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  • 1.
    Bastani, Mehrdad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Persson, Lena
    Beiki, Majid
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Harinen, Ritva
    A radio magnetotelluric study to evaluate the extents of a limestone quarry in Estonia2013In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 61, no 3, p. 678-687Article in journal (Refereed)
    Abstract [en]

    Electromagnetic signals from distant radio transmitters in the frequency range 15250 kHz were measured to model an electrical resistivity structure beneath 7 profiles in the vicinity of the Karinu limestone quarry in Estonia with the aim to map the extent of the economically exploitable limestone. The resistivity models from a 2D inversion of determinant resistivity and phase values using an Occam type of regularization contained reasonably accurate information about the geometry, namely depth to the top and the bottom of the target high-resistivity limestone. The resistivity models correlated well with existing geological evidences as well as information from closely located boreholes. However, the sharp lithological boundaries seen in the boreholes were not resolved exactly in the resistivity models. This is probably because of the smoothing regularization used in the inversion process. Combined use of borehole data together with resistivity models resulted in two major geological interpretations; a) towards the western part of the existing limestone quarry there is a NNW to NS striking fault, covered by post-glacial sediments, b) a potential cost-effective exploitable area containing high quality highly resistive limestone is located south of the existing quarry. This case study shows the applicability of the reasonably fast radio magnetotelluric (RMT) method for the exploration of near-surface resources.

  • 2.
    Beiki, Majid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Estimating magnetic dike parameters using a non-linear constrained inversion technique: an example from the Sarna area, west central Sweden2012In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 60, no 3, p. 526-538Article in journal (Refereed)
    Abstract [en]

    In this paper, we describe a non-linear constrained inversion technique for 2D interpretation of high resolution magnetic field data along flight lines using a simple dike model. We first estimate the strike direction of a quasi 2D structure based on the eigenvector corresponding to the minimum eigenvalue of the pseudogravity gradient tensor derived from gridded, low-pass filtered magnetic field anomalies, assuming that the magnetization direction is known. Then the measured magnetic field can be transformed into the strike coordinate system and all magnetic dike parameters horizontal position, depth to the top, dip angle, width and susceptibility contrast can be estimated by non-linear least squares inversion of the high resolution magnetic field data along the flight lines. We use the Levenberg-Marquardt algorithm together with the trust-region-reflective method enabling users to define inequality constraints on model parameters such that the estimated parameters are always in a trust region. Assuming that the maximum of the calculated gzz (vertical gradient of the pseudogravity field) is approximately located above the causative body, data points enclosed by a window, along the profile, centred at the maximum of gzz are used in the inversion scheme for estimating the dike parameters. The size of the window is increased until it exceeds a predefined limit. Then the solution corresponding to the minimum data fit error is chosen as the most reliable one. Using synthetic data we study the effect of random noise and interfering sources on the estimated models and we apply our method to a new aeromagnetic data set from the Sarna area, west central Sweden including constraints from laboratory measurements on rock samples from the area.

  • 3.
    Buske, Stefan
    et al.
    Techn Univ Freiburg, Freiburg, Germany..
    Bellefleur, Gilles
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Introduction to special issue on "hard rock seismic imaging"2015In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 63, no 4, p. 751-753Article in journal (Other academic)
  • 4.
    García Juanatey, María de los Ángeles
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hübert, Juliane
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tryggavson, Ari
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust B
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Imaging the Kristineberg mining area with two perpendicular magnetotelluric profiles in the Skellefte Ore District, northern Sweden2013In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 61, no 1, p. 200-219Article in journal (Refereed)
    Abstract [en]

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

  • 5.
    Huang, Fei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bergmann, Peter
    GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.; Sintef Petr Res, SP Andersens Vei 15 B, NO-7031 Trondheim, Norway..
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Ivandic, Monika
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Lüth, Stefan
    GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Ivanova, Alexandra
    GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Kempka, Thomas
    GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Henninges, Jan
    GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Sopher, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Zhang, Fengjiao
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Jilin Univ, Xi Min Zhu St 938, Changchun, Jilin, Peoples R China.
    The first post-injection seismic monitor survey at the Ketzin pilot CO2 storage site: results from time-lapse analysis2018In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 66, no 1, p. 62-84Article in journal (Refereed)
    Abstract [en]

