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Publications (10 of 122) Show all publications
Muhamad, H., Juhlin, C., Malehmir, A. & Sopher, D. (2018). Integrated interpretation of geophysical data of the Paleozoic structure in the northwestern part of the Siljan Ring impact crater, central Sweden. Journal of Applied Geophysics, 148, 201-215
Open this publication in new window or tab >>Integrated interpretation of geophysical data of the Paleozoic structure in the northwestern part of the Siljan Ring impact crater, central Sweden
2018 (English)In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 148, p. 201-215Article in journal (Refereed) Published
Abstract [en]

The Siljan Ring impact structure is the largest known impact structure in Europe and is Late Devonian in age. It contains a central uplift that is about 20-30 km in diameter and is surrounded by a ring-shaped depression. The Siljan area is one of the few areas in Sweden where the Paleozoic sequence has not been completely eroded, making it an important location for investigation of the geological and tectonic history of Baltica during the Paleozoic. The Paleozoic strata in this area also provide insight into the complex deformation processes associated with the impact. In this study we focus on the northwestern part of the Siljan Ring, close to the town of Orsa, with the main objective of characterizing the subsurface Paleozoic succession and uppermost Precambrian crystalline rocks along a series of seismic reflection profiles, some of which have not previously been published. We combine these seismic data with gravity and magnetic data and seismic traveltime tomography results to produce an integrated interpretation of the subsurface in the area. Our interpretation shows that the Paleozoic sequence in this area is of a relatively constant thickness, with a total thickness typically between 300 and 500 m. Faulting appears to be predominantly extensional, which we interpret to have occurred during the modification stage of the impact. Furthermore, based on the geophysical data in this area, we interpret that the impact related deformation to differ in magnitude and style from other parts of the Siljan Ring.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-311546 (URN)10.1016/j.jappgeo.2017.10.001 (DOI)000424171900019 ()
Available from: 2016-12-28 Created: 2016-12-28 Last updated: 2018-03-28Bibliographically approved
Brodic, B., Malehmir, A. & Juhlin, C. (2017). Bedrock and Fracture Zone Delineation UsingDifferent Near-surface Seismic Sources. In: : . Paper presented at Near Surface Geoscience 3-7 September 2017, Malmö, Sweden. Amsterdam, Netherlands: European Association of Geoscientists and Engineers (EAGE)
Open this publication in new window or tab >>Bedrock and Fracture Zone Delineation UsingDifferent Near-surface Seismic Sources
2017 (English)Conference paper, Published 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

Place, publisher, year, edition, pages
Amsterdam, Netherlands: European Association of Geoscientists and Engineers (EAGE), 2017
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-327950 (URN)10.3997/2214-4609.201702068 (DOI)
Conference
Near Surface Geoscience 3-7 September 2017, Malmö, Sweden
Projects
TRUST Geoinfra
Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2017-08-22Bibliographically approved
Wang, S., Bastani, M., Kalscheuer, T., Malehmir, A. & Dynesius, L. (2017). Controlled Source Boat-towed Radio-magnetotellurics for Site Investigation at Äspö Hard Rock Laboratory, Southeastern Sweden. In: : . Paper presented at 79th EAGE Conference and Exhibition, 12–15 June 2017, Paris, France (pp. 1-5).
Open this publication in new window or tab >>Controlled Source Boat-towed Radio-magnetotellurics for Site Investigation at Äspö Hard Rock Laboratory, Southeastern Sweden
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2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The radio-magnetotelluric (RMT) method has traditionally been used for land investigations. However, with the development of the boat-towed RMT system, this method is used on shallow water. The lowest frequency of the RMT method is about 14 kHz and in addition water resistivity is quite low in some cases, therefore controlled source measurements is naturally considered for data acquisition. In order to resolve a fracture zone under a brackish water body, the controlled source boat-towed RMT (CSRMT) approach was tested. CSRMT and RMT one-dimensional inversions were carried out separately to analyze galvanic distortions and source effects in our dataset. Serious distortions observed in both inversions as well as the two-dimensional (2D) structure observed in our previous study made us consider 2D inversion for modeling the data. Due to the sufficiently large distance between transmitter and receivers, the CSRMT data were inverted using a 2D inversion code originally designed for plane-wave RMT data. Occam and damped Occam schemes were used in our 2D inversions for CSRMT and RMT data. The results show that CSRMT can better resolve the fracture zone than RMT. This study further illustrates the use of the boat-towed RMT system and particularly when combined with controlled source.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-325421 (URN)10.3997/2214-4609.201700565 (DOI)
Conference
79th EAGE Conference and Exhibition, 12–15 June 2017, Paris, France
Available from: 2017-06-23 Created: 2017-06-23 Last updated: 2018-06-04Bibliographically approved
Mehta, S., Bastani, M., Malehmir, A. & Pedersen, L. B. (2017). CSRMT Survey on Frozen Lake - A New Technique with an Example from the Stockholm Bypass Tunnel. In: : . Paper presented at 23rd European Meeting of Environmental and Engineering Geophysics, 3-7 September 2017, Malmö, Sweden.
Open this publication in new window or tab >>CSRMT Survey on Frozen Lake - A New Technique with an Example from the Stockholm Bypass Tunnel
2017 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

