitudes is not expected in case of a single stationary hot spot being the source of the rapakivi intrusions, as the rock then should carry a magnetization reflecting the same latitudinal position.

  • 164.
    Moakhar, Mohsen Oveisy
    et al.
    Luleå tekniska universitet.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Uplift deduced from a palaeomagnetic study of Neoproterozoic dykes in central Sweden1998In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 16, no Suppl. 1, p. 33-Article in journal (Other academic)
  • 165.
    Moradi, M.
    et al.
    Institute of Geophysics, University of Tehran, Tehran, Iran.
    Oskooi, B.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Institute of Geophysics, University of Tehran, Tehran, Iran.
    Pushkarev, P.
    Department of Geophysical Methods of the Earth Crust Exploration, Moscow State University, Moscow, Russia.
    Smirnov, Maxim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Esmaeili Oghaz, H.
    Natural Iranian Gas Storage Company for Nasr-Abad Area, Tehran, Iran.
    Cooperative inversion of magnetotelluric and seismic data on Shurab diapirs in Central Iran2019In: Environmental Earth Sciences, ISSN 1866-6280, E-ISSN 1866-6299, Vol. 78, no 11, article id 341Article in journal (Refereed)
    Abstract [en]

    Using diapirs as liquid or gas storage structures has increased because salt formations are considered to be extremely impermeable and non-reactive. The process of delineating the diapirs' structures ends in lots of challenges due to their geological complexity. Therefore, the integration of different geophysical methods seems to be necessary to cover different physical characteristics of the diapirs. Shurab diapirs located at the NW of Kashan in Qom basin of Central Iran have been considered as candidates for the first natural gas storages in Iran. A previous 2D seismic survey across the diapir No. 4 of Shurab could not resolve the diapir structure properly and some ambiguities left unresolved. The main goal of this paper is to resolve the structure of diapir No. 4 by employing a cooperative inversion of the seismic and magnetotelluric (MT) data and a comparison with the joint inversion of transverse electric (TE) and transverse magnetic (TM) modes of the MT data. Both inversion schemes show the salt and sedimentary sequences of the stratigraphy of the Qom basin. The sequences of formations from the surface to depth are classified as upper red formation (URF), Qom formation (QF) and lower red formation (LRF). The results also show that the salt body has originated from the LRF. It is worthwhile to mention that the results from the cooperative inversion provide more details especially on the flanks and overhangs of the diapir No. 4. In addition, we have come to the conclusion that the right lateral strike-slip fault system is the most responsible phenomenon for the development of the diapirs in the survey area and the Sen-Sen fault plays a basic role as an elevator to pushing the salt up. The results are in good agreements with the resistivity and density logs of the boreholes. Moreover, the information from the geology, the cooperative inversion results on diapir No. 4, and the coincidence of the path of the Sen-Sen fault with the outcrops of the diapirs No. 1, 3 and 4 obviously provide that the tectonic scenario of the existence for diapir No. 4 could be appointed to the diapirs No. 1 and 3 equally. Another probable consequence would be the under surface continuation of the salt bodies all along the Sen-Sen fault, the verification of which requires regional MT surveys in a regular grid.

