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Journal articlePelecanos L, Kontoe S, Zdravkovic L, 2020,
The effects of dam-reservoir interaction on the nonlinear seismic response of earth dams
, Journal of Earthquake Engineering, Vol: 24, Pages: 1034-1056, ISSN: 1363-2469The objective of this study is to investigate the effects of dam–reservoir interaction (DRI) on the nonlinear seismic response of earth dams. Although DRI effects have for long been considered as insignificant for earth dams, that conclusion was mainly based on linear elastic investigations which focused only on the acceleration response of the crest without examining the seismic shear stresses and strains within the dam body. The present study explores further the impact of DRI focusing on the nonlinear behavior of earth dams. The effects of reservoir hydrodynamic pressures are investigated in terms of both seismic dam accelerations and nonlinear dynamic soil behavior (seismic shear stresses and strains). It is shown that although dam crest accelerations are indeed insensitive to DRI, the stress and strain development within the dam body can be significantly underestimated if DRI is ignored.
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Book chapterJackson CAL, 2018,
Growth of a Salt-Detached Normal Fault and Controls on Throw Rate Variability; Gudrun Field, South Viking Graben, Offshore Norway
, Rift-related coarse-grained submarine fan reservoirs; the Brae Play, South Viking Graben, North Sea, Editors: Turner, Cronin, Publisher: AAPG, Pages: 423-444, ISBN: 978-0-89181-395-8The growth and throw/displacement rate variability on normal faults can reflect fault interaction, plate tectonic forces and, in gravity-driven systems, variations in sediment loading. Because earthquakes may occur as faults slip, it is important to understand what processes influence throw rate variability on normal faults to be able to predict seismic hazards in extensional terranes. Furthermore, the rate of normal fault growth directly controls rift physiography, sediment erosion, dispersal and deposition, and the distribution and stratigraphic architecture of syn-rift reservoirs. Instrumental (e.g. geodetic) data may constrain the very short-term (i.e. days to years) throw rate history of normal faults, whereas palaeoearthquake data may provide important information on medium-term (i.e. 103-105 years) rates. Constraining longer-term (i.e. >106 Myr) variations typically requires the use of seismic reflection data, although their application may be problematic because of poor seismic resolution and the absence of, or poor age constraints on, coeval growth strata. In this study I use 3D seismic reflection and borehole data to constrain the growth and long-term throw rate variability on a gravity-driven, salt-detached normal fault (Middle-to-Late Jurassic) in the South Viking Graben, offshore Norway, and to assess the impact of throw rate variability on the thickness and character of syn-rift reservoirs. I recognise five kinematic phases: (i) Phase 1 (early Callovian) - fault initiation and a phase of moderate fault throw rates (0.06 mm yr-1); (ii) Phase 2 (early Callovian-to-end Callovian) - fault inactivity, during which time the fault was buried by sediment; (iii) Phase 3 (early Oxfordian-to-late Oxfordian) - fault reactivation and a phase of moderate throw rates (up to 0.03 mm yr-1); (iv) Phase 4 (late Oxfordian-to-end Oxfordian) – a marked increase in throw rate (up to 0.27 mm yr-1); and (v) Phase 5 (early Kimmeridgian-to-middle Volgian) – a decl
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Journal articleLiu J, Mason PJ, Bryant EC, 2018,
Regional assessment of geohazard recovery eight years after the Mw7.9 Wenchuan earthquake: a remote-sensing investigation of the Beichuan region
, International Journal of Remote Sensing, Vol: 39, Pages: 1671-1695, ISSN: 0143-1161The earthquake of 12 May 2008 in Wenchuan County, Sichuan Province, China, devastated the entire Beichuan region. Sitting at the intersection of the Yingxiu-Beichuan and Pengguan faults, the region experienced seismic intensities of VIII–XI on the Liedu scale. High seismic intensity combined with inherent geomorphological and climatic susceptibility to slope failure resulted in widespread co-seismic geohazards (slope failures of various types), which decimated the region. The seismic characteristics of the Wenchuan earthquake and the co-seismic geohazard distribution in relation to various conditioning factors have previously been examined in depth. However, there has been a lack of regional assessment of temporal and spatial recovery from co-seismic geohazards. Triggered by the authors’ field observation of rapid recovery, this study presents a temporal series of geohazard maps, produced by manual interpretation of satellite imagery, to present an initial assessment of changes in geohazard occurrence in the Beichuan region since the Wenchuan earthquake. In particular, landscape recovery at the co-seismic geohazard