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  • 1.
    Abbas, Khalid
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Processing of full waveform sonic data for shear wave velocity at the Ketzin CO2 storage site2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The accumulation of carbon dioxide gas (CO2) in the atmosphere is considered be the main cause of global warming effects. These emissions can be reduced substantially by capturing and storing the CO2. The CO2SINK project started in April 2004 in the northeast German Basin (NEGB) at the town of Ketzin near Berlin, Germany. Uppsala University is one of the main participants in the seismic part of the CO2SINK project.

    Full waveform sonic data were acquired in the Ktzi-201 injection well at the Ketzin CO2 storage site. The mode of logging was monopole logging. The target was the Stuttgart Formation, a saline sandstone aquifer at the depth of 500-700m. A total of 1210 shots were conducted and data were recorded on 13 channels. Receiver spacing was 6 inches (15.24 cm). The focus of the CO2SINK project was to develop the basis for the CCS technique by injecting CO2 into a saline aquifer and monitoring of the injected CO2 in the aquifer as a pilot study for future geological storage of CO2 in Europe.

    The objective of this study is to calculate P-wave & S-wave velocities from full waveform sonic data recorded in Ktzi-201 injection well. In hard formations, shear wave velocities can be determined directly from full waveform sonic data recorded in monopole logging. However, in slow formations like Stuttgart Formation as in the Ketzin CO2SINK project, shear wave arrivals are absent in full waveform sonic data recorded in monopole logging. In this case, shear wave velocities can be determined from Stoneley wave velocities provided that one knows the P-wave velocity in the borehole fluid.

    P-wave velocities were calculated by picking the P-wave arrivals on full waveform sonic data. Due to the absence of shear wave arrivals, the shear wave velocities were estimated from the larger amplitude Stoneley waves. The estimated S-wave velocities from Stoneley waves were less than the fluid wave velocity in the borehole, confirming the mode of logging was monopole and the formation is a slow formation.

    The reliability of shear wave velocities estimated from Stoneley waves also depends on five other parameters such as formation permeability, borehole fluid property, tool diameter, borehole radius etc.

  • 2.
    Abdelrahman, Wedissa
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Reprocessing of reflection seismic data from the Skåne area, southern Sweden2007Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Seismic reflection surveying is a powerful method to explore the structures of the Earth’s

    crust and describe it is layers. It is also used extensively in the oil industry.

    Offshore seismic profiles were acquired in southern Sweden (Skane area) for petroleum exploration

    purposes, but no productive fields were discovered in that area. The seismic reflection data were

    collected and processed in the 1970s.

    The purpose of this thesis is to reprocess some of the seismic profiles from the 1970s with new

    processing programs to improve the results and compare it with the previous results. Offshore lines

    208, 206, 212 have been selected in this project because they cross each other and are close to a

    borehole with sonic data. The borehole lies close to lines 208 and 212 as seen from the Skane area

    map.

    Also this report can be used to introduce the reader to fundamentals of seismic data processing.

    The processing was done using Claritas software by applying standard processing steps to produce

    migrated stacked sections for every line as a final product.

  • 3.
    Abdetedal, Mahsa
    et al.
    Institute of Geophysics, Tehran, 14155-6466, Iran.
    Shomali, Z. Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Institute of Geophysics, Tehran, 14155-6466, Iran.
    Gheitanchi, Mohammad Reza
    Institute of Geophysics, Tehran, 14155-6466, Iran.
    Ambient noise surface wave tomography of the Makran subduction zone, south-east Iran: Implications for crustal and uppermost mantle structures2015In: Earthquake Science, ISSN 1674-4519, E-ISSN 1867-8777, Vol. 28, no 4, p. 235-251Article in journal (Refereed)
    Abstract [en]

    Seismic ambient noise of surface wave tomography was applied to estimate Rayleigh wave empirical Green’s functions (EGFs) and then to study crust and uppermost mantle structure beneath the Makran region in south-east Iran. 12 months of continuous data from January 2009 through January 2010, recorded at broadband seismic stations, were analyzed. Group velocities of the fundamental mode Rayleigh wave dispersion curves were obtained from the empirical Green’s functions. Multiple-filter analysis was used to plot group velocity variations at periods from 10 to 50 s. Using group velocity dispersion curves, 1-D v S velocity models were calculated between several station pairs. The final results demonstrate significant agreement to known geological and tectonic features. Our tomography maps display low-velocity anomaly with SW-NE trend, comparable with volcanic arc settings of the Makran region which may be attributable to the geometry of Arabian Plate subducting beneath the overriding the Lut block. The northward subducting Arabian Plate is determined by high-velocity anomaly along the Straits of Hormuz. At short periods (<20 s), there is a sharp transition boundary between low- and high-velocity transition zone with the NW trending at the western edge of Makran which is attributable to the Minab fault system.

  • 4.
    Abdi, Amir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Re-processing of reflection seismic data from line V2 of the HIRE Seismic Reflection Survey in the Suurikuusikko mining and exploration area, northern Finland2011Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    The Suurikuusikko gold deposit is located in northern Finland; it is the largest known gold resource in northern Europe. The acquired high resolution reflection seismic data along the c.30 km long profile V2 of the HIRE reflection survey in the Surrikuusikko gold mining and exploration area have been re-processed. A 15.4 ton Geosvip was used as the source, with a receiver spacing of 12.5 m and source spacing of 25 or 50 m. It was aimed to obtain more detailed structural information of the upper 5 – 6 km crust, and to study the seismic response of the important geological and tectonic structures (e.g. Suasselkä PG fault) along the line V2. The line V2 runs from south to north; in the north, it cuts the mafic graphitic tuffic rocks, which are buried under a layer of tholeiite. It is almost perpendicular to the surface trace of the Suasselkä PG fault in the north. The obtained seismic image showed significant improvements compared with the previous work. The seismic response of the major rock units generated strong reflections, and they can be traced down to at least 3 km depth; the reflections correlate well with the surface geology. The moderately dipping reflections from the PG fault are clearly imaged; the dip direction of the fault is towards the SE with a dip of about 50o, possibly decreasing with depth down to about 35o, the fault can be traced down to about 3 km depth. The reverse movement of the fault most probably caused the neighboring sub-horizontal layers to be folded and generated a duplex structure. The dip direction of the major structures in the southern parts is towards NE; this together with the mentioned information about the fault, can be utilized in order to define the major geological structures and most importantly the tectonic evolution of the area; such information can be used in many crucial aspects such as prediction of the future movements of the bedrock and discovery of new resources.

  • 5.
    Abdi, Amir
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Heinonen, Suvi
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Karinen, Tuomo
    Constraints on the geometry of the Suasselka post-glacial fault, northern Finland, based on reflection seismic imaging2015In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 649, p. 130-138Article in journal (Refereed)
    Abstract [en]

    Unloading of the ice during the last glacial period in northern Fennoscandia is believed to have generated major faulting. These faults, often referred to as post-glacial faults, typically have clear surface exposures, but their geometry at depth is poorly known. In order to better understand the geometry at depth of the Suasselka post-glacial fault in Finland, three high resolution 2D reflection seismic profiles over the fault were reprocessed. Their total profile length is about 60 km and they were acquired as part of a major effort in Finland to map the uppermost crust in mining areas. The reprocessing led to significantly improved images that could be used to map the fault at depth. Two approximately N-S striking profiles and one E-W striking profile were reprocessed. The different azimuths and the crooked nature of the profiles allowed the fault geometry to be relatively well constrained. Clear reflections from the fault, dipping towards the SE, can be traced from the shallow subsurface down to about 3 km. The strike and dip of two sets of dipping reflections in the stacked data along with geometrical constraints and cross-dip analysis give a consistent dip of about 35-45 degrees towards the SE for the fault. The strike and dip vary from N55E with a dip of 35 degrees in the east to a strike of N48E with a dip of 45 degrees in the west. Existence of the two sets of reflections indicates that the fault surface is non-planar. Aside from allowing the geometry of the fault to be determined, the seismic data show a complex reflectivity pattern in the area and indications of both reverse and normal movement along fault planes with similar orientation to the Suasselka post-glacial fault. These images can be used as a basis for better characterizing the 3D geology of the area.

