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  • 1.
    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)
  • 2.
    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)
  • 3.
    Grevemeyer, Ingo
    et al.
    GEOMAR Helmholtz Centre for Ocean Research.
    Cesar, R. Ranero
    Instituto de Ciencias del Mar, CSIC.
    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 1553-040XArtikel 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.

  • 4.
    Mattson, Tobias
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ronchin, Erika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Syn-emplacement fracturing in the Sandfell laccolith, eastern Iceland2018Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Felsic magma commonly pools within mushroom-shaped magma chambers, so-called laccoliths or cryptodomes at shallow crustal levels, which can cause collapse of the volcanic edifice. While deformation of magma in volcanic conduits is an important process for regulating eruptive behaviour (Pistone et al., 2016), the bulk of the deformation associated with laccolith emplacement is considered to occur in the host-rock (Pollard & Johnson, 1973), and the effects of magma deformation on the intrusion emplacement is largely unexplored. Here we describe the deformation associated with the emplacement of the 0.5 km3 rhyolitic Sandfell laccolith in eastern Iceland, which formed in a single intrusive event. By combining field measurements, 3D modelling, anisotropy of magnetic susceptibility, and microstructural analysis, we quantify deformation that occurred in both the host-rock and the magma to investigate its effect on intrusion emplacement. Magmatic and magnetic fabric analyses reveal contact-parallel magma flow during the initial stages of intrusion emplacement. The magma flow fabric is overprinted by strain-localisation bands, which indicate that the magma subsequently became viscously stalled and was deformed by consecutively intruding magma. This change in magma rheology can be attributed to the interaction between the strain-localisation bands and the flow bands, which caused extensive fracture-rich layers in the magma and led to decompression degassing, crystallization, and rapid solidification of half of the magmatic body. Our observations indicate that syn-emplacement rheology change, and associated fracturing of intruding magma not only occur in volcanic conduits, but also play a major role in the emplacement of shallow viscous magma intrusions.

    References:

    Pistone, M., Cordonnier, B., Ulmer, P. & Caricchi, L. 2016: Rheological flow laws for multiphase magmas: An empirical approach. Journal of Volcanology and Geothermal Research 321, 158–170.

    Pollard, D.D. & Johnson, A.M. 1973: Mechanics of growth of some laccolithic intrusions in the Henry mountains, Utah, II: Bending and failure of overburden layers and sill formation. Tectonophysics 18, 311–354.

  • 5.
    Mattsson, Tobias
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Burchardt, Steffi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ronchin, Erika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Mineralogi, petrologi och tektonik.
    Syn-Emplacement Fracturing in the Sandfell Laccolith, Eastern Iceland—Implications for Rhyolite Intrusion Growth and Volcanic Hazards2018Ingår i: Frontiers in Earth Science, ISSN 1096-231X, E-ISSN 1664-8021, Vol. 6, artikel-id 5Artikel i tidskrift (Refereegranskat)
  • 6.
    Huang, Fei
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Bergmann, Peter
    GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.; Sintef Petr Res, SP Andersens Vei 15 B, NO-7031 Trondheim, Norway..
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ivandic, Monika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Lüth, Stefan
    GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Ivanova, Alexandra
    GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Kempka, Thomas
    GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Henninges, Jan
    GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany.
    Sopher, Daniel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Zhang, Fengjiao
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik. Jilin Univ, Xi Min Zhu St 938, Changchun, Jilin, Peoples R China.
    The first post-injection seismic monitor survey at the Ketzin pilot CO2 storage site: results from time-lapse analysis2018Ingår i: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 66, nr 1, s. 62-84Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The injection of CO2 at the Ketzin pilot CO2 storage site started in June 2008 and ended in August 2013. During the 62 months of injection, a total amount of about 67 kt of CO2 was injected into a saline aquifer. A third repeat 3D seismic survey, serving as the first post-injection survey was acquired in 2015, aiming to investigate the recent movement of the injected CO2. Consistent with the previous two time-lapse surveys, a predominantly WNW migration of the gaseous CO2 plume in the up-dip direction within the reservoir is inferred in this first post-injection survey. No systematic anomalies are detected through the reservoir overburden. The extent of the CO2 plume west of the injection site is almost identical to that found in the 2012 second repeat survey (after injection of 61 kt), however there is a significant decrease in its size east of the injection site. Assessment of the CO2 plume distribution suggests that the decrease in the size of the anomaly may be due to multiple factors, such as limited vertical resolution, CO2 dissolution and CO2 diffusion, in addition to the effects of ambient noise. 4D seismic modelling based on dynamic flow simulations indicates that a dynamic balance between the newly injected CO2 after the second repeat survey and the CO2 being dissolved and diffused was reached by the time of the first post-injection survey. Considering the considerable uncertainties in CO2 mass estimation, both patchy and non-patchy saturation models for the Ketzin site were taken into consideration.

