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  • 1. Adamczyk, A.
    et al.
    Malinowski, M.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    High-resolution near-surface velocity model building using full-waveform inversion-a case study from southwest Sweden2014In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 197, no 3, p. 1693-1704Article in journal (Refereed)
    Abstract [en]

    Full-waveform inversion (FWI) is an iterative optimization technique that provides high-resolution models of subsurface properties. Frequency-domain, acoustic FWI was applied to seismic data acquired over a known quick-clay landslide scar in southwest Sweden. We inverted data from three 2-D seismic profiles, 261-572 m long, two of them shot with small charges of dynamite and one with a sledgehammer. To our best knowledge this is the first published application of FWI to sledgehammer data. Both sources provided data suitable for waveform inversion, the sledgehammer data containing even wider frequency spectrum. Inversion was performed for frequency groups between 27.5 and 43.1 Hz for the explosive data and 27.5-51.0 Hz for the sledgehammer. The lowest inverted frequency was limited by the resonance frequency of the standard 28-Hz geophones used in the survey. High-velocity granitic bedrock in the area is undulated and very shallow (15-100 m below the surface), and exhibits a large P-wave velocity contrast to the overlying normally consolidated sediments. In order to mitigate the non-linearity of the inverse problem we designed a multiscale layer-stripping inversion strategy. Obtained P-wave velocity models allowed to delineate the top of the bedrock and revealed distinct layers within the overlying sediments of clays and coarse-grained materials. Models were verified in an extensive set of validating procedures and used for pre-stack depth migration, which confirmed their robustness.

  • 2. Adamczyk, Anna
    et al.
    Malinowski, Michal
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Application of first-arrival tomography to characterize a quick clay landslide site in Southwest Sweden2013In: Acta Geophysica, ISSN 1895-6572, Vol. 61, no 5, p. 1057-1073Article in journal (Refereed)
    Abstract [en]

    First-arrival traveltime tomography was applied to high-resolution seismic data acquired over a known quick-clay landslide scar near the Gota River in southwest Sweden in order to reveal the geometry and physical properties of clay-related normally consolidated sediments. Investigated area proved to be a challenging environment for tomographic imaging because of large P-wave velocity variations, ranging from 500 to 6000 m/s, and relatively steeply-dipping bedrock. Despite these challenges, P-wave velocity models were obtained down to ca. 150 m for two key 2D seismic profiles (each about 500-m long) intersecting over the landslide scar. The models portrait the sandwich-like structure of marine clays and coarse-grained consolidated sediments, but the estimated resolution (20 m) is too small to distinguish thin layers within this structure. Modelled velocity structures match well the results of reflection seismic processing and resistivity tomography available along the same profiles.

  • 3.
    Adamczyk, Anna
    et al.
    Institute of Geophysics - Polish Academy of Sciences.
    Malinowski, Michal
    Institute of Geophysics - Polish Academy of Sciences.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Delineating shallow quick-clay structures using acoustic full-waveform inversion – case studyfrom southwest Sweden2013Conference paper (Refereed)
    Abstract [en]

    Full waveform inversion (FWI) was applied to imageshallow structures of marine-clay sediments and to provideinsight on the mechanism of a quick-clay landslide. Thedata was acquired in a high-resolution seismic surveyconducted over a known landslide scar near the Göta riverin southwest Sweden. Inversion proved to be challengingbecause of contrasted P-wave velocity structure – thevelocities ranged from 500 m/s in weathered top layer to6000 m/s in the shallow granitic bedrock (up to 30 m belowthe surface). FWI applied to 3 profiles provided highresolution2D P-wave velocity models revealing theintercalating layers of clays and coarse-grain material andthe shape of the bedrock. The multiscale approach was usedto mitigate the strong nonlinearity of the inverse problem.The models were used in pre-stack depth migration andproved significant improvement in reflector flattening andfocusing over the starting first-arrival traveltimetomography models.

  • 4.
    Ahmadi, Omid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hedin, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    3D Seismic Interpretation and Forward Modeling: an approach to providing reliable results from 2D seismic data2013In: Proceedings of the 12th Biennial Meeting: Mineral Deposit Research for a High-Tech World / [ed] Johnson, E., 2013, Vol. 1-4, p. 50-53Conference paper (Refereed)
    Abstract [en]

    Accurate 3D interpretations is challenging when only 2D seismic reflection data are available. This can be compensated for by using additional data. Here we present two case studies where 2D seismic reflection data have been used in combination with geological/geophysical data to create and verify 3D interpretations of specific structures targeted for scientific deep drilling and mining. In the first case, a surface geological map and high resolution 2D seismic reflection data were used to create a 3D lithological model of the subsurface structures in an area around a scientific deep drilling site. This model was also compared to results from constrained 3D inverse modeling of gravity data. In the second case, seismic forward ray-trace modeling was used to delineate a massive sulfide ore body by using high resolution 2D seismic reflection data. By comparison of the generated synthetic data with the real data, it was found that the top of the ore body was detected.

  • 5.
    Ahmadi, Omid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Munck, Mie
    Boliden Mines.
    High-resolution 2D seismic imaging and forward modeling of a polymetallic sulfide deposit at Garpenberg, central Sweden2013In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 78, no 6, p. B339-B350Article in journal (Refereed)
    Abstract [en]

    We acquired a high-resolution 2D seismic profile to test the capability of the seismic method in imaging a sulfide ore body at Garpenberg, central Sweden. Delineation of the geologic structures, which surround and host the ore body, is another goal of the survey. Due to the 3D geology of the structures, a cross-dip correction performed to image out-of-the-plane reflections, resulting in a clear high amplitude anomaly at a time and location to that to be expected from near the top of the ore body. Furthermore, DMO processing and migration are applied to the data, providing images of four main reflection groups. The reflections have been interpreted as corresponding to geologic rock units in the area that partly interfere with the potential ore body signal. To further investigate the seismic response of the ore body, forward modeling by ray-tracing is applied using the ore body geometry as mapped by drilling. We use two ray-tracing approaches: standard 3D ray-tracing and an exploding reflector approach. Seven representative samples from the mine area are used to determine P-wave velocities. The measurements show a considerable contrast between the ore body and host rock. By comparing the modeled and observed data, we find that the high amplitude signal in the real seismic section most likely emanates from near the top of one concentrated ore which lies inside the larger mapped ore body that has been modeled as a resource. The base of the ore body is only observed on the synthetic data whereas a signal penetration analysis suggests that the seismic signal penetrated efficiently along the entire survey line. Presence of disseminated ore and lower fold toward the northern end of the profile could be combined reasons that make imaging the base of the ore body difficult.

  • 6.
    Ahmadi, Pouya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Elastic Anisotropy of Deformation Zones: From Lab Measurements to Real Seismic Data, an Example from Eastern Sweden2013Conference paper (Refereed)
    Abstract [en]

    Estimation of elastic anisotropy, which is usually caused by rock fabrics and mineral orientation, has animportant role in exploration seismics and better understanding of crustal seismic reflections. If notproperly taken care of during processing steps, it may lead to wrong interpretation or distorted seismicimage. In this paper, a state-of-the-art under development Laser Doppler Interferometer (LDI) device isused to measure anisotropy of rock samples from a major deformation zone in the Bergslagen region ineastern Sweden. Results are then used to correct for the anisotropy effects using a non-hyperbolic moveoutequation. The resulting stacked section shows partial improvement of the deformation zone compared withthe isotropic processing section. This suggests that rock anisotropy may also contribute to generation ofreflections from the deformation zones in the study area but requires further investigations.