    The injection of CO2 at the Ketzin pilot CO2 storage site started in June 2008 and ended in August 2013. During the 62 months of injection, a total amount of about 67 kt of CO2 was injected into a saline aquifer. A third repeat 3D seismic survey, serving as the first post-injection survey was acquired in 2015, aiming to investigate the recent movement of the injected CO2. Consistent with the previous two time-lapse surveys, a predominantly WNW migration of the gaseous CO2 plume in the up-dip direction within the reservoir is inferred in this first post-injection survey. No systematic anomalies are detected through the reservoir overburden. The extent of the CO2 plume west of the injection site is almost identical to that found in the 2012 second repeat survey (after injection of 61 kt), however there is a significant decrease in its size east of the injection site. Assessment of the CO2 plume distribution suggests that the decrease in the size of the anomaly may be due to multiple factors, such as limited vertical resolution, CO2 dissolution and CO2 diffusion, in addition to the effects of ambient noise. 4D seismic modelling based on dynamic flow simulations indicates that a dynamic balance between the newly injected CO2 after the second repeat survey and the CO2 being dissolved and diffused was reached by the time of the first post-injection survey. Considering the considerable uncertainties in CO2 mass estimation, both patchy and non-patchy saturation models for the Ketzin site were taken into consideration.

  • 6.
    Huang, Fei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Han, Li
    CNOOC Research Institute.
    Sopher, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Ivandic, Monika
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Norden, Ben
    GFZ German Research Centre for Geosciences.
    Deng, Wubing
    University of Saskatchewan.
    Zhang, Fengjiao
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kempka, Thomas
    GFZ German Research Centre for Geosciences.
    Lüth, Stefan
    GFZ German Research Centre for Geosciences.
    Feasibility of utilizing wavelet phase to map the CO2 plume at the Ketzin pilot site, Germany2017In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 65, no 2, p. 523-543Article in journal (Refereed)
    Abstract [en]

    Spectral decomposition is a powerful tool that can provide geological details dependent upon discrete frequencies. Complex spectral decomposition using inversion strategies differs from conventional spectral decomposition methods in that it produces not only frequency information but also wavelet phase information. This method was applied to a time‐lapse three‐dimensional seismic dataset in order to test the feasibility of using wavelet phase changes to detect and map injected carbon dioxide within the reservoir at the Ketzin carbon dioxide storage site, Germany. Simplified zero‐offset forward modelling was used to help verify the effectiveness of this technique and to better understand the wavelet phase response from the highly heterogeneous storage reservoir and carbon dioxide plume. Ambient noise and signal‐to‐noise ratios were calculated from the raw data to determine the extracted wavelet phase. Strong noise caused by rainfall and the assumed spatial distribution of sandstone channels in the reservoir could be correlated with phase anomalies. Qualitative and quantitative results indicate that the wavelet phase extracted by the complex spectral decomposition technique has great potential as a practical and feasible tool for carbon dioxide detection at the Ketzin pilot site.

  • 7.
    Ivandic, Monika
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bergmann, Peter
    Helmholtz Ctr Potsdam, GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany;SINTEF Petr Res, Trondheim, Norway.
    Kummerow, Juliane
    Helmholtz Ctr Potsdam, GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Huang, Fei
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Lueth, Stefan
    Helmholtz Ctr Potsdam, GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Monitoring CO2 saturation using time-lapse amplitude versus offset analysis of 3D seismic data from the Ketzin CO2 storage pilot site, Germany2018In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 66, no 8, p. 1568-1585Article in journal (Refereed)
    Abstract [en]

    The injection of CO2 at the Ketzin pilot site commenced in June 2008 and was terminated in August 2013 after 67 kT had been injected into a saline formation at a depth of 630-650 m. As part of the site monitoring program, four 3D surface seismic surveys have been acquired to date, one baseline and three repeats, of which two were conducted during the injection period, and one during the post-injection phase. The surveys have provided the most comprehensive images of the spreading CO2 plume within the reservoir layer. Both petrophysical experiments on core samples from the Ketzin reservoir and spectral decomposition of the 3D time-lapse seismic data show that the reservoir pore pressure change due to CO2 injection has a rather minor impact on the seismic amplitudes. Therefore, the observed amplitude anomaly is interpreted to be mainly due to CO2 saturation. In this study, amplitude versus offset analysis has been applied to investigate the amplitude versus offset response from the top of the sandstone reservoir during the injection and post-injection phases, and utilize it to obtain a more quantitative assessment of the CO2 gaseous saturation changes. Based on the amplitude versus offset modelling, a prominent decrease in the intercept values imaged at the top of the reservoir around the injection well is indeed associated solely with the CO2 saturation increase. Any change in the gradient values, which would, in case it was positive, be the only signature induced by the reservoir pressure variations, has not been observed. The amplitude versus offset intercept change is, therefore, entirely ascribed to CO2 saturation and used for its quantitative assessment. The estimated CO2 saturation values around the injection area in the range of 40%-60% are similar to those obtained earlier from pulsed neutron-gamma logging. The highest values of 80% are found in the second seismic repeat in close vicinity to the injection and observation wells.

