| 1. |
- Koyi, Hemin, et al.
(författare)
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Numerical models of ductile rebound of crustal roots beneath mountain belts
- 1999
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Ingår i: Geophysical Journal International. - : Blackwell Publishing. - 0956-540X .- 1365-246X. ; 139:2, s. 556-562
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Crustal roots formed beneath mountain belts are gravitationally unstable structures, which rebound when the lateral forces that created them cease or decrease significantly relative to gravity. Crustal roots do not rebound as a rigid body, but undergo intensive internal deformation during their rebound and cause intensive deformation within the ductile lower crust. 2-D numerical models are used to investigate the style and intensity of this deformation and the role that the viscosities of the upper crust and mantle lithosphere play in the process of root rebound. Numerical models of root rebound show three main features which may be of general application: first, with a low-viscosity lower crust, the rheology of the mantle lithosphere governs the rate of root rebound; second, the amount of dynamic uplift caused by root rebound depends strongly on the rheologies of both the upper crust and mantle lithosphere; and third, redistribution of the rebounding root mass causes pure and simple shear within the lower crust and produces subhorizontal planar fabrics which may give the lower crust its reflective character on many seismic images.
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| 2. |
- Niemi, Auli, et al.
(författare)
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Chapter 7: Site Characterization
- 2017
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Ingår i: Geological Storage Of Co<sub>2</sub> in Deep Saline Formations. - Dordrecht : Springer Netherlands. - 9789402409949 - 9789402409963 ; , s. 309-380
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Bokkapitel (refereegranskat)abstract
- A necessary first step in qualifying a specific site for CO2 storage and for quantifying its relevant properties is a proper site characterization. Site characterization provides the ultimate input data for reservoir modeling and for all the predictions concerning the storage complex and its surroundings. It also provides baseline information for monitoring the behavior of injected CO2. It also incorporates input from laboratory experiments described in Chap.6. This chapter gives an overview of site characterization procedures with respect to geological storage of CO2, by starting from regulatory requirements and guidelines and proceeding to specific methodologies for assessing the sites properties in terms of CO2 geological storage.
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| 3. |
- Alcalde, J., et al.
(författare)
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3-D reflection seismic imaging of the Hontomin structure in the Basque-Cantabrian Basin (Spain)
- 2013
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Ingår i: Solid Earth. - : Copernicus GmbH. - 1869-9510 .- 1869-9529. ; 4:2, s. 481-496
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Tidskriftsartikel (refereegranskat)abstract
- The Basque-Cantabrian Basin of the northern Iberia Peninsula constitutes a unique example of a major deformation system, featuring a dome structure developed by extensional tectonics followed by compressional reactivation. The occurrence of natural resources in the area and the possibility of establishing a geological storage site for carbon dioxide motivated the acquisition of a 3-D seismic reflection survey in 2010, centered on the Jurassic Hontomin dome. The objectives of this survey were to obtain a geological model of the overall structure and to establish a baseline model for a possible geological CO2 storage site. The 36 km(2) survey included approximately 5000 mixed (Vibroseis and explosives) source points recorded with a 25 m inline source and receiver spacing. The target reservoir is a saline aquifer, at approximately 1450 m depth, encased and sealed by carbonate formations. Acquisition and processing parameters were influenced by the rough topography and relatively complex geology. A strong near-surface velocity inversion is evident in the data, affecting the quality of the data. The resulting 3-D image provides constraints on the key features of the geologic model. The Hontom n structure is interpreted to consist of an approximately 10(7) m(2) large elongated dome with two major (W-E and NW-SE) striking faults bounding it. Preliminary capacity estimates indicate that about 1.2 Gt of CO2 can be stored in the target reservoir.
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| 4. |
- Alcalde, J., et al.