More than 7% of the Scandinavian landmass is covered with fresh-water bodies in the form of lakes and rivers. This poses a unique challenge to carry out electromagnetic survey on shallow-water bodies for various purposes for example geotechnical investigations. Recently boat-towed RMT (radio-magnetotelluric) technique was introduced and used for measurements over the Lake Mälaren in Stockholm, Sweden. The RMT covers a wide range of frequencies (10-250 kHz) and provides good resolution for shallow subsurface studies although it lacks resolution at greater depths. Using controlled-source frequencies in the range of 1-10 kHz sufficient penetration depths can be achieved for most of the near surface targets. In this study, we present the results from the combined use of controlled-source and RMT (CSRMT) data that were obtained over frozen Lake Mälaren. The objective of this study was to map bedrock surface and fractures in the middle of the profile where using only RMT data these were not adequate. We demonstrate a new technique where CSRMT surveys were carried out over frozen-shallow-water bodies and we expect the idea to be used in the near future for other applications where moderately-resistive water bodies are present. 

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-328045 (URN)10.3997/2214-4609.201702056 (DOI)
Conference
23rd European Meeting of Environmental and Engineering Geophysics, 3-7 September 2017, Malmö, Sweden
Funder
Swedish Research Council Formas, 25220121907
Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2017-08-22Bibliographically approved
Malehmir, A., Maries, G., Bäckström, E., Schon, M. & Marsden, P. (2017). Deep Targeting an Iron-Oxide Ore Body Using a Seismic Landstreamer and a 500-Kg Drop Hammer Source. In: : . Paper presented at 79th EAGE Conference and Exhibition 2017.
Open this publication in new window or tab >>Deep Targeting an Iron-Oxide Ore Body Using a Seismic Landstreamer and a 500-Kg Drop Hammer Source
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2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

In a pilot study, a known down to ca. 850 m deep mineralized iron-oxide zone was targeted in the historical Blötberget-Ludvika mining area of central Sweden using a MEMS-based, 240 m long, comprising of 100 sensors landstreamer (2-4 m spacing) and combined with 74 wireless recorders (mixed 10 Hz and MEMs, 10 m spacing). A Bobcat-mounted drop hammer, 500 kg, was used to generate the seismic signal. Within 4 days, about 3.5 km of seismic data using 2-10 m source and receiver spacing were acquired. At each source location 3 records were made and stacked vertically to improve the signal-to-noise ratio. The streamer moved 9 times, each time 200 m forward, and wireless recorders were kept at both ends of the profile, moved once, to provide long offsets in the data. While in a swampy and challenging near-surface environment, reflection data processing results clearly image the mineralization as a set of strong high amplitude reflections and likely slightly extending beyond the known depth. This is encouraging and suggests such a cost-effective exploration method can be used in the area to delineate deep deposits and their depth and lateral extents.  

