uu.seUppsala universitets publikationer
Ändra sökning
Avgränsa sökresultatet
1234567 1 - 50 av 768
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 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.
    Vachon, Rémi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Dynamic Modelling of Physical Processes in Magmatic Systems: Dyke Emplacement and Flow-Induced Crystal Rotations2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The main motivation for this thesis is to develop and improve numerical tools and methods that help further our comprehension of the volcanic plumbing system and its dynamics.

    The commonly used standard elastic model predicts solutions of dyke shape, thickness, over-pressure and fracturing criteria that do not always fit natural observations. In the first part of the thesis, we want to test whether other host-rock rheologies leads to more realistic dykes. We examine three different rheologies: 1) elasticity with pressure dependent elastic moduli, 2) elastoplasticity with plastic failure in regions of high shear stresses and 3) viscoelasticity to describe ductile flow of rocks by creeping mechanisms in regions of high temperature. Solu-tions from the three tested models give dykes with more rectangular shapes relative to solutions computed from the model of linear elasticity. In addition, the calculated magma pressure for an intrusion of a given thickness is reduced for all tested rheologies. Greatest differences with the linear elastic solution are given by the elastoplastic model, in which computed magma over-pressures are lower than elastic solutions by a factor of 2 to 10. Computed overpressures from this type of rheological model are approximately of the same order than natural magma over-pressures estimated by other methods (1 to 5 MPa). For the model of dyke propagation, the incorporation of brittle failure mechanisms in regions of high stresses strongly affects the dyke propagation criteria because of the energy dissipated by frictional sliding and fracturing in the large process zone located at the intrusion tips.

    The second part of the thesis deals with the rotation of crystals suspended in magmatic flows. We proceed by coupling the rotation dynamics equation of elongated particles, with the Navier-Stokes equation of large-scale flows. The results of the model are first extensively tested for simple flows with known analytical solutions. Results show a perfect fit between both numerical and analytical solutions. Additionally, the numerical methods are applied to more complex flow fields that relate to realistic systems of magma circulation. Results show that elongated crystals mainly align in the direction of flow in convergent systems (e.g. magma flowing from a large reservoir inside a conduit or from a deflating magma chamber). However, the pattern of crystal orientation in divergent flows (e.g. magma flowing from a conduit into a large reservoir or in an inflating magma chamber) does not align in the direction of the flow but instead is globally oriented sub-parallel to the maximum principal strain.

    Delarbeten
    1. Crystal rotations and alignment in spatially varying magma flows: Two-dimensional examples of common subvolcanic flow geometries.
    Öppna denna publikation i ny flik eller fönster >>Crystal rotations and alignment in spatially varying magma flows: Two-dimensional examples of common subvolcanic flow geometries.
    Visa övriga...
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Geofysik
    Identifikatorer
    urn:nbn:se:uu:diva-363231 (URN)
    Tillgänglig från: 2018-10-15 Skapad: 2018-10-15 Senast uppdaterad: 2018-10-15
    2. Mechanical energy balance and fracture toughness for dykes in elastoplastic host rock.
    Öppna denna publikation i ny flik eller fönster >>Mechanical energy balance and fracture toughness for dykes in elastoplastic host rock.
    2018 (Engelska)Ingår i: Artikel i tidskrift (Refereegranskat) Submitted
    Nationell ämneskategori
    Geofysik
    Identifikatorer
    urn:nbn:se:uu:diva-363229 (URN)
    Tillgänglig från: 2018-10-15 Skapad: 2018-10-15 Senast uppdaterad: 2018-10-15
    3. Effect of host-rock rheology on dyke shape, thickness and magma overpressure
    Öppna denna publikation i ny flik eller fönster >>Effect of host-rock rheology on dyke shape, thickness and magma overpressure
    2017 (Engelska)Ingår i: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 208, nr 3, s. 1414-1429Artikel i tidskrift (Refereegranskat) Published
    Nationell ämneskategori
    Geofysik
    Identifikatorer
    urn:nbn:se:uu:diva-360834 (URN)10.1093/gji/ggw448 (DOI)
    Tillgänglig från: 2018-09-18 Skapad: 2018-09-18 Senast uppdaterad: 2018-10-15Bibliografiskt granskad
    4. Evolution of the statistical distribution of crystal orientations in spatially variable viscous flows.
    Öppna denna publikation i ny flik eller fönster >>Evolution of the statistical distribution of crystal orientations in spatially variable viscous flows.
    2018 (Engelska)Ingår i: Artikel i tidskrift (Övrigt vetenskapligt) Submitted
    Nationell ämneskategori
    Geofysik
    Identifikatorer
    urn:nbn:se:uu:diva-363054 (URN)
    Tillgänglig från: 2018-10-11 Skapad: 2018-10-11 Senast uppdaterad: 2018-10-15
  • 7.
    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.