(författare)
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Active seismic characterization experiments of the Hontomin research facility for geological storage of CO2, Spain
- 2013
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836 .- 1878-0148. ; 19:0, s. 785-795
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Tidskriftsartikel (refereegranskat)abstract
- An active source seismic experiment was carried out as part of the subsurface characterization study of the first Spanish Underground Research Facility for Geological Storage of CO2 in Hontomín (Burgos, Spain). The characterization experiment included a 36 km2 3D seismic reflection survey and two three-component seismic profiles. The target reservoir is a saline aquifer located at 1450 m depth within Lower Jurassic carbonates (Lias). The main seal is formed by interlayered marlstones and marly limestones of Early to Middle Jurassic age (Dogger and Lias). The seismic images obtained allow defining the 3D underground architecture of the reservoir site. The structure consists of an asymmetric dome crosscut by a relatively complex fault system. The detailed characterization of the fracture system is currently under study to unravel the geometric distribution of the faults and their extent within the different formations that form the structure. The constrained model has guided the design of the injection and monitoring boreholes and provided the data for the baseline study. The resultant high resolution seismic model will be used as a reference in future monitoring stages.
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| 5. |
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| 6. |
- Andersson, Magnus, et al.
(författare)
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Carbonatite ring-complexes explained by caldera-style volcanism
- 2013
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- Carbonatites are rare, carbonate-rich magmatic rocks that make up a minute portion of the crust only, yet they are of great relevance for our understanding of crustal and mantle processes. Although they occur in all continents and from Archaean to present, the deeper plumbing system of carbonatite ring-complexes is usually poorly constrained. Here, we show that carbonatite ring-complexes can be explained by caldera-style volcanism. Our geophysical investigation of the Alnö carbonatite ring-complex in central Sweden identifies a solidified saucer-shaped magma chamber at ∼3 km depth that links to surface exposures through a ring fault system. Caldera subsidence during final stages of activity caused carbonatite eruptions north of the main complex, providing the crucial element to connect plutonic and eruptive features of carbonatite magmatism. The way carbonatite magmas are stored, transported and erupt at the surface is thus comparable to known emplacement styles from silicic calderas.
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| 7. |
- Ayarza, Puy, et al.
(författare)
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Evolution of the Iberian Massif as deduced from its crustal thickness and geometry of a mid-crustal (Conrad) discontinuity
- 2021
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Ingår i: Solid Earth. - : Copernicus Publications. - 1869-9510 .- 1869-9529. ; 12:7, s. 1515-1547
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Tidskriftsartikel (refereegranskat)abstract
- Y Normal incidence seismic data provide the best images of the crust and lithosphere. When properly designed and continuous, these sections greatly contribute to understanding the geometry of orogens and, along with surface geology, unraveling their evolution. In this paper we present the most complete transect, to date, of the Iberian Massif, the westernmost exposure of the European Variscides. Despite the heterogeneity of the dataset, acquired during the last 30 years, the images resulting from reprocessing the data with a homogeneous workflow allow us to clearly define the crustal thickness and its internal architecture. The Iberian Massif crust, formed by the amalgamation of continental pieces belonging to Gondwana and Laurussia (Avalonian margin), is well structured in the upper and lower crust. A conspicuous mid-crustal discontinuity is clearly defined by the top of the reflective lower crust and by the asymptotic geometry of reflections that merge into it, suggesting that it has often acted as a detachment. The geometry and position of this discontinuity can give us insights into the evolution of the orogen (i.e., of the magnitude of compression and the effects and extent of later-Variscan gravitational collapse). Moreover, the limited thickness of the lower crust below, in central and northwestern Iberia, might have constrained the response of the Iberian microplate to Alpine shortening. Here, this discontinuity, featuring a Vp (P-wave velocity) increase, is observed as an orogen-scale boundary with characteristics compatible with those of the globally debated Conrad discontinuity.
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| 8. |
- Basirat, Farzad, et al.
