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  • Journal article
    Xu S, Freeman SPHT, Rood DH, Shanks RPet al., 2014,

    <sup>26</sup>Al interferences in accelerator mass spectrometry measurements

    , Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, Vol: 333, Pages: 42-45, ISSN: 0168-583X

    The identification of interferences to 26Al was conducted with a 5 MV tandem accelerator mass spectrometer. In addition to 9Be 1+, 17O2+ and 35Cl4+ ions observed previously, this study confirmed existence of the most significant interference 37Cl4+ continuum ion to 16 MeV 26Al3+ by measuring primary standard mixed with Cl with various 37Cl/35Cl ratios. The 37Cl- ions were formed by 37Cl16O- molecular-dissociation before the injection magnet, resulting in -0.7% of 26Al- magnetic rigidity. Subsequently, the 37Cl4+ ions have ME/q2 value that differ from 26Al3+ by -0.1%. These allow the 37Cl - and 37Cl4+ to simultaneously pass through injection magnet, analytical magnet and high-energy analyser, and finally reach the detector with 26Al3+. Further investigations on high charge states (26Al5+ and 26Al7+) indicate that the problem of interferences is generic. That is, interferences closest to 24 MeV 26Al5+ ions include 10B 2+, 16O3+, 35Cl7+ and 37Cl7+ ions, while 32 MeV 26Al7+ ions may be interfered by 7Li2+, 16O 4+, 18O5+, 35Cl9+ and 37Cl9+. However, it remains unclear that 37Cl continuum events observed in 26Al3+-AMS do not exist in 26Al5+ and 26Al7+-AMS operations. © 2014 Elsevier B.V. All rights reserved.
  • Journal article
    Jackson CAL, Jackson MPA, Hudec MR, Rodriguez CRet al., 2014,

    Internal structure, kinematics, and growth of a salt wall; insights from 3D seismic reflection data

    , Geology, Vol: 42, Pages: 307-310

    The detailed kinematics of natural salt walls remain elusive because such structures are typically poorly exposed at outcrop, only partly exposed in mine workings, and diapiric salt is typically poorly reflective in seismic data. We use three-dimensional seismic and borehole data from offshore Brazil to investigate how structural styles vary along strike within a spectacularly well-imaged salt wall. Deformed layering in the salt allows us to map complex, seismic-scale structures in the wall; within the wall's relatively simple external shape is a range of previously undocumented structural styles produced by: (1) initial upwelling and formation of a wall-parallel anticline due to regional extension and differential overburden load, (2) breaching of the anticline, Rayleigh-Taylor overturn, and emplacement of an intrasalt allochthonous sheet driven by a density inversion, and (3) internal thrusting of the mature diapir caused by regional compression. This study is arguably the first detailed documentation of the internal structure and kinematics of a natural salt wall, highlighting the presence of abruptly varying intrasalt structural styles. The structures identified and the inferred kinematics suggest that, given specific mechanical stratigraphy, density-driven overturn within salt diapirs can play a key role in their growth.
  • Journal article
    Prytulak J, Avanzinelli R, Koetsier G, Kreissig K, Beier C, Elliott Tet al., 2014,

    Melting versus contamination effects on <SUP>238</SUP>U-<SUP>230</SUP>Th-<SUP>226</SUP>Ra and <SUP>235</SUP>U-<SUP>231</SUP>Pa disequilibria in lavas from Sao Miguel, Azores

    , CHEMICAL GEOLOGY, Vol: 381, Pages: 94-109, ISSN: 0009-2541
  • Software
    Jacobs CT, Piggott MD, 2014,

    Firedrake-Fluids
  • Journal article
    Borgomeo E, Hebditch KV, Whittaker AC, Lonergan Let al., 2014,

    Characterising the spatial distribution, frequency and geomorphic controls on landslide occurrence, Molise, Italy

    , Geomorphology, Vol: 226, Pages: 148-161
  • Journal article
    Legler B, Hampson GJ, Jackson CA-L, Johnson HD, Massart BYG, Sarginson M, Ravnas Ret al., 2014,

