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Journal articleYoung NE, Briner JP, Rood DH, et al., 2013,
Age of the Fjord Stade moraines in the Disko Bugt region, western Greenland, and the 9.3 and 8.2 ka cooling events
, Quaternary Science Reviews, Vol: 60, Pages: 76-90, ISSN: 0277-3791Retreat of the western Greenland Ice Sheet during the early Holocene was interrupted by deposition of the Fjord Stade moraine system. The Fjord Stade moraine system spans several hundred kilometers of western Greenland's ice-free fringe and represents an important period in the western Greenland Ice Sheet's deglaciation history, but the origin and timing of moraine deposition remain uncertain. Here, we combine new and previously published 10Be and 14C ages from Disko Bugt, western Greenland to constrain the timing of Fjord Stade moraine deposition at two locations ∼60 km apart. At Jakobshavn Isfjord, the northern of two study sites, we show that Jakobshavn Isbræ advanced to deposit moraines ca 9.2 and 8.2-8.0 ka. In southeastern Disko Bugt, the ice sheet deposited moraines ca 9.4-9.0 and 8.5-8.1 ka. Our ice-margin chronology indicates that the Greenland Ice Sheet in two distant regions responded in unison to early Holocene abrupt cooling 9.3 and 8.2 ka, as recorded in central Greenland ice cores. Although the timing of Fjord Stade moraine deposition was synchronous in Jakobshavn Isfjord and southeastern Disko Bugt, within uncertainties, we suggest that Jakobshavn Isbræ advanced while the southeastern Disko Bugt ice margin experienced stillstands during the 9.3 and 8.2 ka events based on regional geomorphology and the distribution of 10Be ages at each location. The contrasting style of ice-margin response was likely regulated by site-specific ice-flow characteristics. Jakobshavn Isbræ's high ice flux results in an amplified ice-margin response to a climate perturbation, both warming and cooling, whereas the comparatively low-flux sector of the ice sheet in southeastern Disko Bugt experiences a more subdued response to climate perturbations. Our chronology indicates that the western Greenland Ice Sheet advanced and retreated in concert with early Holocene temperature variations, and the 9.3 and 8.2 ka events, although brief, were of sufficient du
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Journal articleReeve M, Bell RE, Jackson CA-L, et al., 2013,
Origin and significance of intra-basement seismic reflections offshore western Norway
, Journal of the Geological Society, Vol: 171, Pages: 1-4We use 3D seismic data to image a series of enigmatic, SW-dipping reflection packets within pre-Mesozoic crystalline basement offshore western Norway. Based on their low-angle dip and complex reflection wave-train our preferred interpretation is that the reflection packets are the seismic expression of mylonitic zones generated by nappe emplacement during the Caledonian Orogeny. Late Jurassic faults truncate and offset these reflection packets by several hundred metres, suggesting that these faults did not exploit pre-existing basement weaknesses. Our observations suggest that older basement fabrics may not always play a significant role in determining the geometry of later fault systems.
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Book chapterCollins GS, Wuennemann K, Artemieva N, et al., 2013,
Numerical modelling of impact processes
, Impact Cratering: Processes and Products, Editors: Osinski, Pierazzo, Publisher: Wiley-Blackwell, ISBN: 9781405198295 -
Book chapterKenkmann T, Collins GS, Wuennemann K, 2013,
The modification stage of crater formation
, Impact Cratering: Processes and Products, Editors: Osinski, Pierazzo, Publisher: Wiley-Blackwell, ISBN: 9781405198295 -
Conference paperTumey SJ, Brown TA, Finkel RC, et al., 2013,
The feasibility of isobaric suppression of <sup>26</sup>Mg via post-accelerator foil stripping for the measurement of <sup>26</sup>Al
, Pages: 406-409, ISSN: 0168-583XMost accelerator mass spectrometry measurements of 26Al utilize the Al- ion despite lower source currents compared with AlO - since the stable isobar 26Mg does not form elemental negative ions. A gas-filled magnet allows sufficient suppression of 26Mg thus enabling the use of the more intense 26AlO - ion. However, most AMS systems do not include a gas-filled magnet. We therefore explored the feasibility of suppressing 26Mg by using a post-accelerator stripping foil. With this approach, combined with the use of alternative cathode matrices, we were able to suppress 26Mg by a factor of 20. This suppression was insufficient to enable the use of 26AlO-, however further refinement of our system may permit its use in the future. © 2012 Elsevier B.V. All rights reserved.