  • 7.
    Gudmundsson, Olafur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    1. Sadeghisorkhani, Gudmundsson, Roberts & Tryggvason, 2017. Velocity-measurement bias of the ambient-noise method due to source directivity: a case study for the Swedish National Seismic Network, Geophys. J. Int. 209, 1648-1659, DOI:10.1093/gji/ggx115.2017Ingår i: Geophysical Journal International, Vol. 209, s. 1648-1659Artikel i tidskrift (Refereegranskat)
  • 8.
    Lueth, Stefan
    et al.
    GFZ German Research Centre for Geosciences.
    Bergmann, Peter
    GFZ German Research Centre for Geosciences.
    Huang, Fei
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ivandic, Monika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ivanova, Alexandra
    GFZ German Research Centre for Geosciences.
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Kempka, Thomas
    GFZ German Research Centre for Geosciences.
    4D Seismic Monitoring of CO2 Storage During Injection and Post-closure at the Ketzin Pilot Site2017Ingår i: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    At the Ketzin pilot site for geological CO2 storage, about 67,000 tons of CO2 were injected during the period June 2008 – August 2013. Since August 2013, the site is in its post-closure phase. Before and during the injection phase, a comprehensive monitoring programme was established. In the early post-injection phase, a majority of the monitoring activities have continued. The stepwise abandonment of the pilot site, which is planned to be accomplished in 2018, marks also the termination of most monitoring activities. Four 3D seismic surveys were acquired between 2005 and 2015 for characterizing the reservoir structure and its overburden and for monitoring the propagation of the injected CO2 in the storage formation. The first and second repeat surveys revealed the lateral extension of the CO2 plume after injecting 22 and 61 ktons, respectively. In autumn 2015, the third 3D repeat seismic survey, serving as the first post-injection survey, was acquired. The survey was acquired using the same acquisition geometry as for previous surveys, consisting of 33 templates with five receiver lines and twelve source profiles perpendicular to the receiver lines. Seismic processing of the recently acquired data has resulted in preliminary observations which can be summarized as follows: As in previous seismic repeat surveys, a clear CO2 signature is observed at the top of the storage formation. No systematic amplitude changes are observed above the reservoir which might indicate leakage. Compared to the second repeat survey acquired in 2012, the lateral extent of the CO2 plume seems to have been reduced, which may be an indication for ongoing (and relatively fast) dissolution of the CO2 in the formation brine and diffusion into very thin layers indicating pressure release.