  • 8.
    Ivanova, Alexandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kashubin, Artem
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhojuntti, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kummerow, Juliane
    Henninges, Jan
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Lueth, Stefan
    Ivandic, Monika
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Monitoring and volumetric estimation of injected CO2 using 4D seismic, petrophysical data, core measurements and well logging: a case study at Ketzin, Germany2012In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 60, no 5, p. 957-973Article in journal (Refereed)
    Abstract [en]

    More than 50 000 tons of CO2 have been injected at Ketzin into the Stuttgart Formation, a saline aquifer, at approximately 620 m depth, as of summer 2011. We present here results from the 1st repeat 3D seismic survey that was performed at the site in autumn 2009, after about 22 000 tons of CO2 had been injected. We show here that rather complex time-lapse signatures of this CO2 can be clearly observed within a radius of about 300 m from the injection well. The highly irregular amplitude response within this radius is attributed to the heterogeneity of the injection reservoir. Time delays to a reflection below the injection level are also observed. Petrophysical measurements on core samples and geophysical logging of CO2 saturation levels allow an estimate of the total amount of CO2 visible in the seismic data to be made. These estimates are somewhat lower than the actual amount of CO2 injected at the time of the survey and they are dependent upon the choice of a number of parameters. In spite of some uncertainty, the close agreement between the amount injected and the amount observed is encouraging for quantitative monitoring of a CO2 storage site using seismic methods.

  • 9.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Finite-difference elastic wave propagation in 2D heterogeneous transversely isotropic media1995In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 43, no 6, p. 843-858Article in journal (Refereed)
    Abstract [en]

    The velocity-stress formulation for propagation of elastic seismic waves through 2D heterogeneous transversely isotropic media of arbitrary orientation is presented. The equations are recast into a finite-difference scheme and solved numerically using fourth-order spatial operators and a second-order temporal operator on a staggered grid. Absorbing, free-surface and symmetry boundary conditions have been implemented. Test cases compare well with other published solutions. Synthetic seismograms are calculated over two idealized models: (i) vertical fractures in granite with a dolerite sill reflector and (ii) a dipping anisotropic shale. Comparisons with the isotropic counterparts show significant differences which may have to be accounted for in seismic processing in the future.

  • 10.
    Kazemeini, Sayed Hesammoddin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Zinck-Jørgensen, Kim
    Geological Survey of Denmark and Greenland.
    Norden, Ben
    GeoForschungsZentrum Potsdam, Potsdam, Germany..
    Application of the continuous wavelet transform on seismic data for mapping of channel deposits and gas detection at the CO2SINK site, Ketzin, Germany2009In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 57, no 1, p. 111-123Article in journal (Refereed)
    Abstract [en]

    Conventional seismic data are band limited and therefore, provide limited geological information. Every method that can push the limits is desirable for seismic data analysis.

    Recently, time-frequency decomposition methods are being used to quickly extract geological information from seismic data and, especially, for revealing frequency dependent amplitude anomalies. Higher frequency resolution at lower frequencies and higher temporal resolution at higher frequencies are the objectives for different timefrequency decomposition methods. Continuous wavelet transform techniques, which are the same as narrow-band spectral analysis methods, provide frequency spectra with high temporal resolution without the windowing process associated with other techniques. Therefore, this technique can be used for analysing geological information associated with low and high frequencies that normally cannot be observed in conventional seismic data. In particular, the continuous wavelet transform is being used to detect thin sand bodies and also as a direct hydrocarbon indicator. This paper presents an application of the continuous wavelet transform method for the mapping of potential channel deposits, as well as remnant natural gas detection by mapping low-frequency anomalies associated with the gas. The study was carried out at the experimental CO2 storage site at Ketzin, Germany (CO2SINK). Given that reservoir heterogeneity and faulting will have significant impact on the movement and storage of the injected CO2, our results are encouraging for monitoring the migration of CO2 at the site. Our study confirms the efficiency of the continuous wavelet transform decomposition method for the detection of frequency-dependent anomalies that may be due to gas migration during and after the injection phase and in this way, it can be used for real-time monitoring of the injected CO2 from both surface and borehole

    seismics.