(författare)
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Hydraulic Modeling of Induced and Propagated Fractures : Analysis of Flow and Pressure Data From Hydromechanical Experiments in the COSC-1 Deep Borehole in Crystalline Rock Near Åre, Sweden
- 2021
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 57:11
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Tidskriftsartikel (refereegranskat)abstract
- To characterize the coupled hydromechanical behavior of rock fractures, the step-rate injection method for fracture in-situ properties (SIMFIP) was conducted with a specialized downhole probe developed by Guglielmi et al. (2014, https://doi.org/10.1007/s00603-013-0517-1). In June 2019, a field campaign was carried out near Åre, Sweden, where the SIMFIP probe was applied in the Collisional Orogeny in the Scandinavian Caledonides-1 scientific borehole to understand the dynamics of injection-induced fracture initiation, fracture opening, and shearing due to water injection-withdrawal in a borehole interval isolated by two packers. Three intervals were investigated at ∼500 m depth: (a) an unfractured section (intact rock), (b) a section with non-conductive fractures, and (c) a section with hydraulically conductive fractures. Pressure, injection flow rate, and borehole wall displacement were simultaneously measured during the tests. In the present study, the geometry of the induced fracture and deformation of existing fractures at different time stages of the tests are determined based on a hydrologic model by using the measured pressure and flow data during each time stage of the experiment. A numerical model for the fluid flow within the fracture and the packed-off borehole interval is implemented within COMSOL Multiphysics. By matching model simulations with observed data for all three sections, estimates of the induced and propagated fractures' radius and aperture at successive time stages have been obtained in each case. We could also determine the non-linear relationship between fracture aperture and pressure for values above fracture opening pressures. The model results provide insights for the understanding of pressure-induced fracture initiation and propagation in crystalline rock.
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| 9. |
- Bastida, F, et al.
(författare)
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A cross-section through the Zilair Nappe (southern Urals)
- 1997
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Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 276:1-4, s. 253-263
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A structural transect in the Zilair-Kugarchi area involves the western part of the Suvanyak Complex, the Zilair Nappe and the eastern part of the foreland thrust and fold belt. This section has been analyzed using field, microstructural and seismic data. The cross-section shows the transition from the hinterland to the foreland in the footwall to the suture of the southern Urals. The rocks involved range from early Palaeozoic to Permian in age. A characteristic of the Zilair Nappe is the dominance of a succession of volcanic greywackes and mudrocks of Late Devonian age (Zilair Formation). The metamorphic grade decreases from east to west, from greenschist facies to diagenetic conditions. The structure of the cross-section mainly comprises west-directed thrusts and thrust-related folds with an associated cleavage. Fold vergence changes along the section depending on of the distance to the associated thrust and its geometry. The Zilair thrust which separates the Zilair Nappe from the foreland thrust and fold belt accommodated ca. 10 km displacement and the characteristics of the deformation are similar on both sides of it. The contact between the Zilair Nappe and Suvanyak Complex is a west-dipping normal fault that does not represent a major tectonic boundary.
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| 10. |
- Beckel, Ruth A.
(författare)
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Active and passive seismic methods for investigating the glacially-triggered Burträsk fault
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glacially-triggered faults are of high scientific interest since their formation was likely accompanied by major earthquakes and they are still a centre of seismicity in northern Fennoscandia, today. Imaging their deeper structure mainly relies on reflection seismics since the method generally has the best resolving power at depth of all geophysical methods. This thesis uses data acquired at the glacially-triggered Burträsk fault to advance active and passive seismic imaging methods and improve the understanding of the area. Reprocessing of a vintage, crooked-line reflection dataset using a newly developed module for a local cross-dip correction improved the quality of the reflection image significantly and provided important 3D information for the interpretation of the fault and its surroundings. A fault segment to the southwest of the profile was imaged with a dip of approximately 50° but the segment intersecting the profile was not imaged, likely due to insufficient shot coverage close to the fault. Since the Burträsk area is seismically the most active area in Sweden, passive imaging using a dataset of local microearthquakes was attempted. As a first step, the earthquakes were re-located using a stacking-based location method. In spite of the poor azimuthal coverage of the array, the method yielded surprisingly good location results within 30–40 km from the array. The most important factors for success proved to be combined P- and S-wave location with down-weighted S-wave signals, and the use of a polarity-sensitive characteristic function. The distribution of the hypocentres confirmed that the trace of the Burträsk fault is the currently active fault plane. Disappointingly, passive seismic processing using reflection seismic interferometry (RSI) did not image the known reflections. To improve the planning of future studies, different aspects of imaging dipping faults with RSI were investigated using synthetic data. The results showed that reconstructing steeply dipping reflections requires sources in the hanging-wall and that the interpretation of the RSI sections is complicated due to strong artefacts caused by P-S converted arrivals. Thus, passive imaging needs careful planning and a good knowledge of the source positions for distinguishing between artefacts and subsurface structures. This knowledge can be obtained using the stacking-based location method.
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