sites, as indicated by re-vegetation, is analysed based on temporal/spatial characteristics of geohazard distribution, in relation to co-seismic deformation, distance from the rupture zone and slope angle. Eight years after the Wenchuan earthquake, the overall recovery stands at 65.48%, with approximately uniform annual rates of recovery at 13.45% a year between 2009 and 2011 and 10.56% a year between 2012 and 2016. Whilst co-seismic geohazards are concentrated on the hanging wall of the seismic fault, landscape recovery is more significant in the very highly deformed zone than in other areas. Recovery has been the greatest on slopes of <50° and peaks on 40°–50° slopes, where the area occupied by co-seismic geohazards was the largest. The block-slides and rock topples, which characterize high angle slopes, show much slower
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Journal articleCollins GS, Lynch E, McAdam R, et al., 2017,
A numerical assessment of simple airblast models of impact airbursts
, Meteoritics & Planetary Science, Vol: 52, Pages: 1542-1560, ISSN: 1086-9379Asteroids and comets 10–100 m in size that collide with Earth disrupt dramatically in the atmosphere with an explosive transfer of energy, caused by extreme air drag. Such airbursts produce a strong blastwave that radiates from the meteoroid's trajectory and can cause damage on the surface. An established technique for predicting airburst blastwave damage is to treat the airburst as a static source of energy and to extrapolate empirical results of nuclear explosion tests using an energy-based scaling approach. Here we compare this approach to two more complex models using the iSALE shock physics code. We consider a moving-source airburst model where the meteoroid's energy is partitioned as two-thirds internal energy and one-third kinetic energy at the burst altitude, and a model in which energy is deposited into the atmosphere along the meteoroid's trajectory based on the pancake model of meteoroid disruption. To justify use of the pancake model, we show that it provides a good fit to the inferred energy release of the 2013 Chelyabinsk fireball. Predicted overpressures from all three models are broadly consistent at radial distances from ground zero that exceed three times the burst height. At smaller radial distances, the moving-source model predicts overpressures two times greater than the static-source model, whereas the cylindrical line-source model based on the pancake model predicts overpressures two times lower than the static-source model. Given other uncertainties associated with airblast damage predictions, the static-source approach provides an adequate approximation of the azimuthally averaged airblast for probabilistic hazard assessment.
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Journal articleRyan L, Magee C, Jackson CA-L, 2017,
The kinematics of normal faults in the Ceduna Sub-Basin, offshore Southern Australia; implications for hydrocarbon trapping in a frontier basin
, AAPG Bulletin, Vol: 101, Pages: 321-341, ISSN: 0149-1423The geometry and growth of normal faults is fundamental to the evolution and petroleum prospectivity of sedimentary basins, controlling trap development, source, reservoir and seal rock distribution, and fluid flow. The poorly studied, petroliferous Ceduna Sub-basin located offshore southern Australia contains an ESE-striking, gravity driven fault array, which soles out onto a SW-dipping detachment horizon. Within the sub-basin, structural closures bound by these gravity driven faults represent the main exploration targets. Determining when these faults and associated traps formed relative to petroleum generation and migration and, more specifically, if the faults reactivated, is thus critical to understanding the prospectivity of the Ceduna Sub-basin. In this study, we use a high-quality, time-migrated 2D seismic reflection survey covering the central Ceduna Sub-basin to constrain the geometry and kinematics of the fault array. Fault throw patterns reveal that most nucleated in the Cenomanian. Although some faults display evidence for continuous growth by upper tip propagation throughout the Cenomanian to Maastrichtian, others grew via either dip linkage of isolated segments or fault reactivation. It is apparent that some faults were inactive during the Turonian-Santonian before reactivating and propagating upwards or dip-linking with overlying, newly formed faults. Continuously growing faults primarily occur in the center of the study area, whereas reactivated faults occur proximal to the sediment source and dip-linked faults developed oceanwards. We suggest that this spatial variation fault growth style was primarily controlled by compositional and mechanical heterogeneities in the Tiger and lower Hammerhead supersequences. In addition to providing insights into the petroleum prospectivity of the Ceduna Sub-basin, this study shows how 2D seismic reflection data can be used to probe the kinematics of normal faults.