     

  • 11. Koivisto, E.
    et al.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hellqvist, N.
    Voipio, T.
    Wijns, C.
    Building a 3D model of lithological contacts and near-mine structures in the Kevitsa mining and exploration site, Northern Finland: constraints from 2D and 3D reflection seismic data2015In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 63, no 4, p. 754-773Article in journal (Refereed)
    Abstract [en]

    The Kevitsa mafic-ultramafic intrusion in Northern Finland hosts a large, disseminated nickel-copper sulphide ore body. The Kevitsa intrusion is an active mining and exploration site, for which we have built a 3D model of the main lithological contacts and near-mine structures in the area. To build the 3D model, 2D and 3D reflection seismic data have been used together with borehole data and geological map of the area. The Kevitsa reflection seismic data reveal the internal architecture of the Kevitsa intrusion and the surrounding units. For example, the seismic data have uncovered a previously unknown, deeper continuation of the Kevitsa intrusion. Improved 3D knowledge of the basal contact of the intrusion provides an exploration target for contact-type mineralization. Within the intrusion, a limited area of strong reflections is observed in the data. This has been associated with discontinuous, smaller-scale magmatic layering that is thought to control the extent of the Kevitsa main mineralization. Thus, our 3D model of the extents of the internal reflectors can provide a framework for near-mine and deep exploration of the main type of mineralization in the area. In addition to exploration, the original purpose of the 3D seismic survey was geotechnical planning of the Kevitsa open-pit mine. Accordingly, the 3D seismic data were used to create a 3D model of the subsurface structures, with a focus on the vicinity of the mine. The interpreted structures reveal a complex pattern of fault and fracture zones, some of which will be important for slope stability and operational planning of the final stages of the mine.

  • 12.
    Lahivaara, Timo
    et al.
    Univ Eastern Finland, Dept Appl Phys, Kuopio, Finland.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pasanen, Antti
    Geol Survey Finland, Kuopio, Finland.
    Karkkainen, Leo
    Nokia Bell Labs, Espoo, Finland;Aalto Univ, Dept Elect Engn & Automat, Espoo, Finland.
    Huttunen, Janne M. J.
    Nokia Bell Labs, Espoo, Finland.
    Hesthaven, Jan S.
    Ecole Polytech Fed Lausanne, Computat Math & Simulat Sci, Lausanne, Switzerland.
    Estimation of groundwater storage from seismic data using deep learning2019In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 67, no 8, p. 2115-2126Article in journal (Refereed)
    Abstract [en]

    Convolutional neural networks can provide a potential framework to characterize groundwater storage from seismic data. Estimation of key components, such as the amount of groundwater stored in an aquifer and delineate water table level, from active-source seismic data are performed in this study. The data to train, validate and test the neural networks are obtained by solving wave propagation in a coupled poroviscoelastic-elastic media. A discontinuous Galerkin method is applied to model wave propagation, whereas a deep convolutional neural network is used for the parameter estimation problem. In the numerical experiment, the primary unknowns estimated are the amount of stored groundwater and water table level, while the remaining parameters, assumed to be of less of interest, are marginalized in the convolutional neural network-based solution. Results, obtained through synthetic data, illustrate the potential of deep learning methods to extract additional aquifer information from seismic data, which otherwise would be impossible based on a set of reflection seismic sections or velocity tomograms.

  • 13.
    Malehmir, Alireza
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Andersson, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Lebedev, M.
    Urosevic, M.
    Mikhaltsevitch, V.
    Experimental estimation of velocities and anisotropy of a series of Swedish crystalline rocks and ores2013In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 61, no 1, p. 153-167Article in journal (Refereed)
    Abstract [en]

    To provide a guide for future deep (<1.5 km) seismic mineral exploration and to better understand the nature of reflections imaged by surface reflection seismic data in two mining camps and a carbonatite complex of Sweden, more than 50 rock and ore samples were collected and measured for their seismic velocities. The samples are geographically from the northern and central parts of Sweden, ranging from metallic ore deposits, meta-volcanic and meta-intrusive rocks to deformed and metamorphosed rocks. First, ultrasonic measurements of P- and S-wave velocities at both atmospheric and elevated pressures, using 0.5 MHz P- and S-wave transducers were conducted. The ultrasonic measurements suggest that most of the measured velocities show positive correlation with the density of the samples with an exception of a massive sulphide ore sample that shows significant low P- and S-wave velocities. The low P- and S-wave velocities are attributed to the mineral texture of the sample and partly lower pyrite content in comparison with a similar type sample obtained from Norway, which shows significantly higher P- and S-wave velocities. Later, an iron ore sample from the central part of Sweden was measured using a low-frequency (0.1-50 Hz) apparatus to provide comparison with the ultrasonic velocity measurements. The low-frequency measurements indicate that the iron ore sample has minimal dispersion and attenuation. The iron ore sample shows the highest acoustic impedance among our samples suggesting that these deposits are favourable targets for seismic methods. This is further demonstrated by a real seismic section acquired over an iron ore mine in the central part of Sweden. Finally, a laser-interferometer device was used to analyse elastic anisotropy of five rock samples taken from a major deformation zone in order to provide insights into the nature of reflections observed from the deformation zone. Up to 10% velocity-anisotropy is estimated and demonstrated to be present for the samples taken from the deformation zone using the laser-interferometery measurements. However, the origin of the reflections from the major deformation zone is attributed to a combination of anisotropy and amphibolite lenses within the deformation zone.