  • 7.
    Ahmadi, Pouya
    et al.
    Curtin University, Australia.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Laser Doppler Interferometry (LDI) to obtain full stiffness tensor: A case study on a deformation zone in Sweden2015Conference paper (Refereed)
    Abstract [en]

    Estimation of elastic anisotropy, which is usually caused by rock fabrics and mineral orientations, has an important role in exploration seismology and a better understanding of crustal seismic reflections. If not properly taken care of during data processing steps, it leads to wrong interpretation and/or distorted seismic image. In this work, a state-of-the-art under the development Laser Doppler Interferometer (LDI) device is used to measure phase velocities on the surface of rock samples from a major poly-phase crustal scale deformation zone (Österbybruk Deformation Zone) in the Bergslagen region of eastern Sweden. Then, a general inversion code is deployed to invert the measured phase velocities to obtain full elastic stiffness tensors of two samples from the deformation zone. At the end, results are used to correct for the anisotropy effects using three dimensionless Tsvankin's parameters and a non-hyperbolic moveout equation. The resulting stacked section shows partial reflection improvement of the deformation zone compared with the traditional isotropic processing approach. This illustrates that rock anisotropy contributes to the generation of the reflections from the deformation zones in the study area although they do not show significant density contrast with their surrounding rocks.

  • 8. Alcalde, J.
    et al.
    Martí, D.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Sopher, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Saura, E.
    Marzán, I.
    Ayarza, P.
    Calahorrano, A.
    Pérez-Estaún, A.
    Carbonell, R.
    3-D reflection seismic imaging of the Hontomin structure in the Basque-Cantabrian Basin (Spain)2013In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 4, no 2, p. 481-496Article in journal (Refereed)
    Abstract [en]

    The Basque-Cantabrian Basin of the northern Iberia Peninsula constitutes a unique example of a major deformation system, featuring a dome structure developed by extensional tectonics followed by compressional reactivation. The occurrence of natural resources in the area and the possibility of establishing a geological storage site for carbon dioxide motivated the acquisition of a 3-D seismic reflection survey in 2010, centered on the Jurassic Hontomin dome. The objectives of this survey were to obtain a geological model of the overall structure and to establish a baseline model for a possible geological CO2 storage site. The 36 km(2) survey included approximately 5000 mixed (Vibroseis and explosives) source points recorded with a 25 m inline source and receiver spacing. The target reservoir is a saline aquifer, at approximately 1450 m depth, encased and sealed by carbonate formations. Acquisition and processing parameters were influenced by the rough topography and relatively complex geology. A strong near-surface velocity inversion is evident in the data, affecting the quality of the data. The resulting 3-D image provides constraints on the key features of the geologic model. The Hontom n structure is interpreted to consist of an approximately 10(7) m(2) large elongated dome with two major (W-E and NW-SE) striking faults bounding it. Preliminary capacity estimates indicate that about 1.2 Gt of CO2 can be stored in the target reservoir.

  • 9.
    Andersson, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Almqvist, Bjarne S. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Burchardt, Steffi
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Troll, Valentin R.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Snowball, Ian
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Natural Resources and Sustainable Development.
    Kubler, Lutz
    Geol Survey Sweden, Uppsala, Sweden..
    Magma transport in sheet intrusions of the Alnö carbonatite complex, central Sweden2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 27635Article in journal (Refereed)
    Abstract [en]

    Magma transport through the Earth's crust occurs dominantly via sheet intrusions, such as dykes and cone-sheets, and is fundamental to crustal evolution, volcanic eruptions and geochemical element cycling. However, reliable methods to reconstruct flow direction in solidified sheet intrusions have proved elusive. Anisotropy of magnetic susceptibility (AMS) in magmatic sheets is often interpreted as primary magma flow, but magnetic fabrics can be modified by post-emplacement processes, making interpretation of AMS data ambiguous. Here we present AMS data from cone-sheets in the Alno carbonatite complex, central Sweden. We discuss six scenarios of syn- and post-emplacement processes that can modify AMS fabrics and offer a conceptual framework for systematic interpretation of magma movements in sheet intrusions. The AMS fabrics in the Alno cone-sheets are dominantly oblate with magnetic foliations parallel to sheet orientations. These fabrics may result from primary lateral flow or from sheet closure at the terminal stage of magma transport. As the cone-sheets are discontinuous along their strike direction, sheet closure is the most probable process to explain the observed AMS fabrics. We argue that these fabrics may be common to cone-sheets and an integrated geology, petrology and AMS approach can be used to distinguish them from primary flow fabrics.

  • 10.
    Andersson, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Troll, Valentin R.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Dehghannejad, Mahdieh
    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.
    Ask, Maria
    Carbonatite ring-complexes explained by caldera-style volcanism2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 1677-Article in journal (Refereed)
    Abstract [en]

    Carbonatites are rare, carbonate-rich magmatic rocks that make up a minute portion of the crust only, yet they are of great relevance for our understanding of crustal and mantle processes. Although they occur in all continents and from Archaean to present, the deeper plumbing system of carbonatite ring-complexes is usually poorly constrained. Here, we show that carbonatite ring-complexes can be explained by caldera-style volcanism. Our geophysical investigation of the Alno carbonatite ring-complex in central Sweden identifies a solidified saucer-shaped magma chamber at similar to 3 km depth that links to surface exposures through a ring fault system. Caldera subsidence during final stages of activity caused carbonatite eruptions north of the main complex, providing the crucial element to connect plutonic and eruptive features of carbonatite magmatism. The way carbonatite magmas are stored, transported and erupt at the surface is thus comparable to known emplacement styles from silicic calderas.

  • 11.
    Bastani, Mehrdad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Ismail, Nazli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hedjazi, Farhang
    KAHANROBA Co.
    Delineating hydrothermal stockwork copper deposits using controlled-source and radio-magnetotelluric methods:  A case study from northeast Iran2009In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 74, no 5, p. B167--B181Article in journal (Refereed)
    Abstract [en]

    Radio- and controlled-source-tensor magnetotelluric (RMT and CSTMT)   methods are used to target hydrothermal veins of copper mineralization.   The data were acquired along six eastwest- and three   north-south-trending profiles, covering an area of about 500 x 400   m(2). The tensor RMT data were collected in the 10-250-kHz frequency   band. A double horizontal magnetic dipole transmitter in the 4-12.5-kHz   frequency range allowed us to constrain the deeper parts of the   resistivity models better. To obtain optimum field parameters, ground   magnetic profiling was conducted prior to the RMT and CSTMT surveys.   Although the study area (in Iran) is remote, a number of radio   transmitters with acceptable signal-to-noise ratio were utilized. The   2D inversion of RMT data led to unstable resistivity models with large   data misfits. Thus, the RMT data were used to complement and analyze   the near-surface resistivity anomalies observed in the 2D CSTMT models.   Analyses of strike and dimensionality from the CSTMT data suggests that   the low-resistivity structures are mainly three dimensional; therefore,   2D inversion of determinant data is chosen. Independent 2D inversion   models of the determinant CSTMT data along crossing profiles are in   good agreement. Known copper mineralization is imaged well in the CSTMT   models. The thinning of the conductive overburden correlates very well   with magnetic highs, indicating the bedrock is resistive and magnetic.   In this sense, the magnetic and electromagnetic fields complement each   other. Analysis of the 2D resistivity models indicates the volcanic   rock deepens at the center of the study area. This zone is associated   with a magnetic low and therefore is recommended for detailed   exploration work.