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Journal articleFreitas TMB, Potts DM, Zdravkovic L, 2013,
Some strengths and weaknesses of overstress based elastic viscoplastic models
, Springer Series in Geomechanics and Geoengineering, Pages: 107-114, ISSN: 1866-8755Various elastic viscoplastic models based on the overstress theory by Perzyna [9] have been proposed and are described in the literature. This paper presents the theoretical formulation of this type of models and highlights the abilities and shortcomings of such models to reproduce the time dependent behaviour of clays observed in the laboratory and the implications that these have when used in the analysis of boundary value problems. © Springer-Verlag Berlin Heidelberg 2013.
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Journal articlePortenga EW, Bierman PR, Rizzo DM, et al., 2013,
Low rates of bedrock outcrop erosion in the Central Appalachian mountains inferred from in situ <sup>10</sup>Be
, Bulletin of the Geological Society of America, Vol: 125, Pages: 201-215, ISSN: 0016-7606Bedrock outcrops are common on central Appalachian Mountain ridgelines. Because these ridgelines define watersheds, the rate at which they erode infl uences the pace of landscape evolution. To estimate ridgeline erosion rates, we sampled 72 quartz-bearing outcrops from the Potomac and Susquehanna River Basins and measured in situ-produced 10Be. Ridgeline erosion rates average 9 ± 1 m m.y.-1 (median = 6 m m.y.-1), similar to 10Be-derived rates previously reported for theregion. The range of erosion rates we calculated refl ects the wide distribution of samples we collected and the likely inclusion of outcrops affected by episodic loss of thick slabs and periglacial activity. Outcrops on main ridgelines erode slower than those on mountainside spur ridges because ridgelines are less likely to be covered by soil, which reducesthe production rate of 10Be and increases the erosion rate of rock. Ridgeline outcrops erode slower than drainage basinsin the Susquehanna and Potomac River watersheds, suggesting a landscape in disequilibrium. Erosion rates are more similar for outcrops meters to tens of meters apart than those at greater distances, yet semivariogram analysis suggests that outcrop erosion rates in the same physiographic province are similar even though they are hundreds of kilometers apart. This similarity may refl ect underlying lithological and/or structural properties common to each physiographic province. Average 10Be-derived outcrop erosion rates are similar to denudation rates determined by other means (sediment fl ux, fission-track thermochronology, [U-Th]/He dating), indicating that the pace of landscape evolution in the central Appalachian Mountains is slow, and has been since post-Triassic rifting events. © 2013 Geological Society of America.
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Conference paperRood DH, Brown TA, Finkel RC, et al., 2013,
Poisson and non-Poisson uncertainty estimations of <sup>10</sup>Be/ <sup>9</sup>Be measurements at LLNL-CAMS
, Pages: 426-429, ISSN: 0168-583XWe quantify the routine performance and uncertainties of 10Be measurements made on the CAMS FN accelerator mass spectrometer in combination with the CAMS high-intensity cesium sputter source. Our analysis compiles data from 554 primary and secondary standard targets measured on 47 different wheels in nine different run campaigns over a 1-year interval (September 2009-September 2010). The series includes 87, 86, and 85 measurements of each of three different secondary standards and 296 measurements of our primary standard, KNSTD3110 (01-5-4). The average initial 9Be3+ beam current is 22 ± 3 μA (1 standard deviation). Secondary standard targets, which are measured as unknowns in each of the wheels, have average statistical uncertainties based on counting statistics of 1.8%, 1.3%, and 0.8% (1σ) (September 2009-March 2010) and 1.3%, 1.0%, and 0.6% (April 2010-September 2010) for standard materials with 10Be/9Be = 5.35 × 10-13, 9.72 × 10-13, and 8.56 × 10 -12, respectively. The mean measured ratio for each of the secondary standards (normalized to the primary standard) falls within the 1.1% uncertainties of the reported values for each standard material. The weighted standard deviation around the mean of this large number of runs is 2.5%, 2.0%, and 1.2% (September 2009-March 2010) and 1.5%, 1.1%, and 1.2% (April 2010-September 2010) for each secondary standard. These data indicate an additional source of uncertainty, 0.9-1.8% (April 2010-September 2010) and 0.2-1.0% (April 2010-September 2010), above that calculated from counting statistics alone. These 10Be AMS results demonstrate the precision and accuracy of the LLNL-CAMS system. © 2012 Elsevier B.V. All rights reserved.