  • 14.
    Malehmir, Alireza
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Wang, Shunguo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Lamminen, Jarkko
    Brodic, Bojan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bastani, Mehrdad
    Vaittinen, Katri
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Place, Joachim
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Delineating structures controlling sandstone-hosted base-metal deposits using high-resolution multicomponent seismic and radio-magnetotelluric methods: a case study from Northern Sweden2015In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 63, no 4, p. 774-797Article in journal (Refereed)
    Abstract [en]

    Over the past few decades seismic methods have increasingly been used for the exploration of mineral, geothermal, and groundwater resources. Nevertheless, there have only been a few cases demonstrating the advantages of multicomponent seismic data for these purposes. To illustrate some of the benefits of three-component data, a test seismic survey, using 60 digital three-component sensors spaced between 2 m and 4 m and assembled in a 160 m-long prototype landstreamer, was carried out over shallow basement structures underlying mineralized horizons and over a magnetic lineament of unknown origin. Two different types of seismic sources, i.e., explosives and a sledgehammer, were used to survey an approximately 4 km-long seismic profile. Radio-magnetotelluric measurements were also carried out to provide constraints on the interpretation of the seismic data over a portion of the profile where explosive sources were used. Good quality seismic data were recorded on all three components, particularly when explosives were used as the seismic source. The vertical component data from the explosive sources image the top of the crystalline basement and its undulated/faulted surface at a depth of about 50 m-60 m. Supported by the radio-magnetotelluric results, however, shallower reflections are observed in the horizontal component data, one of them steeply dipping and associated with the magnetic lineament. The vertical component sledgehammer data also clearly image the crystalline basement and its undulations, but significant shear-wave signals are not present on the horizontal components. This study demonstrates that multicomponent seismic data can particularly be useful for providing information on shallow structures and in aiding mineral exploration where structural control on the mineralization is expected.

  • 15.
    Mansoori, I.
    et al.
    Univ Tehran, Inst Geophys, Tehran 141556466, Iran.;Natl Iranian South Oil Co, Ahwaz 617351333, Iran..
    Oskooi, B.
    Univ Tehran, Inst Geophys, Tehran 141556466, Iran..
    Pedersen, Laust Börsting
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Javaheri, R.
    Explorat Directorate Natl Iranian Oil Co, Tehran 193956669, Iran..
    Three-dimensional modelling of magnetotelluric data to image Sehqanat hydrocarbon reservoir in southwestern Iran2016In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 64, no 3, p. 753-766Article in journal (Refereed)
    Abstract [en]

    A detailed magnetotelluric survey was conducted in 2013 in the Sehqanat oil field, southwestern Iran to map the geoelectrical structures of the sedimentary Zagros zone, particularly the boundary between the Gachsaran Formation acting as cap rock and the Asmari Formation as the reservoir. According to the electrical well logs, a large resistivity contrast exists between the two formations. The Gachsaran Formation is formed by tens to hundreds of metres of evaporites and it is highly conductive (ca. 1 m-10 m), and the Asmari Formation consists of dense carbonates, which are considerably more resistive (more than 100 m). Broadband magnetotelluric data were collected along five southwest-northeast directed parallel lines with more than 600 stations crossing the main geological trend. Although dimensionality and strike analysis of the magnetotelluric transfer functions showed that overall they satisfied local 2D conditions, there were also strong 3D conditions found in some of the sites. Therefore, in order to obtain a more reliable image of the resistivity distribution in the Sehqanat oil field, in addition to standard 2D inversion, we investigated to what extent 3D inversion of the data was feasible and what improvements in the resistivity image could be obtained. The 2D inversion models using the determinant average of the impedance tensor depict the main resistivity structures well, whereas the estimated 3D model shows significantly more details although problems were encountered in fitting the data with the latter. Both approaches resolved the Gachsaran-Asmari transition from high conductivity to moderate conductivity. The well-known Sehqanat anticline could also be delineated throughout the 2D and 3D resistivity models as a resistive dome-shaped body in the middle parts of the magnetotelluric profiles.