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Journal articleSummersgill FC, Kontoe S, Potts D, 2017,
On the use of nonlocal regularisation in slope stability problems
, Computers and Geotechnics, Vol: 82, Pages: 187-200, ISSN: 0266-352XThis study examines the use of nonlocal regularisation in a coupled consolidation problem of an excavated slope in a strain softening material. The nonlocal model reduces significantly the mesh dependency of cut slope analyses for a range of mesh layouts and element sizes in comparison to the conventional local approach. The nonlocal analyses are not entirely mesh independent, but the predicted response is much more consistent compared to the one predicted by local analyses. Additional Factor of Safety analyses show that for drained conditions the nonlocal regularisation eliminates the mesh dependence shown by the conventional local model.
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Journal articleMorgan JV, Gulick SPS, Bralower T, et al., 2016,
The formation of peak rings in large impact craters
, Science, Vol: 354, Pages: 878-882, ISSN: 0036-8075Large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peaks transition to peak rings. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Expedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust.
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Journal articleJohnson BC, Blair DM, Collins GS, 2016,
Formation of the Orientale lunar multiring basin
, Science, Vol: 354, Pages: 441-444, ISSN: 0036-8075Multiring basins, large impact craters characterized by multiple concentric topographic rings, dominate the stratigraphy, tectonics, and crustal structure of the Moon. Using a hydrocode, we simulated the formation of the Orientale multiring basin, producing a subsurface structure consistent with high-resolution gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft. The simulated impact produced a transient crater, ~390 kilometers in diameter, that was not maintained because of subsequent gravitational collapse. Our simulations indicate that the flow of warm weak material at depth was crucial to the formation of the basin’s outer rings, which are large normal faults that formed at different times during the collapse stage. The key parameters controlling ring location and spacing are impactor diameter and lunar thermal gradients.
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Journal articleD'Arcy M, Whittaker AC, Roda Boluda DC, 2016,
Measuring alluvial fan sensitivity to past climate changes using a self-similarity approach to grain size fining, Death Valley, California
, Sedimentology, Vol: 64, Pages: 388-424, ISSN: 1365-3091The effects of climate change on eroding landscapes and the terrestrial sedimentary record are poorly understood. Using mountain catchment–alluvial fan systems as simple analogues for larger landscapes, a wide range of theoretical studies, numerical models and physical experiments have hypothesised that a change in precipitation rate could leave a characteristic signal in alluvial fan sediment flux, grain size and down-system fining rate. However, this hypothesis remains largely untested in real landscapes. This study measures grain-size fining rates from apex to toe on two alluvial fan systems in northern Death Valley, California, USA, which each have well-exposed modern and ca 70 ka surfaces, and where the long-term tectonic boundary conditions can be constrained. Between them, these surfaces capture a well-constrained temporal gradient in climate. A grain-size fining model is adapted, based on self-similarity and selective deposition, for application to these alluvial fans. This model is then integrated with cosmogenic nuclide constraints on catchment erosion rates, and observed grain-size fining data from two catchment-fan systems, to estimate the change in sediment flux from canyon to alluvial fan that occurred between mid-glacial and modern interglacial conditions. In a fan system with negligible sediment recycling, an approximately 30% decrease in precipitation rate led to a 20% decrease in sediment flux and a clear increase in the down-fan rate of fining, supporting existing landscape evolution models. Consequently, this study shows that small mountain catchments and their alluvial fan stratigraphy can be highly sensitive to orbital climate changes over <105 year timescales. However, in the second fan system it is observed that this sensitivity is completely lost when sediment is remobilised and recycled over a time period longer than the duration of the climatic perturbation. These analyses offer a new approach to quantitatively reconstructing the
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Journal articleKring DA, Kramer GY, Collins GS, et al., 2016,
Peak-Ring Structure and Kinematics from a Multi-disciplinary Study of the Schrödinger Impact Basin