  • 166.
    Nisca, Dan H.
    Luleå tekniska universitet.
    Nya litologiska-tektoniska modeller för regionen Västerbotten - södra Norrbotten1995Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    High quality bedrock and tectonic maps are the platform for locating natural resources such as ore, oil, gas, and water. Bedrock maps are also used in the design of large constructions, including highways, bridges, dams, power plants, tunnels, nuclear and other waste repositories. The main objective of the thesis is to improve and develop analysis and techniques for bedrock mapping mainly based on regional geophysics. The value of the improved approaches is demonstrated by constructing a lithologic-tectonic map for the Västerbotten - South Norrbotten region in northern Sweden. A fractal model has been adopted for the design and performance of the study. Instead of investigating an area of 50 km x 50 kin or smaller, a whole region or an area of 300 km x 250 has been studied. According to the fractal model, there are genetic connections between small and large geologic structures. The application of this model made possible: (a) the detection of structures, (b) establishing a genetic link between geologic structures and put them into large lithologic-tectonic relations and (c) a better understanding of the initiation, formation and development of different structures. The bedrock mapping is performed by integrating information provided by various sources: as a geoscientific multiand interdisciplinary analysis concept (MIA). Nine different main data sets have been used: (1) aeromagnetic data, (2) gravity data, (3) radiometric data, (4) satellite photo, (5) topography, (6) drainage system, (7) structural geologic map, (8) seismicity map and (9) esker map. For the interpretation a number of different visualizations of gravity data, aeromagnetic data and topographic data have been used. Besides the nine main data sets used in the neotectonic analysis, information on end moraines, highest coastline, isostatic uplift, seismotectonics, in situ stress measurements and documented late- to postglacial faults have been included. The enclosed sketch map shows the new tectonic "backbone" for the region. Some of the zones are defined as reverse faults/thrusts, e.g. the Malå-Skellefte Tectonic Zone (MSTZ) and the Knaften-Bureå Tectonic Zone (KBTZ). A large circular structure with a diameter of about 100 km, Lycksele Ring Structure (LRS), is defined in the central part of the region. Several graben-horst structures have been outlined in the northern part of the region. The so called "Nickelzonen" is interpreted as a dextral shear zone and it is renamed the Burträsk Shear Zone (BSZ). In the eastern part of the region a large scale fault zone, Krukmakar Fault Zone (KFZ) is defined. The major part of the bedrock west of the KFZ consists of granitoids while the eastern part consists mainly of migmatites. Cauldron structures have also been identified, e.g. the Gallejaure structure and the Jörngranite structure situated just north of the Skellefte field. The area between Urneå-Skellefteå or the Lövånger Tectonic Zone (LTZ) belongs to the localities in Sweden with the highest earthquake frequencies. In this thesis, tectonic models are presented for the LTZ, the Burträsk area (BSZ, KBTZ), the Skellefte valley (MSTZ), the Storavan area (horst-graben) and the central part of the study area (LRS). Some of the defined faults coincide with earthquakes and documented late- to postglacial faults, which indicates reactivations of very old weakness zones in the crust. Yet other major findings are: (1) initiation, formation and development of kursu valleys. This has been enigmatic for the last 100 years. It is now obvious, these valleys are caused by neotectonics and erosion. (2) Glaciations/deglaciations are considered to enhance fluid circulation in the crust. A hypothesis of glacial pumping is proposed to explain this process. (3) The interpretation of the tectonics in the study area shows that neotectonic faults are much more extensive than previously documented in the region. (4) The tectonic and neotectonic features recognized by this study are also compared with corresponding features in the central part of the Baltic Shield, e.g. they show large scale connections. The new bedrock mapping technique and the new lithologic - tectonic models presented in the thesis are of utmost consequence for future ore prospecting in the region and for investigations concerning the bedrock stability.

  • 167.
    Nisca, Dan H.
    et al.
    Luleå tekniska universitet.
    Thunehed, Hans
    Luleå tekniska universitet.
    Pesonen, Lauri J.
    Geological Survey of Finland.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The Lycksele structure: a huge ring formation in northern Sweden : result of an impact?1997In: Large meteorite impacts and planetary evolution conference, Sudbury, ON, Canada, Sept. 1-3, 1997, 1997, p. 36-37Conference paper (Other academic)
  • 168. Nisca, Dan H.
    et al.
    Thunehed, Hans
    Pesonen, Lauri J.
    Geological Survey of Finland.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The lycksele structure, a huge ring formation in Northern Sweden: result of an impact?.2000In: S T A R (Online), ISSN 1548-8837, Vol. 38Article in journal (Other academic)
    Abstract [en]

    The current database of impact structures in Fennoscandia reveals 28 proven impact craters of various ages and sizes. Recently, we started to search for large and old impact structures, which may show traces of the impact in their shape or in their rocks and minerals and which can be diagnostically identified through the masking effects of postimpact deformations. Since we are dealing with strongly eroded and often deformed structures, the classical criteria for proving an impact origin are not tenable. Through a combined analysis of topography, drainage, gravity, magnetic, and petrophysical data, a circular structure has been identified in northern Sweden. The structure is characterized by a circular system of faults, arc-shaped contacts between rocks, and a circular distribution of granitic intrusions. The fault zone at the edges is defined from gradients in the gravity data, from magnetic data by arc-shaped anomalies, and from topographic data by an arc-shaped relief, which is also reflected in the drainage pattern. The zone is characterized by vertical faults that also cut the granitic intrusions at the edge of the formation, and from interpretation of gravity data an uplift of high density rocks (about 2850 kg/m(exp 3)) is indicated in the central part. The age of granites and pegmatites ranges from 1.82 to 1.78 Ga. Therefore, based on age data and on paleomagnetic results of various generations of dikes that cut and are truncated by the structure, the age of the formation lies within 1.80-1.26 Ga. The rocks have not been studied petrologically to see if any traces of shock metamorphism can be found. At present, four models for the origin of the structure are possible: (1) basement doming, (2) meteorite impact, (3) large buried pluton, or (4) fault-bounded block. An impact origin, however, seems most plausible.