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Conference paperLiu JG, Mason PJ, Yu E, et al., 2013,
Earthquake damage zone GIS modelling: A modulation between co-seismic deformation and landslide susceptibility
, Pages: 269-277In mountainous regions, earthquake events are typical of naturally-occurring multiple hazards and are frequently the trigger for cascade effects which range from the destruction of the initial shock, to extensive and complex slope failures in the immediate, short and very long-term. The conventional seismic intensity zonationmethod cannot adequately characterise both the current damage level and long-term geohazards, while detailed information is critical in guiding postdisastermitigation and regional development. In studying themost severely damagedBeichuan area by the Mw7.9Wenchuan earthquake, we proceeded with a qualitative numerical method for earthquake damage zonemapping which is novel in its integration of the multi-variable GIS modelling of geohazard susceptibility with co-seismic deformation via amodulation. This new model, we call it earthquake damage, characterise not only the destruction immediately after an earthquake but also the potential for future damage as the consequences of the earthquake. © Springer-Verlag Berlin Heidelberg 2013.
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Journal articleJackson CAL, Chua S-T, Bell RE, et al., 2013,
Structural style and growth of early-stage inversion structures: insights from 3D seismic reflection data, Egersund Basin, offshore Norway
, Journal of Structural Geology, Vol: 46, Pages: 167-185High-quality three-dimensional (3D) seismic reflection and borehole data from the Egersund Basin, offshore Norway are used to characterise the structural style and determine the timing of growth of inversion-related anticlines adjacent to a segmented normal fault system. Two thick-skinned normal faults, which offset Permian clastics and evaporites, delineate the north-eastern margin of the basin. These faults strike NNW-SSE, have up to 1900 m of displacement and are separated by an ESE-dipping, c. 10 km wide relay ramp. Both of these faults display exclusively normal separation at all structural levels and tip out upwards into the upper part of the Lower Cretaceous succession. At relatively shallow structural levels in the hangingwalls of these faults, a series of open, low-amplitude, fault-parallel anticlines are developed. These anticlines, which are asymmetric and verge towards the footwalls of the adjacent faults, are interpreted to have formed in response to mild inversion of the Egersund Basin. The amplitude of and apparent shortening associated with the anticlines vary along strike, and these variations mimic the along-strike variations in throw observed on the adjacent fault segments. We suggest that this relationship can be explained by along-strike changes in the propensity of the normal faults to reactivate during shortening; wider damage zones and lower angles of internal friction, coupled with higher pore fluids pressures at the fault centre, mean that reactivation is easier at this location than at the fault tips or in the undeformed country rock. Seismic-stratigraphic analysis of growth strata indicate that the folds initiated in the latest Turonian-to-earliest Coniacian (c. 88.6 Ma) and Santonian (c. 82.6 Ma); the control on this c. 6 Myr diachroneity in the initiation of fold growth is not clear, but it may be related to strain partitioning during the early stages of shortening. Anticline growth ceased in the Maastrichtian and the inversion event is
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Journal articleJardine RJ, Zhu BT, Foray P, et al., 2013,
Measurement of Stresses around Closed-Ended Displacement Piles in Sand
, Geotechnique, Vol: 63, Pages: 1-17 -
Journal articleTripe R, Kontoe S, Wong TKC, 2013,
Slope topography effects on ground motion in the presence of deep soil layers
, Soil Dynamics and Earthquake Engineering, Vol: 50, Pages: 72-84An extensive investigation has been made into the interaction between topographic amplification and soil layer amplification of seismic ground motion. This interaction is suggested in the literature as a possible cause for the differences between topographic amplification magnitudes observed in field studies and those obtained from numerical analysis. To investigate this issue a numerical finite element (FE) parametric study was performed for a slope in a homogeneous linear elastic soil layer over rigid bedrock subjected to vertically propagating in-plane shear waves (Sv waves). Analyses were carried out using two types of artificial time history as input excitation, one mimicking the build-up and decay of shaking in the time histories of real earthquake events, and the other to investigate the steady-state response. The study identified topographic effects as seen in previous numerical studies such as modification of the free-field horizontal motion, generation of parasitic vertical motion, zones of alternating amplification and de-amplification on the ground surface, and dependence of topographic amplification on the frequency of the input motion. For the considered cases, topographic amplification and soil layer amplification effects were found to interact, suggesting that in order to accurately predict topographic effects, the two effects should not be always handled separately
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Journal articleOlafiranye K, Jackson CAL, Hodgson DM, 2013,
The role of tectonics and mass-transport complex emplacement on upper slope stratigraphic evolution: a 3D seismic case study from offshore Angola
