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  • 1.
    Abtahi, Sayyed Mohammad
    et al.
    Isfahan Univ Technol, Dept Min Engn, Esfahan, Iran.
    Pedersen, Laust Börsting
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Kamm, Jochen
    Univ Munster, Dept Geophys, Munster, Germany.
    Kalscheuer, Thomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    A new reference model for 3D inversion of airborne magnetic data in hilly terrain: A case study from northern Sweden2018Ingår i: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 83, nr 1, s. B1-B12Artikel i tidskrift (Refereegranskat)
    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.

  • 2.
    Basir, Hadi Mahdavi
    et al.
    Amirkabir Univ Technol, Dept Petr Engn, Tehran 158754413, Iran.
    Javaherian, Abdolrahim
    Amirkabir Univ Technol, Dept Petr Engn, Tehran 158754413, Iran;Univ Tehran, Inst Geophys, Tehran 141556466, Iran.
    Shomali, Zaher Hossein
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik. Univ Tehran, Inst Geophys, Tehran 141556466, Iran.
    Firouz-Abadi, Roohollah Dehghani
    Sharif Univ Technol, Dept Aerosp Engn, Tehran 1136511155, Iran.
    Gholamy, Shaban Ali
    Natl Iranian Oil Co, Explorat Directorate, Dept Geophys, Tehran 1994814695, Iran.
    Acoustic wave propagation simulation by reduced order modelling2018Ingår i: Exploration Geophysics, ISSN 0812-3985, E-ISSN 1834-7533, Vol. 49, nr 3, s. 386-397Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wave propagation simulation, as an essential part of many algorithms in seismic exploration, is associated with high computational cost. Reduced order modelling(ROM) is a known technique in many different applications that can reduce the computational cost of simulation by employing an approximation of the model parameters. ROM can be carried out using different algorithms. The method proposed in this work is based on using the most important mode shapes of the model, which can be computed by an efficient numerical method. The numerical accuracy and computational performance of the proposed method were investigated over a simple synthetic velocity model and a portion of the SEG/EAGE velocity model. Different boundary conditions were discussed, and among them the random boundary condition had higher performance for applications like reverse time migration (RTM). The capability of the proposed method for RTM was evaluated and confirmed by the synthetic velocity model of SEG/EAGE. The results showed that the proposed ROM method, compared with the conventional finite element method (FEM), can decrease the computational cost of wave propagation modelling for applications with many simulations like the reverse time migration. Depending on the number of simulations, the proposed method can increase the computational efficiency by several orders of magnitudes.

  • 3.
    Almqvist, Bjarne
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Koyi, Hemin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Bulk strain in orogenic wedges based on insights from magnetic fabrics in sandbox models2018Ingår i: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 46, nr 6, s. 483-486Artikel i tidskrift (Refereegranskat)
    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.

  • 4.
    Sopher, Daniel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Converting scanned images of seismic reflection data into SEG-Y format2018Ingår i: EARTH SCIENCE INFORMATICS, ISSN 1865-0473, Vol. 11, nr 2, s. 241-255Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Archives across the world contain vast amounts of old or "vintage" seismic reflection data, which are largely inaccessible for geo-scientific research, due to the out-dated media on which they are stored. Despite the age of these data, they often have great potential to be of use in modern day research. It is often the case that seismic reflection data within these archives are only available as a processed stacked section, printed on paper or film. In this study, a method for the conversion (vectorization) of scanned images of stacked reflection seismic data to standard SEG-Y format is presented. The method addresses data displayed with a line denoting the waveform, where areas on one side of the baseline are shaded (i.e. wiggle trace, variable fill). The method provides an improvement on other published methods utilized within currently available academic software. Unlike previous studies, the method used to detect trace baselines and to detect and remove timelines on the seismic image is described in detail. Furthermore, a quantitative analysis of the performance of the method is presented, showing that an average trace-to-trace correlation coefficient of between 0.8 and 0.95 can be achieved for typical plotting styles. Finally, a case study where the method is applied to vectorize over 1700 km of land seismic data from the island of Gotland (Sweden) is presented.

