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Journal articleMcPhillips D, Hoke GD, Liu-Zeng J, et al., 2016,
Dating the incision of the Yangtze River gorge at the First Bend using three-nuclide burial ages
, Geophysical Research Letters, Vol: 43, Pages: 101-110, ISSN: 1944-8007Incision of the Yangtze River gorge is widely interpreted as evidence for lower crustal flow beneath the southeast margin of the Tibetan Plateau. Previous work focused on the onset of incision, but the duration of incision remains unknown. Here we present cosmogenic nuclide burial ages of sediments collected from caves on the walls of the gorge that show the gorge was incised ~1 km sometime between 18 and 9 Ma. Thereafter, incision slowed substantially. We resolve middle Miocene burial ages by using three nuclides and accounting for in situ muogenic production. This approach explains the absolute concentrations of 10Be, 26Al, and 21Ne, as well as 26Al/10Be and 21Ne/10Be ratios. A declining incision rate challenges existing geodynamic interpretations by suggesting that either (1) surface uplift has ceased immediately south of the plateau margin or (2) gorge incision is not a useful proxy for the timing of surface uplift.
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Journal articleAllen PA, Michael NA, D'Arcy M, et al., 2016,
Fractionation of grain size in terrestrial sediment routing systems
, BASIN RESEARCH, Vol: 29, Pages: 180-202, ISSN: 0950-091XSediment is fractionated by size during its cascade from source to sink in sediment routing systems. It is anticipated, therefore, that the grain size distribution of sediment will undergo down-system changes as a result of fluvial sorting processes and selective deposition. We assess this hypothesis by comparing grain size statistical properties of samples from within the erosional source region with those that have undergone different amounts of transport. A truncated Pareto distribution describes well the coarser half of the clast size distribution of regolith, coarse channel bed sediment and proximal debris flows (particularly their levees), as well as the coarser half of the clast size distribution of gravels that have undergone considerable amounts of transport in rivers. The Pareto shape parameter a evolves in response to mobilization, sediment transport and, importantly, the selective extraction of particles from the surface flow to build underlying stratigraphy. A goodness of fit statistic, the Kolmogorov–Smirnov vertical difference, illustrates the closeness of the observed clast size distributions to the Pareto, Weibull and log-normal models as a function of distance from the depositional apex. The goodness of fit of the particle size distribution of regolith varies with bedrock geology. Bedload sediment at catchment outlets is fitted well by the log-normal and truncated Pareto models, whereas the exponential Weibull model provides a less good fit. In the Eocene Escanilla palaeo-sediment routing system of the south-central Pyrenees, the log-normal and truncated Pareto models provide excellent fits for distances of up to 80 km from the depositional apex, whereas the Weibull fit progressively worsens with increasing transport distance. A similar trend is found in the Miocene–Pliocene gravels of the Nebraskan Great Plains over a distance of >300 km. Despite the large fractionation in mean grain size and gravel percentage from source region to
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Journal articleTaborda DMG, Potts DM, Zdravkovic L, 2016,
On the assessment of energy dissipated through hysteresis in finite element analysis
, Computers and Geotechnics, Vol: 71, Pages: 180-194, ISSN: 0266-352XThe accurate reproduction of the hysteretic behaviour exhibited by soils under cyclic loading is a crucial aspect of dynamic finite element analyses and is typically described using the concept of damping ratio. In this paper, a general algorithm is presented for assessing the damping ratio simulated by any constitutive model based on the registered behaviour in three-dimensional stress-strain space. A cyclic nonlinear elastic model capable of accurately reproducing a wide range of features of soil behaviour, including the variation of damping ratio with deformation level, is chosen to illustrate the capabilities of the proposed algorithm. The constitutive model is described and subsequently employed in two sets of finite element analyses, one involving the dynamic response of a sand deposit subjected to different types of motion and another focussing on the simulation of a footing subjected to cyclic vertical loading. The application of the presented algorithm provides insight into the processes through which energy is dissipated through hysteresis.