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-326271 (URN)10.3997/2214-4609.201701416 (DOI)
Conference
79th EAGE Conference and Exhibition 2017
Projects
ERAMIN1-StartGeoDelineation
Funder
VINNOVA, 2014-06238
Available from: 2017-07-04 Created: 2017-07-04 Last updated: 2017-07-11Bibliographically approved
Brodic, B., Malehmir, A. & Juhlin, C. (2017). Delineating fracture zones using surface-tunnel-surfaceseismic data, P-S, and S-P mode conversions. Journal of Geophysical Research - Solid Earth, 122(7), 5493-5516
Open this publication in new window or tab >>Delineating fracture zones using surface-tunnel-surfaceseismic data, P-S, and S-P mode conversions
2017 (English)In: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 122, no 7, p. 5493-5516Article in journal (Refereed) Published
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.

National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-327949 (URN)10.1002/2017JB014304 (DOI)000409366700040 ()
Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2017-12-20Bibliographically approved
Malehmir, A., Maries, G., Bäckstrom, E., Schön, M. & Marsden, P. (2017). Developing cost-effective seismic mineral exploration methods using a landstreamer and a drophammer. Scientific Reports, 7, Article ID 10325.
Open this publication in new window or tab >>Developing cost-effective seismic mineral exploration methods using a landstreamer and a drophammer
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2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 10325Article in journal (Refereed) Published
Abstract [en]

To be fully embraced into mineral exploration, seismic data require to be acquired fast, cheaper and with minimum environmental impacts addressing also the often brown-field highly noisy environment where these surveys are employed. Since 2013 and through a number of case studies, we have been testing a newly developed for urban environment, digital-based 240 m long, seismic landstreamer for mine planning and mineral exploration purposes. Here, we present a pilot study examining the potential of the streamer for deep targeting a known, down to approximately 850 m depth, iron-oxide mineralization in the Bergslagen mineral district of central Sweden. Combined streamer (100-3C-MEMS (micro-electromechanical system), 2-4 m spacing) and 75 wireless recorders (mixed 10 Hz and MEMS, 10 m spacing) were used. A Bobcat-mounted drophammer,500 kg, was used to generate the seismic signal. Within 4 days, approximately 3.5 km of seismic data using 2-10 m source and receiver spacing were acquired. Reflection data processing results clearly image the mineralization as a set of strong high-amplitude reflections and likely slightly extending beyond the known 850 m depth. This is encouraging and suggests such a cost-effective exploration method can be used in the area and elsewhere to delineate similar depth range iron-oxide deposits.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2017
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-335402 (URN)10.1038/s41598-017-10451-6 (DOI)000408997700024 ()28871161 (PubMedID)
Funder
VINNOVA, 2014-06238
Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2017-12-05Bibliographically approved
Malehmir, A., Maries, G., Backstrom, E., Schon, M. & Marsden, P. (2017). Developing cost-effective seismic mineral exploration methods using a landstreamer and a drophammer. Scientific Reports, 7, Article ID 10325.
Open this publication in new window or tab >>Developing cost-effective seismic mineral exploration methods using a landstreamer and a drophammer
Show others...
2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 10325Article in journal (Refereed) Published
Abstract [en]

To be fully embraced into mineral exploration, seismic data require to be acquired fast, cheaper and with minimum environmental impacts addressing also the often brown-field highly noisy environment where these surveys are employed. Since 2013 and through a number of case studies, we have been testing a newly developed for urban environment, digital-based 240 m long, seismic landstreamer for mine planning and mineral exploration purposes. Here, we present a pilot study examining the potential of the streamer for deep targeting a known, down to approximately 850 m depth, iron-oxide mineralization in the Bergslagen mineral district of central Sweden. Combined streamer (100-3C-MEMS (micro-electromechanical system), 2-4 m spacing) and 75 wireless recorders (mixed 10 Hz and MEMS, 10 m spacing) were used. A Bobcat-mounted drophammer,500 kg, was used to generate the seismic signal. Within 4 days, approximately 3.5 km of seismic data using 2-10 m source and receiver spacing were acquired. Reflection data processing results clearly image the mineralization as a set of strong high-amplitude reflections and likely slightly extending beyond the known 850 m depth. This is encouraging and suggests such a cost-effective exploration method can be used in the area and elsewhere to delineate similar depth range iron-oxide deposits.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-334400 (URN)10.1038/s41598-017-10451-6 (DOI)000408997700024 ()
Funder
VINNOVA
Available from: 2017-12-08 Created: 2017-12-08 Last updated: 2017-12-08Bibliographically approved
Maries, G., Malehmir, A., Backström, E., Schön, M. & Marsden, P. (2017). Downhole physical property logging for iron-oxide exploration, rock quality, and mining: An example from central Sweden. Ore Geology Reviews, 90, 1-13
Open this publication in new window or tab >>Downhole physical property logging for iron-oxide exploration, rock quality, and mining: An example from central Sweden
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2017 (English)In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 90, p. 1-13Article in journal (Refereed) Published
Abstract [en]