  • 6.
    Abreu, Rafael
    et al.
    Westfalische Wilhelms Univ Munster, Inst Geophys, Corrensstr 24, D-48149 Munster, Germany.;Univ Granada, Inst Andaluz Geofis, Campus Cartuja S-N, E-18071 Granada, Spain..
    Kamm, Jochen
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Westfalische Wilhelms Univ Munster, Inst Geophys, Corrensstr 24, D-48149 Munster, Germany.
    Reiss, Anne-Sophie
    Westfalische Wilhelms Univ Munster, Inst Geophys, Corrensstr 24, D-48149 Munster, Germany..
    Micropolar modelling of rotational waves in seismology2017In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 210, no 2, p. 1021-1046Article in journal (Refereed)
    Abstract [en]

    In this contribution we study elastic wave propagation via the introduction of the micropolar theory. As a generalization of a classical linear elastic medium, a micropolar medium allows each particle to have intrinsic rotational degrees of freedom (spin). We perform numerical experiments using the Pseudospectral method. We find analytical harmonic micropolar solutions for different problem configurations, which result in waveform differences between the classical linear elastic and micropolar media. In contrast to linear elastic media, wave propagation in micropolar media is dispersive. We study how the spin waveform depends on the micropolar elastic parameters and frequency content of the simulation. The micropolar effect on numerical seismograms has a direct implication on the phase, amplitude and arrival time. For frequencies lower than the cut-off frequency, the spin waveform has the same amplitude as the macrorotation field. For frequencies higher than the cut-off frequency, the amplitude of the spin waveform decreases with increasing frequency, so that then it is no longer comparable to the amplitude of macroscopic rotations. When both frequencies are equal there is no wave propagation. This work attempts to clarify the theory of micropolar media for its applications in seismology. We argue that micropolar theory should be further investigated for its potential uses in seismology to, for example, describe energy dissipation, seismograms recorded with rotational seismometers and rupture processes.

  • 7.
    Abtahi, Sayyed Mohammad
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Airborne Gravity Gradient, Magnetic and VLF datasets: Case studies of modelling, inversion and interpretation2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Northern Sweden is one of the largest hosts for mineral resources in Europe and always has been an interesting area for researchers from various disciplines of Earth sciences. This dissertation is a comprehensive summary of three case study papers on airborne VLF, gravity gradient and magnetic data in the area.

    In the first paper, tensor VLF data is extracted from an old data set which contains only the total and the vertical magnetic components. The anomalous part of the horizontal magnetic field components is computed by a Hilbert transform of the vertical magnetic field. The normal part of the horizontal magnetic field component is computed as a function of total, vertical and anomalous part of horizontal magnetic fields. The electric field is also calculated for TE mode and impedance tensor and apparent resistivity are computed. In addition tippers are calculated for two transmitters and inverted by a 3D inversion algorithm. Comparison of the estimated model and geology map of bedrock shows that lower resistivity zones are correlated with mineralizations.

    The second paper deals with the internal consistency of airborne gravity gradient data. The six components of the data are estimated from a common potential function. It is shown that the data is adequately consistent but at shorter land clearances the difference between the estimated data and the original data is larger. The technique is also used for computing the Bouguer anomaly from terrain corrected FTG data. Finally the data is inverted in 3D, which shows that the estimated density model in shallow depth is dominated by short wave length features.

    Inversion of TMI data is the topic of the third paper where a new type of reference model for 3D inversion of magnetic data is proposed by vertically extending the estimated magnetization of a 2D terrain magnetization model. The final estimated 3D result is compared with the magnetization model where no reference model is used. The comparison shows that using the reference model helps the high magnetization zones in the estimated model at shallow depths to be better correlated with measured high remanent magnetization from rock samples. The high magnetization zones are also correlated with gabbros and volcanic metasediments.

    List of papers
    1. Extracting geoelectrical maps from vintage very-low-frequency airborne data, tipper inversion, and interpretation: A case study from northern Sweden
    Open this publication in new window or tab >>Extracting geoelectrical maps from vintage very-low-frequency airborne data, tipper inversion, and interpretation: A case study from northern Sweden
    2016 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 81, no 5, p. B135-B147Article in journal (Refereed) Published
    Abstract [en]

    In 1985, the mining company Luossavaara-Kiirunavaara Aktiebolag collected airborne very-low-frequency (VLF) data in northern Sweden. The operators stored only the vertical component and the total magnetic field, which at that time were believed to be sufficient for qualitative interpretation. Therefore, the data could not be directly used for quantitative tensor VLF processing and inversion. To avoid the costs of resurveying, we have developed a novel technique to estimate the tippers from the measured VLF data by computing anomalous and normal parts of the horizontal components of the magnetic field from two transmitters separately. Retrieval of the normal horizontal components was possible because one component of the horizontal magnetic field was used as the phase reference during the measurements. Additionally, we have determined how the approximate apparent resistivity suitable for data visualization can be computed from the components of the magnetic field assuming an average normal resistivity of the subsurface. Maps of apparent resistivity combined with topography show a clear correlation between high topography and high resistivity, whereas conductive zones are found in valleys in between. More importantly, the 3D model inverted from the calculated tippers shows excellent agreement with a map of the surface geology. Based on this comparison, some less resistive zones can be related to fluids in fractures and others can be related to mineralized contact zones. We suggest to focus further exploration on conductive zones surrounding areas with basaltic composition.

    Place, publisher, year, edition, pages
    Uppsala: , 2016
    Keywords
    case history, inversion, interpretation, electromagnetics
    National Category
    Geophysics
    Identifiers
    urn:nbn:se:uu:diva-300086 (URN)10.1190/GEO2015-0296.1 (DOI)000392752200002 ()
    Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2017-11-28Bibliographically approved
    2. Consistency investigation, vertical gravity estimation and inversion of airborne gravity gradient data – A case study from northern Sweden
    Open this publication in new window or tab >>Consistency investigation, vertical gravity estimation and inversion of airborne gravity gradient data – A case study from northern Sweden
    2016 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 81, no 3, p. B65-B76Article in journal (Refereed) Published
    Abstract [en]

    For airborne gravity gradient data, it is a challenge to distinguish between high-frequency intrinsic and dynamically produced noise caused by the aircraft and small-scale effects from shallow density variations. To facilitate consistent interpretation, techniques that include all of the measured gravity gradient components are particularly promising. We represented the measurements by a common potential function accounting for lateral and height variations. Thus, it was possible to evaluate the internal consistency between the measured components and to identify components with bias or particularly strong noise. As an extra benefit for data sets that contain terrain-corrected and nonterrain-corrected gravity gradient measurements at flight altitude, we estimated terrain-corrected anomalies on the topographic relief using downward continuation and retrieved nonterrain-corrected gravity gradient data suitable for inversion using upward continuation. For a field data set from northern Sweden, the largest differences (up to 50 eotvos) between the measured and estimated components of the gravity gradient data were found in areas of high topographical relief. But the average residual standard deviations of the individual components were between 3.6 and 7.4 eotvos, indicating that the components were consistent in an average sense. We have determined the successful conversion of terrain-corrected airborne gravity gradient data to Bouguer gravity data on the topographic relief using ground-based vertical gravity data as a reference. A 3D inverse model computed from the nonterrain-corrected data clearly showed the depth extent of the geologic structures observed at the surface, but it only produced a weak representation of the shallow structure. In contrast, a 2D surface density model in which only lateral variations of density in the topographic relief was allowed exhibited more realistic density distributions in fair correlation with geology.

    Keywords
    gravity, modeling, noise, processing
    National Category
    Geophysics
    Identifiers
    urn:nbn:se:uu:diva-300024 (URN)10.1190/geo2014-0428.1 (DOI)000384984900008 ()
    Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2017-11-28Bibliographically approved
    3. A new reference model for 3D inversion of airborne magnetic data in hilly terrain – a case study from northern Sweden
    Open this publication in new window or tab >>A new reference model for 3D inversion of airborne magnetic data in hilly terrain – a case study from northern Sweden
    (English)Article in journal (Refereed) Submitted
    National Category
    Geophysics
    Identifiers
    urn:nbn:se:uu:diva-300111 (URN)
    Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-05
  • 8.
    Abtahi, Sayyed Mohammad
    et al.
    Isfahan Univ Technol, Dept Min Engn, Esfahan, Iran.
    Pedersen, Laust Börsting
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kamm, Jochen
    Univ Munster, Dept Geophys, Munster, Germany.
    Kalscheuer, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    A new reference model for 3D inversion of airborne magnetic data in hilly terrain: A case study from northern Sweden2018In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 83, no 1, p. B1-B12Article in journal (Refereed)
    Abstract [en]

    The inherent nonuniqueness in modeling magnetic data can be partly reduced by adding prior information, either as mathematical constructs or simply as bounds on magnetization obtained from laboratory measurements. If a good prior model can be used as a reference model, then the quality of estimated models through an inverse approach can be greatly improved. But even though data on magnetic properties of rocks might exist, their distribution may often be quite irregular on local and regional scales, so that it is difficult to define representative classes of rock types suitable for constraining geophysical models of magnetization. We have developed a new way of constructing a reference model that varies only laterally and is confined to the part of the terrain that lies above the lowest topography in the area. To obtain this model, several estimated 2D magnetization distributions were constructed by data inversion as a function of the iteration number. Then, a suitable 2D model of the magnetization in the topography was chosen as a starting point for constructing a 3D reference model by modifying it with a vertical decay such that its average source depth was the same for all horizontal positions. The average source depth of the reference model was chosen to satisfy the average source depth obtained from analyzing the radial power spectrum of the area studied. Finally, the measured magnetic data were inverted in three dimensions using the given reference model. For a selected reference model, shallow structures indicated a better overall correlation with large remanent magnetizations measured on rock samples from the area. Throughout the entire model, the direction of magnetization was allowed to vary freely. We found that the Euclidean norm of the estimated model was reduced compared with the case where the magnetization direction was fixed.