  • 169.
    Nordqvist, Anders
    Luleå tekniska universitet.
    Application of ultrasonic cross-hole seismics to hard rock conditions1986Licentiate thesis, monograph (Other academic)
  • 170.
    Oskooi, B.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Institute of Geophysics, University of Tehran, Tehran, Iran.
    Moradi, M.
    Institute of Geophysics, University of Tehran, Tehran, Iran.
    Smirnov, Maxim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Integrated interpretation of seismic and magnetotelluric data on Shurab diapirs in Qom basin, Central Iran2019In: Acta Geophysica, ISSN 1895-6572, E-ISSN 1895-7455, Vol. 67, no 4, p. 1071-1090Article in journal (Refereed)
    Abstract [en]

    In recent decades, diapirs are frequently used for CO2 and natural gas storage due to their extremely impermeable and non-reactive characteristics. Among various approaches, we use an integrated interpretation approach to resolve the diapir no. 4 belonging to the Shurab diapirs (SD). The SD is a group of diapirs that have pierced to the surface of the Qom basin of Central Iran, which is a candidate for natural gas storages. The complex geology of the SD is the main cause that previous 2D seismic surveys across the diapir could not provide required information to propose any location for any exploration borehole. Consequentially, 28 magnetotelluric (MT) and 1 audio-magnetotelluric station were measured along a SW-NE profile. Dimensionality and strike analysis for all stations is done by the use of phase tensor analysis. We used the nonlinear conjugate gradient algorithm to invert the TE- and TM-modes data simultaneously in 2D. The resistivity model was compared with the interpreted results of the post-stack depth migration model using seismic attributes. In order to extract the determinative geological information from the low-quality seismic section, envelope, variance, sweetness and instantaneous frequencies attributes were used. The integrated interpretation of the seismic and MT data resolves a precise geometry of the salt body, location of the dense part of the diapir as well as the tectonics around the diapir. The integrated interpretation of seismic and MT data of diapir no. 4 resulted in an exploration drilling program.

  • 171.
    Oskooi, B.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Univ Tehran, Inst Geophys, Tehran, Iran.
    Parnow, S.
    Univ Tehran, Inst Geophys, Tehran, Iran.
    Smirnov, Maxim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Varfinezhad, R.
    Univ Tehran, Inst Geophys, Tehran, Iran.
    Yari, M.
    Univ Tehran, Inst Geophys, Tehran, Iran.
    Attenuation of random noise in GPR data by image processing2018In: Arabian Journal of Geosciences, ISSN 1866-7511, E-ISSN 1866-7538, Vol. 11, no 21, article id 677Article in journal (Refereed)
    Abstract [en]

    Random noise in ground penetrating radar (GPR) data affects the signal-to-noise ratio, blurs the details, and complicates reconnaissance of the useful information. Many methods with different advantages and disadvantages have been proposed to eliminate or weaken the random noise. We have reviewed basic principles of various signal processing techniques including the curvelet transform (CT), non-local mean (NLM), median, and mean filters to remove the random noise and compared their performances using synthetic and actual GPR data. The performances of the four filters were analyzed on synthetic GPR data both in time and frequency domains. On noisy synthetic data, results indicate that the CT filter performs better than NLM, mean, and median filters at attenuating random noise and improving S/N of the GPR data. On the real data, the performance of only the NLM and CT filters was investigated. Comparing the results clearly shows the CT filter robustness for the random noise attenuation and simultaneously its signal preservation

  • 172.
    Paembonan, Andri Yadi
    et al.
    Master Program of Geotechnology, Khon Kaen University.
    Arjwech, Rungroj
    Master Program of Geotechnology, Khon Kaen University.
    Davydycheva, Sofia N.
    KMS Technologies.
    Smirnov, Maxim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Strack, Kurt M.
    KMS Technologies.
    An application of LOTEM around salt dome near Houston, Texas2017In: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 1861, article id 030006Article in journal (Refereed)
    Abstract [en]

    A salt dome is an important large geologic structure for hydrocarbon exploration. It may seal a porous reservoir of rocks that form petroleum reservoirs. Several techniques such as seismic, gravity, and electromagnetic including magnetotelluric have successfully yielded salt dome interpretation. Seismic has difficulties seeing through the salt because the seismic energy gets trapped by the salt due to its high velocity. Gravity and electromagnetics are more ideal methods. Long Offset Transient Electromagnetic (LOTEM) and Focused Source Electromagnetic (FSEM) were tested over a salt dome near Houston, Texas. LOTEM data were recorded at several stations with varying offset, and the FSEM tests were also made at some receiver locations near a suspected salt overhang. The data were processed using KMS's processing software: First, for assurance, including calibration and header checking; then transmitter and receiver data are merged and microseismic data is separated; Finally, data analysis and processing follows. LOTEM processing leads to inversion or in the FSEM case 3D modeling. Various 3D models verify the sensitivity under the salt dome. In addition, the processing was conducted pre-stack, stack, and post-stack. After pre-stacking, the noise was reduced, but showed the ringing effect due to a low-pass filter. Stacking and post-stacking with applying recursive average could reduce the Gibbs effect and produce smooth data

  • 173. Parasnis, Dattatray
    Effect of a uniform overburden on the passage of a thermal wave and the temperatures in the undelying rock1976In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 46, no 1, p. 189-192Article in journal (Refereed)
  • 174. Parasnis, Dattatray
    Geophysical detection of mineral conductors in tropical terrains with target conductors partly embedded in the conductive overburden: comment1988In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 36, no 1, p. 92-93Article in journal (Other academic)
  • 175. Parasnis, Dattatray
    Geothermal flow and phenomena in two Swedish localities north of the Arctic circle1982In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 71, no 3, p. 545-554Article in journal (Refereed)
    Abstract [en]

