D. Sokoutis | Utrecht University (original) (raw)

Papers by D. Sokoutis

First Break, 2015

Geological storage of CO2 is a key technical solution to the climate-energy challenge, but it has... more Geological storage of CO2 is a key technical solution to the climate-energy challenge, but it has a number of technological constraints (Baines and Worden 2004; Halland et al., 2011), broadly under the themes of assuring adequate storage capacity and long-term storage integrity. A suitable CO2-storage reservoir should consist of rock formations with sufficient porosity, permeability and connectivity in order to provide an adequate storage volume. The role of faults and their associated deformation structures (such as deformation bands and fractures) in controlling both storage capacity and long-term storage integrity is thus a key factor in achieving globally significant CO2 storage (Figure 1). Although some sedimentary basins on the Norwegian continental shelf already harbour operational CO2- injection and storage projects such as Sleipner (Zweigel et al., 2004) and Snohvit (Hansen et al., 2013), our understanding of reservoir fluid communication due to compartmentalization is far from complete and will be important for further use of the offshore basins for CO2 storage. In addition to the inherited structural features, elevated injection pressures may cause hydraulic fractures or stimulate fault reactivation which both point to the need to characterize the geomechanical response of the rock system to CO2 injection (Rutqvist, 2012; Iding and Ringrose, 2010). In the present work, we investigate the effects of faults and their related structures on the geomechanical and petrophysical properties of sandstone reservoirs. Important components of fault systems include fractures and deformation bands in the damage zone and fault core (Caine et al., 1996; Shipton and Cowie, 2003; Fossen et al., 2007). Fault systems may enhance or suppress fluid communication, which in turn may affect the storage capacity and conductivity of the candidate reservoirs (Figure 1). As a case study, a reservoir model of the Tubaen Formation at the Snohvit CO2 injection site in the Barents Sea (Grude et al., 2013; Hansen et al., 2013) was investigated using 4D seismic data and fault attribute analysis. The characteristics of deformation structures (e.g. sub-seismic faults, deformation bands and fractures) were investigated by field studies of outcrop analogues and by triaxial laboratory experiments to provide a basis for numerical modelling. Fault architecture within reactivated fault systems was studied by the use of analogue modelling. Key questions addressed in the work include: a) Where and when might strain localize in the reservoir? b) How does rock strain influence fluid communication? c) How might structural architecture affect CO2 storage effectiveness?

Petrology and Structural Geology, 1997

Field data suggest that the epizonal Yakushima granite rose obliquely into the Ryukyu arc of Japa... more Field data suggest that the epizonal Yakushima granite rose obliquely into the Ryukyu arc of Japan (Anma, this volume). Analogue models test the hypothesis that the oblique rise of this buoyant diapir was due to drag by the stiff oceanic plate sinking obliquely beneath it. A simplified model of a sQ)id plate sinking obliquely along its length into a ductile medium induces wedge flow in the overlying asthenosphere. Buoyant inclusions in the model lithospheric/asthenospheric wedge trace possible tracks of plutons above subduction zones. The inclusions rise obliquely toward the trench axis in the nearby wedge where rotational shear is greatest, leaving an inclined diapir tail. By contrast, near the surface away from the trench axis, where arc-normal horizontal extension prevails, buoyant inclusions become tabular in shape and are carried toward the trench. Overall, the observations account for the geometries of the Y akushima and other Miocene granites in Southwest Japan.

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1992

ABSTRACT

Journal of Geophysical Research-Part B-Solid Earth, 2004

Journal of the Geological Society, 1993

Bulletin of the Geological Society of Greece, 2001

Experimental models are used to study the stress control of frictional hangingwall accomodation a... more Experimental models are used to study the stress control of frictional hangingwall accomodation above rigid flat-ramp-flat footwalls. Hangingwall accommodation involves shear or kink-band nucleation above the lower fault bend and migration of these as the hangingwalls climb over the underthrusting footwall. The kinkbands change shape and localise to thrusts as they migrate over the flat-ramp-flat footwall. When the shear stress to gravity stress ratio is low the thrusts reactivate to normal faults. With increase in the shear stress to gravity stress ratio reactivation of the kink bands was by tensile failure, at the upper fault bend. The models show that by changing the strength of materials deforming under otherwise similar conditions it is possible to study the geometry of frictional hangingwall accommodation, at different scales. In nature, hangingwall accommodation by thrust nucleation above thrust ramps and their subsequent normal reactivation may be anticipated in frictional s...