  • 9.
    Abtahi, Sayyed Mohammad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Isfahan Univ Technol, Dept Min Engn, Esfahan, Iran.
    Pedersen, Laust
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kamm, Jochen
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kalscheuer, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Consistency investigation, vertical gravity estimation and inversion of airborne gravity gradient data – A case study from northern Sweden2016In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 81, no 3, p. B65-B76Article in journal (Refereed)
    Abstract [en]

    For airborne gravity gradient data, it is a challenge to distinguish between high-frequency intrinsic and dynamically produced noise caused by the aircraft and small-scale effects from shallow density variations. To facilitate consistent interpretation, techniques that include all of the measured gravity gradient components are particularly promising. We represented the measurements by a common potential function accounting for lateral and height variations. Thus, it was possible to evaluate the internal consistency between the measured components and to identify components with bias or particularly strong noise. As an extra benefit for data sets that contain terrain-corrected and nonterrain-corrected gravity gradient measurements at flight altitude, we estimated terrain-corrected anomalies on the topographic relief using downward continuation and retrieved nonterrain-corrected gravity gradient data suitable for inversion using upward continuation. For a field data set from northern Sweden, the largest differences (up to 50 eotvos) between the measured and estimated components of the gravity gradient data were found in areas of high topographical relief. But the average residual standard deviations of the individual components were between 3.6 and 7.4 eotvos, indicating that the components were consistent in an average sense. We have determined the successful conversion of terrain-corrected airborne gravity gradient data to Bouguer gravity data on the topographic relief using ground-based vertical gravity data as a reference. A 3D inverse model computed from the nonterrain-corrected data clearly showed the depth extent of the geologic structures observed at the surface, but it only produced a weak representation of the shallow structure. In contrast, a 2D surface density model in which only lateral variations of density in the topographic relief was allowed exhibited more realistic density distributions in fair correlation with geology.

  • 10.
    Abtahi, Sayyed Mohammad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Isfahan Univ Technol, Dept Min Engn, Esfahan, Iran.
    Pedersen, Laust
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kamm, Jochen
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Munster, Dept Geophys, Munster, Germany.
    Kalscheuer, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Extracting geoelectrical maps from vintage very-low-frequency airborne data, tipper inversion, and interpretation: A case study from northern Sweden2016In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 81, no 5, p. B135-B147Article in journal (Refereed)
    Abstract [en]

    In 1985, the mining company Luossavaara-Kiirunavaara Aktiebolag collected airborne very-low-frequency (VLF) data in northern Sweden. The operators stored only the vertical component and the total magnetic field, which at that time were believed to be sufficient for qualitative interpretation. Therefore, the data could not be directly used for quantitative tensor VLF processing and inversion. To avoid the costs of resurveying, we have developed a novel technique to estimate the tippers from the measured VLF data by computing anomalous and normal parts of the horizontal components of the magnetic field from two transmitters separately. Retrieval of the normal horizontal components was possible because one component of the horizontal magnetic field was used as the phase reference during the measurements. Additionally, we have determined how the approximate apparent resistivity suitable for data visualization can be computed from the components of the magnetic field assuming an average normal resistivity of the subsurface. Maps of apparent resistivity combined with topography show a clear correlation between high topography and high resistivity, whereas conductive zones are found in valleys in between. More importantly, the 3D model inverted from the calculated tippers shows excellent agreement with a map of the surface geology. Based on this comparison, some less resistive zones can be related to fluids in fractures and others can be related to mineralized contact zones. We suggest to focus further exploration on conductive zones surrounding areas with basaltic composition.

  • 11.
    Adamaki, Angeliki
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Seismicity Analyses Using Dense Network Data: Catalogue Statistics and Possible Foreshocks Investigated Using Empirical and Synthetic Data2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Precursors related to seismicity patterns are probably the most promising phenomena for short-term earthquake forecasting, although it remains unclear if such forecasting is possible. Foreshock activity has often been recorded but its possible use as indicator of coming larger events is still debated due to the limited number of unambiguously observed foreshocks. Seismicity data which is inadequate in volume or character might be one of the reasons foreshocks cannot easily be identified. One method used to investigate the possible presence of generic seismicity behavior preceding larger events is the aggregation of seismicity series. Sequences preceding mainshocks chosen from empirical data are superimposed, revealing an increasing average seismicity rate prior to the mainshocks. Such an increase could result from the tendency of seismicity to cluster in space and time, thus the observed patterns could be of limited predictive value. Randomized tests using the empirical catalogues imply that the observed increasing rate is statistically significant compared to an increase due to simple clustering, indicating the existence of genuine foreshocks, somehow mechanically related to their mainshocks. If network sensitivity increases, the identification of foreshocks as such may improve. The possibility of improved identification of foreshock sequences is tested using synthetic data, produced with specific assumptions about the earthquake process. Complications related to background activity and aftershock production are investigated numerically, in generalized cases and in data-based scenarios. Catalogues including smaller, and thereby more, earthquakes can probably contribute to better understanding the earthquake processes and to the future of earthquake forecasting. An important aspect in such seismicity studies is the correct estimation of the empirical catalogue properties, including the magnitude of completeness (Mc) and the b-value. The potential influence of errors in the reported magnitudes in an earthquake catalogue on the estimation of Mc and b-value is investigated using synthetic magnitude catalogues, contaminated with Gaussian error. The effectiveness of different algorithms for Mc and b-value estimation are discussed. The sample size and the error level seem to affect the estimation of b-value, with implications for the reliability of the assessment of the future rate of large events and thus of seismic hazard.

    List of papers
    1. EVIDENCE OF PRECURSORY PATTERNS IN AGGREGATED TIME SERIES
    Open this publication in new window or tab >>EVIDENCE OF PRECURSORY PATTERNS IN AGGREGATED TIME SERIES
    2016 (English)In: Bulletin of the Geological Society of Greece, vol. L, 2016, Proceedings of the 14th Intern. Congress, Thessaloniki, May 2016, 2016, Vol. 50Conference paper, Published paper (Refereed)
    Abstract [en]

    We investigate temporal changes in seismic activity observed in the West Corinth Gulfand North-West Peloponnese during 2008 to 2010. Two major earthquake sequencestook place in the area at that time (in 2008 and 2010). Our aim is to analyse Greekseismicity to attempt to confirm the existence or non-existence of seismic precursorsprior to the strongest earthquakes. Perhaps because the area is geologically andtectonically complex, we found that it was not possible to fit the data well using aconsistent Epidemic Type Aftershock Sequence (ETAS) model. Nor could weunambiguously identify foreshocks to individual mainshocks. Therefore we soughtpatterns in aggregated foreshock catalogues. We set a magnitude threshold (M3.5)above which all the earthquakes detected in the study area are considered as“mainshocks”, and we combined all data preceding these into a single foreshockcatalogue. This reveals an increase in seismicity rate not robustly observable forindividual cases. The observed effect is significantly greater than that consistent withstochastic models, including ETAS, thus indicating genuine foreshock activity withpotential useful precursory power, if sufficient data is available, i.e. if the magnitudeof completeness is sufficiently low.