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Journal articleJackson CAL, Lewis MM, 2016,
Structural style and evolution of a salt-influenced rift basin margin: the impact of variations in salt composition and the role of polyphase extension
, Basin Research, Vol: 28, Pages: 81-102Because salt can decouple sub- and supra-salt deformation, the structural style and evolution of salt-influenced rifts differs from those developed in megoscopically homogenous and brittle crust. Our understanding of the structural style and evolution of salt-influenced rifts comes from scaled physical models, or subsurface-based studies that have utilised moderate-quality 2D seismic reflection data. Relatively few studies have used high-quality 3D seismic reflection data, constrained by borehole data, to explicitly focus on the role that along-strike displacement variations on sub-salt fault systems, or changes in salt composition and thickness, play in controlling the four-dimensional evolution of supra-salt structural styles. In this study, we use 3D seismic reflection and borehole data from the Sele High Fault System (SHFS), offshore Norway to determine how rift-related relief controlled the thickness and lithology of an Upper Permian salt-bearing layer (Zechstein Supergroup), and how the associated variations in the mechanical properties of this unit influenced the degree of coupling between sub- and supra-salt deformation during subsequent extension. Seismic and borehole data indicate that the Zechstein Supergroup is thin, carbonate-dominated and immobile at the footwall apex, but thick, halite-dominated and relatively mobile in high accommodation areas, such as near the lateral fault tips and in the immediate hangingwall of the fault system. We infer that these variations reflect bathymetric changes related to either syn-depositional (i.e. Late Permian) growth of the SHFS or underfilled, fault scarp-related relief inherited from a preceding (i.e. Early Permian) rift phase. After a period of tectonic quiescence in the Early Triassic, regional extension during the Late Triassic triggered halokinesis and growth of a fault-parallel salt wall, which was followed by mild extension in the Jurassic and forced folding of Triassic overburden above the fault systems upp
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Book chapterAsphaug E, Collins GS, Jutzi M, 2015,
Global Scale Impacts
, Asteroids IV, Editors: Michel, DeMeo, Bottke, Publisher: University of Arizona Press, Pages: 661-678, ISBN: 9780816532131Global scale impacts modify the physical or thermal state of a substantial fraction of a target asteroid. Specific effects include accretion, family formation, reshaping, mixing and layering, shock and frictional heating, fragmentation, material compaction, dilatation, stripping of mantle and crust, and seismic degradation. Deciphering the complicated record of global scale impacts, in asteroids and meteorites, will lead us to understand the original planet-forming process and its resultant populations, and their evolution in time as collisions became faster and fewer. We provide a brief overview of these ideas, and an introduction to models.
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Journal articleWrona T, Jackson CA-L, Huuse M, et al., 2015,
Silica diagenesis in Cenozoic mudstones of the North Viking Graben: physical properties and basin modelling
, Basin Research, Vol: 29, Pages: 556-575, ISSN: 1365-2117Silica diagenesis can significantly change physical properties of the host strata and release large volumes of water. Predicting these changes and their timing is essential to understanding compaction, fluid flow and rock deformation in sedimentary basins. In this paper, the influence of silica diagenesis (opal-A/CT transformation) on physical properties is determined, the sediment volume affected by these changes is mapped, and a new technique to model silica diagenesis is introduced. A petrophysical analysis of 16 exploration wells shows that the opal-A/CT transformation leads to a porosity reduction of c.20% (from 49 to 29%) in Cenozoic mudstones of the North Viking Graben. Using three-dimensional seismic reflection data, it is shown that the c.50 m thick opal-A/CT transformation zone covers an area of >1500 km2, equating to a minimum volume of 75 km3. The spatial and temporal evolution of opal-A/CT transformation is simulated using an innovative basin modelling approach, the results of which indicate that the transformation started around Middle-to-Late Eocene times and then migrated upwards until it gradually fossilised between the Miocene and present. These findings are important, as they help understanding how these sediments compact and when fluids are released by diagenesis.
