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  • 1.
    Autio, U.
    et al.
    Oulu Mining School, University of Oulu.
    Smirnov, Maxim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Savvaidis, Alexandros S.
    Institute of Engineering Seismology and Earthquake Engineering, Thessaloniki.
    Suopios, Pantelis
    Department of Environmental and Natural Resources Engineering, Technological Educational Institute of Crete, Chania.
    Bastani, Mehrdad
    Geological Survey of Sweden.
    Combining electromagnetic measurements in the Mygdonian sedimentary basin, Greece2016In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 135, p. 261-269Article in journal (Refereed)
    Abstract [en]

    We present a novel approach where time-domain electromagnetic (TEM) data are transformed and subsequently used in two-dimensional (2-D) magnetotelluric inversion of the determinant of the impedance tensor. The main idea is to integrate TEM with magnetotelluric (MT) data to produce subsurface electrical resistivity models. Specifically, we show that 2-D MT data inversion of the determinant of the impedance tensor supported by inclusion of TEM–MT-transformed data has superior resolution at the near surface and at the same time static shift afflicting the MT data can be addressed. Thus, the approach allows for practical express integration of TEM data with MT measurements as opposed to a full combined 3-D inversion, which requires significant resources. The approach is successfully applied in the Mygdonian sedimentary basin located in Northern Greece. In addition to TEM and MT data, also controlled source — and radiomagnetotelluric data are available from the Mygdonian basin, which have been subjected to 2-D analysis previously. We have extended the analysis to a full 3-D inversion using ModEM code. All obtained models are analysed and are in a good agreement.

  • 2.
    Beka, Thomas I.
    et al.
    Faculty of Science and Technology, UiT-The Arctic University of Norway.
    Senger, Kim
    Department of Arctic Geology, The University Centre in Svalbard.
    Autio, Uula A
    Oulu Mining School, Geophysics, University of Oulu.
    Smirnov, Maxim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Birkelund, Yngve
    Faculty of Science and Technology, UiT-The Arctic University of Norway.
    Integrated electromagnetic data investigation of a Mesozoic CO2 storage target reservoir-cap-rock succession, Svalbard2017In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 136, p. 417-430Article in journal (Refereed)
    Abstract [en]

    Recently acquired time-domain electromagnetic (TEM) and magnetotelluric (MT) data sets are utilized in the first electromagnetic (EM) characterization of a geological CO2 storage target site in Adventdalen, Arctic Norway. Combining the two EM data sets enabled to resolve the electrical resistivity structure of the target site better than either of the methods alone. 2D inverting the MT data in the audio period interval (0.003–1 s) with supporting input derived from the TEM data (0.01–10 ms) provided a geologically meaningful resistivity model that included information not previously evident from existing seismic and borehole data. The ca. 1.8 × 1 km 2D resistivity model displays a laterally constrained highly conductive anomaly (ca. 10 Ω m) at about 400–500 m depth, where reflectors of a parallel seismic section are concealed and core samples indicate a highly fractured décollement zone formed during Paleogene compression. The base of the permafrost is imaged at ca. 200 m depth. Synthetic inversion tests, however, suggest that this may be exaggerated by tens of meters, due to a thin conductive layer present approximately between 10 and 25 m depth. The resistivity model does not give indication for a fluid pathway we can connect to leakage, in line with water injection and leak-off tests in the reservoir and cap-rock, both of which indicate a sealing shale-dominated cap-rock separating an over-pressured compartment above the sealing shale from a severely under-pressured reservoir interval. The results we present indicate the advantage of integrating EM exploration techniques in a CO2 reservoir-cap-rock study to obtain a more complete picture.

  • 3.
    Brojerdi, Fatemeh Sharifi
    et al.
    Department of Earth Sciences, Uppsala University.
    Juhlin, Christopher
    Department of Earth Sciences, Uppsala University.
    Stephens, Michael
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Malehmir, Alireza
    Department of Earth Sciences, Uppsala University.
    Reflection seismic imaging of the deeper structures at the Forsmark spent nuclear fuel repository site, central Sweden2013In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 89, p. 21-34Article in journal (Refereed)
    Abstract [en]