    Abstract [el]

    Μελετάμε χρονικές μεταβολές της σεισμικής δραστηριότητας στο Δυτικό ΚορινθιακόΚόλπο και τη Βορειοδυτική Πελοπόννησο κατά τα έτη 2008-2010. Δύο σημαντικέςσεισμικές ακολουθίες σημειώθηκαν στην περιοχή σε αυτή την περίοδο (2008 και 2010).Στόχος είναι να αναλύσουμε τη σεισμικότητα ώστε να επιβεβαιώσουμε την ύπαρξη ή μηπροσεισμικής δραστηριότητας πριν από τους μεγαλύτερους σεισμούς. Λόγω τηςγεωλογικής και τεκτονικής πολυπλοκότητας της περιοχής, δεν ήταν εφικτή η εφαρμογήενός ενιαίου μοντέλου Επιδημικού Τύπου Μετασεισμικών Ακολουθιών (ETAS), ούτε ηαναγνώριση προσεισμών μεμονωμένων κυρίων σεισμών. Επομένως, αναζητήσαμεανάλογα μοτίβα σε ενιαίους καταλόγους προσεισμών. Θέσαμε ένα μέγεθος (Μ3.5)πάνω από το οποίο όλοι οι σεισμοί θεωρούνται “κύριοι”, και συνδυάσαμε τα δεδομέναπου προηγούνται αυτών, σε ένα κοινό κατάλογο. Αναδεικνύεται έτσι μια αύξηση τουρυθμού σεισμικότητας που δεν είναι εμφανής σε μεμονωμένες περιπτώσεις και είναι πιοσημαντική από εκείνη που προβλέπεται από στοχαστικά μοντέλα, όπως το ETAS,υποδηλώνοντας την ύπαρξη προσεισμών που μπορούν να δώσουν τη δυνατότηταπρόγνωσης αν υπάρχει ικανοποιητικό πλήθος δεδομένων, δηλ. αν το μέγεθοςπληρότητας είναι αρκετά χαμηλό.

    Keywords
    Corinth Gulf, Seismicity, Aggregated Foreshock Catalogues, Κορινθιακός Κόλπος, Σεισμικότητα, Ενιαίοι Κατάλογοι Προσεισμών
    National Category
    Natural Sciences Geophysics
    Identifiers
    urn:nbn:se:uu:diva-295440 (URN)
    Conference
    14th International Congress, Geological Society of Greece, Thessaloniki, May 2016
    Available from: 2016-06-07 Created: 2016-06-07 Last updated: 2017-08-21Bibliographically approved
    2. Precursory Activity Before Larger Events in Greece Revealed by Aggregated Seismicity Data
    Open this publication in new window or tab >>Precursory Activity Before Larger Events in Greece Revealed by Aggregated Seismicity Data
    2017 (English)In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 174, no 3, p. 1331-1343Article in journal (Refereed) Published
    Abstract [en]

    We investigate the seismicity rate behaviour in and around Greece during 2009, seeking significant changes in rate preceding larger events. For individual larger events it is difficult to clearly distinguish precursory rate changes from other, possibly unrelated, variations in seismicity. However, when we aggregate seismicity data occurring within a radius of 10 km and in a 50-day window prior to earthquakes with, e. g. magnitude C3.5, the resulting aggregated time series show a clearly increasing trend starting 2-3 weeks prior to the "mainshock'' time. We apply statistical tests to investigate if the observed behaviour may be simply consistent with random (poissonian) variations, or, as some earlier studies suggest, with clustering in the sense that high activity rates at some time may imply increased rates later, and thus (randomly) greater probability of larger coming events than for periods of lower seismicity. In this case, rate increases have little useful predictive power. Using data from the entire catalogue, the aggregated rate changes before larger events are clearly and strongly statistically significant and cannot be explained by such clustering. To test this we choose events at random from the catalogue as potential "mainshocks''. The events preceding the randomly chosen earthquakes show less pronounced rate increases compared to the observed rate changes prior to larger events. Similar behaviour is observed in data sub-sets. However, statistical confidence decreases for geographical subsets containing few "mainshocks'' as it does when data are weighted such that "mainshocks'' with many preceding events are strongly downweighted relative to those with fewer. The analyses suggest that genuine changes in aggregated rate do occur prior to larger events and that this behaviour is not due to a small number of mainshocks with many preceding events dominating the analysis. It does not automatically follow that it will be possible to routinely observe precursory changes prior to individual larger events, but there is a possibility that this may be feasible, e. g. with better data from more sensitive networks.

    Place, publisher, year, edition, pages
    SPRINGER BASEL AG, 2017
    Keywords
    Temporal seismicity patterns, aggregated data, precursory activity, Greece
    National Category
    Geophysics
    Identifiers
    urn:nbn:se:uu:diva-320921 (URN)10.1007/s00024-017-1465-6 (DOI)000396834700039 ()
    Available from: 2017-04-27 Created: 2017-04-27 Last updated: 2017-08-21Bibliographically approved
    3. Advantages and Limitations of Foreshock Activity as a Useful Tool for Earthquake Forecasting
    Open this publication in new window or tab >>Advantages and Limitations of Foreshock Activity as a Useful Tool for Earthquake Forecasting
    (English)Manuscript (preprint) (Other academic)
    Keywords
    Accelerating Seismicity, Earthquake Predictability
    National Category
    Geophysics
    Research subject
    Geophysics with specialization in Seismology
    Identifiers
    urn:nbn:se:uu:diva-328055 (URN)
    Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2017-08-21
    4. Impact of Magnitude Uncertainties on Seismic Catalogue Properties
    Open this publication in new window or tab >>Impact of Magnitude Uncertainties on Seismic Catalogue Properties
    Show others...
    (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246XArticle in journal (Refereed) Submitted
    Keywords
    Statistical Seismology, Earthquake Catalogue Properties, Completeness Magnitude, b-value
    National Category
    Earth and Related Environmental Sciences
    Research subject
    Statistics; Geophysics with specialization in Seismology
    Identifiers
    urn:nbn:se:uu:diva-328053 (URN)
    Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2017-08-21
  • 12.
    Adamaki, Angeliki K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Roberts, Roland G.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Precursory Activity Before Larger Events in Greece Revealed by Aggregated Seismicity Data2017In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 174, no 3, p. 1331-1343Article in journal (Refereed)
    Abstract [en]

    We investigate the seismicity rate behaviour in and around Greece during 2009, seeking significant changes in rate preceding larger events. For individual larger events it is difficult to clearly distinguish precursory rate changes from other, possibly unrelated, variations in seismicity. However, when we aggregate seismicity data occurring within a radius of 10 km and in a 50-day window prior to earthquakes with, e. g. magnitude C3.5, the resulting aggregated time series show a clearly increasing trend starting 2-3 weeks prior to the "mainshock'' time. We apply statistical tests to investigate if the observed behaviour may be simply consistent with random (poissonian) variations, or, as some earlier studies suggest, with clustering in the sense that high activity rates at some time may imply increased rates later, and thus (randomly) greater probability of larger coming events than for periods of lower seismicity. In this case, rate increases have little useful predictive power. Using data from the entire catalogue, the aggregated rate changes before larger events are clearly and strongly statistically significant and cannot be explained by such clustering. To test this we choose events at random from the catalogue as potential "mainshocks''. The events preceding the randomly chosen earthquakes show less pronounced rate increases compared to the observed rate changes prior to larger events. Similar behaviour is observed in data sub-sets. However, statistical confidence decreases for geographical subsets containing few "mainshocks'' as it does when data are weighted such that "mainshocks'' with many preceding events are strongly downweighted relative to those with fewer. The analyses suggest that genuine changes in aggregated rate do occur prior to larger events and that this behaviour is not due to a small number of mainshocks with many preceding events dominating the analysis. It does not automatically follow that it will be possible to routinely observe precursory changes prior to individual larger events, but there is a possibility that this may be feasible, e. g. with better data from more sensitive networks.

  • 13.
    Adamaki, Angeliki
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Advantages and Limitations of Foreshock Activity as a Useful Tool for Earthquake ForecastingManuscript (preprint) (Other academic)
  • 14.
    Adamaki, Angeliki
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    EVIDENCE OF PRECURSORY PATTERNS IN AGGREGATED TIME SERIES2016In: Bulletin of the Geological Society of Greece, vol. L, 2016, Proceedings of the 14th Intern. Congress, Thessaloniki, May 2016, 2016, Vol. 50Conference paper (Refereed)
    Abstract [en]

    We investigate temporal changes in seismic activity observed in the West Corinth Gulfand North-West Peloponnese during 2008 to 2010. Two major earthquake sequencestook place in the area at that time (in 2008 and 2010). Our aim is to analyse Greekseismicity to attempt to confirm the existence or non-existence of seismic precursorsprior to the strongest earthquakes. Perhaps because the area is geologically andtectonically complex, we found that it was not possible to fit the data well using aconsistent Epidemic Type Aftershock Sequence (ETAS) model. Nor could weunambiguously identify foreshocks to individual mainshocks. Therefore we soughtpatterns in aggregated foreshock catalogues. We set a magnitude threshold (M3.5)above which all the earthquakes detected in the study area are considered as“mainshocks”, and we combined all data preceding these into a single foreshockcatalogue. This reveals an increase in seismicity rate not robustly observable forindividual cases. The observed effect is significantly greater than that consistent withstochastic models, including ETAS, thus indicating genuine foreshock activity withpotential useful precursory power, if sufficient data is available, i.e. if the magnitudeof completeness is sufficiently low.