Tectonics, 2020

New structural and thermochronological (zircon and apatite fission track) data from the eastern m... more New structural and thermochronological (zircon and apatite fission track) data from the eastern most Alps highlight distinct deformation phases affecting the Austroalpine unit along a major sinistral strike-slip fault system, the Mur-Mürz fault (MMF). The data link deformation to vertical motions prior to, during, and after the main phase of lateral extrusion of the orogen. Zircon fission track ages document rapid (ca. 15°C/Myr) and diachronous (eastward younging) cooling and rock exhumation during the latest Cretaceous to Paleocene. Subsequent regional Eocene to early Miocene cooling below the closure temperature of the apatite fission track system occurred at slow rates (ca. 2°C/Myr), suggesting that the region was not subject to major surface uplift and erosion during that period. Fault kinematic analysis along the MMF document pre-extrusion NNW-SSE contraction, middle Miocene syn-extrusion NE-SW to NNE-SSW directed shortening, and Late Miocene E-W contraction. All phases are characterized by strike-slip fault regimes. Formation of the complex MMF zone triggered the exhumation of small, fault-bound crustal blocks within the fault zone as documented by middle Miocene apatite fission track ages. Overall, ages are similar on both sides of the fault suggesting that lateral extrusion along the MMF was not associated with significant differential vertical motions. Local Pliocene rock cooling and exhumation was probably related to the buttressing effect of the underthrust Bohemian basement spur. Whereas large-scale, post-extrusion surface uplift of the extruding crustal wedges, such as the "Styrian block," must have been related to long-wavelength deformation processes affecting the easternmost Alps.

Tectonophysics, 2018

The Main Ethiopian Rift, East Africa, is characterised by the presence of major, enigmatic struct... more The Main Ethiopian Rift, East Africa, is characterised by the presence of major, enigmatic structures which strike approximately orthogonal to the trend of the rift valley. These structures are marked by important deformation and magmatic activity in an off-axis position in the plateaus surrounding the rift. In this study, we present new structural data based on a remote and field analysis, complemented with analogue modelling experiments, and new geochemical analysis of volcanic rocks sampled in different portions of one of these transversal structures: the Goba-Bonga volcano-tectonic lineament (GBVL). This integrated analysis shows that the GBVL is associated with roughly E-Wtrending prominent volcano-tectonic activity affecting the western plateau. Within the rift floor, the approximately E-W alignment of Awasa and Corbetti calderas likely represent expressions of the GBVL. Conversely, no tectonic or volcanic features of similar (E-W) orientation have been recognized on the eastern plateau. Analogue modelling suggests that the volcano-tectonic features of the GBVL have probably been controlled by the presence of a roughly E-W striking pre-existing discontinuity beneath the western plateau, which did not extend beneath the eastern plateau. Geochemical analysis supports this interpretation and indicate that, although magmas have the same sub-lithospheric mantle source, limited differences in magma evolution displayed by products found along the GBVL may be ascribed to the different tectonic framework to the west, to the east, and in the axial zone of the rift. These results support the importance of the heterogeneous

Journal of the Geological Society, 1994

Ivan S. Zagorèev writes: The problem of the Late Cenozoic extension in the Northern Aegean has be... more Ivan S. Zagorèev writes: The problem of the Late Cenozoic extension in the Northern Aegean has been discussed for more than 30 years. The approach by Sokoutis et al. 1993 and by Dinter & Royden (1993) seeks the control of this extension in the displacements along very low-angle normal faults of great extent and offset (detachments) which resulted also in a fast unroofing of deep crustal levels in the footwall, and intense sediment deposition on the downthrown side (i.e., formation of depocentres). This problem is traditionally discussed without taking into account the abundant evidence from the adjacent to the north, and well-exposed and mapped Central-Balkan neotectonic region (Zagorèev 1992b). The following important facets of this problem should be taken into consideration. (1) Age of the faulting event, and identification of fault movements of a given age. The region is characterized by several Alpine phases of thrusting proven with fossildocumented sediments within the following limits: (i) Berriasian (Aptian?)—Turonian (Cenomanian?); (ii) Campanian (Maastrichtian?)—Late Eocene (Palaeocene?); (iii) Mid-Eocene—Late Eocene; (iv) Mid-Oligocene (?); (v) earliest Miocene—Badenian. Normal faulting is proven (again with fossiliferous sediments) in the following times: (i) Late Triassic (Carnian—Rhaetian); (ii) Early Jurassic (Hettangian—Pliensbachian); (iii) Bathonian; (iv) Callovian; (v) Tithonian—Berriasian; (vi), Cenomanian— Turonian; (vii) Coniacian—Campanian; (Viii) Maastrichtian; (ix) Palaeocene—Early Eocene; (X) Late Eocene; (xi) Mid-Oligocene—Early Miocene; (xii) Late Badenian—Maeotian; (xiii) Pontian—Romanian; (xiv) Pleistocene— Holocene (e.g. Boyanov et al. 1989; Zagorèev 1992a, b). Experience in southwest Bulgaria shows that some fault