    The Forsmark area belongs to the Paleoproterozoic Svecokarelian orogen (c. 1.9-1.8 Ga), the principal geological entity inside the Fennoscandian Shield, and is the site where Sweden has proposed to store its spent nuclear fuel. Three major sub-vertical (at the surface), composite ductile and brittle deformation zones that strike in a WNW or NW direction are present in the area. In between these zones the bedrock is less deformed and considered suitable for a repository. We present reprocessed reflection seismic data from seven profiles in which we have focused on improving the images in the depth range 1–5 km by passing lower frequencies through the processing flow at the cost of poorer resolution in the near-surface realm. The new images indicate that sub-horizontal to moderately dipping structures are possibly more extensive at depth than previously thought. Three main deeper reflective zones have been identified, one that is sub-horizontal and two that dip moderately to the southwest. The sub-horizontal reflective zone may represent a 1.27-1.26 Ga dolerite sill at about 3 km depth. One of the moderately dipping reflective zones may originate either from another dolerite sill or from a brittle fault system. The other moderately dipping structure may be present throughout most of the area and could cut all three sub-vertical deformation zones at depth. The new images and corresponding interpretation do not require a re-evaluation of the Forsmark site for storage of spent fuel, but they do influence how to interpret the deeper structures and, as a consequence, the tectonic evolution of the area.

  • 4.
    Dehghannejad, Mahdieh
    et al.
    Uppsala universitet.
    Juhlin, Christopher
    Uppsala universitet.
    Malehmir, Alireza
    Uppsala universitet.
    Skyttä, Pietari
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Reflection seismic imaging of the upper crust in the Kristineberg mining area, northern Sweden2010In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 71, no 4, p. 125-136Article in journal (Refereed)
    Abstract [en]

    The Kristineberg mining area is located in the western part of the Palaeoproterozoic Skellefte Ore District, one of the most important mining districts in Europe. As a part of a 3D geologic modeling project, two new reflection seismic profiles were acquired with a total length of about 20 km. One profile (HR), parallel to previous seismic profiles, was acquired using a 10 m receiver and source interval and crosses the steeply dipping structures of the Kristineberg mine. The other profile (Profile 2) runs perpendicular to all existing profiles in the area. 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. Our general interpretation of the seismic images is that the Kristineberg mine and associated mineral horizon are located in the northern part of a series of steeply south dipping structures. Overall, main structures plunge to the west at about 30° - 40°. Cross-dip analysis and reflection modeling were 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. This helped, for example, to obtain the 3D geometry of a deep reflection that was previously interpreted as structural basement to volcanic rocks. 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.

  • 5.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jensen, Mai-Britt Mose
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A correlation of AMS and rock quality in crystalline and sedimentary rocks in the Kiirunavaara hanging wall2012In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 86, p. 54-69Article in journal (Refereed)
    Abstract [en]

    A study of the magnetic fabric and rock quality has been performed on crystalline and sedimentary rocks from the hanging wall of the Kiirunavaara iron ore deposit, northern Sweden. The rock samples were taken from 12 outcrops and three oriented drillcores and consist of quartzite, siltstone, conglomerate, porphyritic basalts, quartz-bearing porphyry and mylonite.Anisotropy of magnetic susceptibility (AMS) was used to determine the texture of the rocks by defining the shape of the magnetic susceptibility ellipsoids, the orientation of the magnetic foliation planes and the degree of magnetic anisotropy. AMS data from the outcrops as well as data from the uppermost part of two of the drillcores was used to produce a surface contour map which indicates that both the dip of the magnetic foliation plane and the degree of magnetic anisotropy decreases towards the east. These two parameters thus generally follow the major structural features of the Kiruna region.Two classical rock mechanical parameters, RQD (Rock Quality Designation) and F/m (fractures pr. meter), were used to quantify the amount of discontinuities and fractures in the drill cores. RQD and F/m was subsequently correlated with the AMS data, and a correlation was observed, with the correlation coefficient r varying between 0.6142-0.7557. The correlation was limited to just one of the drillcores however it could be traced across rock type boundaries. The correlation indicates that AMS may be used as an indicator tool of the rock mechanical properties in both crystalline and sedimentary rocks.