    Facies Relationships and Stratigraphic Architecture of Distal, Mixed Tide- and Wave-Influenced Deltaic Deposits: Lower Sego Sandstone, Western Colorado, U.S.A

    , Journal of Sedimentary Research, Vol: 84, Pages: 605-625, ISSN: 1527-1404
  • Journal article
    Carlson AE, Winsor K, Ullman DJ, Brook EJ, Rood DH, Axford Y, Legrande AN, Anslow FS, Sinclair Get al., 2014,

    Earliest Holocene south Greenland ice sheet retreat within its late Holocene extent

    , Geophysical Research Letters, Vol: 41, Pages: 5514-5521, ISSN: 0094-8276

    Early Holocene summer warmth drove dramatic Greenland ice sheet (GIS) retreat. Subsequent insolation-driven cooling caused GIS margin readvance to late Holocene maxima, from which ice margins are now retreating. We use 10Be surface exposure ages from four locations between 69.4°N and 61.2°N to date when in the early Holocene south to west GIS margins retreated to within these late Holocene maximum extents. We find that this occurred at 11.1 ± 0.2 ka to 10.6 ± 0.5 ka in south Greenland, significantly earlier than previous estimates, and 6.8 ± 0.1 ka to 7.9 ± 0.1 ka in southwest to west Greenland, consistent with existing 10Be ages. At least in south Greenland, these 10Be ages likely provide a minimum constraint for when on a multicentury timescale summer temperatures after the last deglaciation warmed above late Holocene temperatures in the early Holocene. Current south Greenland ice margin retreat suggests that south Greenland may have now warmed to or above earliest Holocene summer temperatures.
  • Journal article
    Rodriguez-Marek A, Rathje EM, Bommer JJ, Scherbaum F, Stafford PJet al., 2014,

    Application of single-station sigma and site-response characterization in a probabilistic seismic-hazard analysis for a new nuclear site

    , Bulletin of the Seismological Society of America, Vol: 104, Pages: 1601-1619, ISSN: 0037-1106

    Aleatory variability in ground‐motion prediction, represented by the standard deviation (sigma) of a ground‐motion prediction equation, exerts a very strong influence on the results of probabilistic seismic‐hazard analysis (PSHA). This is especially so at the low annual exceedance frequencies considered for nuclear facilities; in these cases, even small reductions in sigma can have a marked effect on the hazard estimates. Proper separation and quantification of aleatory variability and epistemic uncertainty can lead to defensible reductions in sigma. One such approach is the single‐station sigma concept, which removes that part of sigma corresponding to repeatable site‐specific effects. However, the site‐to‐site component must then be constrained by site‐specific measurements or else modeled as epistemic uncertainty and incorporated into the modeling of site effects. The practical application of the single‐station sigma concept, including the characterization of the dynamic properties of the site and the incorporation of site‐response effects into the hazard calculations, is illustrated for a PSHA conducted at a rock site under consideration for the potential construction of a nuclear power plant.
  • Journal article
    Stafford PJ, 2014,

    Source-Scaling Relationships for the Simulation of Rupture Geometry within Probabilistic Seismic-Hazard Analysis

    , BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, Vol: 104, Pages: 1620-1635, ISSN: 0037-1106
  • Journal article
    Modica A, Stafford PJ, 2014,

    Vector fragility surfaces for reinforced concrete frames in Europe

    , BULLETIN OF EARTHQUAKE ENGINEERING, Vol: 12, Pages: 1725-1753, ISSN: 1570-761X
  • Journal article
    Whipp PS, Jackson CAL, Gawthorpe RL, Dreyer T, Quinn Det al., 2014,

    Fault array evolution above a reactivated rift fabric; a subsurface example from the northern Horda Platform fault array