    Temperature measurements in eight holes reaching vertical depths between 287 and 1100m below ground surface in the Malmberget area (lat. 67° 10' N, long. 20° 40' E Gr.) and the Kiruna area (lat. 67° 52' N, long. 20° 9' E Gr.) in the Swedish Precambrian are reported. The mean equilibrium heat flow in this part of the Swedish shield after climatic correction is 52.6 ± 1.7mWm-2. The mean uncorrected heat flow is 46.6 mWm-2. Comparison with other shield areas shows that in common with the S. African and Indian shields, the north Swedish shield has a greater heat flow than the remaining shield areas of the world.

  • 176.
    Parasnis, Dattatray
    Luleå tekniska universitet.
    Geothermal measurements, search for hot groundwater and geothermal power1976In: Vol. 14, no 3-4, p. 264-Article in journal (Other academic)
  • 177.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geothermal work at the University of Luleå, Sweden in relation to EGT11985In: Vol. 5, no 4, p. 398-Article in journal (Other academic)
  • 178.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mining geophysics1973 (ed. 2 rev.)Book (Other academic)
  • 179.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    More comments on "A theorem for DC regimes and some of its consequences" by A. Roy1984In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 32, no 1, p. 139-141Article in journal (Other academic)
  • 180.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Principles of applied geophysics1986 (ed. 4)Book (Other academic)
  • 181.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Principles of applied geophysics1997 (ed. 5)Book (Other academic)
  • 182.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Reciprocity theorems in geoelectric and geoelectromagnetic work1988In: Geoexploration, ISSN 0016-7142, Vol. 25, no 3, p. 177-198Article in journal (Refereed)
    Abstract [en]

    The following two theorems are proved and discussed: 1. (1) the open-circuit potential difference between two electrodes M,N when steady current is passing through electrodes A,B is equal to that between A and B if the same current is passed through M,N for any arbitrary conductivity distribution in the ground provided only the ground is a linear medium;2. (2) the complex electromotive force developed in a receiver circuit R of small dimensions, due to alternating current flowing in a transmitter circuit T of small dimensions is exactly equal to the complex e.m.f. in T if the same current is flowing in circuit R, no matter how arbitrary the distribution of conductivity, magnetic permeability and dielectric permittivity in the ground, provided only the ground is a linear medium.A linear medium is one in which the current density, magnetic flux density and electric displacement are linear functions of electric and magnetic field intensities. The more general form of the second theorem when the dimensions of the circuits are not small is proved first and the special case of (2) derived from it.

  • 183.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Temperature phenomena and heat flow estimates in two precambrian ore-bearing areas in north Sweden1975In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 43, no 2, p. 531-554Article in journal (Refereed)
    Abstract [en]

    Temperature measurements in 17 drillholes reaching vertical depths between 365 and 780 m below ground surface in the Skellefte area (lat. 65° 52deg;N, long. 20° 20° E Gr) and Aitik area (lat. 67° 5deg;N, long. 21° E Gr) in the Swedish precambrian are reported. The absolute accuracy of the measurements was about 0.03°C and the relative one about 0.005°C. A large number of thermal diffusivity measurements were made on rock samples from the two areas in order to estimate the correction to the observed steady geothermal gradients due to climatic amelioration at the end of the Pleistocene. The corrected gradients are between 0.01266°C m-1 and 0.01485°C m-1 (Skellefte) and between 0.01684°C m-1 and 0.02268°C m-1 (Aitik). The diffusivity measurements were supplemented by thermal conductivity determinations on 265 drillcore samples from the different rock formations in the holes.The undisturbed heat flow in the Skellefte area is found to be 48.7 mW m-2 and that in the Aitik area to be 49.8 mW m-2. Distortion of the heat flow due to a sulphide ore in the Skellefte area is demonstrated. The heat flow through the Långsele ore in this area is of the order of 70 mW m-2.

  • 184.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The geophysics of fracture zones in hard-rock areas1981In: Second biennial conference and exhibition, 1981, p. 78-Conference paper (Other academic)
  • 185.
    Parasnis, Dattatray
    Luleå tekniska universitet.
    Thermal parameters of some precambrian rocks in Sweden1977In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 114, no 2, p. 319-Article in journal (Other academic)
  • 186. Parasnis, Dattatray
    et al.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The non-magnetic house of the University of Luleå1982In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 104, no 2, p. 186-188Article in journal (Refereed)
    Abstract [en]

    The building of a very quiet non-magnetic house can raise special problems in Precambrian areas and in the cold climate of northern Sweden. The special precautions taken in the construction of a non-magnetic house belonging to the University of Lule have resulted in a laboratory for high-precision rock magnetic and palaeomagnetic work. The mean total field in the house one metre above the floor is 52011 ±3 nT and the maximum variation inside is 12 nT. The geographical, position is the mountain Rneklen, latitude 65.8°N, longitude 22.3°EGr, about 30 km north of Lule.