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Journal articleBommer JJ, Dost B, Edwards B, et al., 2015,
Developing an Application-Specific Ground-Motion Model for Induced Seismicity
, Bulletin of the Seismological Society of America, Vol: 106, Pages: 158-173, ISSN: 1943-3573A key element of quantifying both the hazard and risk due to inducedearthquakes is a suite of appropriate ground-motion prediction equations (GMPEs) thatencompass the possible shaking levels due to such events. Induced earthquakes arelikely to be of smaller magnitude and shallower focal depth than the tectonic earthquakesfor which most GMPEs are derived. Furthermore, whereas GMPEs formoderate-to-large magnitude earthquakes are usually derived to be transportable todifferent locations and applications, taking advantage of the limited regional dependenceobserved for such events, the characteristics of induced earthquakes warrant thedevelopment of application-specific models. A preliminary ground-motion model forinduced seismicity in the Groningen gas field in The Netherlands is presented as anillustration of a possible approach to the development of these equations. The GMPE iscalibrated to local recordings of small-magnitude events and captures the epistemicuncertainty in the extrapolation to larger magnitude considered in the assessment ofthe resulting hazard and risk.
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Journal articleHolgate NE, Jackson CA-L, Hampson GJ, et al., 2015,
Seismic stratigraphic analysis of the Middle-Upper Jurassic Krossfjord and Fensfjord formations, Troll oil and gas field, northern North Sea
, Marine and Petroleum Geology, Vol: 68, Pages: 352-380, ISSN: 1873-4073The “syn-rift” Middle-to-Late Jurassic Krossfjord and Fensfjord formations, Troll Field, northern North Sea contain a complex distribution of wave- and tide-dominated deltaic, shoreline and shelf depositional environments of varying reservoir potential. Uncertainty exists in depositional models used to explain the spatial and temporal distribution of these depositional environments and the absence of coeval coastal plain deposits. To date, the proposed influence of growing rift-related structures on stratigraphic architectures and sedimentation patterns in the units has been poorly defined. In this study, 3D seismic data are integrated with core, biostratigraphic and wireline-log data to produce a consistent geological interpretation for the formations. Seismic analysis has identified nine parasequences (‘series’) containing NNE-SSW-striking, delta-scale clinoforms that prograded westwards over much of the field. Quantitative analysis highlights an increase in height and dip of clinoforms from proximal to distal locations, coincident with an increase in grain size. Clinoform geometry is sigmoidal, with well-developed topsets that, based on core data, lack subaerial deposits. These geometrical and sedimentological characteristics suggest that a subaqueous delta depositional system deposited the Krossfjord and Fensfjord formations in the Troll Field. In the northeast of the field, clinoforms exhibit highly variable strike and oblique cross-sectional geometries, which suggest that sediment was supplied from here, and then redistributed through southward-directed wave and longshore current activity. Rift-related faulting is recognised to have occurred in thewestern part of the Troll Field only during deposition of the youngest Fensfjord Formation ‘series’, thus challenging the notion that these units are ‘syn-rift’. Seismically imaged clinoforms in the under-explored area south of the Troll Field prograded southward, and a
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Conference paperJacobs CT, Avdis A, Mouradian SL, et al., 2015,
Integrating Research Data Management into Geographical Information Systems
, http://ceur-ws.org/Vol-1529/, 5th International Workshop on Semantic Digital Archives (SDA 2015), Pages: 7-17Ocean modelling requires the production of high-fidelity computational meshes upon which to solve the equations of motion. The production of such meshes by hand is often infeasible, considering the complexity of the bathymetry and coastlines. The use of Geographical Information Systems (GIS) is therefore a key component to discretising the region of interest and producing a mesh appropriate to resolve the dynamics. However, all data associated with the production of a mesh must be provided in order to contribute to the overall recomputability of the subsequent simulation. This work presents the integration of research data management in QMesh, a tool for generating meshes using GIS. The tool uses the PyRDM library to provide a quick and easy way for scientists to publish meshes, and all data required to regenerate them, to persistent online repositories. These repositories are assigned unique identifiers to enable proper citation of the meshes in journal articles.