  • 15. 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.

  • 16. 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.

  • 17.
    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.

  • 18.
    Afsar, Fatima
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    ANALYSIS AND INTERPRETATION OF 2D/3D SEISMIC DATA OVER DHURNAL OIL FIELD, NORTHERN PAKISTAN2013Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
    Abstract [en]

    The study area, Dhurnal oil field, is located 74 km southwest of Islamabad in the Potwar basin of Pakistan. Discovered in March 1984, the field was developed with four producing wells and three water injection wells. Three main limestone reservoirs of Eocene and Paleocene ages are present in this field. These limestone reservoirs are tectonically fractured and all the production is derived from these fractures. The overlying claystone formation of Miocene age provides vertical and lateral seal to the Paleocene and Permian carbonates. The field started production in May 1984, reaching a maximum rate of 19370 BOPD in November 1989. Currently Dhurnal‐1 (D-1) and Dhurnal‐6 (D-6) wells are producing 135 BOPD and 0.65 MMCF/D gas. The field has depleted after producing over 50 million Bbls of oil and 130 BCF of gas from naturally fractured low energy shelf carbonates of the Eocene, Paleocene and Permian reservoirs. Preliminary geological and geophysical data evaluation of Dhurnal field revealed the presence of an up-dip anticlinal structure between D-1 and D-6 wells, seen on new 2003 reprocessed data. However, this structural impression is not observed on old 1987 processed data. The aim of this research is to compare and evaluate old and new reprocessed data in order to identify possible factors affecting the structural configuration. For this purpose, a detailed interpretation of old and new reprocessed data is carried out and results clearly demonstrate that structural compartmentalization exists in Dhurnal field (based on 2003 data). Therefore, to further analyse the available data sets, processing sequences pertaining to both vintages have been examined. After great effort and detailed investigation, it is concluded that the major parameter giving rise to this data discrepancy is the velocity analysis done with different gridding intervals. The detailed and dense velocity analysis carried out on the data in 2003 was able to image the subtle anticlinal feature, which was missed on the 1987 processed seismic data due to sparse gridding. In addition to this, about 105 sq.km 3D seismic data recently (2009) acquired by Ocean Pakistan Limited (OPL) is also interpreted in this project to gain greater confidence on the results. The 3D geophysical interpretation confirmed the findings and aided in accurately mapping the remaining hydrocarbon potential of Dhurnal field.

  • 19.
    Agerberg, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Re-Processing of the DACIA-PLAN Reflection Seismic Dataset2008Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Reflection seismology is a geophysical exploration method that is used to estimate the physical properties of the earth. It is by far the most used and well-known geophysical technique and it has dominated the industry of oil and gas exploration since the beginning. Moreover, it is an important scientific tool for mapping and studying the subsurface structures. The predominance of the seismic reflection method over other geophysical techniques is a combined effect of high resolution, high accuracy and great penetration. Compared to other geophysical means, where the final result many times can look a little bit obscure, the resulting seismic section will be a direct image of the subsurface.

    Seismic sections can be produced to reveal geological features on scales of metres to that of the whole lithosphere. The last 20 years the sophistication of the technique has improved considerably, much as a result of massive investments in its development made by the hydrocarbon industry, but also as a result of more accurate electronic and powerful computing technology.

    The quality of the final seismic image is much dependent on the processing phase following the acquisition. For such a well tested method as reflection seismology a kind of step-by-step procedure has emerged over the years. Still, the geophysicists roll in the processing is critical since it is up to him or her to test and find the parameters that optimize the result in every single step.

    The processed data comes from a large scale seismic survey (DACIA-PLAN) made in the south east of Romania. The purpose of the project was to map the geological structure under the eastern part of the Carpathians and the basins developed in the Vrancea zone, one of the most seismological active areas in Europe (Landers et al., 2003). As a result of extensive geophysical and geological projects this area is now quite well mapped. However, the exact cause of what triggers the earthquakes is still not fully understood and will probably generate further investigations of the area.

    The data outputted from the DACIA-PLAN survey has been used in a number of scientific reports. In Panea et al., (2005) the data was processed to form two independent stacked sections. One containing data from the whole profile stacked to a depth of 20 s. The other section was processed from a subset of the DACIA-PLAN data, focusing on the upper 10 s of the Focsani Basin. Reason for doing two independent processing sequences was the decreasing quality of data obtained within and beneath the trust belt.

    For this thesis processing was committed to a depth of 20 s for the whole seismic line, but both a full and partial stack are presented in chapter 6. Also a discussion and comparison with the result presented by Panea et al. (2005) follows in this chapter.

    The main purpose with this thesis was to be familiar with the theory of reflection seismology and get to work with some of the typical steps, that are used in most processing sequences, and apply them on a real dataset. By reprocessing the DACIA-PLAN data the ambition was to improve the final seismic image, but also there was a hope to reveal some new information, particularly in the harsh area around the thrust belt.

  • 20.
    Agustsson, Kristjan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kristjansdottir, Sigridur
    Flovenz, Olafur G
    Gudmundsson, Olafur
    Induced Seismic Activity during Drilling of Injection Wells at the Hellisheiði Power Plant, SW Iceland.2015In: Induced Seismic Activity during Drilling of Injection Wells at the Hellisheiði Power Plant, SW Iceland., 2015Conference paper (Refereed)
  • 21.
    Ahmadi, Omid
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Application of the Seismic Reflection Method in Mineral Exploration and Crustal Imaging: Contributions to Hardrock Seismic Imaging2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The seismic reflection method has been used extensively in mineral exploration and for imaging crustal structures within hardrock environments. In this research the seismic reflection method has been used and studied to address problems associated with hardrock settings. Papers I and II, address delineating and imaging a sulfide ore body and its surrounding rocks and structures in Garpenberg, central Sweden, at an active mine. 3D ray-tracing and finite-difference modeling were performed and the results suggest that although the detection of the ore body by the seismic reflection method is possible in the area, the presence of backfilled stopes in the mine makes seismic imaging of it difficult. In paper III the deeper structures of the Pärvie fault system in northern Sweden were revealed down to about 8 km through 2D seismic reflection profiling. The resulting images were interpreted using microearthquake data as a constraint. Based on the interpretation, some locations were suggested for future scientific deep drilling into the fault system. In paper IV, the seismic signature of complex geological structures of the Cue-Weld Range area in Western Australia was studied using a portion of a deep 2D seismic reflection profile. The pronounced reflections on the seismic images were correlated to their corresponding rock units on an available surface geological map of the study area. 3D constant velocity ray-tracing was performed to constrain the interpretation. Furthermore, the proposed structural model was tested using a 2D acoustic finite-difference seismic modeling method. Based on this study, a new 3D structural model was proposed for the subsurface of the area. These studies have investigated the capability of the seismic reflection method for imaging crustal structures within challenging hardrock and complex geological settings and show some its potential, but also its limitations.

    List of papers
    1. High-resolution 2D seismic imaging and forward modeling of a polymetallic sulfide deposit at Garpenberg, central Sweden
    Open this publication in new window or tab >>High-resolution 2D seismic imaging and forward modeling of a polymetallic sulfide deposit at Garpenberg, central Sweden
    2013 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 78, no 6, p. B339-B350Article in journal (Refereed) Published
    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.