  • 187.
    Park, R.G.
    et al.
    Keele University, Department of Earth Sciences, Keele.
    Mertanen, S.
    Geological Survey of Finland.
    Pesonen, L.J
    Geological Survey of Finland.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Buchan, K.L.
    Geological Survey of Canada.
    Laurentia-Baltica relationships in the Palaeoproterozoic: geological significance of key palaeomagnetic poles1997In: Ottawa '97: GAC/MAC Annual meeting, May 19-21, 1997, Abstracts volume = Ottawa '97 : Réunion annuelle AGC/AMC du 19 au 21 mai 1997, recueil des résumés, Geological and Mineralogical Association of Canada, 1997, p. 112-Conference paper (Other academic)
  • 188.
    Paul, Sudhir
    Luleå tekniska universitet.
    Some model experiments in Turam1988Licentiate thesis, monograph (Other academic)
  • 189.
    Pease, Victoria
    et al.
    Department of Geology and Geochemistry, Stockholm University.
    Daly, J.S.
    School of Geological Sciences, University College Dublin.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kumpulainen, R.
    Department of Geology and Geochemistry, Stockholm University.
    Moczydlowska, M.
    Department of Earth Sciences, Uppsala University.
    Puchkov, V.
    Institute of Geology, Ufimian Science Centre RAS, Ufa.
    Roberts, D.
    Geological Survey of Norway.
    Saintot, A.
    Faculty of Life and Earth Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam.
    Stephenson, R.
    Faculty of Life and Earth Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam.
    Baltica in the Cryogenian 850-630 Ma2008In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 160, no 1-2, p. 46-65Article in journal (Refereed)
    Abstract [en]

    This new tectonic synthesis provides a framework for understanding the dynamic evolution of Baltica and for constraining tectonic correlations within the context of the Neoproterozoic break-up of Rodinia-Pannotia. Cryogenian Baltica is described with respect to five geographic regions: the northwest, norBaltica; Rodinia; Neoproterozoic; Orogeny; Paleogeographyheast, east, south, and southwest (modern coordinates). These geographic regions define three principal Cryogenian tectonic margins: a rifting northwestern margin, a passive northeastern margin, and a poorly understood southern margin.The northwest region is characterized by Neoproterozoic to lower Ordovician sedimentary successions deposited on Archean to late Mesoproterozoic crystalline complexes, reworked during Caledonian orogenesis. Lare Neoproterozoic to lower Ordovician sedimentary strata record the change from an alluvial setting to a marine environment, and eventually to a partially starved (?) turbidite basin. They document rifting from the Rodinian-Pannotian supercontinent, which was unsuccessful until ca. 620-550 Ma when voluminous dikes and mafic/ultramafic complexes were intruded.Baltica's northeastern and eastern regions document episodic intracratonic rifting throughout the Mesoproterozoic, followed by pericontinental passive margin deposition throughout the Cryogenian. In the northeast platformal and deeper-water basin deposits are preserved, whereas the eastern region was later affected by Paleozoic rifting and preserves only shelf deposits. The northeastern and eastern regions define Baltica's Cryogenian northeastern tectonic margin, which was an ocean-facing passive margin of the Rodinia-Pannotia supercontinent. It remained a passivemargin until the onset of Timanian orogenesis at ca. 615 Ma, approximately synchronous with the time of Rodinia-Pannotia rifting.Baltica's southern and southwestern regions remain enigmatic and controversial. Precambrian basement is generally hidden beneath thick successions of Ediacaran and younger platform sediments. Similarities between these regions exist, however, and suggest that they may share a similar tectonic evolution in the Cryogenian and therefore define the southern tectonic margin of Baltica at this time. Paleo- to Mesoproterozic basement was affected by Neoproterozoic and younger tectonism, including Cryogenian (?) and Ediacaran rifting. This was followed by Ediacaran(ca. 550 Ma) passive margin sediment deposition at the time of Rodinia-Pannotia break-up, until Early Paleozoic accretion of allochthonous terranes record the transition from rifting to a compressional regime.Paleomagnetic and paleontological data are consistent with Baltica and Laurentia drifting together between ca. 750 and 550 Ma, when they had similar apparent polar wander paths. Microfossil assemblages along the eastern margin of Laurentia and the western margin of Baltica (modern coordinates), suggest proximity between these two margins at this time. At ca. 550 Ma, Laurentia and Baltica separated, consistent with paleomagnetic, paleontological, and geological data, and a late break-up for Rodinia-Pannotia.