    , Basin Research, Vol: 26, Pages: 523-549

    The impact of a pre-existing rift fabric on fault array evolution during a subsequent phase of lithospheric extension is investigated using 2D and 3D seismic reflection, and borehole data from the northern Horda Platform, Norwegian North Sea. Two fault populations are developed: (i) a population comprising relatively tall (>2 km), N-S-striking faults, which have >1.5 km of throw. These faults are up to >60 km long, penetrate down into crystalline basement and bound the eastern margins of 6-15 km wide half-graben, which contain >3 km of pre-Jurassic, likely Permo-Triassic, but possibly Devonian age syn-rift strata; and (ii) a population comprising vertically restricted (<1 km), NW-SE-striking faults, which are more closely-spaced (0.5-5 km), have lower displacements (30-100 m) and not as long (2-10 km) as those in the N-S-striking population. The NW-SE-striking population typically occur between the N-S-striking population, and may terminate against or cross-cut the larger structures. NW-SE-striking faults do not bound pre-Jurassic half-graben and are largely restricted to the Jurassic-to-Cretaceous succession. Seismic-stratigraphic observations and the stratigraphic position of the fault tips in both fault populations allow us to reconstruct the Late Jurassic-to-Early Cretaceous growth history of the northern Horda Platform fault array. We suggest the large, N-S-striking population was active during the Permo-Triassic and possibly earlier (Devonian?), before becoming inactive and buried during the Early and Middle Jurassic. After a period of relative tectonic quiescence and in response to Late Jurassic extension, the N-S-striking, pre-Jurassic fault population propagated through the Early-Middle Jurassic cover and individual fault systems rapidly (within <10 Ma) established their maximum length. These fault systems became the dominant structures in the newly formed fault array and defined the locations of the main, Late Jurassic-to-Early Cretaceous
  • Journal article
    Bell RE, Holden C, Power W, Wang X, Downes Get al., 2014,

    Hikurangi margin tsunami earthquake generated by slow seismic rupture over a subducted seamount

    , Earth and Planetary Science Letters, Vol: 397, Pages: 1-9, ISSN: 0012-821X

    Tsunami earthquakes generate much larger tsunami than their surface wave magnitude would suggest and are a problem for tsunami warning systems. They are often not accompanied by intense or even strong ground shaking and hence do not provide a natural warning for self-evacuation. The lesser-known 1947 Offshore Poverty Bay and Tolaga Bay earthquakes along the east coast of the North Island, New Zealand share many characteristics with other well-known tsunami earthquakes (including low amplitude shaking, long durations and anomalously large tsunami), however these two New Zealand events are rare in that their source area has been imaged directly by long-offset 2D seismic reflection profiles. In this contribution we propose a source model for the 1947 Offshore Poverty Bay tsunami earthquake, recognising that the hypocentre occurs in a region where seismic reflection and magnetic data support the existence of a shallow (<10 km) subducted seamount updip of an area that experiences slow slip events. We propose a fault source model for the 1947 Offshore Poverty Bay event with two potential slip scenarios: i) uniform slip of 2.6 m across the fault; or ii) variable slip with slip of up to 5–6 m in the region of a more strongly geodetically coupled subducted seamount. Both the uniform and variable slip models require an unusually low rupture velocity of 150–300 m/s in order to model regional and teleseismic seismograms. Tsunami modelling shows that tsunami run-up heights are more than doubled when low rupture speeds of 150–300 m/s are employed, rather than assuming instantaneous rupture. This study suggests that subducted topography can cause the nucleation of up to earthquakes with complex, low velocity rupture scenarios that enhance tsunami waves, and their role in seismic hazard should not be under-estimated.
  • Journal article
    Nelson AH, Bierman PR, Shakun JD, Rood DHet al., 2014,

    Using in situ cosmogenic <sup>10</sup>Be to identify the source of sediment leaving Greenland

    , Earth Surface Processes and Landforms, Vol: 39, Pages: 1087-1100, ISSN: 0197-9337