  • 8.
    Rashidi, Amin
    et al.
    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.
    Dutykh, Denys
    Univ Grenoble Alpes, Univ Savoie Mt Blanc, CNRS, LAMA, F-73000 Chambery, France;Univ Savoie Mt Blanc, LAMA UMR CNRS 5127, Campus Sci, F-73376 Le Bourget Du Lac, France.
    Khah, Nasser Keshavarz Faraj
    Res Inst Petr Ind, Tehran, Iran.
    Evaluation of tsunami wave energy generated by earthquakes in the Makran subduction zone2018Ingår i: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 165, s. 131-139Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The MAKRAN subduction zone, an approximate 1000 km section of the EURASIAN-ARABIAN plate, is located offshore of SOUTHERN IRAN and PAKISTAN. In 1945, the MAKRAN subduction zone (MSZ) generated a tsunamigenic earthquake with a magnitude of M-w 8.1. The region has also experienced large historical earthquakes but the data regarding these events are poorly documented. Therefore, the need to investigate tsunamis in MAKRAN must be taken into serious consideration. Using hydrodynamic numerical simulation, we evaluate the tsunami wave energy generated by bottom motion for a tsunamigenic source model distributed along the full length of the MAKRAN subduction zone. The whole rupture of the plate boundary is divided into 20 segments with width of the order of 200 km and a co-seismic slip of 10 m but with various lengths. Exchanges between kinetic and potential components of tsunami wave energy are shown. The total tsunami wave energy displays only 0.33 % of the seismic energy released from the earthquake source. As a result, for every increase in magnitude by one unit, the associated tsunami wave energy becomes about 10(3) times greater.

  • 9.
    Bazargan, Mohsen
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Hieronymus, Christoph F.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Vachon, Remi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Evolution of the statistical distribution of crystal orientations in spatially variable viscous flows.2018Ingår i: Artikel i tidskrift (Övrigt vetenskapligt)
  • 10.
    Chen, Chaojian
    et al.
    Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Ren, Zhengyong
    Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Pan, Kejia
    Cent S Univ, Sch Math & Stat, Changsha 410083, Hunan, Peoples R China.
    Tang, Jingtian
    Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Kalscheuer, Thomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Maurer, Hansruedi
    Swiss Fed Inst Technol, Inst Geophys, Dept Earth Sci, CH-8091 Zurich, Switzerland.
    Sun, Ya
    Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Li, Yang
    Chinese Acad Sci, Inst Geol & Geophys, Beijing 100029, Peoples R China.
    Exact solutions of the vertical gravitational anomaly for a polyhedral prism with vertical polynomial density contrast of arbitrary orders2018Ingår i: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 214, nr 3, s. 2115-2132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present general closed-form solutions for the vertical gravitational anomaly caused by a polyhedral prism with mass density contrast varying with depth. Our equations are the first ones to implement a polynomial vertical mass density contrast of arbitrary order. Singularities in the gravity field which arise when the observation site is close to or in the anomalous polyhedral prism are removed in our analytic expressions. Therefore, the observation site can be located outside, on the faces of or inside the anomalous mass bodies. A simple prismatic body of anomalous density is adopted to test the accuracy of our newly developed closed-form solution. Cases of constant, linear, quadratic, cubic and quartic polynomial orders of mass density contrast are tested. For cases of constant, linear, quadratic and cubic polynomial orders, the relative errors between our results and other published exact solutions are less than 10(-11)%. For the case of quartic polynomial order, relative errors less than 10(-10)% are obtained between our solutions and those computed by a high-order Gaussian quadrature rule (512 x 512 x 512 = 134 217 728 quadrature points), where our new analytic solution needs significantly less computational time (0.0009 versus 31.106 s). These numerical experiments not only verified the accuracy of our new formula but also demonstrated their potential in computing exact gravity anomalies for complicated mass density distributions in the Earth.

  • 11.
    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.