  • 5.
    Ivandic, Monika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Deep Seismic sounding Data_Annex2018Dataset
  • 6.
    Ghosal, D.
    et al.
    Indian Inst Technol Kanpur, Kanpur 208016, Uttar Pradesh, India.
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Estimation of dispersion attributes at seismic frequency-a case study from the Frigg-Delta reservoir, North sea2018Ingår i: Journal of Geophysics and Engineering, ISSN 1742-2132, E-ISSN 1742-2140, Vol. 15, nr 5, s. 1799-1810Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Estimation of the reservoir physical parameters in hydrocarbon zones is important for seismic exploration. Frequency analysis has proven to provide useful information on the velocity dispersion and attenuation of seismic wave-fields propagating through porous media. In this study we have carried out a velocity and reflectivity dispersion analysis using borehole and post-stack angle dependent seismic datasets from the Frigg-Delta reservoir in the North Sea. Rock physics analysis using borehole datasets indicate that in the seismic frequency range (1-100 Hz) dispersion maxima appear at similar to 5 Hz frequency, assuming an oil saturation associated with the reservoir ranging between 40% and 60%, porosity as 30% and permeability as 1 Darcy. Moreover, the P-wave velocity (V-p) dispersion is estimated similar to 5 times less for the high oil saturation in the upper part of the reservoir compared to that for low oil saturation in the deeper part of the reservoir. Dispersion analysis on the angle dependent seismic migrated sections is carried out by inverting spectrally decomposed isofrequency sections using a least squares algorithm. The inverted results show that the top of the reservoir is more clearly demarcated at low frequency (similar to 7Hz) than at higher frequencies.

  • 7.
    Amini, Samar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Roberts, Roland
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Raeesi, Mohammad
    SeisAnalysis AS, Bergen, Norway.
    Shomali, Zaher Hossein
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Lund, Björn
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Zarifi, Zoya
    Univ Western Ontario, Dept Earth Sci, London, ON, Canada.
    Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet2018Ingår i: Journal of Seismology, ISSN 1383-4649, E-ISSN 1573-157X, Vol. 22, nr 4, s. 815-831Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An intraplate earthquake doublet, with 11-min delay between the events, devastated the city of Varzeghan in northwestern Iran on August 11, 2012. The first Mw 6.5 strike-slip earthquake, which occurred after more than 200 years of low seismicity, was followed by an Mw 6.4 oblique thrust event at an epicentral separation of about 6 km. While the first event can be associated with a distinct surface rupture, the absence of a surface fault trace and no clear aftershock signature makes it challenging to identify the fault plane of the second event. We use teleseismic body wave inversion to deduce the slip distribution in the first event. Using both P and SH waves stabilize the inversion and we further constrain the result with the surface rupture extent and the aftershock distribution. The obtained slip pattern shows two distinct slip patches with dissimilar slip directions where aftershocks avoid high-slip areas. Using the estimated slip for the first event, we calculate the induced Coulomb stress change on the nodal planes of the second event and find a preference for higher Coulomb stress on the N-S nodal plane. Assuming a simple slip model for the second event, we estimate the combined Coulomb stress changes from the two events on the focal planes of the largest aftershocks. We find that 90% of the aftershocks show increased Coulomb stress on one of their nodal planes when the N-S plane of the second event is assumed to be the correct fault plane.