  • 9.
    Lueth, Stefan
    et al.
    GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
    Bergmann, Peter
    GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
    Huang, Fei
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ivandic, Monika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ivanova, Alexandra
    GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Kempka, Thomas
    GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
    4D Seismic Monitoring of CO2 Storage During Injection and Post-closure at the Ketzin Pilot Site2017Ingår i: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102Artikel i tidskrift (Refereegranskat)
  • 10.
    Li, Ka Lok
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Sgattoni, Giulia
    Sadeghisorkhani, Hamzeh
    Roberts, Roland
    Gudmundsson, Olafur
    A double-correlation tremor-location method2017Ingår i: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 208, nr 2, s. 1231-1236Artikel i tidskrift (Refereegranskat)
  • 11.
    Yan, Ping
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Garcı́a Juanatey, Marı́a A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Kalscheuer, Thomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Hedin, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Savvaidis, Alexandros
    Univ Texas Austin, Bur Econ Geol, Jackson Sch Geosci, Austin, TX 78712 USA..
    Lorenz, Henning
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Kück, Jochem
    GFZ German Res Ctr Geosci, Helmholtz Ctr Potsdam, Ctr Sci Drilling, Potsdam, Germany..
    A magnetotelluric investigation of the Scandinavian Caledonides in western Jämtland, Sweden, using the COSC borehole logs as prior information2017Ingår i: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 208, nr 3, s. 1465-1489Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In connection with the Collisional Orogeny in the Scandinavian Caledonides (COSC) project, broad-band magnetotelluric (MT) data were acquired at 78 stations along a recent ca. 55km- long NW-SE directed reflection seismic profile (referred to as the COSC Seismic Profile; CSP), with the eastern end located similar to 30 km to the west of the orogenic Caledonian front. The MT component of the project aims at (i) delineating the highly conductive (similar to 0.1 Omega . m) alum shales that are associated with an underlying main decollement and (ii) calibrating the MT model to borehole logs. Strike and distortion analyses of the MT data show a 3-D structure in the western 10 km of the profile around the 2.5 km deep COSC-1 borehole (IGSN: ICDP5054EHW1001) and a preferred strike angle of N34 degrees E in the central and eastern parts of the profile. 2-D modelling of MT impedances was tested using different inversion schemes and parameters. To adjust the resistivity structure locally around the borehole, resistivity logging data from COSC-1 were successfully employed as prior constraints in the 2-D MT inversions. Compared with the CSP, the model inverted from the determinant impedances shows the highest level of structural similarity. A shallow resistor (> 1000 Omega . m) in the top 2-3 km depth underneath the western most 10 km of the profile around COSC-1 corresponds to a zone of high seismic reflectivity, and a boundary at less than 1 km depth where the resistivity decreases rapidly from > 100 to < 1 Omega . m in the central and eastern parts of the profile coincides with the first seismic reflections. The depth to this boundary is well constrained as shown by 1-D inversions of the MT data from five selected sites and it decreases towards the Caledonian front in the east. Underneath the easternmost part of the profile, the MT data show evidence of a second deeper conductor (resistivity < 1 Omega . m) at > 3 km depth. Based upon the COSC-1 borehole logs, the CSP reflection seismic image, and the surface geologic map, the MT resistivity models were interpreted geologically. In the vicinity of COSC-1, the resistor down to 2-3 km depth pertains to the metamorphic Middle Allochthon. The up to 1000-m-thick shallow resistor in the central and eastern parts of the profile is interpreted to overly an imbricated unit at the bottom of the Lower Allochthon that includes the alum shales. In the MT resistivity model, the 300-500 m thick imbricated unit masks the main Caledonian decollement at its bottom. A second possible interpretation, though not favoured here, is that the decollement occurs along a much deeper seismic reflection shallowing from 4.5 km depth in the west to similar to 600 m depth in the east. An additional borehole (COSC-2) is planned to penetrate the Lower Allochthon and the main decollement surface in the central part of the profile and can provide information to overcome this interpretational ambiguity. Using a synthetic study, we evaluate how resistivity logs from COSC-2 can improve the 2-D inversion model.