  • 12.
    Bastani, Mehrdad
    et al.
    Geological Survey of Sweden.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Savvaidis, Alexandros
    ITSAK, Greece.
    Combined use of controlled-source and radio-magnetotelluric methods for near surface studies2015Conference paper (Refereed)
    Abstract [en]

    Combination of the controlled source and radio magnetotelluric, the so-called CSRMT, method has been used in modelling near surface electrical resistivity structures with the main aim of studying mineralization and engineering issues. In the controlled source mode, we used a remotely controlled double horizontal magnetic dipole that transmits signal in the frequency range 1-12.5 kHz. The signal sources for the RMT method are the distant radio transmitters in the frequency range 14-250 kHz. Three near surface case studies are presented in this work. In the first case, conductive hydrothermal stockwork copper deposits in an area in Iran were modelled in 2D and the results were compared to the existing borehole information. In the second case located in Greece using the CSRMT method we could model the location and geometry of a subvertical fault that was covered by conductive quaternary sediments. In the third case from Sweden, 3D resistivity models from the inversion of CSRMT data were used to determine presence and boundaries of quick-clay formation and a coarse-grained layer that is in turn responsible for a peculiar retrogressive landslide type in the study area. The three case studies have proven that a combination of controlled source and radio magnetotelluric methods has a considerable potential in addressing near surface problems. Comparison between the existing borehole data and the resistivity models from the inversion of the CSRMT data in each study area revealed reasonable correlation in delineating target structures especially depth to the good conductors. However, special attention needs to be given when using the CSMT data, especially at lower frequencies where they may be affected by the near-field phenomenon.

  • 13.
    Bastani, Mehrdad
    et al.
    SGU.
    Persson, Lena
    SGU.
    Mehta, Suman
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Boat-towed radio-magnetotellurics: A new technique and case study from the city of Stockholm2015In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 80, no 6, p. B193-B202Article in journal (Refereed)
    Abstract [en]

    We have developed a new data acquisition system and technique to measure the radio magnetotelluric (RMT) signals from distant radio transmitters with the objective of mapping and modeling electric resistivity structures below a river or lake. The acquisition system is towed by a boat; therefore, we call the technique boat-towed RMT. The data acquisition is fast with a production rate of approximately 1  km/hr using a nominal sampling spacing of 10–15 m. Given the ample number of radio transmitters available in most parts of the world, the method can be used for near-surface studies of various targets. We have developed boat-towed RMT measurements on Lake Mälaren near the city of Stockholm in Sweden to determine the feasibility of the method. Approximately 15 km of RMT data were collected during three days above a planned 60-m-deep bypass tunnel with the goal of providing information on the bedrock depth and possible weak zones within the bedrock. The measured resistivity and phase data were of high quality with errors on the order of a few percent. The resistivity models from 2D inversion of the data showed a good correlation with available geologic data in resolving bedrock depth and also resistivity layering within the lake. Resistivity maps derived from the dense 2D models suggested a northeast–southwest-striking low-resistivity zone at less than a 30-m depth. The zone likely represents fractured crystalline bedrock. The boat-towed RMT technique is well suited for water bodies with moderate electric resistivity such as in brackish and freshwater environments.

  • 14. Bellefleur, Gilles
    et al.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Mueller, Christof
    Elastic finite-difference modeling of volcanic-hosted massive sulfide deposits: A case study from Half Mile Lake, New Brunswick, Canada2012In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 77, no 5, p. WC25-WC36Article in journal (Refereed)
    Abstract [en]

    We present elastic finite-difference modeling results over a geologically realistic 2D representation of the Half Mile Lake volcanic-hosted massive sulfide deposit, New Brunswick, Canada. The model is constrained by geologic information from surface mapping and boreholes, whereas petrophysical properties are provided by wireline logging data acquired in two boreholes intersecting different parts of the deposit. We analyzed the P-P, P-S, S-P, and S-S responses of the lower and deep mineralized zones and assessed some compositional effects by substituting massive sulfides with gabbro properties in the model. Finite-difference modeling results predict complex scattering signature associated with the lower and deep sulfide zones. Both zones scattered back P-P, P-S, S-P, and S-S waves generally having strongest amplitudes in the stratigraphy down-dip direction. The P-S, S-P, and S-S scattered waves, if properly recorded on multicomponent data, represent useful signal that could help the targeting of deep sulfide mineralization. Finite-difference simulations further reveal phase-reversals on P-P wavefields scattered at the lower and deep zones. The phase reversals are not observed for gabbro inclusions, suggesting that this signature could be used to discriminate gabbro units from sulfide mineralization. The finite-difference simulation successfully reproduces many events of the VSP data, in particular P-S and S-S events on the radial component and P-P and S-P events on the vertical component. Comparison with 3D data is rather poor and only shows weak correlation with P-P events from the lower and deep zones. Despite the poor correlation, a prestack time migrated S-P section displays an amplitude anomaly at the location of the deep zone, suggesting that S-P waves were recorded on the 3D data, although this survey was acquired with explosive sources and vertical geophones.

  • 15.
    Bellefleur, Gilles
    et al.
    Geological Survey of Canada.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Müller, Christof
    GNS Science.
    A finite-difference modeling analysis of mode-converted scattering from massive sulfide deposits, Bathurst mining camp, Canada2012Conference paper (Refereed)
    Abstract [en]

    We present elastic finite-difference modeling results over a geologically realistic 2D representation of the Halfmile Lake volcanic-hosted massive sulfide deposit, New Brunswick, Canada. The model is constrained by geological information from surface mapping and boreholes whereas petrophysical properties are provided by wireline logging data acquired in two boreholes intersecting different parts of the deposit. We analyzed the P-P, P-S, S-P, and S-S responses of the Lower and Deep mineralized zones and assessed some compositional effects by substituting massive sulfides with gabbro properties in the model. Finite-difference modeling results predict complex scattering including P-P, P-S, S-P, and S-S waves generally having strongest amplitudes in the stratigraphy down-dip direction. The P-S, S-P, and S-S scattered waves if properly recorded on multi-component data, represent useful signal that could help the targeting of deep sulfide mineralization. Finite-difference simulations further reveal phase-reversals on P-P wavefields scattered at the massive sulfide zones. The phase reversals are not observed for gabbro inclusions, suggesting that this signature could be used to discriminate gabbro units from sulfide mineralization. The FD simulation successfully reproduces many events of the VSP data, in particular P-S and S-S events on the radial component and P-P and S-P events on the vertical component.

  • 16.
    Bellefleur, Gilles
    et al.
    Geological Survey of Canada.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Müller, Christof
    GNS Science.
    A finite-difference modeling analysis of mode-converted scattering from massive sulfidedeposits, Bathurst mining camp, Canada2012Conference paper (Refereed)
    Abstract [en]

    We present elastic finite-difference modeling results over ageologically realistic 2D representation of the HalfmileLake volcanic-hosted massive sulfide deposit, NewBrunswick, Canada. The model is constrained bygeological information from surface mapping andboreholes whereas petrophysical properties are provided bywireline logging data acquired in two boreholesintersecting different parts of the deposit. We analyzed theP-P, P-S, S-P, and S-S responses of the Lower and Deepmineralized zones and assessed some compositional effectsby substituting massive sulfides with gabbro properties inthe model. Finite-difference modeling results predictcomplex scattering including P-P, P-S, S-P, and S-S wavesgenerally having strongest amplitudes in the stratigraphydown-dip direction. The P-S, S-P, and S-S scattered waves,if properly recorded on multi-component data, representuseful signal that could help the targeting of deep sulfidemineralization. Finite-difference simulations further revealphase-reversals on P-P wavefields scattered at the massivesulfide zones. The phase reversals are not observed forgabbro inclusions, suggesting that this signature could beused to discriminate gabbro units from sulfidemineralization. The FD simulation successfully reproducesmany events of the VSP data, in particular P-S and S-Sevents on the radial component and P-P and S-P events onthe vertical component.