  • 8.
    Heinrichs, Jannica
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Olsson, Mikael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap. Materials Science, Dalarna University, Sweden.
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Jacobson, Staffan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Initial surface failure and wear of cemented carbides in sliding contact with different rock types2018Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 408-409, s. 43-55Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The initial wear, deformation and degradation of cemented carbide in contact with different rock types are studied using a crossed cylinder sliding test. The sliding distance is limited to centimetres at a time, interrupted by successive SEM analysis. This allows for careful studies of the gradually changing microstructure of the cemented carbide during the test. Five different rock types are included; granite, metal sulphide ore, mica schist, quartzite and marble. All rock types are very different in microstructure, composition and properties. The cemented carbide grade used for the evaluation contains 6 wt% Co and fine (~ 1 µm) WC grains, a grade commonly used in rock drilling. The results show that the cemented carbide microstructure becomes altered already during the very first contact with rock. The initial wear rate and wear character is highly influenced by the rock type. The initial wear of the cemented carbide is highest against quartzite and lowest against marble.

  • 9.
    Muhamad, Harbe
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper. Department of Geology, Salahaddin University, Erbil, Kurdistan Region, Iraq.
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Malehmir, Alireza
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Sopher, Daniel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Integrated interpretation of geophysical data of the Paleozoic structure in the northwestern part of the Siljan Ring impact crater, central Sweden2018Ingår i: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 148, s. 201-215Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 10.
    Andersson, Magnus
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Malehmir, Alireza
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Internal architecture of the Alnö alkaline and carbonatite complex (central Sweden) revealed using 3D models of gravity and magnetic data2018Ingår i: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 740-741, s. 53-71Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Alnö Complex in central Sweden is one of the largest alkaline and carbonatite ring-shaped intrusions in the world. Presented here is the 3D models of ground gravity and aeromagnetic data that confirm some of the previous ideas about the 3D geometry of the complex but also suggest that the complex may continue laterally further to north than previously expected. The data show the complex as (i) a strong positive Bouguer anomaly, around 20 mGal, and (ii) a strong positive magnetic anomaly, exceeding 2000 nT. Magnetic structures are clearly discernible within the complex and surrounding area. Both gravity and magnetic inversion models suggest that dense (> 2850 kg/m(3)) and magnetic ( > 0.05 SI) rocks extend down to about 3.5-4 km depth. Previous studies have suggested a solidified magma reservoir at this approximate depth. The inversion models further suggest that two apparently separate regions within the complex are likely connected at depth, starting from 800 to 1000 m, implying a common source for the rocks observed in these two regions. Modelling of the aeromagnetic data indicates that a > 3 km wide ring-shaped magnetic high situated in the sea north of Alnö Island may be a part of the complex. This could link a smaller satellite intrusion in Soraker on mainland to the larger intrusion on Alnö Island. While the rim of the ring must consist of highly magnetic rocks to support the anomaly, the centre has relatively low magnetisation and is probably made up of low-magnetic wall-rocks or metasomatised wall-rocks down to about 2 km depth. Below this depth the 3D susceptibility model suggests higher magnetic susceptibility values. Worldwide alkaline and carbonatite complexes are the main resources for rare earth elements (REEs), and owing to the size of the Alnö Complex, it can be highly prospective for REEs at depth.

  • 11.
    Wang, Shunguo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Kalscheuer, Thomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Bastani, Mehrdad
    Malehmir, Alireza
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Pedersen, Laust Börsting
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Dahlin, Torleif
    Meqbel, Naser
    Joint inversion of lake-floor electrical resistivity tomography and boat-towed radio-magnetotelluric data illustrated on synthetic data and an application from the Äspö Hard Rock Laboratory site2018Ingår i: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 213, nr 1, s. 511-533Artikel i tidskrift (Refereegranskat)
  • 12.
    Mattsson, Hannes
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik. Institute of Geochemistry and Petrology, Department of Earth Sciences, Swiss Federal Institute of Technology (ETH Zürich), Zürich, Switzerland.
    Balashova, Anna
    Institute of Geochemistry and Petrology, Department of Earth Sciences, Swiss Federal Institute of Technology (ETH Zürich), Zürich, Switzerland.
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Bosshard-Stadlin, Sonja
    Weidendorfer, Daniel
    Magnetic mineralogy and rock magnetic properties of silicate and carbonatite rocks from Oldoinyo Lengai volcano (Tanzania)2018Ingår i: Journal of African Earth Sciences, ISSN 0899-5362, Vol. 142, s. 193-206Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Oldoinyo Lengai, a stratovolcano in northern Tanzania, is most famous for being the only currently active carbonatite volcano on Earth. The bulk of the volcanic edifice is dominated by eruptive products produced by silica-undersaturated, peralkaline, silicate magmas (effusive, explosive and/or as cumulates at depth). The recent (2007–2008) explosive eruption produced the first ever recorded pyroclastic flows at this volcano and the accidental lithics incorporated into the pyroclastic flows represent a broad variety of different rock types, comprising both extrusive and intrusive varieties, in addition to various types of cumulates. This mix of different accidental lithics provides a unique insight into the inner workings of the world's only active carbonatite volcano.