  • 6.
    Malmgren, Lars
    et al.
    Mining Technology R and D, LKAB Kiruna Mine.
    Saiang, David
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Töyrä, Jimmy
    Bodare, A.
    Division of Soil and Rock Mechanics, Royal Institute of Technology, Stockholm.
    The excavation disturbed zone (EDZ) at Kiirunavaara mine, Sweden: by seismic measurements2007In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 61, no 1, p. 1-15Article in journal (Refereed)
    Abstract [en]

    The presence of an excavation disturbed zone (EDZ) around an excavation boundary can significantly affect the overall performance of the excavation and the general safety of men and equipment. Hence, it has been an important subject of research in various rock excavation projects. The EDZ is generally defined as the rock zone beyond the excavation boundary where the physical, mechanical and hydraulic properties of the rock have been significantly affected due to the excavation and redistribution of stresses. For LKAB's Kiirunavaara underground iron ore mine in Sweden, the understanding of the EDZ is essential for optimal design of rock support. With this main objective an EDZ investigation was conducted at the mine using seismic measurement techniques. Cross-hole seismics and spectral analyses of surfaces waves (SASW) were the main techniques used. Borehole Image Processing Systems (BIPS) complemented the seismic measurements. The results show that an EDZ with a thickness of 0.5–1. 0 m existed behind the boundaries of the mining drifts being investigated. The magnitude of the Young's modulus of this zone was 50% to 90% of that of the undisturbed rock.

  • 7.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Wattanasen, Kamhaeng
    Phommasone, Khamphouth
    Department of Physics, National University of Laos.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Characterization of aquifers in the Vientiane Basin, Laos, using magnetic resonance sounding and vertical electrical sounding2011In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 73, no 3, p. 207-220Article in journal (Refereed)
    Abstract [en]

    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 the hydrogeological parameters in three areas in the Vientiane basin, Laos. The investigated areas are part of the Khorat Plateau where halite is naturally occurring at depths as shallow as 50 m in the Thangon Formation. Magnetic Resonance Sounding (MRS) has been used in combination with Vertical Electrical Sounding (VES) in different geological environments. In total, 46 sites have been investigated and the MRS and VES recognized the stratigraphic unit N2Q1-3, consisting of alluvial unconsolidated sediments, as the main water bearing unit. The aquifer thickness varies usually between 10 and 40 m and the depth to the main aquifer range from 5 to 15 m. The free water content is here up to 30%, and the decay times vary between 100 and 400 ms, suggesting a mean pore size equivalent to fine sand to gravel. The resistivity is highly variable, but usually around 10-1500 Ω-m, except for some sites in areas 1 and 2, where the aquifer is of low resistivity, probably related to salt water. Hydraulic and storage-related parameters such as transmissivity, hydraulic column, have been estimated from the MRS. The MRS together with VES has been shown to be a useful and important tool for identifying and distinguishing freshwater from possible salt-affected water as well as the salt-related clay layer of the Thangon Formation. This clay layer is characterized by very low free water content and a resistivity lower than 5 Ω-m and can be found in all 3 areas at depths from 15 to 50 m

  • 8.
    Sandrin, Alessandro
    et al.
    Geological Institute.
    Berggren, Robert
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geophysical targeting of Fe-oxide Cu-(Au) deposits west of Kiruna, Sweden2007In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 61, no 2, p. 92-101Article in journal (Refereed)
    Abstract [en]

    Ore deposits are frequently associated with various types of rock alteration that may affect the physical properties of rocks, and result in a characteristic signature of the deposits. The present work focuses on the use of geophysical data in targeting areas hosting Fe-oxide Cu-Au (IOCG) deposits west of the Kiruna mining district, northern Sweden. It is noted that IOCG deposits in different areas worldwide (e.g., Australia, Canada) are preferentially located in proximity to faults associated with deformation zones of regional relevance, and that the deposits are hosted in areas affected by potassic to sodic alteration. This study shows that at a semi-regional scale IOCG deposits occur within areas of high positive gravity anomalies, high values of estimated potassium content and high K/Th ratios, which is an expression of potassic alteration. High magnetic anomalies are associated with magnetite occurrences, while low linear magnetic anomalies mark fault/shear zones, in proximity of which the majority of the IOCG deposits occur.