  • 17.
    Brodic, Bojan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bastani, Mehrdad
    Geological Survey of Sweden.
    Mehta, Suman
    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.
    Lundberg, Emil
    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.
    Multi-component digital-based seismic landstreamer and boat-towed radio-magnetotelluric acquisition systems for improved subsurface characterization in the urban environment2017In: First Break, ISSN 0263-5046, E-ISSN 1365-2397, Vol. 35, no 8, p. 41-47Article in journal (Other academic)
    Abstract [en]

    It is estimated that urban life will be the norm for around 60% of the world’s population by 2040, leading to a more centralized distribution of people and making the city as the main place of residence (Whiteley, 2009). This population centralization inherently implies rapidly expanding cities and imposes the need for more infrastructure within, around and between the present city boundaries. However, infrastructure projects nowadays have to follow strict civil engineering standards that require detailed knowledge of subsurface conditions during different stages of the construction processes. Since direct methods conventionally used for site characterization (e.g., drilling and/or core testing) are still relatively expensive the focus in the last two decades has been on non-invasive, geophysical methods. However, geophysical site characterization in urban areas is not an easy task owing to numerous challenges and various types of noise sources. Challenges such as electric/electromagnetic (EM) noise, pipelines and other subsurface objects (sometimes even unknown or undocumented), the inability to properly couple sensors because of pavement, traffic noises and limited space are common in urban environment. Since geophysical surveys need to be done with the least amount of disturbances to the environment, residents and traffic, new geophysical techniques for fast, non-invasive and high-resolution site characterization are needed. To overcome some of these challenges, a nationwide joint industry-academia project was launched in 2012 TUST GeoInfra, www.trust-geoinfra.se). As a component in the project, Uppsala University developed two new data acquisition systems. These are a fully digital MEMS-based (Micro-machined Electro-Mechanical Sensor) three component (3C) seismic landstreamer and a boat-towed radio-magnetotelluric (RMT) acquisition system. Both systems were specifically designed to address urban environments with the RMT system particularly aiming at efficient and cost-effective geophysical surveying on shallow-water bodies, which constitute 7% of Scandinavia. In this article, we will describe the two systems and present two case studies illustrating their potential. A number of published accounts are now available from the two systems showing what type of problems they can address (e.g., Bastani et al., 2015; Brodic et al., 2015; Malehmir et al., 2015a, 2015b, 2016a, 2016b, 2017; Dehghannejad et al., 2017; Maries et al., 2017; Mehta et al., 2017; Brodic et al., 2017).

  • 18.
    Brodic, Bojan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    All wave-modes converted and reflected from fracture systems: A tunnel-surface seismic experiment2015Manuscript (preprint) (Other academic)
  • 19.
    Brodic, Bojan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bedrock and Fracture Zone Delineation UsingDifferent Near-surface Seismic Sources2017Conference paper (Other academic)
    Abstract [en]

    To delineate the bedrock surface and a fracture zone intersected by a well at c. 50 m depth, a seismic survey wasconducted using four different near-surface seismic sources. These were a 5-kg sledgehammer, a metal I-beamhit laterally, an accelerated weight drop and a prototype source tested for the first time called Udarnik. TheUdarnik source has two hammers whose impacts are initiated by an electromagnetic force of the stable coilexciting its inner moving part. Two hammers separated by a distance of approximately 50 cm successively hittwo contact plates mounted on the bottom of the source. The sweep length is adjustable and maximum 18 hitscan be made per second. In this study, we compare the performance of every source used and present reflectionseismic sections and tomography results from the high-fold (star-type acquisition was used) combinedlandstreamer and wireless recorder survey. Preliminary results indicate that bedrock was well delineated both ontomography results and stacked sections for all sources and some weak reflectivity is observed where thefracture zone is expected with most of the sources used showing the potential of the seismic methods forfracture zone imaging and near-surface characterization

  • 20.
    Brodic, Bojan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Delineating fracture zones using surface-tunnel-surfaceseismic data, P-S, and S-P mode conversions2017In: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 122, no 7, p. 5493-5516Article in journal (Refereed)
    Abstract [en]

    A surface-tunnel-surface seismic experiment was conducted at the Äspö Hard Rock Laboratoryto study the seismic response of major fracture systems intersecting the tunnel. A newly developedthree-component microelectromechanical sensor-based seismic landstreamer was deployed inside the noisytunnel along with conventional seismic receivers. In addition to these, wireless recorders were placed on thesurface. This combination enabled simultaneous recording of the seismic wavefield both inside the tunneland on the surface. The landstreamer was positioned between two geophone-based line segments, alongthe interval where known fracture systems intersect the tunnel. First arrival tomography produced a velocitymodel of the rock mass between the tunnel and the surface with anomalous low-velocity zones correlatingwell with locations of known fracture systems. Prominent wave mode converted direct and reflected signals,P-S and S-P waves, were observed in numerous source gathers recorded inside the tunnel. Forward traveltime and 2-D finite difference elastic modeling, based on the known geometry of the fracture systems, showthat the converted waves are generated at these systems. Additionally, the landstreamer data were used toestimate Vp/Vs, Poisson’s ratio, and seismic attenuation factors (Qp and Qs) over fracture sets that havedifferent hydraulic conductivities. The low-conductivity fracture sets have greater reductions in P wavevelocities and Poisson’s ratio and are more attenuating than the highly hydraulically conductive fracture set.Our investigations contribute to fracture zone characterization on a scale corresponding to seismicexploration wavelengths.

  • 21.
    Brodic, Bojan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Dynesius, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bastani, Mehrdad
    Palm, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Multicomponent broadband digital-based seismic landstreamer for near-surface applications2015In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 123, p. 227-241Article in journal (Refereed)
    Abstract [en]

    During the last few decades there has been an increased demand for infrastructure, along with a greater awareness of environmental issues in the construction industry. These factors have contributed to an increased interest in using seismic methods for near surface characterization, particularly in urban environments. Seismic sensors not affected by anthropogenic electromagnetic noise are therefore important, as well as an acquisition system that is easy to deploy, move and non-invasive. To address some of these challenges, a multicomponent broadband MEMS (micro-electro mechanical system) based landstreamer system was developed. The landstreamer system is fully digital, therefore it is less sensitive to electrical or electromagnetic noise. Crosstalk, leakage and tilting tests show that the system is superior to its predecessors. The broadband nature of the sensors (theoretically 0–800 Hz), 3C (three-component) recording and the close spacing of the sensors enable high-resolution imaging. The current streamer configuration consists of 20 sensors 4 m apart and 80 sensors 2 m apart. The streamer can easily be combined with wireless recorders for simultaneous data acquisition. In this study, we present results from testing of the streamer with various sources, such as a shear wave vibrator and different types of impact sources. MEMS-sensors and their high sensitivity allowed recording clear reflections that were not observed with coil-based sensors. A complementary test was also carried out at a planned access ramp for an urban tunnel where potential poor quality rocks had been identified by drilling. First-break traveltime tomography showed that these poor quality rocks correlate with low velocity zones. The presented landstreamer system has great potential for characterizing the subsurface in noisy environments.