  • 190.
    Pedersen, Laust Börsting
    et al.
    Uppsala Universitet, Department of Earth Sciences.
    Juhlin, Christopher
    Department of Earth Sciences, Uppsala University.
    Rasmussen, Thorkild Maack
    Uppsala Universitet, Department of Earth Sciences.
    Electric resistivity in the Gravberg-1 deep well, Sweden1992In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 97, no 6B, p. 9171-9182Article in journal (Refereed)
    Abstract [en]

    The Siljan impact structure located in central Sweden has been the object of intense geophysical and geological studies for several decades. This paper presents the results of electrical resistivity measurements on the surface, in the hole, and on core samples from shallow coreholes distributed over the whole impact structure. Magnetotelluric data constrain the central part of the structure to be essentially one-dimensional with an upper crustal unit of about 10 000 Ωm followed by a less resistive impact related unit of 1000 Ωm from a depth of about 6 km to a depth of 20 km. The lower crust is a homogeneous unit of about 300 Ωm extending down to about 40 km, where the upper mantle is marked by an increase in resistivity of about 1000 Ωm. Major fracture zones, some of which coincide with the horizontal dolerite sills, known to extend over tens of kilometers, are probably the main carriers of current. Saline fluids recovered below 5.4-km depth and the magnetotelluric results lead us to conclude that pore fluids are highly saline below this depth even on a regional scale.

  • 191.
    Pedersen, Laust Börsting
    et al.
    Section of Solid Earth Physics, University of Uppsala.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Section of Solid Earth Physics, University of Uppsala.
    Inversion of magnetotelluric data: a nonline least-squares approach1989In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 37, no 6, p. 669-695Article in journal (Refereed)
    Abstract [en]

    The inverse problem of magnetotellurics over a horizontally stratified earth is described, with emphasis on practical application. The inversion is divided into basically two steps. The construction of some best solution, and the analysis of that solution with regard to uncertainty and complexity. For the construction of best solutions a robust non‐linear solver was developed, and for the estimation of parameter errors a modified eigenvalue‐eigenvector analysis is performed to better describe non‐linear effects. The choice of the number of layers is shown to be intimately connected with the structure of data errors and the misfit between model and data. An example from the Siljan impact structure in Sweden illustrates the power of the technique.

  • 192.
    Pedersen, Laust Börsting
    et al.
    Uppsala Universitet, Department of Earth Sciences.
    Rasmussen, Thorkild Maack
    Uppsala Universitet, Department of Earth Sciences.
    Some techniques for enhancement of gravity and magnetic maps1991In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 113, no 2-3, p. 264-Article in journal (Refereed)
  • 193.
    Pedersen, Laust Börsting
    et al.
    Uppsala Universitet, Department of Earth Sciences.
    Rasmussen, Thorkild Maack
    Uppsala Universitet, Department of Earth Sciences.
    The gradient tensor of potential field anomalies: some implications on data collection and data processing of maps1990In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 55, no 12, p. 1558-1566Article in journal (Refereed)
    Abstract [en]

    The full gradient tensor is presently not measured routinely onboard airplanes or on land. This paper describes some improvements that can be made in strategies of data collection and in processing of potential field maps if such tensor measurements were available. We suggest that, in addition to producing for example standard total field anomaly maps, the invariants of the tensor be mapped

  • 194.
    Pedersen, Laust Börsting
    et al.
    Department of Geophysics, Section of Solid Earth Physics, University of Uppsala.
    Rasmussen, Thorkild Maack
    Department of Geophysics, Section of Solid Earth Physics, University of Uppsala.
    Dyrelius, Dan
    Department of Geophysics, Section of Solid Earth Physics, University of Uppsala.
    Construction of component maps from aeromagnetic total field anomaly maps1990In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 38, no 7, p. 795-804Article in journal (Refereed)
    Abstract [en]

    Total field anomalies as defined from normal aeromagnetic surveys give good approximations of the anomalous components along the direction of the main geomagnetic field, which is generally much larger than the anomalous field. Using the relations between vertical and horizontal components of the field, the total field anomaly is related to any vertical or horizontal component and the corresponding horizontal and vertical derivatives. An example from the Siljan impact structure indicates that such directional filters may be applied to extract useful information from magnetic maps.