, Nature Communications, Vol: 7, ISSN: 2041-1723The Schrödinger basin on the lunar farside is ~320 km in diameter and the best-preservedpeak-ring basin of its size in the Earth–Moon system. Spectral and photogeologic analyses ofdata from the Moon Mineralogy Mapper instrument on the Chandrayaan-1 spacecraft and theLunar Reconnaissance Orbiter Camera (LROC) on the LRO spacecraft indicate the peak ring iscomposed of anorthositic, noritic, and troctolitic lithologies that were juxtaposed by severalcross-cutting faults during peak ring formation. Hydrocode simulations indicate the lithologieswere uplifted from depths up to 30 km, representing the crust of the lunar farside. Combining2geological and remote-sensing observations with numerical modeling, here we show a DisplacedStructural Uplift model is best for peak rings, including that in the K-T Chicxulub impact crateron Earth. These results may help guide sample selection in lunar sample return missions that arebeing studied for the multi-agency International Space Exploration Coordination Group.Determining which lunar landing site may yield information about the lunar interior is veryimportant with impact basins usually the best sites. Kring et al. provide a geological map of theSchrödinger basin on the moon via a multidisciplinary approach of remote sensing and numericalmodeling.
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Journal articleForman LV, Bland PA, Timms NE, et al., 2016,
Hidden Secrets Of Deformation: Impact-Induced Compaction Within A CV Chondrite
, Earth and Planetary Science Letters, Vol: 452, Pages: 133-145, ISSN: 0012-821XThe CV3 Allende is one of the most extensively studied meteorites in worldwide collections. It is currently classified as S1—essentially unshocked—using the classification scheme of Stöffler et al. (1991), however recent modelling suggests the low porosity observed in Allende indicates the body should have undergone compaction-related deformation. In this study, we detail previously undetected evidence of impact through use of Electron Backscatter Diffraction mapping to identify deformation microstructures in chondrules, AOAs and matrix grains. Our results demonstrate that forsterite-rich chondrules commonly preserve crystal-plastic microstructures (particularly at their margins); that low-angle boundaries in deformed matrix grains of olivine have a preferred orientation; and that disparities in deformation occur between chondrules, surrounding and non-adjacent matrix grains. We find heterogeneous compaction effects present throughout the matrix, consistent with a highly porous initial material. Given the spatial distribution of these crystal-plastic deformation microstructures, we suggest that this is evidence that Allende has undergone impact-induced compaction from an initially heterogeneous and porous parent body. We suggest that current shock classifications (Stöffler et al., 1991) relying upon data from chondrule interiors do not constrain the complete shock history of a sample.
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Journal articleAllen H, Jackson CA-L, Fraser AJ, 2016,
Gravity-driven deformation of a youthful saline giant: the interplay between gliding and spreading in the Messinian Basins of the Eastern Mediterranean
, Petroleum Geoscience, Vol: 22, Pages: 340-356, ISSN: 1354-0793The triggers and drivers for salt-related deformation on continental margins are intensely debated, reflecting uncertainties regarding the diagnostic value of certain structural styles, in addition to the fundamental mechanics associated with the two principal mechanisms (gliding and spreading). Determining the triggers and drivers for salt-related deformation is important because they provide insights into continent-scale geodynamic processes, the regional kinematics of gravity-driven deformation, and sediment dispersal and hydrocarbon prospectivity. The processes associated with and timing of deformation of Messinian salt in the offshore eastern Mediterranean are uncertain, thus is our understanding of the geodynamic evolution of this tectonically complex region. We here use an extensive 2D and 3D seismic reflection dataset to test models for the salt-tectonic development of Messinian salt. We contend that gliding and spreading were not mutually exclusive, but likely overlapped through time and space, showing a close relationship local and far-field tectonics (gliding), as well as differential overburden loading (spreading). We also argue that intrasalt strain and seismic-stratigraphic patterns can be explained by a model invoking a single, post-Messinian period of salt-related deformation, rather than a more complex model involving two separate, non-coaxial deformation events occurring during and after salt deposition.