  • 22.
    Brodic, Bojan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Maries, Georgiana
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    SH- and Surface-wave Imaging Potential of a 3C-digital-based Seismic Landstreamer Illustrated at an Esker Site in SW Finland2017Conference paper (Other academic)
    Abstract [en]

    Within the last decade, multicomponent seismic imaging has proven to be beneficial in various areas ofapplications, from hydrocarbon to mineral exploration, as well as for environmental and infrastructure planninginvestigations. To demonstrate the potential and need for multicomponent seismic imaging for infrastructureplanning project, we show an example of a seismic profile acquired using a recently developed digital-based 3Cseismic landstreamer and a cost-effective drop-hammer seismic source for planning of wells for pumping water(aquifer recharge) at an esker site that supplies drinking water for the entire city of Turku, Finland. The studyillustrates the importance of 3C data recording and shows the potential of the landstreamer in imaging theshallow subsurface using both P- and SH-waves generated from the vertical impact source. Synthetic modeling,particle motion studies and surface-wave analysis of the data are used to scrutinize the data and investigate thenature of the signal and underlying physical properties of the subsurface.

  • 23.
    Buntin, Sebastian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malinowski, Michal
    Polish Academy of Sciences.
    Högdahl, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Thybo, Hans
    University of Copenhagen, Denmark.
    Buske, Stefan
    TUBAF, Germany.
    Seismic reprocessing of the BABEL lines for improved interpretation of the whole crust – preliminary results2016In: Lithosphere 2016: Ninth Symposium On Structure, Composition And Evolution Of The Lithosphere In Fennoscandia / [ed] Ilmo Kukkonen, Suvi Heinonen, Kati Oinonen, Katriina Arhe, Olav Eklund, Fredrik Karell, Elena Kozlovskaya, Arto Luttinen, Raimo Lahtinen, Juha Lunkka, Vesa Nykänen, Markku Poutanen , Eija Tanskanen and Timo Tiira, Helsinki, Finland: University of Helsinki, Institute of Seismology , 2016, p. 9-12Conference paper (Refereed)
    Abstract [en]

    This ongoing study focuses on the reprocessing of the historical BABEL (Baltic and Bothnian Echoes from the Lithosphere, 1989) seismic lines in the Bay of Bothnia in preparation for the acquisition of a 400 km long onshore reflection and refraction profile in central part of Sweden. The main aim of the project is to increase the understanding of the tectonic evolution of the mineral-rich Bergslagen region both offshore and onshore. The seismic data have been recovered and currently being reprocessed using up-to-date processing methods and preliminary results show promising outcome from this work.

  • 24.
    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)
  • 25.
    Cheraghi, Saeid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bellefleur, Gilles
    3D imaging challenges in steeply dipping mining structures: New lights on acquisition geometry and processing from the Brunswick no. 6 seismic data, Canada2012In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 77, no 5, p. WC109-WC122Article in journal (Refereed)
    Abstract [en]

    We have analyzed and processed a 38-km(2) nonorthogonal 3D surface reflection seismic data in the Brunswick no. 6 area to better understand the effect of acquisition geometry on the resultant image and to provide 3D information about the main geologic structures hosting the mineralization. The 3D data were processed using a conventional prestack dip moveout (DMO) and poststack migration algorithm with special focus on refraction static corrections, velocity analysis, and DMO corrections that are important for the data recorded in crystalline environment. However, the nonorthogonal nature of the 3D data combined with its narrow-azimuth, irregular offset distributions, and 2D nature of midpoint distribution in common depth point bins resulted in a lower quality seismic image than those observed on a series of 2D seismic profiles collected in the area prior to the 3D data acquisition. 2D wavenumber spectrum of the data suggests acquisition footprint associated with the data. Most of the noise associated with the acquisition footprint manifested itself as short-length, high-amplitude shallow reflections but largely were attenuated using a dip filter running in the wavenumber domain. Various bin size and geometries were tested, and the best result was obtained using rectangular bins aligned in the orientation of the shot lines. The processing results indicated that the highly prospective and mineralized Brunswick horizon is part of a continuous reflective package that could guide future deep mineral exploration in this mining camp.

  • 26.
    Cheraghi, Saeid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bellefleur, Gilles
    Geological Survey of Canada.
    Crustal-scale reflection seismic investigations in the Bathurst Mining Camp, New Brunswick, Canada2011In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 506, no 1-4, p. 55-72Article in journal (Refereed)
  • 27.
    Cheraghi, Saeid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bellefleur, Gilles
    Geological Survey of Canada.
    Reflection seismic investigations in the Brunswick no. 6 Mining area, Bathurst Mining Camp, Canada2010In: Society of Petroleum Engineers - 72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010 - Incorporating SPE EUROPEC 2010, Barcelona, 2010, Vol. 5, p. 3834-3838Conference paper (Refereed)
    Abstract [en]

    The Bathurst Mining Camp of northern New Brunswick, Canada is a major base-metal producing region that includes the super-giant Brunswick No. 12 and smaller size Brunswick No. 6 mines. Seismic reflection data along with borehole geochemical and petrophysical measurements from the Brunswick No. 6 mine are studied in this work. Acoustic impedance values for the Brunswick horizon and host rock structures indicate that the mineralized horizon is not strongly reflective in comparison with the mafic-ultramafic rocks. Although the data is acquired in crystalline environment, it shows an excellent data quality with a series of steeply dipping reflections imaged down to 3 s. The results demonstrate that reflection seismic imaging is particularly effective for imaging structures of the Brunswick No. 6 mine, many of which intersect the surface and thus allow for correlation with surface geology. Even more encouraging, the Brunswick horizon and associated iron mineralization are identifiable within a distinctive reflective package that can be used as a guide for deep base-metal exploration in the region.© 2010, Society of Petroleum Engineers.

  • 28.
    Cheraghi, Saeid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bellefleur, Gilles
    Geological Survey of Canada, Ottawa, Ontario-Canada.
    Bongajum, Emmanuel
    University of Alberta, Edmonton, Alberta, Canada.
    Bastani, Mehrdad
    Geological Survey of Sweden, Uppsala, Sweden.
    Scaling behavior and the effects of heterogeneity on shallow seismic imaging of mineral deposits: a case study from Brunswick No. 6 mining area, Canada2013In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 90, p. 1-18Article in journal (Refereed)
    Abstract [en]

    We have studied the scaling behavior of compressional-wave velocity and density logs from an exploration borehole that extends down to about 700 m depth in the Brunswick No. 6 mining area, Bathurst Mining Camp, Canada. Using statistical methods, vertical and horizontal scale lengths of heterogeneity were estimated. Vertical scale length estimates from the velocity, density and calculated acoustic impedance are 14 m, 33 m, and about 20 m, respectively. Although the estimated scale length for the acoustic impedance implies a weak scattering environment, elastic finite difference modeling of seismic wave propagation in 2D heterogeneous media demonstrates that even this weak scattering medium can mask seismic signals from small, but yet economically feasible, massive sulphide deposits. Further analysis of the synthetic seismic data suggests that in the presence of heterogeneity, lenticular-shaped targets may only exhibit incomplete diffraction signals whereby the down-dip tails of these diffractions are mainly visible on the stacked sections. Therefore, identification of orebody generated diffractions is much easier on the unmigrated stacked sections than on migrated stacked sections. The numerical seismic modeling in 2D heterogeneous media indicates that in the presence of large horizontal, but small vertical scale lengths (structural anisotropy), identification of massive sulphide deposits is possible, but their delineation at depth requires detailed velocity modeling and processing algorithms which can handle the anisotropy.