  • 195.
    Perttu, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Assessment of hydrogeological and water quality parameters, using MRS and VES in the Vientiane Basin, Laos2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Water is essential for all life on the planet, sustaining and ensuring the earth's ecosystem. Groundwater from a global perspective provides about 50% of the potable water supplies, 40% of the industrial water and 20% of the irrigated agriculture. For drinking water, deep groundwater has many advantages compared to surface water and shallow groundwater, since it demands little or no treatment and the access is secured against temporary droughts. However, salinity in deep groundwater is common in coastal areas and in areas where rock salt is occurring naturally in the soil and bedrock. Drilling wells is expensive and unprofitable if it is made without knowing the groundwater potential and the location of salt affected groundwater. Vertical Electrical Soundings (VES) has been widely used to characterize aquifers and to identify salt affected water since there may be a relation between the conductivity of the aquifer and the salinity of the water. However, it is not possible to distinguish high conductive groundwater from e.g. increased clay content. Magnetic Resonance Sounding (MRS) gives a direct image of the water content of the ground and hence the vertical distribution of an aquifer. By combining MRS with VES, salt affected groundwater could be distinguished from high conductive sediments and freshwater aquifers. The aim of this study is to define and characterize water bearing geological formation and to test the possibility of using geophysical techniques to determine hydrogeological parameters and water quality parameters relating to salinity in the Vientiane basin, Laos. The investigation area is part of the Khorat Plateau where halite is naturally occurring as shallow as 50 m in depth in the Thangon Formation. In total, 32 sites and 28 sampled wells, located in three different areas were investigated. MRS and VES recognized the stratigraphic unit N2Q1-3, consisting of alluvial unconsolidated sediments, as the main water bearing unit. The aquifer thickness varies between 10 to 40 m and the depth to the main aquifer range from 5 to 15 m. The water content is here relatively high, up to 16 % and decay times varying between 100 and 400 ms, suggest a mean pore size equivalent to medium sand to gravel. The resistivity is highly variable, but usually around 10-100 ohm-m, which suggests fresh water. Hydraulic and storage related parameters such as transmissivity, hydraulic column, specific yield and specific storage have been estimated from MRS and transverse resistance has been estimated from VES. MRS together with VES has also shown to be a useful and important tool in identifying the salt related clay layer of the Thangon Formation. This layer is characterized by low water content and a resistivity lower than 5 ohm-m. This formation can be found in all 3 areas on depth of 20 to 50 m. Several approaches have been used to look for a relation between the water conductivity collected from wells and the aquifer conductivity determined from VES, including Archie's law. The best correlation is achieved using a linear fit between VES conductivity and water conductivity for deep wells (EC[μS/cm ]= 0.3821VES[μS/cm], R2=0.81). The conductivity of water from shallow wells does not show any relation to VES conductivity (R2=0.09). This is probably because deep wells usually have higher conductivity than shallow wells and hence contributing more to the aquifer conductivity. Interpolated maps of TDS in area 3 from deep wells together with maps of the conductivity of the bottom layer and aquifer layer, MRS transmissivity and hydrostatic column indicates that the salt originate from the underlying layer situated beneath the main aquifer. The most important water quality parameters influencing the water conductivity are TDS, hardness and chloride, which all have a high correlation to the EC of water and thus VES conductivity. This makes MRS and VES a very promising tool for guidance of future drillings and water quality estimation.

  • 196.
    Perttu, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnetic Resonance Sounding (MRS) in groundwater exploration, with applications in Laos and Sweden2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Water is essential for all life on the planet, sustaining and ensuring the earth’s ecosystem. Groundwater from a global perspective provides about 50 % of the potable water, 40 % of the industrial water and 20 % of the irrigation water. For drinking water, deep groundwater has many advantages compared to surface water and shallow groundwater, since it demands little or no treatment and the access is secured against temporary droughts. However, drilling wells for deep groundwater is expensive and unprofitable if it is made without knowing the groundwater potential and development of techniques for exploration are therefore of high priority. The petrophysical properties of aquifers are to a large extent influenced by the water content and salinity, e.g. electrical conductivity and electric permittivity, which can be determined from Vertical Electrical Sounding (VES) and Ground Penetrating Radar (GPR) measurements, respectively. Magnetic Resonance Sounding (MRS), based on the principle of nuclear magnetic resonance, is a relatively new, non invasive technique, which in contrast to other geophysical techniques gives a direct measure of the free water content, but also the pore size distribution with depth. With MRS it is possible to determine both storage and hydraulic related parameters far less ambiguously than with classical geophysical techniques. This thesis presents four studies, where the MRS technique have been tested and developed in combination with other geophysical techniques in three different geological environments; (1) The sedimentary basin of Vientiane, Laos, with naturally occurring salt in the bedrock as shallow as 50 m in depth, which inevitably affects drinking and irrigation water from deep wells; (2) In karst limestone, on the island of Gotland, Sweden, where saltwater intrusion, both recent and relic together with pollution from pesticides and fertilizers are major threats to an already exhausted drinking water supply; (3) Test of the MRS spin-echo (SE) technique in Norrbotten, Sweden, where the presence of magnetic rocks and sediments have made it impossible to do MRS with a standard measuring procedure.In Laos (1), MRS and VES have proven to be very efficient in to locate the fresh-salt water interface and distinguish freshwater aquifers from clays. The electrical conductivity (EC) of the aquifers determined from VES correlates well with EC of water collected from shallow and deep wells, which makes the method promising for future water quality estimation in the Vientiane basin. In Gotland (2), the performance of MRS, VES, GPR and Radiomagnetotelluric (RMT) were tested. The use of multiple techniques has shown to give a more coherent interpretation, but MRS and RMT showed to be more efficient in detecting groundwater and characterizing the aquifer. MRS SE measurements have also been conducted in the Bothnian bay (3). It offers a good environment to test the influence of large scale magnetic gradients on the MRS signals but also the reliability of MRS SE result. The MRS SE technique has further been tested for different soil types. The measuring procedure has subsequently been tested and optimized to meet conditions of magnetic environments.