    We use the concentration of in situ 10Be in quartz isolated from fluvial and morainal sand to trace sediment sources and to determine the relative contribution of glacerized and deglaciated terrain to Greenland's sediment budget. We sampled along the western, eastern, and southern margins of the Greenland Ice Sheet, and collected sediment sourced from glacerized (n=19) and non-glacerized terrain (n=10), from channels where sediment from glacerized and non-glacerized terrain is mixed (n=28), from Holocene glacial-fluvial terraces (n=4), and from one sand dune. In situ 10Be concentrations in sediment range from 1600 to 34 000 atoms g-1. The concentration of in situ 10Be in sediment sourced from non-glacerized terrain is significantly higher than in sediment sourced from glacerized areas, in mixed channel sediment, and in terrace sediment that was deposited during the Holocene. To constrain the timing of landscape exposure for the deglaciated portion of the Narsarsuaq field area in southern Greenland, we measured in situ 10Be concentration in bedrock (n=5) and boulder (n=6) samples. Paired bedrock and boulder ages are indistinguishable at 1σ uncertainty and indicate rapid exposure of the upland slopes at ~10.5ka.The isotope concentration in sediment sourced from non-glacerized terrain is higher than in sediment sourced from glacerized terrain because the non-glacerized landscape has been exposed to cosmic radiation since early Holocene deglaciation. Sediment from glacerized areas contains a low, but measurable concentration of 10Be that probably accumulated at depth during a prolonged period of exposure, probably before the establishment of the Greenland Ice Sheet. The concentration of 10Be in mixed fluvial sediment and in terrace sediment is low, and similar to the concentration in sediment from glacerized areas, which indicates that the Greenland Ice Sheet is the dominant source of sediment moving through the landscape outside the glacial margin in the areas we
  • Journal article
    Patruno S, Hampson GJ, Jackson CAL, Whipp PSet al., 2014,

    Quantitative progradation dynamics and stratigraphic architecture of ancient shallow-marine clinoform sets: a new method and its application to the Upper Jurassic Sognefjord Formation, Troll Field, offshore Norway

    , Basin Research, Vol: 27, Pages: 412-452, ISSN: 0950-091X

    This paper presents a new numerical inversion method to estimate progradation rates in ancient shallow-marine clinoform sets, which is then used to refine the tectono-stratigraphic and depositional model for the Upper Jurassic Sognefjord Formation reservoir in the super-giant Troll Field, offshore Norway. The Sognefjord Formation is a 10-200 m thick, coarse-grained clastic wedge, that was deposited in ca. 6 Myr by a fully marine, westward-prograding, subaqueous delta system sourced from the Norwegian mainland. The formation comprises four, 10-60 m thick, westerly-dipping, regressive clinoform sets, which are mapped for several tens of kilometres along strike. Near-horizontal trajectories are observed in each clinoform set, and the sets are stacked vertically. Clinoform age and progradation rates are constrained by: (1) regionally correlatable bioevents, tied to seismically mapped clinoforms and clinoform-set boundaries that intersect wells, (2) exponential age-depth interpolations between bioevent-dated surfaces and a distinctive foreset-to-bottomset facies transition within each well, and (3) distances between wells along seismic transects that are oriented perpendicular to the clinoform strike and tied to well-based stratigraphic correlations. Our results indicate a fall in progradation rate (from 170-500 to 10-65 km/Myr) and net sediment flux (from 6-14 to ≤1 km2/Myr) westwards towards the basin, which is synchronous with an overall rise in sediment accumulation rate (from 7-16 to 26-102 m/Myr). These variations are attributed to progradation of the subaqueous delta into progressively deeper waters, and a concomitant increase in the strength of along-shore currents that transported sediment out of the study area. Local spatial and temporal deviations from these overall trends are interpreted to reflect a subtle structural control on sedimentation. This method provides a tool to improve the predictive potential of sequence stratigraphic and clinoform trajectory
  • Journal article
    Osagiede EE, Duffy OB, Jackson CA-L, Wrona T, Osagiede EE, Duffy O, Jackson CAL, Wrona Tet al., 2014,