  • 16. Manzi, Musa
    et al.
    Cooper, Gordon
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Durrheim, Raymond
    Nkosi, Zamaswazi
    Integrated interpretation of 3D seismic data to enhance the detection of the gold-bearing reef: Mponeng Gold mine, Witwatersrand Basin (South Africa)2015In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 63, no 4, p. 881-902Article in journal (Refereed)
    Abstract [en]

    We present an integrated approach to the seismic interpretation of one of the world's deepest gold ore body (Carbon Leader Reef) using three-dimensional seismic data, ultrasonic velocity measurements at elevated stresses, and modified instantaneous attribute analysis. Seismic wave velocities of the drill-core samples (quartzite, shale, and conglomeratic reef) from the mine are sensitive to uniaxial stress changes, i.e., they slowly increase with increasing pressure until they reach maximum value at similar to 25 MPa. For all the samples, seismic velocities are constant above 25 MPa, indicating a possible closure of microcracks at stress corresponding to 1.0 km-1.5 km. A reflection coefficient of 0.02 computed between hanging wall and footwall quartzites of the Carbon Leader Reef ore body suggests that it may be difficult to obtain a strong seismic reflection at their interface. Our modified seismic attribute algorithm, on the other hand, shows that the detection of the lateral continuity of the Carbon Leader Reef reflector can significantly be improved by sharpening the seismic traces. Three-dimensional seismic data reveal that faults with throws greater than 25 m that offset the Carbon Leader Reef can clearly be seen. Faults with throws less than 25 m but greater than 2-m throw were identified through horizon-based attribute analysis, while most dykes and sills with thickness less than 25 m were invisible. The detection of the lateral continuity of the Carbon Leader Reef reflector and its depth position is greatly improved by integrating the modified instantaneous attributes with controls from borehole observations. The three-dimensional visualization and effective interpretation of the Carbon Leader Reef horizon shows a host of structurally complex ore body blocks that may impact future shaft positioning and reduce its associated risks.

  • 17.
    Pedersen, Laust B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Geological Survey of Sweden.
    Kamm, Jochen
    Bastani, Mehrdad
    Geological Survey of Sweden.
    A priori models and inversion of gravity gradient data in hilly terrain2019In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478Article in journal (Refereed)
    Abstract [en]

    The increased popularity of airborne measurements of the gravity gradient tensor for resource studies and geological mapping has resulted in a new awareness of the importance of terrain effects. In these measurements, the terrain effect often overwhelms that of the underlying crust and it becomes important to formulate a strategy for taking it into account when presenting the data and when inverting the data into density models. Using newly acquired data from Northern Sweden, we first attempted to estimate a variable terrain density model by inverting the data using a terrain model with a laterally varying density. Using data weights related to the topography variations, we find the best estimate of the lateral variation of the terrain density. We translate this model into a full three‐dimensional model such that all columns have the same vertical centre of mass as estimated from inspecting the radially averaged power spectrum of the area. This then defines a reference model for subsequent three‐dimensional inversion of the gravity gradient tensor dataset. We tested this approach first on synthetic data calculated from the measured topography including two density anomalies before we applied it to the measured data. The result is a model in which the surface density variations are propagated downwards in a systematic manner now in better agreement with measured densities of rock samples in the area.

  • 18. Persson, Lena
    et al.
    Lundin, Ildiko Antal
    Pedersen, Laust B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Claeson, Dick
    Combined magnetic, electromagnetic and resistivity study over a highly conductive formation in Orrivaara, Northern Sweden2011In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 59, no 6, p. 1155-1163Article in journal (Refereed)
    Abstract [en]

    Different geophysical methods were used to determine the characteristics of a highly conductive structure in Northern Sweden, first discovered on airborne data. Airborne electromagnetic (very low frequency) data indicate a high conductivity structure coincident with low magnetic patterns. The airborne data were processed in different ways to enhance various structures/features. In particular we introduce a new transformation to current density that is suitable for delineating conductive structures. Ground measurements of the total magnetic field, radiomagnetotelluric measurements and resistivity imaging provided valuable information that was used in the compilation of a new bedrock map over the area. The results of our measurements indicate that the conducting structure consists of metasedimentary rocks containing thin horizons of pyrrhotite and graphite.

  • 19.
    Shan, Chunling
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust Börsting
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Interference effects of aircraft on the Earth's electromagnetic response at Very Low Frequency and Low Frequency2015In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 63, no 1, p. 211-224Article in journal (Refereed)
    Abstract [en]