  • 12.
    Benediktsdottir, Asdis
    et al.
    Univ Iceland, Inst Earth Sci, Nord Volcanol Ctr, Sturlugata 7, IS-101 Reykjavik, Iceland.;Univ Iceland, Dept Earth Sci, Sturlugata 7, IS-101 Reykjavik, Iceland..
    Gudmundsson, Ólafur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Brandsdottir, Bryndis
    Univ Iceland, Sci Inst, Inst Earth Sci, Reykjavik, Iceland..
    Tryggvason, Ari
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ambient noise tomography of Eyjafjallajokull volcano, Iceland2017Ingår i: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Vol. 347, s. 250-263Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a shear-velocity model for the Eyjafjallajokull stratovolcano, based on ambient seismic noise tomography applied to seven months of data from six permanent stations and -10 temporary seismic stations, deployed during and after the 2010 volcanic unrest. Vertical components of noise were cross correlated resulting in 30 robust phase-velocity dispersion curves between 1.6 and 6.5 s in period, displaying a +/- 20% variation in phase velocity beneath the volcano. The uneven distribution of noise sources, evaluated using signal-to-noise ratios, was estimated to cause less than 2% error in most curves. Sensitivity kernels showed resolution down to 10 km and the lateral resolution of the resulting phase-velocity maps was about 5 km. The model reveals east-west oriented high-velocity anomalies due east and west of the caldera. Between these a zone of lower velocity is identified, coinciding with the location of earthquakes that occurred during the summit eruption in April 2010. A shallow, southwest elongated low-velocity anomaly is located 5 km southwest of the caldera. The limited depth resolution of the shear-velocity model precludes detection of melt within the volcano.

  • 13.
    Jeddi, Zeinab
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Gudmundsson, Ólafur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Tryggvason, Ari
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Ambient-noise tomography of Katla volcano, south Iceland2017Ingår i: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Vol. 347, s. 264-277Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A shear-wave velocity model of subglacial Katla volcano, southern Iceland, has been developed using ambient seismic noise tomography based on data from a temporary network operating between May 2011 and August 2013 and permanent stations around the volcano. Phase-velocity dispersion curves were obtained using cross correlations of vertical components of 136 station pairs and non-linearly inverted for phase-velocity maps between 1.7 and 7.5 s. Local dispersion curves were inverted for shear-velocity variation with depth using a grid search imposing a fixed ice layer at the top. The resulting one-dimensional (1-D) velocity models were combined to obtain a pseudo three-dimensional (3-D) model with estimated lateral resolution of 8 km and depth resolution varying from close to 1 km near the surface to about 8 km at 10 km depth. Shear wave velocities are generally higher within the Katla central volcano than in its surroundings. The most striking feature of the model is a high-velocity anomaly beneath the caldera at >6 km depth interpreted to be due to cumulates resulting from differentiation of shallower magma intrusions and remelting of subsiding upper crust. No shallow low-velocity anomaly is resolved beneath the central caldera, but a low-velocity region is found at 2-4 km depth beneath the western half of the caldera. V-p/V-s ratios, estimated from average velocity-depth profiles from surface-wave data and higher frequency P-wave data, are anomalously high (>1.9) compared to average Icelandic crust, particularly in the top 2-3 km. This is argued not to be an artifact due to lateral refraction or topography. Instead, this anomaly could be explained as an artifact caused by velocity dispersion due to attenuation and a difference in frequency content, and possibly to a degree by the compositional difference between the transalkalic Fe-Ti basalts of Katla and average tholeiitic Icelandic crust.

  • 14.
    Sadeghisorkhani, Hamzeh
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Analyses and Application of Ambient Seismic Noise in Sweden: Source, Interferometry, Tomography2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Ambient seismic noise from generation to its application for determination of sub-surface velocity structures is analyzed using continuous data recordings from the Swedish National Seismic Network (SNSN). The fundamental aim of the thesis is to investigate the applicability of precise velocity measurements from ambient noise data. In the ambient noise method, a form of interferometry, the seismic signal is constructed from long-term cross correlation of a random noise field. Anisotropy of the source distribution causes apparent time shifts (velocity bias) in the interferometric signals. The velocity bias can be important for the study area (Sweden) which has relatively small velocity variations. This work explores the entire data path, from investigating the noise-source distribution to a tomographic study of southern Sweden.

    A new method to invert for the azimuthal source distribution from cross-correlation envelopes is introduced. The method provides quantitative estimates of the azimuthal source distribution which can be used for detailed studies of source generation processes. An advantage of the method is that it uses few stations to constrain azimuthal source distributions. The results show that the source distribution is inhomogeneous, with sources concentrated along the western coast of Norway. This leads to an anisotropic noise field, especially for the secondary microseisms. The primary microseismic energy comes mainly from the northeast.