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Journal articleBaker DMH, Head JW, Collins GS, et al., 2015,
The formation of peak-ring basins: working hypotheses and path forward in using observations to constrain models of impact-basin formation
, Icarus, Vol: 273, Pages: 146-163, ISSN: 0019-1035Impact basins provide windows into the crustal structure and stratigraphy of planetary bodies; however, interpreting the stratigraphic origin of basin materials requires an understanding of the processes controlling basin formation and morphology. Peak-ring basins (exhibiting a rim crest and single interior ring of peaks) provide important insight into the basin-formation process, as they are transitional between complex craters with central peaks and larger multi-ring basins. New image and altimetry data from the Lunar Reconnaissance Orbiter as well as a suite of remote sensing datasets have permitted a reassessment of the origin of lunar peak-ring basins. We synthesize morphometric, spectroscopic, and gravity observations of lunar peak-ring basins and describe two working hypotheses for the formation of peak rings that involve interactions between inward collapsing walls of the transient cavity and large central uplifts of the crust and mantle. Major facets of our observations are then compared and discussed in the context of numerical simulations of peak-ring basin formation in order to plot a course for future model refinement and development.
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Journal articleHan B, Yang Z, Zdravkovic L, et al., 2015,
Non-linearity of gravelly soils under seismic compressional deformation based on KiK-net downhole array observations
, Geotechnique Letters, Vol: 5, Pages: 287-293, ISSN: 2045-2543In this paper the nonlinear behaviour of gravelly soils under seismiccompressional deformation is investigated based on KiK-net downhole array earthquakeobservations in Japan. By comparing the amplification spectra between the verticalresponse at the ground surface and at the bottom of downholes subjected to strongmotions with those subjected to weak motions, empirical curves for constrainedmodulus degradation are obtained considering different levels of vertical confiningpressure. Results show that the nonlinearity associated with the compressionaldeformation can be as significant as that of the shear deformation, for gravelly soilsabove water tables. The proposed curves provide satisfactory predictions for thecompressional soil nonlinearity investigated in previous studies. Furthermore, theproposed curves are formulated by a modified cyclic nonlinear model, which canaccount for constrained modulus degradation under a variety of confining pressureconditions and therefore extends the application of the proposed reference curves tononlinear numerical analysis of geotechnical structures under multi-directional seismicloads.
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Journal articleArmitage JJ, Allen PA, Burgess PM, et al., 2015,
Sediment transport model for the Eocene Escanilla sediment-routing system: Implications for the uniqueness of sequence stratigraphic architectures.