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Journal articleBurberry CM, Jackson CA-L, Chandler S, 2016,
Seismic reflection imaging of karst in the Persian Gulf; Implications for the characterization of carbonate reservoirs
, AAPG Bulletin, Vol: 100, Pages: 1561-1584, ISSN: 0149-1423Karstification positively and negatively affects the quality of carbonate reservoirs; for example, dissolution and brecciation can increase porosity and permeability, whereas cavern collapse or cementation driven by postkarstification fluid flow may occlude porosity and reduce permeability. Karst may also pose challenges to drilling because of the unpredictable and highly variable porosity and permeability structure of the rock and the corresponding difficulty in predicting drilling mud weight. When combined, outcrop, petrographic, and geochemical data can constrain the style, distribution, and origin of seismic-scale karst, which may provide an improved understanding of carbonate reservoir architecture and allow development of safer drilling programs. However, relatively few studies have used seismic reflection data to characterize the regional development of seismic-scale karst features. In this study we use time-migrated two-dimensional seismic reflection data to determine the distribution, scale, and genesis of karst in a 3-km-thick (9800-ft-thick), Jurassic–Miocene carbonate-dominated succession in the Persian Gulf. We map 43 seismic-scale karst features, which are expressed as vertical pipe columns of chaotic reflections capped by downward-deflected depressions that are onlapped by overlying strata. The columns are up to 2 km (6500 ft) tall, spanning the Upper Jurassic to Upper Cretaceous succession, and are up to 5.5 km (18,000 ft) in diameter. We interpret these pipes to have formed in response to hypogene karstification by fluids focused along preexisting faults, with hypogene-generated depressions enhanced by epigene processes during key intervals of exposure. Our study indicates that seismic reflection data can and should be used in conjunction with petrographic and geochemical techniques to determine the presence of hypogene karst plays and to help improve the characterization of carbonate reservoirs and associated drilling hazards.
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Journal articleAlbalushi A, Neumaier M, Fraser AJ, et al., 2016,
The impact of the Messinian Salinity Crisis on the petroleum system of the Eastern Mediterranean: a critical assessment using 2D-petroleum system modelling
, Petroleum Geoscience, Vol: 22, Pages: 357-379, ISSN: 1354-0793The offshore Levant Basin demonstrates one of the most phenomenal natural examples of a working petroleum system associated with a relatively rapid unloading and loading cycle caused by the the Messinian Salinity Crisis (MSC). In this study, 2D basin and petroleum systems modelling suggests that the geologically instantaneous water unloading of c. 2070 m and subsequent rapid salt deposition and refill impacts the subsurface pore pressure and temperature in the underlying sediments. The pressure drop is modelled to be instantaneous, whereas the impact on temperature is more of a transient response. This has important consequences for the shallow sub-Messinian biogenic petroleum system, which is assumed to have experienced fluid brecciation associated with massive fluid escape events. Deeper Oligo-Miocene sediments are far less affected, thus indicating a "preservation window" for biogenic gas accumulations, which hosts the recent discoveries (Tamar, Leviathan, Aphrodite). Hydrocarbon accumulations of a "bubble point oil" composition are modelled to have experienced cap expansion during the drawdown, with the pressure drop being the primary control. This study suggests that seal-limited traps are expected to have undergone a catastrophic seal failure whereas the impact of the MSC is modelled to be less destructive for size-limited and particularly charge-limited traps.