    Here, we focus on the magnetic mineralogy and the rock magnetic properties of a wide selection of samples spanning the spectrum of Oldoinyo Lengai rock types compositionally, as well from a textural point of view. Here we show that the magnetic properties of most extrusive silicate rocks are dominated by magnetite-ulvöspinel solid solutions, and that pyrrhotite plays a larger role in the magnetic properties of the intrusive silicate rocks. The natrocarbonatitic lavas, for which the volcano is best known for, show distinctly different magnetic properties in comparison with the silicate rocks. This discrepancy may be explained by abundant alabandite crystals/blebs in the groundmass of the natrocarbonatitic lavas.

    A detailed combination of petrological/mineralogical studies with geophysical investigations is an absolute necessity in order to understand, and to better constrain, the overall architecture and inner workings of the subvolcanic plumbing system. The results presented here may also have implications for the quest in order to explain the genesis of the uniquely natrocarbonatitic magmas characteristic of Oldoinyo Lengai.

  • 13. Bender, Hagen
    et al.
    Ring, Uwe
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Grasemann, Bernard
    Stephens, Mike
    Metamorphic zonation by out‐of‐sequence thrusting at back‐stepping subduction zones: Sequential accretion of the Caledonian internides, central Sweden2018Ingår i: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194Artikel i tidskrift (Refereegranskat)
  • 14.
    Ivandic, Monika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Kummerow, Juliane ()
    GFZ German Research Centre for Geosciences, Helmholtz Centre PotsdamTelegrafenberg, Potsdam, Germany.
    Huang, Fei ()
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Juhlin, Christopher ()
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Lueth, Stefan ()
    GFZ German Research Centre for Geosciences, Helmholtz Centre PotsdamTelegrafenberg, Potsdam, Germany.
    Monitoring CO2 saturation using time–lapse AVO analysis of 3D seismic data from the Ketzin CO2 storage pilot site, Germany2018Ingår i: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478Artikel i tidskrift (Refereegranskat)
  • 15.
    Roberts, Roland
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Carbonell, Ramon
    Adamaki, Angeliki
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ivandic, Monika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Position Document on Future DSS Data Accessibility2018Rapport (Övrig (populärvetenskap, debatt, mm))
  • 16.
    Ivandic, Monika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Position Document on Future DSS Data Accessibility_Annex2018Dataset
  • 17.
    Xu, Zhuo
    et al.
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China;Minist Land & Resources, Key Lab Appl Geophys, Changchun 130026, Jilin, Peoples R China.
    Sopher, Daniel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Han, Liguo
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China;Minist Land & Resources, Key Lab Appl Geophys, Changchun 130026, Jilin, Peoples R China.
    Gong, Xiangbo
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China;Minist Land & Resources, Key Lab Appl Geophys, Changchun 130026, Jilin, Peoples R China.
    Radon-domain interferometric interpolation for reconstruction of the near-offset gap in marine seismic data2018Ingår i: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 151, s. 125-141Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In towed marine seismic data acquisition, a gap between the source and the nearest recording channel is typical. Therefore, extrapolation of the missing near-offset traces is often required to avoid unwanted effects in subsequent data processing steps. However, most existing interpolation methods perform poorly when extrapolating traces. Interferometric interpolation methods are one particular method that have been developed for filling in trace gaps in shot gathers. Interferometry-type interpolation methods differ from conventional interpolation methods as they utilize information from several adjacent shot records to fill in the missing traces. In this study, we aim to improve upon the results generated by conventional time-space domain interferometric interpolation by performing interferometric interpolation in the Radon domain, in order to overcome the effects of irregular data sampling and limited source-receiver aperture. We apply both time-space and Radon-domain interferometric interpolation methods to the Sigsbee2B synthetic dataset and a real towed marine dataset from the Baltic Sea with the primary aim to improve the image of the seabed through extrapolation into the near-offset gap. Radon-domain interferometric interpolation performs better at interpolating the missing near offset traces than conventional interferometric interpolation when applied to data with irregular geometry and limited source-receiver aperture. We also compare the interferometric interpolated results with those obtained using solely Radon transform (RT) based interpolation and show that interferometry-type interpolation performs better than solely RT-based interpolation when extrapolating the missing near-offset traces. After data processing, we show that the image of the seabed is improved by performing interferometry-type interpolation, especially when Radon-domain interferometric interpolation is applied.