    The deduced azimuthal source distributions are used to study the level of expected bias invelocity estimates within the SNSN. The results indicate that the phase-velocity bias is less than 1% for most station pairs but can be larger for small values of the ratio of inter-station distance over wavelength. In addition, the nature of velocity bias due to a heterogeneous source field is investigated in terms of high and finite-frequency regimes.

    Graphical software for phase-velocity dispersion measurements based on new algorithms is presented and validated with synthetic data and by comparisons to other methods. The software is used for phase-velocity measurements, and deduced azimuthal source distributions are used for velocity-bias correction. Derived phase-velocity dispersion curves are used to construct two-dimensional velocity maps of southern Sweden at different periods based on travel-time tomography. The effect of the bias correction is investigated, and velocity maps are interpreted in comparison to previous geological and geophysical information.

    Delarbeten
    1. Mapping the source distribution of microseisms using noise covariogram envelopes
    Öppna denna publikation i ny flik eller fönster >>Mapping the source distribution of microseisms using noise covariogram envelopes
    2016 (Engelska)Ingår i: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 205, nr 3, s. 1473-1491Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We introduce a method for mapping the noise-source distribution of microseisms which uses information from the full length of covariograms (cross-correlations). We derive a forward calculation based on the plane-wave assumption in 2-D, to formulate an iterative, linearized inversion of covariogram envelopes in the time domain. The forward calculation involves bandpass filtering of the covariograms. The inversion exploits the well-known feature of noise cross-correlation, that is, an anomaly in the noise field that is oblique to the interstation direction appears as cross-correlation amplitude at a smaller time lag than the in-line, surface wave arrival. Therefore, the inversion extracts more information from the covariograms than that contained at the expected surface wave arrival, and this allows us to work with few stations to find the propagation directions of incoming energy. The inversion is naturally applied to data that retain physical units that are not amplitude normalized in any way. By dividing a network into groups of stations, we can constrain the source location by triangulation. We demonstrate results of the method with synthetic data and one year (2012) of data from the Swedish National Seismic Network and also look at the seasonal variation of source distribution around Scandinavia. After preprocessing and cross-correlation, the stations are divided into five groups of 9-12 stations. We invert the envelopes of each group in eight period ranges between 2 and 25 s. Results show that the noise sources at short periods (less than 12 s) lie predominantly in the North Atlantic Ocean and the Barents Sea, and at longer periods the energy appears to have a broader distribution. The strongly anisotropic source distribution in this area is estimated to cause significant biases of velocity measurements compared to the level of heterogeneity in the region. The amplitude of the primary microseisms varies little over the year, but secondary microseisms are much weaker in summer than in winter. Furthermore, the peak period of the secondary microseisms shifts from 5-6 s in winter to 4-5 s during the summer.

    Nyckelord
    Inverse theory, Interferometry, Surface waves and free oscillations, Wave propagation, Europe
    Nationell ämneskategori
    Geovetenskap och miljövetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-302233 (URN)10.1093/gji/ggw092 (DOI)000376380000011 ()
    Externt samarbete:
    Tillgänglig från: 2016-09-01 Skapad: 2016-08-31 Senast uppdaterad: 2017-11-21Bibliografiskt granskad
    2. Velocity-measurement bias of the ambient noise method due to source directivity: A case study for the Swedish National Seismic Network
    Öppna denna publikation i ny flik eller fönster >>Velocity-measurement bias of the ambient noise method due to source directivity: A case study for the Swedish National Seismic Network
    (Engelska)Ingår i: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246XArtikel i tidskrift (Refereegranskat) Epub ahead of print
    Abstract [en]