, Journal of Sedimentary Research, Vol: 85, Pages: 1510-1524, ISSN: 1527-1404 -
Journal articleMorel CRG, van Reeuwijk M, Graf T, 2015,
Systematic investigation of non-Boussinesq effects in variable-density groundwater flow simulations
, JOURNAL OF CONTAMINANT HYDROLOGY, Vol: 183, Pages: 82-98, ISSN: 0169-7722- Author Web Link
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- Citations: 14
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Book chapterWhipp PS, Jackson CA-L, Schlische RW, et al., 2015,
Spatial distribution and evolution of fault-segment boundary types in rift systems; observations from experimental clay models
, Geometry and Growth of Normal Faults, Editors: ChildsFault-segment boundaries initiate, evolve and die as a result of the propagation, interaction and linkage of normal faults during crustal extension. In this study we use a series of scaled physical models (wet clay) to investigate the distribution and evolution of fault-segment boundaries within an evolving normal fault population during orthogonal extension. From the models we can establish a simple geometric classification for segment-boundaries, analyse their spatial and temporal evolution and identify key factors that influence their variability. Development of overlapping fault tips is a pre-requisite for fault growth via segment linkage. Synthetic segment boundaries are the most common segment-boundary type developed in the models. The proportion of synthetic segment boundaries in the total fault population increases with increased strain, whereas conjugate (antithetic) segment boundaries are very rare. Hangingwall-breached relay ramps are the most common type (>70%) of breached segment-boundary, followed by footwall-breached relay ramps (<25%). Transfer faults are uncommon in our models. The fault overlap to fault spacing aspect ratio of a synthetic segment-boundary does not allow for predictions of the type of breached segment-boundary that will develop. Fault linkage occurs in a range of styles across a wide range of fault overlap-spacing ratios (1:1 to 7:1).Volume Editor Assigned
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Journal articleSchofield N, Holford S, Millett J, et al., 2015,
Regional Magma Plumbing and emplacement mechanisms of the Faroe-Shetland Sill Complex: Implications for magma transport and petroleum systems within sedimentary basins
, Basin Research, Vol: 29, Pages: 41-63, ISSN: 1365-2117The movement of magma through the shallow crust and the impact of subsurface sill complexes on the hydrocarbon systems of prospective sedimentary basins has long been an area of interest and debate. Based on 3D seismic reflection and well data, we present a regional analysis of the emplacement and magmatic plumbing system of the Palaeogene Faroe-Shetland Sill Complex (FSSC), which is intruded into the Mesozoic and Cenozoic sequences of the Faroe-Shetland Basin (FSB). Identification of magma flow directions through detailed seismic interpretation of approximately 100 sills indicates that the main magma input zones into the FSB were controlled primarily by the NE-SW basin structure that compartmentalise the FSB into its constituent sub-basins. An analysis of well data shows that potentially up to 88% of sills in the FSSC are <40 m in thickness, and thus below the vertical resolution limit of seismic data at depths at which most sills occur. This resolution limitation suggests that caution needs to be exercised when interpreting magmatic systems from seismic data alone, as a large amount of intrusive material could potentially be missed. The interaction of the FSSC with the petroleum systems of the FSB is not well understood. Given the close association between the FSSC and potential petroleum migration routes into some of the oil/gas fields (e.g. Tormore), the role the intrusions may have played in compartmentalization of basin fill needs to be taken fully into account to further unlock the future petroleum potential of the FSB.
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Journal articleMilbury C, Johnson BC, Melosh HJ, et al., 2015,
Preimpact porosity controls the gravity signature of lunar craters
, Geophysical Research Letters, Vol: 42, Pages: 9711-9716, ISSN: 1944-8007We model the formation of lunar complex craters and investigate the effect of preimpact porosity on their gravity signatures. We find that while preimpact target porosities less than ~7% produce negative residual Bouguer anomalies (BAs), porosities greater than ~7% produce positive anomalies whose magnitude is greater for impacted surfaces with higher initial porosity. Negative anomalies result from pore space creation due to fracturing and dilatant bulking, and positive anomalies result from destruction of pore space due to shock wave compression. The central BA of craters larger than ~215 km in diameter, however, are invariably positive because of an underlying central mantle uplift. We conclude that the striking differences between the gravity signatures of craters on the Earth and Moon are the result of the higher average porosity and variable porosity of the lunar crust.
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Conference paperJardine RJ, Brosse A, Coop MR, et al., 2015,
Shear strength and stiffness anisotropy of geologically aged stiff clays.
