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  • 1.
    Abtahi, Sayyed Mohammad
    et al.
    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.
    Kamm, Jochen
    Kalscheuer, Thomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    A new reference model for 3D inversion of airborne magnetic datain 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)
  • 2.
    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 1943-2682Artikel i tidskrift (Refereegranskat)
  • 3.
    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.
    Almqvist, Bjarne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Jacobsson, 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)
  • 4.
    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.

  • 5.
    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)
  • 6.
    Mattsson, Hannes
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Balashova, Anna
    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)
  • 7.
    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)
  • 8.
    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)
  • 9.
    Fälth, Billy
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik. Clay Technology AB.
    Simulating Earthquake Rupture and Near-Fault Fracture Response2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

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

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

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

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

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

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

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

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

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

    Nationell ämneskategori
    Geofysik
    Forskningsämne
    Geofysik med inriktning mot seismologi
    Identifikatorer
    urn:nbn:se:uu:diva-347597 (URN)
    Tillgänglig från: 2018-04-04 Skapad: 2018-04-04 Senast uppdaterad: 2018-04-04
  • 10.
    Grevemeyer, Ingo
    et al.
    GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany.
    R. RaneroCesar, Cesar
    Instituto de Ciencias del Mar, CSIC, Barcelona, Spain.
    Ivandic, Monika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Structure of oceanic crust and serpentinization at subduction trenches2018Ingår i: Geosphere, ISSN 1553-040X, E-ISSN 1553-040XArtikel 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.

  • 11.
    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.

  • 12.
    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)
  • 13.
    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.

  • 14.
    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.
    Farajkhah, Nasser Keshavarz
    RIPI, Tehran, Iran.
    Tsunami Simulations in the Western Makran Using Hypothetical Heterogeneous Source Models from World's Great Earthquakes2018Ingår i: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 175, nr 4, s. 1325-1340Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The western segment of Makran subduction zone is characterized with almost no major seismicity and no large earthquake for several centuries. A possible episode for this behavior is that this segment is currently locked accumulating energy to generate possible great future earthquakes. Taking into account this assumption, a hypothetical rupture area is considered in the western Makran to set different tsunamigenic scenarios. Slip distribution models of four recent tsunamigenic earthquakes, i.e. 2015 Chile M-w 8.3, 2011 Tohoku-Oki M-w 9.0 (using two different scenarios) and 2006 Kuril Islands M-w 8.3, are scaled into the rupture area in the western Makran zone. The numerical modeling is performed to evaluate near-field and far-field tsunami hazards. Heterogeneity in slip distribution results in higher tsunami amplitudes. However, its effect reduces from local tsunamis to regional and distant tsunamis. Among all considered scenarios for the western Makran, only a similar tsunamigenic earthquake to the 2011 Tohoku-Oki event can re-produce a significant far-field tsunami and is considered as the worst case scenario. The potential of a tsunamigenic source is dominated by the degree of slip heterogeneity and the location of greatest slip on the rupture area. For the scenarios with similar slip patterns, the mean slip controls their relative power. Our conclusions also indicate that along the entire Makran coasts, the southeastern coast of Iran is the most vulnerable area subjected to tsunami hazard.

  • 15.
    Kalscheuer, Thomas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Juhojuntti, Niklas
    Vaittinen, Katri
    Two-dimensional audiomagnetotelluric and magnetotelluric modelling of ore deposits: Improvements in model constraints by inclusion of borehole measurements2018Ingår i: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 39, nr 3, s. 467-507Artikel i tidskrift (Refereegranskat)
  • 16.
    Kulhánek, Ota
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Persson, Leif
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Nuannin, Paiboon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper.
    Variations of b-values preceding large earthquakes in the shallow subduction zones of Cocos and Nazca plates2018Ingår i: Journal of South American Earth Sciences, ISSN 0895-9811, E-ISSN 1873-0647, Vol. 82, s. 207-214Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The potential of b-value variations as a medium-term (months, years) precursor was investigated by focusing on the eight largest earthquakes, M-w >= 7.0, occurring between January 2000 and April 2010 in the shallow subduction zones of Cocos and Nazca plates. The available ISC and NEIC lists of events are complete for threshold magnitudes 4.3 (4569 events) and 4.6 (2742 events), respectively. Spatial and temporal perturbations of b were investigated in six regions surrounding the eight largest shocks. A technique of moving spatial- and temporal-windows was applied. Deduced b-values reveal large variations between 0.6 and 2.2. All eight earthquakes took place within regions of low b and were all preceded by significant drops in b-values. Observed correspondence between low b and the occurrence of large earthquakes suggests that b(t) has a potential to be employed in medium-term earthquake predictions in subduction zones of Central and South America.

  • 17.
    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)
  • 18.
    Lueth, Stefan
    et al.
    GFZ German Research Centre for Geosciences, Potsdam, Germany.
    Bergmann, Peter
    GFZ GermanResearch Centre for Geosciences, 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, Potsdam, Germany.
    Juhlin, Christopher
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Kempka, Thomas
    GFZ German Research Centre for Geosciences, 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 1876-6102, Vol. 114, s. 5761-5767Artikel 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.

  • 19.
    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)
  • 20.
    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.

  • 21.
    Jeddi, Zeinab
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    Sgattoni, Giulia
    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.
    Lund, Björn
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Geofysik.
    A peculiar cluster of microearthquakes on the eastern flank of Katla volcano, southern Iceland2017Ingår i: Jökull: Journal of The Glaciological and Geological Societies of Iceland, ISSN 0449-0576, Vol. 67, s. 1-16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A peculiar cluster of seismicity near the tip of Sandfellsjokull on the eastern flank of Katla volcano in southern Iceland has been analyzed in detail using data from a temporary seismic network. A total of 300 events were detected between July 2011 and August 2013, most of them from a swarm between December 4th and 12th, 2011. The sparser permanent network detected a small fraction of these events, but also a larger swarm in November 2010. When seismic activity started in this area is uncertain because of changes in the detection capability of the network over time. The events are of low magnitude (-0.5 < ML < 0.5) and the b-value of their magnitude distribution is high (1.6 +/- 0.1). Based on their frequency content (4-25 Hz) and clear P and S arrivals, the events are classified as volcano-tectonic. Two multiplets probably with different source mechanism are identified in their population. The events locate at approximately 3.5 km depth. Most of them are tightly clustered according to double difference relative locations in a volume that is only about 400 m in diameter in all directions. Several events are scattered up to 800 m beneath this volume. There is some suggestion of elongate structure in the cluster with a NNE/SSW strike and a dip of 60 degrees. We argue that these events cannot be due to a glacial or a broad tectonic process. Possibly, a localized source of fluid pressure, e.g., a small magma body at depth may be the source of these events.

  • 22.
    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.

  • 23.
    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.

  • 24.
    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