    The bias of velocity measurements from ambient-noise covariograms due to an anisotropic distribution of noise sources is studied assuming that the noise field consists of planar surface waves from large distance. First, general characteristics of the bias are described in terms of their dependence on wavelength, source-anomaly amplitude and width. Second, the expected bias of measurements in Sweden based on a noise-source model for the adjacent regions is analysed. The bias is conceptually explained and described in terms of two regimes, namely a high-frequency and a finite-frequency regime and their parameter domains quantified. Basic scaling laws are established for the bias. It is generally found to be small compared to lateral heterogeneity, except in the finite-frequency regime when inter-station distance is small compared to a wavelength and in regions of low levels of heterogeneity. The potential bias, i.e., its peak-to-peak variation, is generally higher for group-velocity than phase-velocity measurements. The strongly varying noise-source distribution as seen from Sweden results in predictions of relatively strong bias in the area at relevant frequencies and inter-station distances. Levels of heterogeneity in the Baltic shield are relatively low, rendering the potential bias significant. This highlights the need for detailed studies of source anisotropy before application of ambient-noise tomography, particularly in regions with weak velocity heterogeneity. Predicted bias only partially explains deviations of phase-velocity measurements from a regional average for individual station pairs. Restricting measurements to station pairs with inter-station distance exceeding five wavelengths limits the potential velocity bias in the area to within 1%. This rather dramatic restriction can be relaxed by directional analysis of the noise-source field and application of azimuthal restrictions to the selected station pairs for measurement.

    Nationell ämneskategori
    Geofysik
    Identifikatorer
    urn:nbn:se:uu:diva-320163 (URN)10.1093/gji/ggx115 (DOI)
    Tillgänglig från: 2017-04-16 Skapad: 2017-04-16 Senast uppdaterad: 2017-11-29
    3. GSpecDisp: a Matlab GUI package for phase-velocity dispersion measurements from ambient-noise correlations
    Öppna denna publikation i ny flik eller fönster >>GSpecDisp: a Matlab GUI package for phase-velocity dispersion measurements from ambient-noise correlations
    (Engelska)Ingår i: Computers & Geosciences, ISSN 0098-3004, E-ISSN 1873-7803Artikel i tidskrift (Refereegranskat) Submitted
    Nationell ämneskategori
    Geofysik
    Identifikatorer
    urn:nbn:se:uu:diva-320166 (URN)
    Tillgänglig från: 2017-04-16 Skapad: 2017-04-16 Senast uppdaterad: 2017-11-29
    4. Surface wave tomography of southern Sweden from ambient seismic noise
    Öppna denna publikation i ny flik eller fönster >>Surface wave tomography of southern Sweden from ambient seismic noise
    Visa övriga...
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Geofysik
    Identifikatorer
    urn:nbn:se:uu:diva-320167 (URN)
    Tillgänglig från: 2017-04-16 Skapad: 2017-04-16 Senast uppdaterad: 2017-04-17
  • 15. Wagner, F.
    et al.
    Tryggvason, A.
    Roberts, R.
    Lund, Björn
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Gudmundsson, O.
    Automatic seismic event detection using migration and stacking: a performance and parameter study in Hengill, southwest Iceland2017Ingår i: Geophysical Journal International, Vol. 209, nr 3, s. 1866-1877Artikel i tidskrift (Refereegranskat)
  • 16.
    Gee, David G.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Andreasson, Per-Gunnar
    Lund Univ, Dept Geol, Lund, Sweden..
    Li, Yuan
    MLR Inst Geol, Beijing, Peoples R China..
    Krill, Allan
    Norwegian Univ Sci & Technol, Dept Geol & Mineral Resources, Trondheim, Norway..
    Baltoscandian margin, Sveconorwegian crust lost by subduction during Caledonian collisional orogeny2017Ingår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 139, nr 1, s. 36-51Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Underthrusting of Laurentia by the continental margin of Baltica during Caledonian orogeny resulted in the lateral emplacement of Iapetus Ocean-related terranes of the Upper Allochthon at least 500 km onto Baltica. The underlying Lower and Middle allochthons of the Baltoscandian margin mostly comprise Cryogenian, Ediacaran and Cambro-Silurian sedimentary successions; basement to these formations are present only as minor, isolated fragments, except at the base of the Middle Allochthon and within the underlying windows. The upper parts of the Middle Allochthon are notable for the presence of early Ediacaran dyke-swarms and other components of the Baltoscandian continent-ocean transition zone (COT). New data are presented here on the c. 610 Ma age of the COT-related dolerites in the Kalak Nappe Complex in Northern Norway and also on detrital zircons in the underlying Laksefjord and Gaissa nappes. The former confirms that the Baltoscandian COT has a similar age along the length of the orogen; the latter shows that the detrital zircon signatures in the Lower and Middle allochthons are comparable throughout the orogen. These sedimentary rocks have dominating populations of Mesoproterozoic to latest Palaeoproterozoic zircons similar to those from southern parts of the orogen, where Sveconorwegian complexes comprise the basement to the Caledonides. Thus, they help define the probable character and age of the crystalline basement that existed along this outer margin of Baltica during the Neoproterozoic, continental lower crust that was partly subducted during Ordovician continent-arc collision and subsequently lost beneath Laurentia during the 50 million years of Scandian collisional orogeny.