, Marine and Petroleum Geology, Vol: 44, Pages: 196-216Three dimensional seismic-reflection data of the mid-Pliocene-to-Holocene upper slope succession, offshore Angola, provide an opportunity to constrain the stratigraphic context, distribution, external morphology and internal strain within mass-transport deposits (MTDs). These data also allow an assessment of the impact that erosion and relief associated with MTDs have on upper slope stratigraphy and depositional patterns, and the role that MTDs play in achieving ‘grade’ on submarine slopes. The study area is dissected by a series of NW-SE-striking, thin-skinned, salt-detached normal faults, which bound a slope-perpendicular, intra-slope horst that divides the study area into two depocentres. Three main seismic packages and their six constituent units have been mapped across the study area and reveal that, during the initial stages of deposition, a series of MTDs were emplaced, the thickness and distribution of which are controlled by the intra-slope horst. Substantial volumes of substrate were removed and entrained into the parent flow, and significant and irregular relief (150 m) was developed along MTDs upper surface. This MTD-rich package is interpreted to document a time when the slope was above grade, degradational processes dominated and sediment was trapped on the upper slope due to tectonic accommodation. Subsequent deposition was from either turbidity currents or and suspension fallout, at a time when the slope had begun to achieve ‘grade’ and depositional processes dominated. The associated depositional units display only minimal thickness variations with respect to the intra-slope horst, which had been ‘healed’ by this time; however, the unit displays pronounced and abrupt changes in thickness due to infilling of relief at the top of the preceding MTDs. The uppermost strata document a time when the slope was at grade and constructional process (i.e. aggradation and progradation) dominated. Deposition at this time was c
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Journal articleJardine RJ, Aghakouchak A, Sim WW, 2013,
Cyclic triaxial tests to aid offshore pile analysis and design
, Proceedings of the ICE - Geotechnical Engineering, Vol: 166, Pages: 111-121, ISSN: 1353-2618Renewable offshore energy structures experience unusually high levels of cyclic loading under storm and operating conditions. Laboratory and full-scale tests provide one route to develop rational foundation design approaches for such structures. Analytical approaches may also be developed from soil element testing and modelling. This paper outlines preliminary results from such a study. Computer-controlled stress path triaxial equipment, employing high-resolution local strain instrumentation, is adopted for experiments on Dunkerque and Fontainebleau sands designed to support parallel full-scale field and laboratory-model testing programmes involving axial pile loading. The triaxial experiments comprise suites of constant-volume uniform cyclic tests on K 0 over-consolidated specimens employing different amplitudes, performed in conjunction with static and multi-stage experiments that examine the effects of non-uniform cyclic loading. Preliminary results reveal the relationships between cyclic deviator stress, mean effective stress changes and number of cycles, as well as patterns of permanent and cyclic strain development.
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Journal articleKumar K, Stafford PJ, Elghazouli AY, 2013,
Influence of ground motion characteristics on drift demands in steelmoment frames designed to Eurocode 8
, Engineering Structures, Vol: 52, Pages: 502-517 -
Journal articleKumar M, Stafford PJ, Elghazouli AY, 2013,
Seismic shear demands in multi-storey steel frames designed to Eurocode 8
, Engineering Structures, Vol: 52, Pages: 69-87 -
Journal articleDorra EM, Stafford PJ, Elghazouli AY, 2013,
Earthquake loss estimation for Greater Cairo and the national economic implications
, Bulletin of Earthquake Engineering, ISSN: 1570-761X -
Journal articleArmitage JJ, Dunkley Jones T, Duller RA, et al., 2013,
Temporal buffering of climate-driven sediment flux cycles by transient catchment response
, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 369-370, Pages: 200-210 -
Journal articleAgar S, Geiger S, Leonide P, et al., 2013,
Summary of the AAPG–SPE–SEG Hedberg Research Conference on “Fundamental Controls on Flow in Carbonates”
, AAPG Bulletin, Vol: 97, Pages: 533-552A joint AAPG–Society of Petroleum Engineers–Society of Exploration Geophysicists Hedberg Research Conference was held in Saint-Cyr sur Mer, France, on July 8 to 13, 2012, to review current research and explore future research directions related to improved production from carbonate reservoirs. Eighty-seven scientists from academia and industry (split roughly equally) attended for five days. A primary objective for the conference was to explore novel connections among different disciplines (primarily within geoscience and reservoir engineering) as a way to define new research opportunities. Research areas represented included carbonate sedimentology and stratigraphy, structural geology, geomechanics, hydrology, reactive transport modeling, seismic imaging (including four-dimensional seismic, tomography, and seismic forward modeling), geologic modeling and forward modeling of geologic processes, petrophysics, statistical methods, numerical methods for simulation, reservoir engineering, pore-scale processes, in-situ flow experiments (e.g., x-ray computed tomography), visualization, and methods for data interaction.
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Journal articleJackson CA-L, Chua ST, Bell RE, et al., 2013,
Structural style and early stage growth of inversion structures: 3D seismic insights from the Egersund Basin, offshore Norway
, Journal of Structural Geology, Vol: 46, Pages: 167-185
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