  • 18.
    Xu, Zhuo
    et al.
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China;Minist Land & Resources, Key Lab Appl Geophys, Changchun 130026, Jilin, Peoples R China.
    Sopher, Daniel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Han, Liguo
    Jilin Univ, Coll Geoexplorat Sci & Technol, Changchun 130026, Jilin, Peoples R China;Minist Land & Resources, Key Lab Appl Geophys, Changchun 130026, Jilin, Peoples R China.
    Reconstruction of the near-offset gap in marine seismic data using seismic interferometric interpolation2018Ingår i: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 66, nr S1, s. 1-26Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 19.
    Basir, Hadi Mandavi
    et al.
    Amirkabir Univ Technol, Dept Petr Engn, Tehran, Iran.
    Javaherian, Abdolrahim
    Amirkabir Univ Technol, Dept Petr Engn, Tehran, Iran;Univ Tehran, Inst Geophys, Tehran, Iran.
    Shomali, Zaher Hossein
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik. Univ Tehran, Inst Geophys, Tehran, Iran.
    Firouz-Abadi, Roohollah Dehghani
    Sharif Univ Technol, Dept Aerosp Engn, Tehran, Iran.
    Gholamy, Shaban Ali
    Natl Iranian Oil Co, Explorat Directorate, Dept Geophys, Tehran, Iran.
    Reverse time migration by Krylov subspace reduced order modeling2018Ingår i: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 151, s. 298-308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Imaging is a key step in seismic data processing. To date, a myriad of advanced pre-stack depth migration approaches have been developed; however, reverse time migration (RTM) is still considered as the high-end imaging algorithm. The main limitations associated with the performance cost of reverse time migration are the intensive computation of the forward and backward simulations, time consumption, and memory allocation related to imaging condition. Based on the reduced order modeling, we proposed an algorithm, which can be adapted to all the aforementioned factors. Our proposed method benefit from Krylov subspaces method to compute certain mode shapes of the velocity model computed by as an orthogonal base of reduced order modeling. Reverse time migration by reduced order modeling is helpful concerning the highly parallel computation and strongly reduces the memory requirement of reverse time migration. The synthetic model results showed that suggested method can decrease the computational costs of reverse time migration by several orders of magnitudes, compared with reverse time migration by finite element method.