    Very Low Frequency (VLF) electromagnetics (EM) has been widely and successfully applied in mineral exploration and ground water exploration in the past decades. Many radio transmitters with strong signal to noise ratios are scattered in the Very Low Frequency (VLF) band and the Low Frequency (LF) band. Based on the experiences gained from ground measurements with the Radio Magnetotelluric (RMT) technique operating in the frequency interval 1-250 kHz, broad band magnetometers have been utilized to cover both the VLF (3-30 kHz) and LF (30-300 kHz) bands to increase the resolution of the near surface structure. The metallic aircraft as a conductive body will distort the magnetic signal to some extent, and thus an investigation of the interference of the aircraft on the electromagnetic signal is important. Noise studies due to the rotation of the aircraft and the aircraft itself as a metallic conductive body has been carried out by three different methods: 3D wave polarization, determination of transmitter direction and full tipper estimation. Both VLF and LF frequency bands were investigated. The results show that the magnetic field is independent of the aircraft at low frequencies in the VLF and part of the LF bands (below 100 kHz). At high frequencies (above 100 Hz), the signals are more influenced by the aircraft and the wave polarization directions are more scattered as seen when the aircraft turns.  Some aircraft generated noise which is mixed with the radio transmitter signals are detected as 'dummy' signals by the 3D wave polarization method. The estimated scalar magnetic transfer functions have dependence on the aircraft flight directions at high frequencies which is caused by the aircraft interference.  The aircraft eigen response in the transfer functions (tippers) between vertical and horizontal magnetic field components can be compensated for in the real part of the estimated tippers, but some unknown effect is still observed in the imaginary parts.

  • 20.
    Tavakoli, Saman
    et al.
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Bauer, Tobias
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Rasmussen, Thorkild Maack
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Weihed, Pär
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Luleå tekniska universitet.
    Elming, Sten-åke
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Deep massive sulphide exploration using 2D and 3D geoelectrical and induced polarization data in Skellefte mining district, northern Sweden2016In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 64, no 6, p. 1602-1619Article in journal (Refereed)
    Abstract [en]

    Geoelectrical and induced polarization data from measurements along three profiles and from one 3D survey are acquired and processed in the central Skellefte District, northern Sweden. The data were collected during two field campaigns in 2009 and 2010 in order to delineate the structures related to volcanogenic massive sulphide deposits and to model lithological contacts down to a maximum depth of 1.5 km. The 2009 data were inverted previously, and their joint interpretation with potential field data indicated several anomalous zones. The 2010 data not only provide additional information from greater depths compared with the 2009 data but also cover a larger surface area. Several high-chargeability low-resistivity zones, interpreted as possible massive sulphide mineralization and associated hydrothermal alteration, are revealed. The 3D survey data provide a detailed high-resolution image of the top ∼450 m of the upper crust around the Maurliden East, North, and Central deposits. Several anomalies are interpreted as new potential prospects in the Maurliden area, which are mainly concentrated in the central conductive zone. In addition, the contact relationship between the major geological units, e.g., the contact between the Skellefte Group and the Jörn Intrusive Complex, is better understood with the help of 2010 deep-resistivity/chargeability data. The bottommost part of the Vargfors basin is imaged using the 2010 geoelectrical and induced polarization data down to ∼1-km depth.

  • 21.
    Tavakoli, Saman
    et al.
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Thunehed, Hans
    Geovista AB.
    Bauer, Tobias
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Weihed, Pär
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Luleå tekniska universitet.
    Elming, Sten-åke
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Targeting VMS ore deposits within the upper 1.5 km of the crust in the central Skellefte District, northern Sweden, using 2D and 3D-resistivity/IP data2016In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478Article in journal (Refereed)
    Abstract [en]

    As a part of a 4D geologic modelling project, resistivity and induced polarisation (IP) data from measurements along three profiles and from one 3D survey have been analysed in the central Skellefte district (CSD), northern Sweden. The data were collected during two field campaigns (2009 and 2010) in order to delineate the structures related to volcanogenic massive sulphide (VMS) deposits, and to visualise lithological contacts down to a maximum of 1.5 km in depth. The 2009 data were previously inverted and their joint interpretation with potential field data indicated several anomalous zones. The geophysical interpretations are supported by determined physical properties of the rocks (resistivity and chargeability) measured on drill-hole samples, as well as surface geological data and results from previous geological and geophysical studies in the area. The results revealed several high chargeability-low resistivity zones, interpreted as possible massive sulphide mineralisation and associated hydrothermal alteration. The 3D data provides a detailed, high resolution image of the top ~450 m of the upper crust around the Maurliden-East, North and Central deposits. Joint interpretation of the resistivity/chargeability data delineates the3D geometry of the Maurliden deposits and several anomalies are interpreted as new potential prospects. In addition, the geometry of geological contacts in the study area, i.e. the contact between the Skellefte Group and the Jörn Intrusive Complex and the contact between the Vargfors and Skellefte Groups, was clarified in this study.