    Keywords
    2D, processing, ray tracing, modeling
    National Category
    Geophysics
    Identifiers
    urn:nbn:se:uu:diva-210135 (URN)10.1190/geo2013-0098.1 (DOI)000330223800003 ()
    Available from: 2013-11-01 Created: 2013-11-01 Last updated: 2017-12-06
    2. The effect of the backfilled stopes on seismic imaging of a sulfide deposit in Garpenberg, central Sweden
    Open this publication in new window or tab >>The effect of the backfilled stopes on seismic imaging of a sulfide deposit in Garpenberg, central Sweden
    2015 (English)Manuscript (preprint) (Other academic)
    National Category
    Geophysics
    Research subject
    Geophysics with specialization in Solid Earth Physics
    Identifiers
    urn:nbn:se:uu:diva-259140 (URN)
    Available from: 2015-07-27 Created: 2015-07-27 Last updated: 2015-08-28
    3. Revealing the deeper structure of the end-glacial Parvie fault system in northern Sweden by seismic reflection profiling
    Open this publication in new window or tab >>Revealing the deeper structure of the end-glacial Parvie fault system in northern Sweden by seismic reflection profiling
    2015 (English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 6, no 2, p. 621-632Article in journal (Refereed) Published
    Abstract [en]

    A new seismic reflection survey for imaging deeper levels of the end-glacial Parvie fault system in northern Sweden was acquired in June 2014. The Parvie fault system hosts the largest fault scarp so far documented in northern Scandinavia, both in terms of its length and calculated magnitude of the earthquake that generated it. Present-day microearthquakes occur along the length of the fault scarp on the eastern side of the scarp, in general agreement with an east-dipping main fault. In the central section of the fault system, where there is a number of subsidiary faults east of the main Parvie scarp, it has been unclear how the earthquakes relate to the structures mapped at the surface. A seismic profile across the Parvie fault system acquired in 2007, with a mechanical hammer as a source, showed a good correlation between the surface mapped faults and moderate to steeply dipping reflections. The most pronounced reflectors could be mapped to about 3 km depth. In the new seismic survey, for deeper penetration an explosive source with a maximum charge size of 8.34 kg in 20 m deep shot holes was used. Reflectors can now be traced to deeper levels with the main 65A degrees east-dipping fault interpreted as a weakly reflective structure. As in the previous profile, there is a strongly reflective 60A degrees west-dipping structure present to the east of the main fault that can now be mapped to about 8 km depth. Extrapolations of the main and subsidiary faults converge at a depth of about 11.5 km, where current earthquake activity is concentrated, suggesting their intersection has created favorable conditions for seismic stress release. Based on the present and previous seismic reflection data, we propose potential locations for future boreholes for scientific drilling into the fault system. These boreholes will provide a better understanding of the reflective nature of the fault structures and stress fields along the faults at depth.

    National Category
    Geophysics
    Research subject
    Geophysics with specialization in Solid Earth Physics
    Identifiers
    urn:nbn:se:uu:diva-259138 (URN)10.5194/se-6-621-2015 (DOI)000357128400020 ()
    Available from: 2015-07-27 Created: 2015-07-27 Last updated: 2017-12-04Bibliographically approved
    4. Seismic signatures of complex geological structures in the Cue-Weld range area, Murchison domain, Yilgarn Craton, Western Australia
    Open this publication in new window or tab >>Seismic signatures of complex geological structures in the Cue-Weld range area, Murchison domain, Yilgarn Craton, Western Australia
    2016 (English)In: Tectonophysics, Vol. 689, p. 56-66Article in journal, Meeting abstract (Refereed) Published
    Abstract [en]

    The Murchison domain forms the northwest part of the Youanmi Terrane, a tectonic unit within the Neoarchean Yilgarn Craton in Western Australia. In the Cue-Weld Range area the Murchison domain has experienced a complex magmatic and deformation history that resulted in a transposed array of greenstone belts that host significant iron, gold, and base metal deposits. In this study, we interpret the upper 2 s (about 6 km) of a deep crustal seismic profile TOGA-YU1, near the town of Cue, and correlate rock units and structures in outcrop with corresponding reflections. We performed 3D constant velocity ray-tracing and calculate the corresponding travel times for the reflectionsfor time domain pre-stack and post-stack seismic data. This allows us to link shallow reflections with mafic volcanic rocks of the Glen Group and basaltic rocks of the Polelle Group in outcrop. Based on our interpretation and published geological maps and data, we propose a model in which the local stratigraphy represents a refolded thrust system. To test our hypothesis, we applied 2D acoustic finite difference forward modeling. The corresponding synthetic data were processed in the same way as the acquired data. Comparisons between the acquired and the synthetic data show that the model is consistent with observations. We propose a new model for the subsurface of the Cue-Weld Range area and argue that some of the lithologies in the area are repeated structurally at different levels. Our approach highlights the benefit of imaging and modeling of deep seismic transects to resolve local structural complexity in Archean granite-greenstone terrains.

    Keywords
    Seismic interpretation; 3D structural model; Ray-tracing; Finite difference modeling; Weld range; Murchison domain
    National Category
    Geophysics Geology
    Research subject
    Geophysics with specialization in Solid Earth Physics; Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
    Identifiers
    urn:nbn:se:uu:diva-259139 (URN)10.1016/j.tecto.2016.02.020 (DOI)000387522100006 ()
    Available from: 2015-08-01 Created: 2015-07-27 Last updated: 2017-01-25Bibliographically approved
  • 22.
    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.

  • 23.
    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.
    Seismic Forward Modeling of a Poly-metallic Massive sulfide Deposit at Garpenberg, Central Sweden2013In: 75th EAGE Conference & Exhibition incorporating SPE EUROPEC 2013, 2013Conference paper (Refereed)
  • 24.
    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.
    The effect of the backfilled stopes on seismic imaging of a sulfide deposit in Garpenberg, central Sweden2015Manuscript (preprint) (Other academic)
  • 25.
    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.
    Ask, Maria
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Revealing the deeper structure of the end-glacial Parvie fault system in northern Sweden by seismic reflection profiling2015In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 6, no 2, p. 621-632Article in journal (Refereed)
    Abstract [en]

    A new seismic reflection survey for imaging deeper levels of the end-glacial Parvie fault system in northern Sweden was acquired in June 2014. The Parvie fault system hosts the largest fault scarp so far documented in northern Scandinavia, both in terms of its length and calculated magnitude of the earthquake that generated it. Present-day microearthquakes occur along the length of the fault scarp on the eastern side of the scarp, in general agreement with an east-dipping main fault. In the central section of the fault system, where there is a number of subsidiary faults east of the main Parvie scarp, it has been unclear how the earthquakes relate to the structures mapped at the surface. A seismic profile across the Parvie fault system acquired in 2007, with a mechanical hammer as a source, showed a good correlation between the surface mapped faults and moderate to steeply dipping reflections. The most pronounced reflectors could be mapped to about 3 km depth. In the new seismic survey, for deeper penetration an explosive source with a maximum charge size of 8.34 kg in 20 m deep shot holes was used. Reflectors can now be traced to deeper levels with the main 65A degrees east-dipping fault interpreted as a weakly reflective structure. As in the previous profile, there is a strongly reflective 60A degrees west-dipping structure present to the east of the main fault that can now be mapped to about 8 km depth. Extrapolations of the main and subsidiary faults converge at a depth of about 11.5 km, where current earthquake activity is concentrated, suggesting their intersection has created favorable conditions for seismic stress release. Based on the present and previous seismic reflection data, we propose potential locations for future boreholes for scientific drilling into the fault system. These boreholes will provide a better understanding of the reflective nature of the fault structures and stress fields along the faults at depth.

  • 26.
    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.
    Gessner, Klaus
    New Insights from Seismic Imaging Over the Youanmi Terrane, Yilgarn Craton, Western Australia2014In: Energy Procedia, Vol. 59, p. 113-119Article in journal (Refereed)
  • 27.
    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.

  • 28.
    Ahmadi, Omid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Koyi, Hemin
    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.
    Gessner, Klaus
    Geol Survey Western Australia, 100 Plain St, East Perth, WA 6004, Australia.
    Seismic signatures of complex geological structures in the Cue-Weld range area, Murchison domain, Yilgarn Craton, Western Australia2016In: Tectonophysics, Vol. 689, p. 56-66Article in journal (Refereed)
    Abstract [en]

    The Murchison domain forms the northwest part of the Youanmi Terrane, a tectonic unit within the Neoarchean Yilgarn Craton in Western Australia. In the Cue-Weld Range area the Murchison domain has experienced a complex magmatic and deformation history that resulted in a transposed array of greenstone belts that host significant iron, gold, and base metal deposits. In this study, we interpret the upper 2 s (about 6 km) of a deep crustal seismic profile TOGA-YU1, near the town of Cue, and correlate rock units and structures in outcrop with corresponding reflections. We performed 3D constant velocity ray-tracing and calculate the corresponding travel times for the reflectionsfor time domain pre-stack and post-stack seismic data. This allows us to link shallow reflections with mafic volcanic rocks of the Glen Group and basaltic rocks of the Polelle Group in outcrop. Based on our interpretation and published geological maps and data, we propose a model in which the local stratigraphy represents a refolded thrust system. To test our hypothesis, we applied 2D acoustic finite difference forward modeling. The corresponding synthetic data were processed in the same way as the acquired data. Comparisons between the acquired and the synthetic data show that the model is consistent with observations. We propose a new model for the subsurface of the Cue-Weld Range area and argue that some of the lithologies in the area are repeated structurally at different levels. Our approach highlights the benefit of imaging and modeling of deep seismic transects to resolve local structural complexity in Archean granite-greenstone terrains.