  • 12.
    Ren, Zhengyong
    et al.
    Cent S Univ, Minist Educ, Key Lab Metallogen Predict Nonferrous Met & Geol, Changsha 410083, Hunan, Peoples R China;Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Zhong, Yiyuan
    Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Chen, Chaojian
    Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Tang, Jingtian
    Cent S Univ, Minist Educ, Key Lab Metallogen Predict Nonferrous Met & Geol, Changsha 410083, Hunan, Peoples R China;Cent S Univ, Sch Geosci & Infophys, Changsha 410083, Hunan, Peoples R China.
    Kalscheuer, Thomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Maurer, Hansruedi
    Swiss Fed Inst Technol, Inst Geophys, Dept Earth Sci, CH-8092 Zurich, Switzerland.
    Li, Yang
    Chinese Acad Sci, Inst Geol & Geophys, Key Lab Earth & Planetary Phys, Beijing 100029, Peoples R China.
    Gravity Gradient Tensor of Arbitrary 3D Polyhedral Bodies with up to Third-Order Polynomial Horizontal and Vertical Mass Contrasts2018Ingår i: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 39, nr 5, s. 901-935Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    During the last 20 years, geophysicists have developed great interest in using gravity gradient tensor signals to study bodies of anomalous density in the Earth. Deriving exact solutions of the gravity gradient tensor signals has become a dominating task in exploration geophysics or geodetic fields. In this study, we developed a compact and simple framework to derive exact solutions of gravity gradient tensor measurements for polyhedral bodies, in which the density contrast is represented by a general polynomial function. The polynomial mass contrast can continuously vary in both horizontal and vertical directions. In our framework, the original three-dimensional volume integral of gravity gradient tensor signals is transformed into a set of one-dimensional line integrals along edges of the polyhedral body by sequentially invoking the volume and surface gradient (divergence) theorems. In terms of an orthogonal local coordinate system defined on these edges, exact solutions are derived for these line integrals. We successfully derived a set of unified exact solutions of gravity gradient tensors for constant, linear, quadratic and cubic polynomial orders. The exact solutions for constant and linear cases cover all previously published vertex-type exact solutions of the gravity gradient tensor for a polygonal body, though the associated algorithms may differ in numerical stability. In addition, to our best knowledge, it is the first time that exact solutions of gravity gradient tensor signals are derived for a polyhedral body with a polynomial mass contrast of order higher than one (that is quadratic and cubic orders). Three synthetic models (a prismatic body with depth-dependent density contrasts, an irregular polyhedron with linear density contrast and a tetrahedral body with horizontally and vertically varying density contrasts) are used to verify the correctness and the efficiency of our newly developed closed-form solutions. Excellent agreements are obtained between our solutions and other published exact solutions. In addition, stability tests are performed to demonstrate that our exact solutions can safely be used to detect shallow subsurface targets.

  • 13.
    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.

  • 14.
    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.

  • 15.
    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.

  • 16.
    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)
    Abstract [en]

     

    Summary

    The electrical resistivity tomography (ERT) method provides moderately good constraints for both conductive and resistive structures, while the radio-magnetotelluric (RMT) method is well suited to constrain conductive structures. Additionally, RMT and ERT data may have different target coverage and are differently affected by various types of noise. Hence, joint inversion of RMT and ERT data sets may provide a better constrained model as compared to individual inversions. In this study, joint inversion of boat-towed RMT and lake-floor ERT data has for the first time been formulated and implemented. The implementation was tested on both synthetic and field data sets incorporating RMT transverse electrical mode and ERT data. Results from synthetic data demonstrate that the joint inversion yields models with better resolution compared with individual inversions. A case study from an area adjacent to the Äspö Hard Rock Laboratory (HRL) in southeastern Sweden was used to demonstrate the implementation of the method. A 790-m-long profile comprising lake-floor ERT and boat-towed RMT data combined with partial land data was used for this purpose. Joint inversions with and without weighting (applied to different data sets, vertical and horizontal model smoothness) as well as constrained joint inversions incorporating bathymetry data and water resistivity measurements were performed. The resulting models delineate subsurface structures such as a major northeasterly directed fracture system, which is observed in the HRL facility underground and confirmed by boreholes. A previously uncertain weakness zone, likely a fracture system in the northern part of the profile, is inferred in this study. The fractures are highly saturated with saline water, which make them good targets of resistivity-based geophysical methods. Nevertheless, conductive sediments overlain by the lake water add further difficulty to resolve these deep fracture zones. Therefore, the joint inversion of RMT and ERT data particularly helps to improve the resolution of the resistivity models in areas where the profile traverses shallow water and land sections. Our modification of the joint inversion of RMT and ERT data improves the study of geological units underneath shallow water bodies where underground infrastructures are planned. Thus, it allows better planning and mitigating the risks and costs associated with conductive weakness zones.