  • 17.
    Brodic, Bojan
    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.
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Bedrock and Fracture Zone Delineation UsingDifferent Near-surface Seismic Sources2017Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

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

  • 18.
    Gudmundsson, Olafur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Benediktsdottir, Asdis, Gudmundsson, Olafur, Brandsdottir, Bryndis, Tryggvason, Ari, 2017.  Ambient noise tomography of Eyjafjallajökull volcano, Iceland, J. Volc. Geoth. Res. 347, 250-263.2017Ingår i: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Jornal of Volcanology and Geothermal Research, ISSN 0377-0273, Vol. 347, s. 250-263Artikel i tidskrift (Refereegranskat)
  • 19.
    Gudmundsson, Olafur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Benediktsdottir, Gudmundsson, Brandsdottir, Tryggvason, 2017.  Ambient-noise tomography of Eyjafjallajökull volcano, Iceland, J. Volc Geoth. Res. 347, 250-263.2017Ingår i: Journal of Volcanology and Geothermal Research, Vol. 347Artikel i tidskrift (Refereegranskat)
  • 20.
    Niemi, A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Edlmann, Katriona
    Carrera, Jesus
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Tatomir, Alexandru
    Ghergut, Iulia
    Sauter, Martin
    Bensabat, Jacob
    Fagerlund, Fritjof
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Rasmusson, Kristina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Cornet, Francois H.
    Vilarrasa, Victor
    McDermott, Christopher Ian
    Chapter 7: Site Characterization2017Ingår i: GEOLOGICAL STORAGE OF CO2IN DEEP SALINE FORMATIONS / [ed] Niemi, A., Bear, J. and Bensabat, J., Springer Netherlands, 2017Kapitel i bok, del av antologi (Refereegranskat)
  • 21.
    Niemi, A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Bensabat, J.
    Bergmann, Peter
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Tatomir, Alexandru
    Ghergut, Iulia
    Sauter, Martin
    Freifeld, Barry
    Chapter 8: Field Injection Operations andMonitoring of the Injected CO22017Ingår i: GEOLOGICAL STORAGE OF CO2IN DEEP SALINE FORMATIONS / [ed] Niemi, A., Bear, J. and Bensabat, J, Springer Netherlands, 2017Kapitel i bok, del av antologi (Refereegranskat)
  • 22.
    Wang, Shunguo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Bastani, Mehrdad
    Kalscheuer, Thomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Malehmir, Alireza
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Dynesius, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Controlled Source Boat-towed Radio-magnetotellurics for Site Investigation at Äspö Hard Rock Laboratory, Southeastern Sweden2017Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 23.
    Mehta, Suman
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Bastani, Mehrdad
    Geological Survey of Sweden.
    Malehmir, Alireza
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Pedersen, Laust B.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik. Uppsala University.
    CSRMT Survey on Frozen Lake - A New Technique with an Example from the Stockholm Bypass Tunnel2017Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 24.
    Malehmir, Alireza
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Maries, Georgiana
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Bäckström, Emma
    Nordic Iron Ore AB.
    Schon, Monika
    Nordic Iron Ore AB.
    Marsden, Paul
    Nordic Iron Ore AB.
    Deep Targeting an Iron-Oxide Ore Body Using a Seismic Landstreamer and a 500-Kg Drop Hammer Source2017Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 25.
    Brodic, Bojan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Malehmir, Alireza