  • 29.
    Dehghannejad, M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Weihed, P.
    Luleå University of Technology.
    High-resolution reflection seismic imaging in the Kristineberg mining area, Northern Sweden2010In: Society of Petroleum Engineers - 72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010 - Incorporating SPE EUROPEC 2010, Barcelona: Curran Associates, Inc., 2010, Vol. 7, p. 5368-5371Conference paper (Refereed)
    Abstract [en]

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

  • 30.
    Dehghannejad, Mahdieh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bauer, Tobias E.
    Division of Geosciences, Luleå University of Technology, Sweden.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Weihed, Pär
    Division of Geosciences, Luleå University of Technology, Sweden.
    Crustal geometry of the central Skellefte district, northern Sweden – constraints from reflection seismic investigations2012In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 524, p. 87-99Article in journal (Refereed)
    Abstract [en]

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

  • 31.
    Dehghannejad, Mahdieh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    García Juanatey, María de los Ángeles
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Skytta, Pietari
    Bauer, Tobias E
    Weihed, Par
    Reflection seismic imaging in the Skellefte ore district, northern Sweden2013In: Mineral depostits for a high-tech world: Proceedings of the 12th SGA Biennial Meeting 2013, Uppsala: Sveriges Geologiska Undersökning , 2013, p. 126-129Conference paper (Refereed)
  • 32.
    Dehghannejad, Mahdieh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Skyttä, Pietari
    Division of Ore Geology, Luleå University of Technology, Luleå, Sweden.
    Weihed, Pär
    Division of Ore Geology, Luleå University of Technology, Luleå, Sweden.
    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 degrees-40 degrees. 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.

  • 33.
    Dehghannejad, Mahdieh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Skytta, Pietari
    Division of Ore Geology, Luleå University of Technology, Luleå, Sweden.
    3D constraints and finite-difference modeling of massive sulfide deposits: The Kristineberg seismic lines revisited, northern Sweden2012In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 77, no 5, p. WC69-WC79Article in journal (Refereed)
    Abstract [en]

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

  • 34. Ehsan, Siddique Akhtar
    et al.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Dehghannejad, Mandieh
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Re-processing and interpretation of 2D seismic data from the Kristineberg mining area, northern Sweden2012In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 80, p. 43-55Article in journal (Refereed)
    Abstract [en]

    The Kristineberg mining area in the western part of the Skellefte ore district, northern Sweden, contains the largest massive sulphide deposit in the district. In 2003, two parallel seismic lines, Profiles 1 and 5, each about 25 km long and about 8 km apart were acquired in the Kristineberg area. The initial processing results were successful in imaging the large-scale structures of the area down to 12 km of the crust, but resulted in relatively poor seismic image near the mine. In this paper, we re-processed the seismic data along Profile 1 that crosses the mine. The main objective was to improve the seismic section near the mine for further correlation with new seismic data recently acquired in the area. The crooked-line acquisition geometry, very low fold coverage of less than 17, complex geology and sparse outcrops in the area made the data re-processing and interpretation challenging. Despite these challenges, significant improvement is observed in the seismic data, in terms of event continuity and resolution. Refraction static corrections allowed high frequencies to be retained, which improved the seismic section. The refraction static solution was manually checked and adjusted at every iteration to avoid unstable solutions. 3D visualization of the re-processed data with other seismic profiles recently acquired in the area allowed the seismic reflections to be correlated. The majority of the reflections are interpreted to originate from either fault zones or lithological contacts. A very shallow reflection correlates well with the location of the Kristineberg mineralized horizon.

  • 35.
    Eklöf, Sara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Högdahl, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Jonsson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Sveriges Geologiska Undersökning.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Michael, Setter
    Nordic Iron Ore.
    Towards a structural framework for apatite-iron oxide deposits in the Grängesberg-Blötberget area, Bergslagen, Sweden2016Conference paper (Refereed)
  • 36.
    Garcia Juanatey, Maria de los Angeles
    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.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tryggavson, Ari
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Integrated MagnetoTelluric and seismic reflection study: Skellefte Ore District, northern Sweden2011Conference paper (Refereed)
    Abstract [en]

    The Skellefte District is a very rich mining area in northern Sweden. The main deposits consist of volcanic-hosted massive sulphides VHMS rich in zinc, copper, lead, gold and silver. Since the area has been mined and explored for over a century, today's challenge is to locate deeper deposits. The VINNOVA 4D modeling project aims to address this challenge by understanding the regional setting of the district and its evolution over time. © 2011 Society of Exploration Geophysicists.

  • 37.
    Hedin, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Gee, David G.
    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.
    Dyrelius, Dan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    3D interpretation by integrating seismic and potential field data in the vicinity of the proposed COSC-1 drill site, central Swedish Caledonides2014In: Geological Society Special Report, ISSN 0309-670X, Vol. 390, p. 301-319Article in journal (Refereed)
    Abstract [en]

    The scientific drilling project COSC (Collisional Orogeny in the Scandinavian Caledonides), designed to study key questions concerning orogenic processes, aims to drill two fully cored boreholes to depths of c. 2.5 km each at carefully selected locations in west-central Sweden. The first of these, COSC-1, is scheduled for start late spring 2014 and will target the Seve Nappe Complex, characterized by inverted metamorphism and with parts that have evidently been subjected to hot ductile extrusion. In this study available seismic sections have been combined with surface geology to produce a 3D interpretation of the tectonic structures in the vicinity of the COSC-1 borehole. Constrained 3D inverse gravity modelling over the same area supports the interpretation, and the high-density Seve Nappe Complex stands out clearly in the model. Interpretation and models show that the maximum depth extent of the Seve Nappe Complex is less than 2.5 km, consistent with reflection seismic data. The gravity modelling also requires underlying units to comprise low-density material, consistent with the Lower Allochthon, but the modelling is unable to discern the décollement separating the allochthons from the crystalline Precambrian basement.

  • 38.
    Hedin, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Gee, David
    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.
    Dan, Dyrelius
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    COSC Geophysical and Geological Site Investigations2013Conference paper (Refereed)
    Abstract [en]

    Drilling of the first borehole, about 2.5 km deep, for the continental scientific deep drilling project COSC(Collisional Orogeny in the Scandinavian Caledonides) is scheduled to begin in the summer of 2013. Herewe present the project, a 3D interpretation of seismic data, combined with surface geology and potentialfield data, used for locating the most suitable drill site and planning of the drilling. An evaluation of theseismic interpretations by constrained 3D inverse modeling of potential field data shows a good fit toobserved data, further supporting the choice of the drill site.