  • 9.
    Tavakoli, Saman
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Thunehed, Hans
    Geovista AB.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Regional-scale geometry of the central Skellefte district, northern Sweden: results from 2.5D potential field modeling along three previously acquired seismic profiles2012In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 85, p. 43-58Article in journal (Refereed)
    Abstract [en]

    The Skellefte district in northern Sweden is one of the most important mining districts in Europe hosting approximately 80 volcanic massive sulfide (VMS) deposits. Due to its economical importance, geological and geophysical studies were carried out in order to create an image of the geometry of the upper crustal structure and integral geological elements and to evaluate their relationship to mineral deposits. Consequently, seismic reflection data along three sub-parallel profiles were acquired during 2009–2010 to map the spatial relationships between the geological structures down to a depth of ~4.5 km. Although these seismic studies helped researchers understand the regional relationship between geologic units in the central Skellefte district (CSD), the seismic reflection data did not succeed entirely in mapping the lithological contacts in the area. In this study, themodel derived fromthe seismic reflection datawas examined by using 2.5D modeling of potential field data (down to a 5 km depth) constrained by physical properties of the rocks and surface geology.Moreover, we modeled gravity and magnetic data along the non-reflective or poorly reflective parts of the seismic profiles to identify major lithological contacts and shear zones in the CSD, which could not be modeled on the basis of the seismic reflection data. Gravity and magnetic data helped reveal the spatial relationship between the Skellefte volcanic rocks, Vargfors groupmeta-sedimentary rocks and two metaintrusive complexes.Results suggest amaximum depth extent of 2.1 kmfor the tectonic contact at the southern border of the Jörn granitoid. Furthermore, this north-dipping Skellefte–Jörn contact coincides closely with magnetic lows and gravity highs, which implies that the Jörn intrusive rocks have a greater thickness than the underlying basalt. Further to the NW, gravity and magnetic data suggest a depth extent of 2 km for the Gallejaur complex, which coincides with a set of gently dipping reflectors. In addition, this study supports previous concepts of fault geometries and fault patterns as a result of upper-crustal extension and subsequent inversion during crustal shortening. In the final model interpretations of the IP data were included, thus relating indications of mineralization to the geological structures.

  • 10.
    Tavakoli, Saman
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Thunehed, Hans
    Geovista AB.
    Geophysical modelling of the central Skellefte district, Northern Sweden: an integrated model based on the electrical, potential field and petrophysical data2012In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 82, p. 84-100Article in journal (Refereed)
    Abstract [en]

    The central Skellefte district (CSD) is a part of a major ore-bearing district in northern Sweden. Studying the depth and patterns of the contact relationship between the two major stratigraphic units of the CSD, the Skellefte Group and the Vargfors Group, is a key issue to understand the geometry and structure of the area and to guide exploration of base metals. In this study, we interpret geoelectrical data collected along two profiles and magnetic and gravity data obtained from the database of the Swedish Geological Survey (SGU) and Boliden Mineral, to reveal contact relationship and depth extension of the major geological structures. Petrophysical analyses of the different lithologies were conducted on samples from the database of the SGU. Electric resistivity, induced polarization (IP), magnetic susceptibility and density were determined on 154 core samples representing the different lithologies of the area. The resistivity/IP data were acquired to define structural relations down to a maximum depth of ~ 430 m. The major contact between sediments of the Vargfors basin and volcanic rocks of the Skellefte Group were outlined from the inversion of the resistivity/IP sections, suggesting a synform boundary between the Vargfors Group and Skellefte Group. The contact relationship between the felsic and mafic volcanic rocks of the Skellefte Group is also understood with the help of the resistivity/IP data. The resistivity models were tested using the magnetic data and magnetic susceptibility inferred on the resistivity bodies. The result suggests a good correlation between the initial resistivity model and the magnetic and gravity field calculated from that model. The integration and interpretation of geological and geophysical data improved the basic understanding of the geometry of CSD. Based on previous geological investigations, the potential ore deposits are believed to be found along the volcano-sedimentary contact. The result from this study can thus be used for the base metal exploration, finding the locations of potential sulphide deposits and give a better understanding about spatial relationship between different geology structures in the CSD.

  • 11. Wattanasen, Kamhaeng
    et al.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Direct and indirect methods for groundwater investigations: a case of MRS and VES in the southern part of Sweden2008In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 66, no 3-4, p. 104-117Article in journal (Refereed)
    Abstract [en]

    Magnetic Resonance Sounding (MRS) has been successfully tested for detecting groundwater in two areas in southern Sweden. Measurements of Schlumberger VES have been conducted in the same place as the MRS and the results are generally consistent. Low resistivity layers interpreted as clay are sometimes identified close to the surface. The MRS result in site 2 is a good example of signals penetrating through the clay and deeper aquifer still being detected. The MRS data suggest aquifers that are not only hosted in soft sediment materials (moraine, sand, and mixed materials), but hosted in basement rocks. Based on the MRS and borehole pumping test data, the results agree with yield, average water content and subsurface geological data.

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