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Conference paperTsiampousi A, Zdravkovic L, Potts DM, 2016,
Soil-atmosphere interaction in unsaturated cut slopes
, 3rd European Conference on Unsaturated Soils, Publisher: EDP Sciences, ISSN: 2267-1242Interaction between atmosphere and soil has only recently attracted significant interest. Soil-atmosphereinteraction takes place under dynamic climatic conditions, which vary throughout the year and are expected to sufferconsiderable alterations due to climate change. However, Geotechnical Analysis has traditionally been limited tosimplistic approaches, where winter and summer pore water pressure profiles are prescribed. Geotechnical Structures,such as cut slopes, are known to be prone to large irreversible displacements under the combined effect of wateruptake by a complex vegetation root system and precipitation. If such processes take place in an unsaturated materialthe complexity of the problem renders the use of numerical analysis essential. In this paper soil-atmosphereinteraction in cut slopes is studied using advanced, fully coupled partially saturated finite element analyses. The effectof rainfall and evapotranspiration is modelled through sophisticated boundary conditions, applying actualmeteorological data on a monthly basis. Stages of low and high water demand vegetation are considered for a periodof several years, before simulating the effect of vegetation removal. The analysis results are presented with regard tothe serviceability and stability of the cut slope.
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Conference paperPedone G, Tsiampousi A, Cotecchia F, et al., 2016,
Effects of soil-vegetation-atmosphere interaction on the stability of a clay slope: a case study
, 3rd European Conference on Unsaturated Soils, Publisher: EDP Sciences, ISSN: 2267-1242Deep and slow landslide processes are frequently observed in clay slopes located along the Southern Apennines (Italy). A case study representative of these processes, named Pisciolo case study, is discussed in the paper. The geo-hydro-mechanical characteristics of the materials involved in the instability phenomena are initially discussed. Pluviometric, piezometric, inclinometric and GPS monitoring data are subsequently presented, suggesting that rainfall infiltration constitutes the main factor inducing slope movements. The connection between formation of landslide bodies and slope-atmosphere interaction has been demonstrated through a hydro-mechanical finite element analysis, whose results are finally reported in the work. This analysis has been conducted employing a constitutive model that is capable of simulating both saturated and unsaturated soil behaviour, as well as a boundary condition able to simulate the effects of the soil-vegetation-atmosphere interaction.
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Journal articleTsaparli V, Kontoe S, Taborda D, et al., 2016,
Vertical ground motion and its effects on liquefaction resistance of fully saturated sand deposits
, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 472, Pages: 1-21, ISSN: 1364-5021Soil liquefaction has been extensively investigated over the years with the aim to understand its fundamental mechanism and successfully remediate it. Despite the multi-directional nature of earthquakes, the vertical seismic component is largely neglected, as it is traditionally considered to be of much lower amplitude than the components in the horizontal plane. The 2010–2011 Canterbury earthquake sequence in New Zealand is a prime example that vertical accelerations can be of significant magnitude, with peak amplitudes well exceeding their horizontal counterparts. As research on this topic is very limited, there is an emerging need for a more thorough investigation of the vertical motion and its effect on soil liquefaction. As such, throughout this study, uni- and bidirectional finite-element analyses are carried out focusing on the influence of the input vertical motion on sand liquefaction. The effects of the frequency content of the input motion, of the depth of the deposit and of the hydraulic regime, using variable permeability, are investigated and exhaustively discussed. The results indicate that the usual assumption of linear elastic response when compressional waves propagate in a fully saturated sand deposit does not always hold true. Most importantly post-liquefaction settlements appear to be increased when the vertical component is included in the analysis.