  • 39.
    Hübert, Juliane
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    García Juanatey, María de los Ángeles
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    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.
    The upper crustal 3-D resistivity structure of the Kristineberg area, Skellefte district, northern Sweden revealed by magnetotelluric data2013In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 192, no 2, p. 500-513Article in journal (Refereed)
    Abstract [en]

    A 3-D model of the crustal electrical resistivity was constructed from the inversion of magnetotelluric data in the Kristineberg area, Skellefte district, the location of one of Sweden's most successful mining activities. Forward modelling of vertical magnetic transfer data supports our model which was derived from the magnetotelluric impedance only. The dominant features in the 3-D model are the strong conductors at various depth levels and resistive bodies of variable thickness occurring in the shallower subsurface. The deepest conductor, previously associated with the Skellefte crustal conductivity anomaly, is imaged in the southern part of the area as a north-dipping feature starting at similar to 4 km depth. Several shallow conductors are attributed to graphite in the black shales defining the contact between the metasedimentary rocks and the underlying metavolcanic rocks. Furthermore, an elongated intermediate depth conductor is possibly associated with alteration zones in the metavolcanic rocks that host the ore occurrences. The most prominent crustal resistors occur in the southern and northern part of the area, where their lateral extent on the surface coincides with the late-orogenic Revsund type intrusions. To the east, a resistive feature can be correlated to the early-orogenic Viterliden intrusion. The 3-D model is compared with two previous 2-D inversion models along two perpendicular profiles. The main electrical features are confirmed with the new model and previous uncertainties regarding 3-D effects, caused by off-profile conductors, can be better assessed in 3-D, although the resolution is lower due to a coarser model discretization. The comparison with seismic sections along two north-south profiles reveals structural correspondence between electrical features, zones of different reflectivity and geological units.

  • 40.
    Hübert, Juliane
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Smirnov, Maxim
    Oulu University, Finland.
    Tryggvason, 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.
    MT measurements in the western part of the Paleoproterozoic Skellefte Ore District, Northern Sweden: a contribution to an integrated geophysical study2009In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 475, no 3-4, p. 493-502Article in journal (Refereed)
    Abstract [en]

    A 2D conductivity model of the Kristineberg area in the Skellefte Ore District, Northern Sweden, has been derived from new magnetotelluric measurements. This complements an intensive geophysical and geological study of the area, including reflection seismics, gravity and aeromagnetic data modeling as well as geological field observations. In a pilot study, 20 broadband MT stations were installed in May 2007 along a 20 km long north–south profile. Dimensionality analysis shows that a 2D interpretation of the data is justified, although the presumed geoelectric strike direction of N75°E is not consistent over the whole profile. The new conductivity model of the upper crust agrees well with the results from the seismic studies. Interpreting both independent data sets confirms the major features from the previous model, such as the thickness of the Revsund granites in the south, the existence of a structural basement with metasedimentary origin, and gives new insight into the nature of the volcanic rocks and their possible mineral content.

  • 41.
    Juhlin, Christopher
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Dehghannejad, Mahdieh
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pratt, Gerhard
    Reflection seismic imaging of the end-glacial Pärvie Fault system, northern Sweden2010In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 70, no 4, p. 307-316Article in journal (Refereed)
    Abstract [en]

    Reflection seismic data were acquired along a c. 23 km long profile over the Pärvie Fault system with a nominal receiver and source spacing of 20 m. An hydraulic breaking hammer was used as a source, generating signals with a penetration depth of about 5–6 km. Steeply dipping reflections from the end-glacial faults are observed, as well as sub-horizontal reflections. The location and orientation of the reflections from the faults agree well with surface geological observations of fault geometries. Reflections from a potential fourth end-glacial fault is observed further to the east along the profile. The more sub-horizontal reflections may originate from gabbroic bodies within the granitic basement or from deeper lying greenstones. Our results indicate that the end-glacial faults dip at moderate to steep dips down to at least 2–3 km depth, and possibly continue at this dip to depths of 6 km. This result has significant implications for determining the state of stress required to activate the faults in the past and in the future.

  • 42.
    Junno, Niina
    et al.
    University of Helsinki.
    Koivisto, Emilia A
    University of Helsinki.
    Kukkonen, Ilmo
    University of Helsinki.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Wijns, Christopher
    First Quantum Minerals Ltd., Australia.
    Data mining to discover the causes of internal reflectivity within the Ni-Cu-PGE-bearing Kevitsa intrusion2016In: / [ed] Geological Survey of Finland, Helsinki, Finland: University of Helsinki, 2016, p. 43-46Conference paper (Refereed)
    Abstract [en]

    The Kevitsa Ni-Cu-PGE disseminated sulphide deposit is hosted by the Kevitsa mafic to ultramafic intrusion, located within the Central Lapland Greenstone Belt in northern Finland. A 3D seismic reflection survey was conducted in Kevitsa in 2010 for mine planning and deep mineral exploration purposes. Within the Kevitsa resource area, the 3D seismic data are characterized by laterally continuous reflections. Here we use data mining, namely Self-Organizing Map (SOM), analysis to better understand the possible causes of reflectivity within the Kevitsa intrusion. The results show that the mineralized zones within the intrusion could be potential causes of reflectivity, and hence could set potential exploration targets in the area.

  • 43.
    Kammann, J.
    et al.
    University of Copenhagen.
    Bækgaard, J.
    University of Copenhagen.
    Albrechtsen, C.
    University of Copenhagen.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Nielsen, Lars
    University of Copenhagen.
    Seismic Shear-wave Acquisition Parameters for Characterization of Chalk Reservoir Analogues2017Conference paper (Refereed)
    Abstract [en]

    Inclusion of shear-wave seismic studies in the characterization of reservoir analogues has a great potential to provide a more detailed understanding of changes in petrophysical properties and their direct impact on the seismic reflectivity. Presented in this study are mainly shear-wave shot records to illustrate the data quality and difficulties that can occur during acquisition, from two field sites in Denmark: (1) Stevns Klint, southeast Denmark,with numerous supplementary data and outcrops at a nearby cliff profiles and quarry walls. At Stevns Klint a 500 m long shear-wave data set was already acquired. (2) The Rørdal chalk quarry in Aalborg, northern Denmark, which offers the opportunity to sample plugs horizontally and vertically with a very close tie planned high-resolution seismic profiles. Stevns and Rørdal are characterized by different acquisition conditions. While measurements at Stevns were carried out on an asphalt road, Rørdal gives the opportunity to measure directly on the chalk surface. However, we show through examples how excavating machines in Rørdal can produce reflections similar to the ones produced by the source signal and, therefore, preclude data acquisition during ongoing quarrying. 

  • 44. Karimpouli, Sadegh
    et al.
    Hassani, Hossein
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Nabi-Bidhendi, Majid
    Khoshdel, Hossein
    Understanding the fracture role on hydrocarbon accumulation and distribution using seismic data: A case study on a carbonate reservoir from Iran2013In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 96, p. 98-106Article in journal (Refereed)
    Abstract [en]

    The South Pars, the largest gas field in the world, is located in the Persian Gulf. Structurally, the field is part of the Qatar-South Pars arch which is a regional anticline considered as a basement-cored structure with long lasting passive folding induced by salt withdrawal. The gas-bearing reservoir belongs to Kangan and Dalan formations dominated by carbonate rocks. The fracture role is still unknown in gas accumulation and distribution in this reservoir. In this paper, the Scattering Index (SI) and the semblance methods based on scattered waves and diffraction signal studies, respectively, were used to delineate the fracture locations. To find the relation between fractures and gas distribution, desired facies containing the gas, were defined and predicted using a method based on Bayesian facies estimation. The analysis and combination of these results suggest that preference of fractures and/or fractured zones are negligible (about 1% of the total volume studied in this paper) and, therefore, it is hard to conceive that they play an important role in this reservoir. Moreover, fractures have no considerable role in gas distribution (less than 30%). It can be concluded from this study that sedimentary processes such as digenetic, primary porosities and secondary porosities are responsible for the gas accumulation and distribution in this reservoir.