Journal of Structural Geology, 2000

Experimental models are used to study the role of material rheology in hanging wall accommodation... more Experimental models are used to study the role of material rheology in hanging wall accommodation above rigid¯at±ramp± at thrust footwalls. The deformation in the hanging wall was accomplished by forwards sliding along a rigid basal staircase trajectory with a variable ramp angle, a, ranging from 158 to 608. We model dierent ramp angles to examine hanging wall accommodation styles above thrust ramps of overthrust faults (a ranging from 158 to 308), as well as above pre-existing normal faults (a ranging from 458 to 608). For the hanging walls we used strati®ed frictional (sand) and viscous (silicone putty) materials. In this paper we study three types of models. Type 1 models represent purely frictional hanging walls where accommodation above thrust ramps was by layer-parallel thickening and by generating a series of back thrusts. Type 2 and 3 models represent strati®ed frictional/viscous hanging walls. In these models, accommodation was by a complex association of reverse and normal faults, mainly controlled by the rheological anisotropy as well as by the ramp inclination angle a. In Type 2 models the silicone covered only the lower¯at, while in Type 3 models it also covered the rigid ramp. For a 308 in Type 2 models and a 458 in Type 3 models, the viscous layer inhibited the development of back thrusts in the frictional hanging wall, instead the silicone thickened to develop a`ductile ramp'. For a-values higher than 308 in Type 2 models and a=458 in Type 3 models, back thrusts develop in response to the bulk compression. The experiments simulate many structures observed above natural thrust ramps with a 308 and pre-existing normal faults with ar458. The models emphasise the importance of a basal ductile layer, which allows the hanging wall to step-up over the rigid ramp by building up its own ductile ramp. The models also emphasise that foreland-directed normal faulting can develop at a thrust front in the case that the vertical stress due to gravity exceeds the horizontal stress due to end-loading within a thrust wedge.

Journal of Geophysical Research: Solid Earth, 2003

Even though the rheology of thrust wedges is mostly frictional, a basal ductile decollement is of... more Even though the rheology of thrust wedges is mostly frictional, a basal ductile decollement is often involved. By comparison with purely frictional wedges, such brittleductile wedges generally display anomalous structures such as backward vergence, widely spaced thrust units, and nonfrontward sequences of thrust development. Laboratory experiments are used here to study the deformation of brittle-ductile thrust wedges. Results are compared with natural systems in the Jura Mountains and the northern Pakistan Salt Range and Potwar Plateau. Two series of three models are used to illustrate the effects of varying the basal wedge angle (b) and shortening rate (V). These two parameters directly control variations in relative strength between brittle and ductile layers (BD coupling). Wedges with strong BD coupling (low b and high V) give almost regular frontward sequences with closely spaced thrust units and, as such, are not significantly different from purely frictional wedges. Weak BD coupling (high b and low V) gives dominantly backward thrusting sequences. Intermediate BD coupling produces frontwardbackward oscillating sequences. The spacing of thrust units increases as coupling decreases. Back thrusts develop in parts of a wedge where BD coupling is weak, regardless of the thrust sequence. Wedges with weak BD coupling need large amounts of bulk shortening (more than 30%) to attain a state of equilibrium, at which stable sliding along the base occurs. On this basis, we argue that a state of equilibrium has not yet been attained in at least some parts of the Jura Mountains and eastern Salt Range and Potwar Plateau thrust systems.

Geophysical Research Letters, 2003

Earth and Planetary Science Letters, 1993

Abstract Our understanding of the flow properties of deforming rocks in the Earth&amp;amp... more Abstract Our understanding of the flow properties of deforming rocks in the Earth&amp;amp;amp;amp;#x27;s lithosphere is mainly based on theoretical work and on the extrapolation of high-strain-rate experimental data to the low strain rates of rock deformation in nature. The geometry of structures in naturally deformed rocks can be an additional source of information on the rheology of the lithosphere. Flow experiments show that the geometry of a mantle of recrystallised material around a rigid object can be used to distinguish between a linear or ...