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Journal articlePhillips T, Jackson CA-L, Bell RE, et al., 2016,
Reactivation of intrabasement structures during rifting: a case study from offshore southern Norway
, Journal of Structural Geology, Vol: 91, Pages: 54-73, ISSN: 0191-8141Pre-existing structures within crystalline basement may exert a significant influence over the evolution of rifts. However, the exact manner in which these structures reactivate and thus their degree of influence over the overlying rift is poorly understood. Using borehole-constrained 2D and 3D seismic reflection data from offshore Southern Norway we identify and constrain the three-dimensional geometry of a series of enigmatic intrabasement reflections. Through 1D waveform modelling and 3D mapping of these reflection packages, we correlate them to the onshore Caledonian thrust belt and Devonian shear zones. Based on the seismic-stratigraphic architecture of the post-basement succession we identify several phases of reactivation of the intrabasement structures associated with multiple tectonicevents. Reactivation preferentially occurs along relatively thick (c. 1km), relatively steeply dipping (c. 30°) structures, with three main styles of interactions observed between them and overlying faults: (i) faults exploiting intrabasement weaknesses represented by intra-shear zone mylonites; (ii) faults that initiate within the hangingwall of the shear zones, inheriting their orientation and merging with said structure at depth; or (iii) faults that initiate independently from and cross-cut intrabasement structures. We demonstrate that large-scale discrete shear zones act as a long-lived structural template for fault initiation during multiple phases of rifting.
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Journal articleMiljkovic K, Collins GS, 2016,
Subsurface morphology and scaling of lunar impact basins
, Journal of Geophysical Research: Planets, Vol: 121, Pages: 1695-1712, ISSN: 2169-9097Impact bombardment during the first billion years after the formation of the Moon produced at least several tens of basins. The Gravity Recovery and Interior Laboratory (GRAIL) mission mapped the gravity field of these impact structures at significantly higher spatial resolution than previous missions, allowing for detailed subsurface and morphological analyses to be made across the entire globe. GRAIL-derived crustal thickness maps were used to define the regions of crustal thinning observed in centers of lunar impact basins, which represents a less unambiguous measure of a basin size than those based on topographic features. The formation of lunar impact basins was modeled numerically by using the iSALE-2D hydrocode, with a large range of impact and target conditions typical for the first billion years of lunar evolution. In the investigated range of impactor and target conditions, the target temperature had the dominant effect on the basin subsurface morphology. Model results were also used to update current impact scaling relationships applicable to the lunar setting (based on assumed target temperature). Our new temperature-dependent impact-scaling relationships provide estimates of impact conditions and transient crater diameters for the majority of impact basins mapped by GRAIL. As the formation of lunar impact basins is associated with the first ~700 Myr of the solar system evolution when the impact flux was considerably larger than the present day, our revised impact scaling relationships can aid further analyses and understanding of the extent of impact bombardment on the Moon and terrestrial planets in the early solar system.
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Journal articleTvedt ABM, Rotevatn A, Jackson CA-L, 2016,
Supra-salt normal fault growth during the rise and fall of a diapir: perspectives from 3D seismic reflection data, Norwegian North Sea
, Journal of Structural Geology, Vol: 91, Pages: 1-26, ISSN: 1873-1201Normal faulting and the deep subsurface flow of salt are key processes controlling the structural development of many salt-bearing sedimentary basins. However, our detailed understanding of the spatial and temporal relationship between normal faulting and salt movement is poor due to a lack of natural examples constraining their geometric and kinematic relationship in three-dimensions. To improve our understanding of these processes we here use 3D seismic reflection and borehole data from the Egersund Basin, offshore Norway to determine the structure and growth of a normal fault array formed during the birth, growth and decay of an array of salt structures. We show that the fault array and salt structures developed in response to; (i) Late Triassic-to-Middle Jurassic extension, which involved thick-skinned, sub-salt and thin-skinned supra-salt faulting, with the latter driving reactive diapirism; (ii) Early Cretaceous extensional collapse of the walls; and (iii) Jurassic-to-Neogene, active and passive diapirism, which was at least partly coeval with and occurred along-strike from areas of reactive diapirism and wall collapse. Our study supports physical model predictions, showcasing a three-dimensional example of how protracted, multiphase salt diapirism can influence the structure and growth of normal fault arrays.
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