  • 45. Karimpouli, Sadegh
    et al.
    Hassani, Hossein
    Nabi-Bidhendi, Majid
    Khoshdel, Hossein
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Application of probabilistic facies prediction and estimation of rock physics parameters in a carbonate reservoir from Iran2013In: Journal of Geophysics and Engineering, ISSN 1742-2132, E-ISSN 1742-2140, Vol. 10, no 1, p. 015008-Article in journal (Refereed)
    Abstract [en]

    In this study, a carbonate field from Iran was studied. Estimation of rock properties such as porosity and permeability is much more challenging in carbonate rocks than sandstone rocks because of their strong heterogeneity. The frame flexibility factor (gamma) is a rock physics parameter which is related not only to pore structure variation but also to solid/pore connectivity and rock texture in carbonate reservoirs. We used porosity, frame flexibility factor and bulk modulus of fluid as the proper parameters to study this gas carbonate reservoir. According to rock physics parameters, three facies were defined: favourable and unfavourable facies and then a transition facies located between these two end members. To capture both the inversion solution and associated uncertainty, a complete implementation of the Bayesian inversion of the facies from pre-stack seismic data was applied to well data and validated with data from another well. Finally, this method was applied on a 2D seismic section and, in addition to inversion of petrophysical parameters, the high probability distribution of favorable facies was also obtained.

  • 46. Karimpouli, Sadegh
    et al.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Neuro-Bayesian facies inversion of prestack seismic data from a carbonate reservoir in Iran2015In: Journal of Petroleum Science and Engineering, ISSN 0920-4105, E-ISSN 1873-4715, Vol. 131, p. 11-17Article in journal (Refereed)
    Abstract [en]

    Facies study is a powerful tool to better understand complexities of carbonate reservoirs. Porosity, frame flexibility factor and bulk modulus of fluid are believed to be the most proper rock physical parameters to define desired facies in carbonate rocks. Bayesian inversion is a natural choice to invert the desired facies from seismic data. The inversion method then often includes (1) Bayesian inversion of elastic parameters from seismic data, (2) Bayesian inversion of rock physical parameters from elastic parameters by considering an appropriate up-scaling method and (3) Bayesian classification of fades from inverted rock physical parameters. Neuro-Bayesian inversion method has been introduced in this study, which is a combination of an artificial neural network (ANN) classifier and Bayesian inversion of rock physical parameters that allows an improved facies prediction. Comparison between Bayesian and neuro-Bayesian methods is performed to illustrate the accuracy of predicting the facies, improved from 67% to 73% in the final results. Moreover, the Bayesian method predicted just two of the three fades where Neuro-Bayesian method predicted all the three facies successfully.

  • 47. Karimpouli, Sadegh
    et al.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hassani, Hossein
    Khoshdel, Hossein
    Nabi-Bidhendi, Majid
    Automated diffraction delineation using an apex-shifted Radon transform2015In: Journal of Geophysics and Engineering, ISSN 1742-2132, E-ISSN 1742-2140, Vol. 12, no 2, p. 199-209Article in journal (Refereed)
    Abstract [en]

    Diffraction arrivals are important data that have increasingly been used to delineate the sources of diffractors and to explore subsurface discontinuities. In prestack data, diffractions are both zero- and non-zero offset hyperbolas while reflections are only zero-offset hyperbolas. An iterative algorithm using an apex-shifted Radon transform (ASRT) approach is presented in this paper that uses the diffraction hyperbolic trajectory similar to that of prestack time migration in order to locate diffractors and to estimate their corresponding background velocities. Because diffraction energy is generally weak in seismic data and particularly in prestack data, noise attenuation and edge enhancement methods are applied on the instantaneous phase of the seismic data instead of the amplitude data. This means that the phase data are input to the ASRT algorithm. The method is then tested on two synthetic datasets (a point-diffraction model with randomly distributed diffractors and the 2D BP/SEG salt model) and one real data example. Results show that this method can locate the diffractors reasonably well on the rough surfaces of the salt dome and the discontinuities associated with structures such as paleo-channels and faults. Our analysis of the estimated velocities suggests that they are generally valid for diffraction delineation; however, the accuracy of the estimation decreases as background velocity and depth increase.

  • 48.
    Kashubin, A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, C.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Luth, S.
    GFZ, Potsdam.
    Ivanova, A.
    GFZ, Potsdam.
    Juhojuntti, N.
    Geological Survey of Sweden.
    A footprint of rainfall on land seismic data repeatability at the CO2 storage pilot site, Ketzin, Germany2011Other (Other academic)
    Abstract [en]

    Two vintages of land time-lapse seismic data were acquired in 2005 and in 2009 at the Ketzin CO2 storage site in Germany. The datasets showed some differences in frequency content, signal-to-noise ratio and refraction statics despite that they were acquired with the same equipment and during the same seasons. The spatial variations in the data appeared to show good correlation with the difference in precipitation during the campaigns. These observations provide a ground for estimation of spatially varying operators that may be used in pre-stack or post-stack cross-equalization corrections of the time-lapse datasets. © 2011 Society of Exploration Geophysicists.

  • 49. 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.

  • 50. Koivisto, Emilia
    et al.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Heikkinen, Pekka
    Heinonen, Suvi
    Kukkonen, Ilmo
    2D reflection seismic investigations at the Kevitsa Ni-Cu-PGE deposit, northern Finland2012In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 77, no 5, p. WC149-WC162Article in journal (Refereed)
    Abstract [en]

    In 2007, a 2D reflection seismic survey was conducted at the Kevitsa Ni-Cu-PGE (platinum group elements) deposit in northern Finland. The aims of the survey were to delineate the overall extent of the ore-bearing Kevitsa ultramafic intrusive complex, to study the seismic response of the disseminated ore deposit, to potentially find indications for new ore deposits, and to extract structural information at depth that may be associated with mineralization. In the processing sequence, specific focus was given to finding optimal CDP-line geometries for the crooked-line survey profiles and, due to highly variable bedrock velocities, to detailed velocity analysis. Our conventional processing sequence, involving prestack DMO corrections followed by poststack migration, resulted in high-quality images of the subsurface. First, the data were used to establish the shape and extent of the Kevitsa intrusion, thus providing an overall framework for future exploration in the area. In particular, the data suggest deeper, up to about 1.5 km depth, continuation of the intrusion than previously thought. Furthermore, the images reveal variable reflectivity characteristics within the intrusion from nonreflective to internally reflective. The Kevitsa deposit is located within a part of the intrusion which is associated with distinct, gently dipping reflectivity fabric down to a depth of about 1 km, spatially constrained within a restricted zone internal to the intrusion. This zone can be used as a guideline for the near-mine exploration efforts, and the reflectivity is dominantly associated with magmatic layering controlling the extent of the bulk of economic mineralization. The seismic data also reveal a complex pattern of faults, in particular a series of major fault and shear zones bracketing and crosscutting the Kevitsa intrusion as a whole. Additionally, our interpretation of the data indicates a possible shared origin of the Kevitsa intrusion and the nearby Satovaara intrusion.

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