Several physical properties obtained from geophysical logging and laboratory measurements were analyzed in order to characterize iron-oxide mineralization and host rocks in the Blotberget mining area of central Sweden. Seven boreholes intersecting the mineralization between 300 and 600 m depth in a volcano-sedimentary setting were downhole logged for this purpose. The downhole logging included full-waveform triple sonic, natural gamma, magnetic susceptibility, formation resistivity, fluid temperature and conductivity while laboratory measurements consisted of density, rock quality designation and magnetite content measurements. Full-waveform sonic data were used for rock quality assessments of the mineralized zones and their host rocks and proved their potential to be used for mine planning purposes. The ore-bearing rocks are primarily distinguished by increased density and dynamic elastic moduli estimated from the full-waveform sonic logging. Although seismic velocities do not follow a linear increase with the density for the mineralized rocks, as expected for igneous rocks, it is observed that a strong seismic signal from the mineralization can be expected primarily due to their high density. In addition, the full-waveform sonic data could be used as a proxy for fracture delineations and in situ rock quality assessment. For example, zones of washed-up amplitudes in these data correlate well with zones of poor quality rocks, identified by core logging. Based on the full-waveform sonic data, seismic attenuation and its reciprocal, the seismic quality factor, were calculated. A decrease in the seismic quality factor was observed at zones with low rock quality designation, but also correlated with the mineralized zones suggesting several fracture zones in the mineralization and that the ore-bearing rocks might be less competent than the surrounding host rocks. Eventual rock support and reinforcement might be required for future mining operations. Full-waveform sonic data have the potential to improve rock quality assessments for mine planning and exploration purposes.

Place, publisher, year, edition, pages
Elsevier, 2017
Keyword
Downhole physical property logging, Iron oxide deposits, Elastic constants, Seismic quality factor, Sweden
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-345223 (URN)10.1016/j.oregeorev.2017.10.012 (DOI)000423248600001 ()
Available from: 2018-03-14 Created: 2018-03-14 Last updated: 2018-03-14Bibliographically approved
Lähivaara, T., Pasanen, A., Malehmir, A. & Kaipio, J. (2017). Full-waveform Seismic Inversion for Estimating Aquifer Dimensions and Hydrologic Parameters. In: : . Paper presented at 23rd European Meeting of Environmental and Engineering Geophysics, 3-7 September 2017, Malmö, Sweden.
Open this publication in new window or tab >>Full-waveform Seismic Inversion for Estimating Aquifer Dimensions and Hydrologic Parameters
2017 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

This study aims at developing computational tools to estimate aquifer dimensions and hydrologic parameters using seismic data. The poroelastic signature from an aquifer is simulated and using this signature we estimate water-table level and aquifer porosity, and infer the location of aquifer-basement boundary. We use discontinuous Galerkin method to solve the forward model that characterizes the propagation of seismic waves in coupled poroelastic-elastic media. The inverse problem is solved in a Bayesian framework, which enables to take into account modeling uncertainties. For the inverse problem, we use the Bayesian approximation error method, which reduces the overall computational demand. At this stage, results for a 2D synthetic model are presented to illustrate the potential of the algorithm for hydrogeological applications. 

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-328044 (URN)10.3997/2214-4609.201702020 (DOI)
Conference
23rd European Meeting of Environmental and Engineering Geophysics, 3-7 September 2017, Malmö, Sweden
Funder
Swedish Research Council Formas, 25220121907
Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2017-08-22Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1241-2988

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