  • 29.
    Ahmadi, Omid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    3D Seismic Waveform Modeling of an Ore Body within a Stochastic Heterogeneous Medium2016Conference paper (Refereed)
    Abstract [en]

    Shallow mineral deposits of giant sizes are rapidly mined out and thus to sustain mining and help the economic growth, there is a tendency to explore deeper deposits. Most economic size mineral deposits are hosted within a complex and heterogeneous medium affected by various stages of deformation and metamorphism. Therefore, to understand their seismic responses, 3D heterogeneous modeling of various scale lengths should be considered. Here we present an algorithm that allows to build a model with various degrees of heterogeneity and structural anisotropy for the medium and use that to study a 6 Mt massive sulfide deposit at about 1 km depth. The seismic response was simulated using a 3D acoustic finite-difference method. Wavefield records through the model show imaging of the ore body in the presence of a high-degree of structural anisotropy/heterogeneity is difficult, but the associated amplitude anomaly appeared as diffraction can be detected within the 3D recorded wavefields and likely possible to be imaged using high-fold seismic data. The recorded wavefield however suggests some asymmetric pattern for the diffraction due to the high-degree of structural anisotropy introduced and hence care must be taken when processing and locating these deposits within highly preferentially-oriented heterogeneous medium.  

  • 30.
    Ahmadi, Pouya
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Elastic Anisotropy of Deformation Zones in both Seismic and Ultrasonic Frequencies: An Example from the Bergslagen Region, Eastern Sweden2013Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
    Abstract [en]

    Estimation of elastic anisotropy, which is usually caused by rock fabrics and mineral orientation, has an important role in exploration seismology and better understanding of crustal seismic reflections. If not properly taken care of during processing steps, it may lead to wrong interpretation or distorted seismic image. In this thesis, 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 deformation zone (Österbybruk Deformation Zone) in the Bergslagen region of eastern Sweden. Then, a general inversion code is deployed to invert measured phase velocities to obtain full elastic stiffness tensors of two samples from the major deformation zone in the study area. 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 isotropic processing section. This suggests that rock anisotropy may also contribute to the generation of reflections from the deformation zones in the study area but requires further investigations.

  • 31.
    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.

  • 32.
    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.

  • 33.
    Ahokangas, E.
    et al.
    University of Turku.
    Maries, Georgiana
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Mäkinen, J.
    University of Turku.
    Pasanen, A.
    Geological Survey of Finland (GTK).
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Seismic Imaging of Esker Sediments within the Satakunta Sandstone Depression in Köyliö, SW Finland2016Conference paper (Refereed)
    Abstract [en]

    The Satakunta sandstone depression infilled by the Pori-Koski interlobate esker sediments hosts a major high-quality groundwater reservoir in Köyliö, SW Finland. These up to 100 m thick sediments were delineated for the first time down to bedrock level by high-resolution reflection seismic method using a newly developed landstreamer consisting of 80-3C MEMs (micro electro mechanical) broadband sensors together with 50 wireless recorders connected to 10 Hz geophones to obtain greater depth penetrations. The 5-day survey resulted in about 5 km long seismic data (2-4 m receiver and shot spacing) and two profiles. Indications of crystalline basement are lacking in the tomography sections, implying that the (fractured) Rapakivi granite area extends further southeast than expected. The sandstone contact position was also ca. 500 m further to the east than expected. The sandstone depression and infilling esker sediments and the bedrock level were shown with good accuracy in both tomographic model and the reflection section. The hydraulically conductive esker core does not follow the sandstone contact and is underlain by older sediments. This case study illustrates the capability of high-resolution seismic surveys with the parameters used in this study for hydrogeological investigations and in particular in thick glacial sediments.

  • 34. Alcalde, J.
    et al.
    Marti, D.
    Calahorrano, A.
    Marzan, I.
    Ayarza, P.
    Carbonell, R.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pérez-Estaún, A.
    Active seismic characterization experiments of the Hontomin research facility for geological storage of CO2, Spain2013In: International Journal of Greenhouse Gas Control, ISSN 1750-5836, E-ISSN 1878-0148, Vol. 19, no 0, p. 785-795Article in journal (Refereed)
    Abstract [en]

    An active source seismic experiment was carried out as part of the subsurface characterization study of the first Spanish Underground Research Facility for Geological Storage of CO2 in Hontomín (Burgos, Spain). The characterization experiment included a 36 km2 3D seismic reflection survey and two three-component seismic profiles. The target reservoir is a saline aquifer located at 1450 m depth within Lower Jurassic carbonates (Lias). The main seal is formed by interlayered marlstones and marly limestones of Early to Middle Jurassic age (Dogger and Lias). The seismic images obtained allow defining the 3D underground architecture of the reservoir site. The structure consists of an asymmetric dome crosscut by a relatively complex fault system. The detailed characterization of the fracture system is currently under study to unravel the geometric distribution of the faults and their extent within the different formations that form the structure. The constrained model has guided the design of the injection and monitoring boreholes and provided the data for the baseline study. The resultant high resolution seismic model will be used as a reference in future monitoring stages.

  • 35. 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.

  • 36. Alcalde, Juan
    et al.
    Marzan, Ignacio
    Saura, Eduard
    Marti, David
    Ayarza, Puy
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Perez-Estaun, Andres
    Carbonell, Ramon
    3D geological characterization of the Hontomin CO2 storage site, Spain: Multidisciplinary approach from seismic, well-log and regional data2014In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 627, p. 6-25Article in journal (Refereed)
    Abstract [en]

    The first Spanish Technological Development plant for CO2 storage is currently under development in Hontomin (Spain), in a fractured carbonate reservoir. The subsurface 3D geological structures of the Hontomin site were interpreted using well-log and 3D seismic reflection data. A shallow low velocity zone affects the wave propagation and decreases the coherency of the underlying seismic reflections, deteriorating the quality of the seismic data, and thus preventing a straightforward seismic interpretation. In order to provide a fully constrained model, a geologically supervised interpretation was carried out. In particular, a conceptual geological model was derived from an exhaustive well-logging analysis. This conceptual model was then improved throughout a detailed seismic facies analysis on selected seismic sections crossing the seismic wells and in consistency with the regional geology, leading to the interpretation of the entire 3D seismic volume. This procedure allowed characterizing nine main geological levels and four main fault sets. Thus, the stratigraphic sequence of the area and the geometries of the subsurface structures were defined. The resulting depth-converted 3D geological model allowed us to estimate a maximum CO2 storage capacity of 5.85 Mt. This work provides a 3D geological model of the Hontomin subsurface, which is a challenging case study of CO2 storage in a complex fractured carbonate reservoir. 

  • 37.
    Alfonzo, Miguel
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Post‐processing of Airborne data using the Broadband Frequency Receiver instrument ADU072009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In August 2008 and June 2009 two sets of airborne measurements were made in Falun and Borlänge, respectively, by the Geological Survey of Sweden (SGU). The purpose of these campaigns was to test the new Multi Frequency Receiver (MFR) instrument called ADU07 for the collection of airborne data in the VLF and LF bands. This system was designed by Metronix and adapted by Uppsala University together with the SGU in the frame of a joint research project.

    The SGU in its bedrock mapping program routinely records VLF signals from only two transmitters in the frequency band of 14‐30 kHz. The RMT technique also makes use of electromagnetic signals in both the VLF and LF bands in the frequency range of 10‐250 kHz. By measuring all the three magnetic field components in this broader band, the data acquired by the new MFR system can provide high lateral and vertical resolution compared to the VLF data. This can be done by applying the concepts used for the EnviroMT. The joint research therefore aims at extending the VLF technique currently used by the SGU for geophysical investigations and whereby generating improved and more detailed anomaly maps.

    The airborne measurements with the ADU07 system were performed by continuously recording the three magnetic field components with a sampling frequency of 512 kHz in three channels. The prior evaluation of the data gave good results in the beginning. However, later tests showed that there were some near field sources onboard the aeroplane that contaminated the data and highly affected the estimation of transfer functions from the radio transmitters’ signals. The noise was basically generated by other measuring instrumentation and the common power supply used to feed both the ADU07 and the PC controller. The main aim of the present project is to develop a processing method that identifies frequencies from these near field sources and filters them out from the spectral ADU07 data. This work has been carried out by writing MATLAB routines. After the filtering, more reliable transfer functions that provide relevant information about the Earth’s resistivity structure can be estimated.