, International Symposium on Deformation Behaviour of Geomaterials, Publisher: IOS Press, Pages: 156-191This paper considers the deformation behaviour of four geologically aged, medium-plasticity, heavily overconsolidated stiff clays that affect a broad swathe of infrastructure projects in the SE of the United Kingdom. Static triaxial and hollow cylinder stress path experiments on high quality samples are examined along with dynamic multi-axial bender element and resonant-column measurements. Patterns of undrained shear strength anisotropy are revealed that are governed by the clays' meso and micro-structures. The clays are brittle in shear and their stiffness characteristics are shown to be markedly anisotropic, highly non-linear and pressure dependent. The results obtained have many implications for practical geotechnical engineering.
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Journal articleVan Reeuwijk M, Craske J, 2015,
Energy-consistent entrainment relations for jets and plumes
, Journal of Fluid Mechanics, Vol: 782, Pages: 333-355, ISSN: 0022-1120We discuss energetic restrictions on the entrainment coefficient α for axisymmetric jets and plumes. The resulting entrainment relation includes contributions from the mean flow, turbulence and pressure, fundamentally linking α to the production of turbulence kinetic energy, the plume Richardson number Ri and the profile coefficients associated with the shape of the buoyancy and velocity profiles. This entrainment relation generalises the work by Kaminski et al. (J. Fluid Mech., vol. 526, 2005, pp. 361–376) and Fox (J. Geophys. Res., vol. 75, 1970, pp. 6818–6835). The energetic viewpoint provides a unified framework with which to analyse the classical entrainment models implied by the plume theories of Morton et al. (Proc. R. Soc. Lond. A, vol. 234, 1955, pp. 1–23) and Priestley & Ball (Q. J. R. Meteorol. Soc., vol. 81, 1954, pp. 144–157). Data for pure jets and plumes in unstratified environments indicate that to first order the physics is captured by the Priestley and Ball entrainment model, implying that (1) the profile coefficient associated with the production of turbulence kinetic energy has approximately the same value for pure plumes and jets, (2) the value of α for a pure plume is roughly a factor of 5/3 larger than for a jet and (3) the enhanced entrainment coefficient in plumes is primarily associated with the behaviour of the mean flow and not with buoyancy-enhanced turbulence. Theoretical suggestions are made on how entrainment can be systematically studied by creating constant- Ri flows in a numerical simulation or laboratory experiment.
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Journal articleFox MJ, Stafford PJ, Sullivan TJ, 2015,
Seismic hazard disaggregation in performance-based earthquake engineering: occurrence or exceedance?
, Earthquake Engineering & Structural Dynamics, Vol: 45, Pages: 835-842, ISSN: 1096-9845Seismic hazard disaggregation is commonly used as an aid in ground-motion selection for the seismic response analysis of structures. This short communication investigates two different approaches to disaggregation related to the exceedance and occurrence of a particular intensity. The impact the different approaches might have on a subsequent structural analysis at a given intensity is explored through the calculation of conditional spectra. It is found that the exceedance approach results in conditional spectra that will be conservative when used as targets for ground-motion selection. It is however argued that the use of the occurrence disaggregation is more consistent with the objectives of seismic response analyses in the context of performance-based earthquake engineering.
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Journal articleStafford PJ, 2015,
Extension of the Random-Effects Regression Algorithm to Account for the Effects of Nonlinear Site Response
, Bulletin of the Seismological Society of America, Vol: 105, Pages: 3196-3202, ISSN: 0037-1106The random-effects regression algorithm, made popular within engineeringseismology by Abrahamson and Youngs (1992), is arguably the most commonly usedapproach for developing empirical ground-motion models. The original presentation ofthis algorithm relates to the most simple application of a far more general mixed-effectsmodel formulation. In recent years, it has become increasingly common to incorporatenonlinear site response effects within empirical, or semi-empirical, ground-motion models,but the original random-effects algorithm does not apply to cases in which the randomeffects enter the model in a nonlinear manner. This article presents a more generalalgorithm for fitting mixed-effects models that can accommodate nonlinear site effects(among other effects). The presented algorithm deliberately mirrors that of Abrahamsonand Youngs (1992) but allows for the treatment of far more elaborate variance structures.
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