  • 20.
    Gudmundsson, Olafur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Sadeghisorkhani, Gudmundsson, Tryggvason, 2018. GSpecDisp: A matlab GUI package for phase-velocity dispersion measurements from ambient-noise correlations, Computers and Geosciences 110, 41-53.2018Ingår i: Computers and Geosciences, Vol. 110, s. 41-53Artikel i tidskrift (Refereegranskat)
  • 21.
    Gudmundsson, Olafur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Sadeghisorkhani, Hamzeh, Gudmundsson, Olafur, Tryggvason, Ari, 2018.  GSpecDisp: A matlab GUI package for phase-velocity dispersion measurements from ambient-noise correlograms, Computers and Geosciences 110, 41-53.2018Ingår i: Computers and Geosciences, Vol. 110, s. 41-53Artikel i tidskrift (Refereegranskat)
  • 22.
    Fälth, Billy
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik. Clay Technology AB.
    Simulating Earthquake Rupture and Near-Fault Fracture Response2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Sweden is presently a low seismicity area where most earthquakes are small and pose no serious threat to constructions. For the long-term perspectives of safety assessments of geological repositories for spent nuclear fuel, however, the effects of large earthquakes have to be considered. For the Swedish nuclear waste storage concept, seismically induced secondary fracture shear displacements across waste canister positions could pose a long-term seismic risk to the repository.

    In this thesis, I present earthquake simulations with which I study the potential for near-fault secondary fracture shear displacements. As a measure I use the Coulomb Failure Stress (CFS), but also calculate explicit fracture displacements. I account for both the dynamic and quasi-static stress perturbations generated during the earthquake. As numerical tool I use the 3DEC code, whose performance I validate using Stokes closed-form solution and the Compsyn code as benchmarks. In a model of a Mw 6.4 earthquake, I investigate how fault roughness, the fault rupture propagation model and rupture velocity may impact the near-fault CFS evolution. I find that fault roughness can reduce the amount of fault slip by tens of percent, but also increase the near-fault CFS with similar amounts locally. Furthermore, different fault rupture models generate similar CFS levels. I also find that the secondary stresses scale with rupture velocity.

    In a model based on data from the Forsmark nuclear waste repository site, and assuming stress conditions prevailing at the end of a glaciation, I simulate several high stress drop ~Mw 5.6 earthquake scenarios on the gently dipping fault zone ZFMA2 and calculate secondary fracture displacements on 300 m diameter planar fractures. Less than 1% of the fractures at the shortest distance from ZFMA2 generate displacements exceeding the 50 mm criterion established by the Swedish Nuclear Fuel and Waste Management Co. Given the high stress drops and the assumption of fracture planarity, I consider the calculated displacements to represent upper bound estimates of possible secondary displacements at Forsmark. Hence, the results should strengthen the confidence in the safety assessment of the nuclear waste repository at the Forsmark site.

    Delarbeten
    1. Simulating earthquake rupture and off-fault fracture response: Application to the safety assessment of the Swedish nuclear waste repository
    Öppna denna publikation i ny flik eller fönster >>Simulating earthquake rupture and off-fault fracture response: Application to the safety assessment of the Swedish nuclear waste repository
    Visa övriga...
    2015 (Engelska)Ingår i: Bulletin of The Seismological Society of America (BSSA), ISSN 0037-1106, E-ISSN 1943-3573, Vol. 105, nr 1, s. 134-151Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    To assess the long‐term safety of a deep repository of spent nuclear fuel, upper bound estimates of seismically induced secondary fracture shear displacements are needed. For this purpose, we analyze a model including an earthquake fault, which is surrounded by a number of smaller discontinuities representing fractures on which secondary displacements may be induced. Initial stresses are applied and a rupture is initiated at a predefined hypocenter and propagated at a specified rupture speed. During rupture we monitor shear displacements taking place on the nearby fracture planes in response to static as well as dynamic effects. As a numerical tool, we use the 3Dimensional Distinct Element Code (3DEC) because it has the capability to handle numerous discontinuities with different orientations and at different locations simultaneously. In tests performed to benchmark the capability of our method to generate and propagate seismic waves, 3DEC generates results in good agreement with results from both Stokes solution and the Compsyn code package. In a preliminary application of our method to the nuclear waste repository site at Forsmark, southern Sweden, we assume end‐glacial stress conditions and rupture on a shallow, gently dipping, highly prestressed fault with low residual strength. The rupture generates nearly complete stress drop and an Mw 5.6 event on the 12  km2 rupture area. Of the 1584 secondary fractures (150 m radius), with a wide range of orientations and locations relative to the fault, a majority move less than 5 mm. The maximum shear displacement is some tens of millimeters at 200 m fault‐fracture distance.