  • 197.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-Åke
    Estimation of water quality parameters of aquifers in the Vientiane Basin, Laos, using MRS and VES2009In: Proceedings, 4th International Workshop on Magnetic Resonance Sounding, MRS 2009, 2009, p. 171-176Conference paper (Refereed)
  • 198.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-Åke
    Evaluation of MRS signals in brackish water with large magnetic gradients2009In: Proceedings, 4th International Workshop on Magnetic Resonance Sounding, MRS 2009, 2009, p. 177-182Conference paper (Refereed)
  • 199.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-åke
    New geophysical techniques for determining quantity and quality of ground water: an exemple from the Vientiane basin, Laos2008Conference paper (Other academic)
    Abstract [en]

    The access to clean drinking water in the rural Laos is often restricted. This, together with a poor hygiene, results in serious health problems. In a drilling program for water only around 30% of the boreholes carried water usable for drinking (JICA, 2000). The reason for the poor water quality was often a high content of salt. The aim of this study is to define water bearing geological formation and to test the possibility of using geophysical techniques to determine the quality of the groundwater in the Vientiane basin, Laos. This we do by the use of a combination of Magnetic Resonance Sounding (MRS), Vertical Electrical Sounding (VES) and water quality data gathered from wells in different geological environments. The MRS gives a direct image of the vertical distribution of water content and the electrical measurements are sensitive to the conductivity/quality of the water.The investigation area is part of the Khorat Plateau where rock salt is naturally occurring as shallow as 50 m in depth (Long et al., 1986), which inevitable affects the water quality in some deep wells. The results of the study show that MRS and VES measurements are effective in locating formations carrying fresh water as well as the salt bearing formation. Aquifers are identified in 19 of the 32 sites of measurements. The aquifers are related to specific geological formations and most often located at depths of 20 to 30 m and with water contents varying between 4 to 16 %. The decay times of the MRS signal suggests these aquifers to be predominantly composed of medium grained sand to gravel. The salt bearing formation is usually related to clay or mudstone, with low water contents and high VES  conductivity and can usually be found all over the basin at depths beneath 30 to 50 m.The electrical conductivity (EC) of water samples collected from shallow and deep wells correlates with the conductivities determined with VES and a fairly good correlation can be seen between EC, total dissolved solids (TDS), chloride and hardness. Layers of water with high quality, medium conductivity, are identified at specific depths and in restricted areas. The results demonstrate geophysics to be effective tools for localizing high quality groundwater and the results are important for guiding future drilling.

  • 200.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Persson, Lena
    Geological Survey of Sweden.
    Erlström, Mikael
    Geological Survey of Sweden.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnetic resonance sounding and radiomagnetotelluric measurements used to characterize a limestone aquifer in Gotland, Sweden2012In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 424-425, p. 184-195Article in journal (Refereed)
    Abstract [en]

    Almost all drinking water in Gotland is groundwater and is mainly found in karst limestone. However, the unpredictable location and geometry of the karst cracks and caverns makes it very difficult to estimate groundwater storage and movement, as well as contaminant transport. The aim of this study was to test the performance of different geophysical techniques like Magnetic Resonance Sounding (MRS), Radiomagnetotelluric (RMT), Vertical Electrical Sounding (VES) and Ground Penetrating Radar (GPR) to characterize aquifers in Gotland, in respect to geometry and storage as well as connectivity over a wider area. The investigated area is located on the south-eastern part of Gotland. The geology here is dominated by 50 to 60 m thick successions of limestone that gradually turn into marlstone. The use of multiple techniques has shown to give a more coherent interpretation. However, the shallow penetration depth of GPR and the lack of soil cover in some places of the investigated area limit the use of geoelectrical methods and GPR. With MRS, water are found down to 60 m in depth, with a maximum water content at depths of 20 to 30 m. This coincides with the most resistive sections of the limestone. The water content varies between 0 and 3%, with a relaxation time (T1MRS) less than 400 ms suggesting that the aquifer is hosted in small fractures, molds and vugs rather than larger karst fractures and caverns. Two potential aquifers were identified with MRS, possibly separated by marlstone. From modelling it can be seen that such boundary separating two aquifer apart can be more easily discriminated in the N/S-, than in the E/W direction. In summary, MRS is therefore the only method in this survey that can detect and determine the vertical and lateral distribution of water within the aquifer together with the total volume of free water. The RMT method has shown to be effective in characterizing the limestone/marl interface, but also to locate anomalous low resistive zones, possibly associated with salt water. RMT also helps to constrain the final MRS model by choosing a suitable regularization for the MRS 3D inversion. All together, the combination of MRS and RMT seems most efficient of the tested methods and therefore most promising for future groundwater explorations in geological environments like in eastern Gotland.

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