    Quantifying the Growth History of Seismically Imaged Normal Faults

    , Journal of Structural Geology, Vol: 66, Pages: 382-399

    Throw-depth profiles and expansion index plots are typically used to constrain the growth history of seismically imaged normal faults. However, the ability to accurately correlate displaced stratigraphic horizons across faults and hence constrain stratigraphic thickness changes is typically limited by the vertical resolution of, and noise within, the seismic reflection dataset. Vertical seismic resolution is a function of seismic velocities and the source wavelet frequency used during data collection. Here, we test how variations in source wavelet frequency and seismic noise influence imaging of normal faults, and our ability to determine the fault growth history from the construction of throw-depth profiles and expansion index plots. To achieve this, two input models were developed to mimic the geometry and growth history of polycyclic growth faults and blind normal faults. These models provided an input for a series of 2D seismic forward models from which we produced synthetic seismic profiles. The models were run at different peak frequencies and seismic noise levels, so as to mimic variations in seismic data quality associated with changes in the depth of burial. Throw-depth profiles and expansion index plots were derived from the synthetic seismic profiles and used to constrain the fault kinematics, and these results were compared to those derived from the input models. Our results indicate that, at lower peak frequencies and higher seismic noise levels, fault height can be underestimated, and strikingly, that the fault growth history can be misinterpreted. The results of our study indicate that geologists need to be aware of the imaging resolution of seismic reflection data when using these data to determine fault growth history of normal faults. Furthermore, hydrocarbon explorationists should be aware that seismic reflection data, the principal exploration tool, may not allow accurate determination of fault length and height, which may impact risking of hydro
  • Journal article
    Taborda DM, Zdravkovic L, Kontoe S, Potts DMet al., 2014,

    Computational study on the modification of a bounding surface plasticity model for sands

    , Computers and Geotechnics, Vol: 59, Pages: 145-160, ISSN: 0266-352X

    The accurate simulation of complex dynamic phenomena requires the availability of advanced constitutive models capable of simulating a wide range of features of soil behaviour under cyclic loading. One possible strategy is to improve the capabilities of existing bounding surface plasticity models, as this framework is characterised by its modularity and flexibility. As a result, specific components of the formulation of this type of model may be adjusted to improve the reproduction of any aspect of soil behaviour deemed essential to the problem being analysed. In this paper, a series of computational studies are performed in order to establish the impact of expanding a bounding surface plasticity model for sands on its modelling capabilities and to suggest ways of mitigating the associated increase in complexity. Changes to three distinct aspects of the selected constitutive model are examined: the shape of the Critical State Line in p′ − e space, the expression used for calculating the hardening modulus and the form of the yield surface. It is shown that the introduced changes have the potential to increase significantly the ability to control how certain aspects of soil response, such as degradation of stiffness and flow liquefaction with limited deformation, are reproduced by the model. Moreover, this paper presents a systematic approach to the expansion of this type of constitutive model, establishing how alterations to the formulation of a model may be assessed in terms of improved accuracy and potential benefits.
  • Journal article
    Rathje EM, Wang Y, Stafford PJ, Antonakos G, Saygili Get al., 2014,

    Probabilistic assessment of the seismic performance of earth slopes

    , BULLETIN OF EARTHQUAKE ENGINEERING, Vol: 12, Pages: 1071-1090, ISSN: 1570-761X
  • Conference paper
    Summersgill F, Kontoe S, Potts DM, 2014,

    A comparison of the mesh dependence of the nonlocal and local strain softening methods in a biaxial compression analysis

    , 8th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE), Pages: 289-294
  • Conference paper
    Han B, Zdravkovic L, Kontoe S, 2014,

    Analytical and theoretical investigations on the vertical seismic site response

    , 8th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE), Pages: 1123-1128
  • Software
    Jacobs CT, Avdis A, Gorman GJ, Piggott MDet al., 2014,

    PyRDM

    PyRDM is a Python-based library for research data management (RDM). It facilitates the automated publication of scientific software and associated input and output data.

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