    Nyckelord
    earthquake rupture modelling fracure
    Nationell ämneskategori
    Geofysik
    Forskningsämne
    Geofysik med inriktning mot seismologi
    Identifikatorer
    urn:nbn:se:uu:diva-237807 (URN)10.1785/0120140090 (DOI)000348898700008 ()
    Tillgänglig från: 2014-12-05 Skapad: 2014-12-05 Senast uppdaterad: 2018-04-04Bibliografiskt granskad
    2. Simulation of co-seismic secondary fracture displacements for different earthquake rupture scenarios at the proposed nuclear waste repository site in Forsmark
    Öppna denna publikation i ny flik eller fönster >>Simulation of co-seismic secondary fracture displacements for different earthquake rupture scenarios at the proposed nuclear waste repository site in Forsmark
    2016 (Engelska)Ingår i: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 84, s. 142-158Artikel i tidskrift (Refereegranskat) Published
    Nyckelord
    Secondary displacement; Forsmark; Nuclear waste disposal; Stress drop; Seismic efficiency
    Nationell ämneskategori
    Geofysik
    Forskningsämne
    Geofysik med inriktning mot seismologi
    Identifikatorer
    urn:nbn:se:uu:diva-283128 (URN)10.1016/j.ijrmms.2016.02.009 (DOI)000371895200015 ()
    Tillgänglig från: 2016-04-11 Skapad: 2016-04-11 Senast uppdaterad: 2018-04-10
    3. Influence of Fault Roughness on Co-Seismic Near-Fault Stress Evolution
    Öppna denna publikation i ny flik eller fönster >>Influence of Fault Roughness on Co-Seismic Near-Fault Stress Evolution
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Co-seismic displacements on fractures and faults close to large earthquakes may not contribute significantly to the shaking hazard for surface infrastructures. However, for deep geological nuclear waste repositories, such secondary displacements could, if large enough, damage intersected waste containers and constitute a significant long-term safety concern. To study how the potential for such displacements may depend on the earthquake rupture evolution, we simulate dynamic earthquake ruptures, and calculate the co-seismic evolution of Coulomb Failure Stress (CFS) on hypothetical fracture planes in the near-fault continuum. Poroelastic coupling is accounted for via Skempton’s coefficient B. We study three cases: (1) A planar fault with homogeneous properties. (2) A planar fault where the dynamic friction increases gradually along the fault edge to obtain a gentler rupture arrest. (3) An undulated fault with fractal properties. For Case 3, we consider ten different fault surface realizations. Since the undulations reduce fault slip, we also run models with adjusted dynamic friction coefficients, such that they generate seismic moments on par with that of Case 1. We observe the following: (i) The initial stress field, rather than the co-seismic stress effects, is the dominating influence on the fracture orientations that obtain the highest CFS values. (ii) Lower slip gradients and less fault slip in Case 2 reduce the maximum CFS by 10-15% relative to the reference case. (iii) Fault roughness may increase CFS locally by tens of percent. (iv) Given our reference value of B=0.5, B-value variations of ±0.5 would give CFS variations of ±20%, at most.