  • 22.
    Xu, Zhuo
    et al.
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China;Minist Land & Resources, Key Lab Appl Geophys, Changchun 130026, Jilin, Peoples R China.
    Sopher, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Han, Liguo
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China;Minist Land & Resources, Key Lab Appl Geophys, Changchun 130026, Jilin, Peoples R China.
    Reconstruction of the near-offset gap in marine seismic data using seismic interferometric interpolation2018In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 66, no S1, p. 1-26Article in journal (Refereed)
    Abstract [en]

    In conventional seismic exploration, especially in marine seismic exploration, shot gathers with missing near-offset traces are common. Interferometric interpolation methods are one of a range of different methods that have been developed to solve this problem. Interferometric interpolation methods differ from conventional interpolation methods as they utilise information from multiples in the interpolation process. In this study, we apply both conventional interferometric interpolation (shot domain) and multi-domain interferometric interpolation (shot and receiver domain) to a synthetic and a real-towed marine dataset from the Baltic Sea with the primary aim of improving the image of the seabed by extrapolation of a near-offset gap. We utilise a matching filter after interferometric interpolation to partially mitigate artefacts and coherent noise associated with the far-field approximation and a limited recording aperture size. The results show that an improved image of the seabed is obtained after performing interferometric interpolation. In most cases, the results from multi-domain interferometric interpolation are similar to those from conventional interferometric interpolation. However, when the source-receiver aperture is limited, the multi-domain method performs better. A quantitative analysis for assessing the performance of interferometric interpolation shows that multi-domain interferometric interpolation typically performs better than conventional interferometric interpolation. We also benchmark the interpolated results generated by interferometric interpolation against those obtained using sparse recovery interpolation.

  • 23.
    Yordkayhun, Sawasdee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Ivanova, Alexandra
    GeoForschungsZentrum (GFZ), Potsdam, Germany.
    Giese, Ruediger
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Cosma, Calin
    Comparison of surface seismic sources at the CO2SINK site, Ketzin, Germany2009In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 57, no 1, p. 125-139Article in journal (Refereed)
    Abstract [en]

    In 2004 three seismic surface sources (VIBSIST, accelerated weight drop and MiniVib) were tested in a pilot study at the Ketzin test site, Germany, a study site for geological storage of CO2 (EU project CO2SINK). The main objectives of this pilot study were to 1) evaluate the response of the Ketzin site to reflection seismics, especially at the planned injection depth, 2) test different acquisition parameters and 3) use the results to guide the planning of the 3D survey. As part of these objectives, we emphasize the source performance comparison in this study. The sources were tested along two perpendicular lines of 2.4 km length each. Data were acquired by shooting at all stations (source and receiver spacing of 20 m) on both lines, allowing common-midpoint stacked sections to be produced. The sources' signal characteristics based on signal-to-noise ratio, signal penetration and frequency content of raw shot records were analysed and stacked sections were compared. The results show that all three surface sources are suitable for reflection seismic studies down to a depth of about 1 km and provide enough bandwidth for resolving the geological targets at the site, i.e., the Weser and Stuttgart Formations. Near surface conditions, especially a thick weathering layer present in this particular area, strongly influence the data quality, as indicated by the difference in reflectivity and signal-to-noise ratio of the two common-midpoint lines. The stacked sections of the MiniVib source show the highest frequency signals down to about 500 ms traveltime (approximately 500 m depth) but also the shallowest signal penetration depth. The VIBSIST source generates signals with the highest signal-to-noise ratio and greatest signal penetration depth of the tested sources. In particular, reflections below 900 ms (approximately 1 km depth) are best imaged by the VIBSIST source. The weight drop performance lies in between these two sources and might be recommended as an appropriate source for a 3D survey at this site because of the shorter production time compared to the VIBSIST and MiniVib sources.

  • 24.
    Zhang, Fengjiao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Ivandic, Monika
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Luth, Stefan
    Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum.
    Application of seismic waveform tomography to monitoring of CO2 injection: modeling and a real data example from the Ketzin site, Germany2013In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 61, no Suppl.s1, p. 284-299Article in journal (Refereed)
    Abstract [en]

    Seismic monitoring of the injected carbon dioxide (CO2) distribution at depth is an important issue in the geological storage of CO2. To help monitor changes in the subsurface during CO2 injection a series of 2D seismic surveys were acquired within the framework of the CO2SINK and CO2MAN projects at Ketzin, Germany at different stages of the injection process. Here we investigate using seismic waveform tomography as a qualitative tool for time-lapse seismic monitoring given the constraints of the limited maximum offsets of the 2D seismic data. Prior to applying the inversion to the real data we first made a number of benchmark tests on synthetic data using a similar geometry as in the real data. Results from the synthetic benchmark tests show that it is difficult to recover the true value of the velocity anomaly due to the injection, but that it is possible to qualitatively locate the distribution of the injected CO2. After the synthetic studies, we applied seismic waveform tomography on the real time-lapse data from the Ketzin site along with conventional time-lapse processing. Both methods show a similar qualitative distribution of the injected CO2 and agree well with expectations based upon more extensive 3D time-lapse monitoring in the area.

1 - 24 of 24
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