  • 17.
    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.

  • 18.
    Vachon, Remi
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Hieronymus, Christoph F.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Mechanical energy balance and fracture toughness for dykes in elastoplastic host rock.2018Ingår i: Artikel i tidskrift (Refereegranskat)
  • 19. 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 1944-9194, Vol. 37, nr 10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Exhumation of the high‐grade metamorphic Seve Nappe Complex and its emplacement between lower‐grade nappes has been related to wedge extrusion in the central Scandinavian Caledonides. To test this hypothesis, the kinematic evolution of the Caledonian nappe pile is studied by systematic structural mapping in central and northern Jämtland, Sweden. Structural data, combined with petrological and quartz microstructure observations, document pervasive top‐to‐the‐ESE, foreland‐directed shearing under progressively decreasing metamorphic grade across the entire nappe pile. Mylonitic foliation, foliation‐parallel boudinage, and abundant top‐to‐the‐ESE and rare, scattered top‐to‐the‐WNW shear‐sense indicators imply foreland‐directed general shear. This deformation regime caused exhumation by concurrent thrusting and vertical ductile thinning. We propose a specific succession of in‐ and out‐of‐sequence thrusts that generated the metamorphic zonation. Our model envisions in‐sequence propagation of thrusts during exhumation of the Seve Nappe Complex, related to subduction of Baltica beneath a volcanic arc within Iapetus. Concurrently, Iapetus subducted beneath Laurentia farther to the west. When Iapetus was closed, Baltica subduction stepped westward and continued beneath Laurentia. The back stepping of subduction at the onset of continental collision caused out‐of‐sequence propagation of the orogenic wedge. Thrusting cut downsection across the existing tectonostratigraphy, emplacing units of lower metamorphic grade above the high‐grade Seve Nappe Complex. This imbrication generated the present metamorphic zonation of the Caledonian nappe pile during sustained convergence between Laurentia and Baltica.

  • 20.
    Basir, Hadi Mahdavi
    et al.
    Amirkabir Univ Technol, Dept Petr Engn, Tehran 158754413, Iran.
    Javaherian, Abdolrahim
    Univ Tehran, Inst Geophys, Tehran 141556466, Iran;Amirkabir Univ Technol, Dept Petr Engn, Tehran 158754413, 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, Dept Geophys, Explorat Directorate, Tehran 1994814695, Iran.
    Modified imaging condition for reverse time migration based on reduction of modelling time2018Ingår i: Exploration Geophysics, ISSN 0812-3985, E-ISSN 1834-7533, Vol. 49, nr 4, s. 494-505Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reverse time migration (RTM) is considered as a high-end imaging algorithm due to its ability to image geologically complex environments. However, this algorithm suffers from very high computational costs and low-frequency artefacts. The former drawback is the result of the intensive computations and huge memory allocation involved in RTM. Wave propagation modelling, as a kernel of RTM, demands intensive computations, and conventional imaging conditions are associated with huge memory allocation. In this paper, a modification of imaging condition is proposed that improves the efficiency of RTM as a reduction of computational cost, memory (RAM) allocation and low-frequency artefacts. The proposed imaging condition is similar to the conventional imaging condition but with the reduction of modelling time to near half the maximum time of recording. As the main idea of the proposed imaging condition, the impact of wave propagation modelling time is investigated on the quality of RTM and illumination of reflectors. The performance of the proposed method is considered using two synthetic models (SEG/EAGE and BP) and a real dataset from an Iranian oilfield in the south of Iran. Results showed that the new imaging condition can properly image the reflectors and enhance the efficiency of RTM. By using the proposed imaging condition, we achieved similar to 25% increase in CPU performance and 50% decrease in the memory allocation. Despite the improvement of the performance, results showed that the proposed imaging condition had no significant effect on the illumination.

  • 21.
    Ivandic, Monika
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Bergmann, Peter
    Helmholtz Ctr Potsdam, GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany;SINTEF Petr Res, Trondheim, Norway.
    Kummerow, Juliane
    Helmholtz Ctr Potsdam, GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Huang, Fei
    Uppsala 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
    Helmholtz Ctr Potsdam, GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Monitoring CO2 saturation using time-lapse amplitude versus offset analysis of 3D seismic data from the Ketzin CO2 storage pilot site, Germany2018Ingår i: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 66, nr 8, s. 1568-1585Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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