    Different methods were applied in order to detect the noise in the data. The mean value of the real part of the vertical magnetic field component (Hz) and the scalar tippers were firstly calculated along the profiles. These values should normally be close to zero. These methods did not give any valuable information since no patterns could be seen in the results. Afterwards, the vertical signal‐to‐noise ratio (VSNR) was calculated for every frequency at each station. This criterion showed that, for the first campaign, there were practically two sets of noise frequencies in the spectra: the first group corresponds to the even and odd harmonics of frequency 8 kHz, and the second group to frequency 23.47 kHz and its harmonics. For the last campaign, frequency 10.28 kHz and its harmonics were identified. The band averaging technique that splits the main frequency band into 9 overlapping sub‐bands with 1 octave of width was used. Finally, Prediction Errors (PE’s) were estimated to detect the remaining noise. A threshold was then chosen in order to remove from the spectra those frequencies with a PE above 3 and up to 20% of the number of transmitters in the sub‐bands. These processing steps improved considerably the tipper behaviour for the VLF band along the profiles, although some noise was also added. For the LF band, the filtering steps seem to have worsened the data quality and therefore the tipper estimation.

    The removal of important frequencies that were hidden in the high noise levels and the useof some other instruments during the data collection could be the causes of these responses.

  • 38.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Biedermann, Andrea
    Klonowska, Iwona
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Misra, Santanu
    Petrofabric development during experimental partial melting and recrystallization of a mica-schist analogue2015In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 16, no 10, p. 3472-3483Article in journal (Refereed)
  • 39.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bosshard, Sonja
    Hirt, Ann
    Mattsson, Hannes Björn
    Hetényi, György
    Internal flow structures in columnar jointed basalt from Hrepphólar, Iceland: II. Magnetic anisotropy and rock magnetic properties2012In: Bulletin of Volcanology, ISSN 0258-8900, E-ISSN 1432-0819Article in journal (Refereed)
  • 40.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Burg, Jean-Pierre
    Berger, Julien
    Burlini, Luigi
    Seismic properties of the Kohistan oceanic arc root: insights from laboratory measurements and thermodynamic modeling2013In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 14, no 6, p. 1819-1841Article in journal (Refereed)
    Abstract [en]

    P-wave velocities (Vp) have been measured in the laboratory and calculated using thermodynamic modeling for seven representative rock samples from the lower crust to mantle section of the Kohistan paleo-island arc. Lower crustal rocks comprise plagioclase-rich gabbro, garnet-bearing gabbro, and hornblendite; mantle rocks comprise garnetite, pyroxenite, websterite, and dunite. Measurements were performed at confining pressures up to 0.5GPa and temperatures up to 1200 degrees C. Vp were also calculated using rock major element chemistry with the Perple_X software package. Calculated Vp match closely the laboratory measurements. At depths representative for the arc root, Vp of upper mantle rocks vary from 7.7-8.1km/s, whereas the lower crustal rocks have velocities between 6.9-7.5km/s. P-wave anisotropy is small, with exceptions of sheared gabbros. Measured and calculated seismic properties are consistent with, and complement a growing database of published seismic properties from the Kohistan arc. In the light of such data, we discuss seismic imaging of present-day island arcs. Intermediate Vp (7.4-7.7km/s) in arc roots can be explained by pyroxenites and garnet-bearing mafic rocks. Strong seismic reflectors may be related to garnetites (8.0-8.2km/s).

  • 41.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Burlini, Luigi
    Mainprice, David
    Hirt, Ann
    Elastic properties of anisotropic synthetic calcite-muscovite aggregates2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115Article in journal (Refereed)
  • 42.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Henry, Bernard
    Jackson, Mike
    Werner, Tomasz
    Lagroix, France
    Methods and applications of magnetic anisotropy: A special issue in recognition of the career of Graham J. Borradaile2014In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 629, p. 1-5Article in journal (Refereed)
  • 43.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Herwegh, Marco
    Schmidt, Volkmar
    Pettke, Thomas
    Hirt, Ann
    Magnetic susceptibility as a tool to study deformed calcite with variable impurity content2010In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 11, no 1Article in journal (Refereed)
  • 44.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hirt, Ann
    Herwegh, Marco
    Ebert, Andreas
    Walter, Jens
    Leiss, Bernd
    Burlini, Luigi
    Seismic anisotropy in the Morcles nappe shear zone: Implications for seismic imaging of crustal scale shear zones2013In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 603, p. 162-178Article in journal (Refereed)
    Abstract [en]

    Microstructures and textures of calcite mylonites from the Morcles nappe large-scale shearzone in southwestern Switzerland develop principally as a function of 1) extrinsic physical parameters including temperature, stress, strain, strain rate and 2) intrinsic parameters, such as mineral composition. We collected rock samples at a single location from this shear zone, on which laboratory ultrasonic velocities, texture and microstructures were investigated and quantified. The samples had different concentration of secondary mineral phases (<5 up to 40 vol.%). Measured seismic P waveanisotropy ranges from 6.5% for polyphase mylonites (similar to 40 vol.%) to 18.4% in mylonites with <5 vol.% secondary phases. Texture strength of calcite is the main factor governing the seismic P wave anisotropy. Measured S wave splitting is generally highest in the foliation plane, but its origin is more difficult to explain solely by calcite texture. Additional texture measurements were made on calcite mylonites with low concentration of secondary phases (<= 10 vol.%) along the metamorphic gradient of the shear zone (15 km distance). A systematic increase in texture strength is observed moving from the frontal part of the shear zone (anchimetamorphism: 280 degrees C) to the higher temperature, basal part (greenschist facies: 350-400 degrees C). Calculated P wave velocities become increasingly anisotropic towards the high-strain part of the nappe, from an average of 5.8%in the frontal part to 13.2% in the root of the basal part. Secondary phases raise an additional complexity, and may act either to increase or decrease seismic anisotropy of shear zone mylonites. Inlight of our findings we reinterpret the origin of some seismically reflective layers in the Grone-Zweisimmen line in southwestern Switzerland (PNR20 Swiss National Research Program). We hypothesize that reflections originate in part from the lateral variation in textural and microstructural arrangement of calcite mylonites in shear zones. 

  • 45.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hirt, Ann
    Herwegh, Marco
    Leiss, Bernd
    Magnetic anisotropy reveals Neogene tectonic overprint in higly strained carbonate mylonites from the Morcles nappe, Switzerland2011In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 33, p. 1010-1022Article in journal (Refereed)
  • 46.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hirt, Ann
    Schmidt, Volkmar
    Dietrich, Dorothee
    Magnetic fabrics of the Morcles nappe complex2009In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 466, p. 89-100Article in journal (Refereed)
  • 47.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Bulk strain in orogenic wedges based on insights from magnetic fabrics in sandbox models2018In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 46, no 6, p. 483-486Article in journal (Refereed)
    Abstract [en]

    Anisotropy of magnetic susceptibility (AMS) analysis is used as a petrofabric indicator for a set of four identical-setup sandbox models that were shortened by different amounts and simulate contraction in a fold-and-thrust belt. During model shortening, a progressive reorientation of the initial magnetic fabric occurs due to horizontal compaction of the sand layers. At the early stages of shortening, magnetic lineation (k(1) axis) rotates parallel to the model backstop with subhorizontal orientation, whereas the minimum susceptibility (k(3) axis) is subvertical, which indicates a partial tectonic overprint of the initial fabric. With further shortening, the k(3) axis rotates to subhorizontal orientation, parallel to shortening direction, marking the development of a dominant tectonic magnetic fabric. A near-linear transition in magnetic fabric is observed from the initial bedding to tectonic fabric in all four models, which reflects a progressive transition in deformation from foreland toward hinterland. Model results confirm a long-held hypothesis where the AMS pattern and degree of anisotropy have been suggested to reflect the amount of layer-parallel shortening, based on field observations in many mountain belts. Results furthermore indicate that grain rotation may play a significant role in low-grade compressive tectonic regimes. The combination of analogue models with AMS enables the possibility to predict magnetic fabrics in different tectonic settings and to develop quantitative links between AMS and strain.

  • 48.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Mainprice, David
    Seismic properties and anisotropy of the continental crust: Predictions based on mineral texture and rock microstructure2017In: Reviews of geophysics, ISSN 8755-1209, E-ISSN 1944-9208, Vol. 55, no 2, p. 367-433Article, review/survey (Refereed)
  • 49.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Mainprice, David
    Madonna, Claudio
    Burlini, Luigi
    Hirt, Ann
    Application of differential effective medium, magnetic pore fabric analysis, and X-ray microtomography to calculate elastic properties of porous and anisotropic rock aggregates2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116Article in journal (Refereed)
  • 50.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Misra, Santanu
    Klonowska, Iwona
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Mainprice, David
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Ultrasonic velocity drops and anisotropy reduction in mica-schist analogues due to melting with implications for seismic imaging of continental crust2015In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 425, p. 24-33Article in journal (Refereed)
1234567 1 - 50 of 786
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