    Nationell ämneskategori
    Geofysik
    Identifikatorer
    urn:nbn:se:uu:diva-346811 (URN)
    Tillgänglig från: 2018-04-04 Skapad: 2018-04-04 Senast uppdaterad: 2018-04-04
    4. How does the Fault Rupture Model affect Simulated Co-Seismic Near-Fault Stress Evolution?
    Öppna denna publikation i ny flik eller fönster >>How does the Fault Rupture Model affect Simulated Co-Seismic Near-Fault Stress Evolution?
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The dynamic and static stress perturbations generated in an earthquake affect the stability of faults and fractures in the vicinity of the rupture. Estimates of co-seismic near-fault stress effects can be made using numerical simulations. Here, we study the co-seismic stress evolution close to an earthquake using two different models to simulate the rupture. One model is the linear slip-weakening (SW) model, where a spontaneous earthquake rupture is simulated. We compare this to a constant rupture velocity time-weakening (TW) model, which we implement in four different instances of rupture velocity Vr and strength reduction time interval Δtred. We evaluate the near-fault stress effects using the Coulomb Failure Stress (CFS), which we calculate from the stress evolution at various positions relative to the rupture plane. The results show that the TW method is capable of generating similar secondary effects as those generated by the SW model. However, the assumption of constant values of Δtred and Vr implies that there will always be locations on the rupture plane where these values are incompatible. We also see that variationsin Δtred and Vr have a significant impact on the results. Particularly, Vr is important for how the stresses around the rupture front are superimposed, and is thus important for the temporal evolution and spatial distribution of CFS around the fault. Lower Vr tends to generate a gentler near-fault stress evolution and lower peak CFS values. The results also indicate that not only the momentary value of Vr is important for the secondary stress effects at a near-fault position passed by the rupture, but also the integrated Vr-history up to that position.

    Nationell ämneskategori
    Geofysik
    Forskningsämne
    Geofysik med inriktning mot seismologi
    Identifikatorer
    urn:nbn:se:uu:diva-347597 (URN)
    Tillgänglig från: 2018-04-04 Skapad: 2018-04-04 Senast uppdaterad: 2018-04-04
  • 23.
    Grevemeyer, Ingo
    et al.
    GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany.
    R. RaneroCesar, Cesar
    Instituto de Ciencias del Mar, CSIC, Barcelona, Spain; CREA, Barcelona, Spain.
    Ivandic, Monika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Structure of oceanic crust and serpentinization at subduction trenches2018Ingår i: Geosphere, ISSN 1553-040X, E-ISSN 1553-040X, Vol. 14, nr 2, s. 395-418Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The subducting oceanic lithosphere may carry a large amount of chemically bound water into the deep Earth interior, returning water to the mantle, facilitating melting, and hence keeping the mantle mobile and, in turn, nurturing plate tectonics. Bending-related faulting in the trench–outer rise region prior to subduction has been recognized to be an important process, promoting the return flux of water into the mantle. Extensional faults in the trench–outer rise are opening pathways into the lithosphere, supporting hydration of the lithosphere, including alteration of dry peridotite to water-rich serpentine. In this paper, we review and summarize recent work suggesting that bend faulting is indeed a key process in the global water cycle, albeit not yet well understood. Two features are found in a worldwide compilation of tomographic velocity models derived from wide-angle seismic data, indicating that oceanic lithosphere is strongly modified when approaching a deep-sea trench: (1) seismic velocities in both the lower crust and upper mantle are significantly reduced compared to the structure found in the vicinity of mid-ocean ridges and in mature crust away from subduction zones; and (2) profiles shot perpendicular to the trench show both crustal and upper mantle velocities decreasing systematically approaching the trench axis, highlighting an evolutionary process because velocity reduction is related to deformation, alteration, and hydration. P-wave velocity anomalies suggest that mantle serpentinization at trenches is a global feature of all subducting oceanic plates older than 10–15 Ma. Yet, the degree of serpentinization in the uppermost mantle is not firmly established, but may range from <4% to as much as 20%, assuming that velocity reduction is solely due to hydration. A case study from the Nicaraguan trench argues that the ratio between P-wave and S-wave velocity (Vp/Vs) is a key parameter in addressing the amount of hydration. In the crust, the Vp/Vs ratio increases from <1.8 away from the trench to >1.9 in the trench, supporting the development of water-filled cracks where bend faulting occurs. In the mantle, the Vp/Vs ratio increases from ∼1.75 in the outer rise to values of >1.8 at the trench, indicating the increasing intensity of serpentinization.

  • 24.