Results
- Showing results for:
- Reset all filters
Search results
-
Journal articleJardine RJ, Zhu BT, Foray P, et al., 2013,
Interpretation of stress measurements made around closed-ended displacement piles in sand
, GEOTECHNIQUE, Vol: 63, Pages: 613-627, ISSN: 0016-8505- Author Web Link
- Open Access Link
- Cite
- Citations: 61
-
Journal articleOishi Y, Piggott MD, Maeda T, et al., 2013,
Three-dimensional tsunami propagation simulations using an unstructured mesh finite element model
, Journal of Geophysical Research: Solid Earth, Vol: 118, Pages: 2998-3018, ISSN: 2169-9313 -
Conference paperHan B, Zdravkovic L, Kontoe S, 2013,
The stability of the Generalised-α time integration method for dynamic coupled consolidation problems
, COMPDYNThis paper investigates the stability of the Generalised-α time integration method (the CH method) for a fully coupled solid-pore fluid formulation. Theoretical stability conditions are derived, which are shown to simplify to the existing ones of the CH method for the one–phase formulation when the solid-fluid coupling is ignored. Finite Element (FE) analyses considering a range of loading conditions are conducted to validate the analytically derived stability condition, showing that the numerical results are in agreement with the theoretical investigation. The CH method is a generalisation of a number of other tine integration schemes and hence the derived stability conditions are relevant for most of the commonly utilised time integration methods for fully coupled two-phase formulation.
-
Conference paperKontoe S, Christopoulos A, May R, 2013,
Site response analysis for vertical ground motion
, COMPDYNThis study initially considers a uniform soil layer subjected to vertically propagating harmonic P-waves. The response of the layer is calculated analytically, considering one-dimensional propagation, and numerically employing time domain coupled consolidation Finite Element analysis for a range of input frequencies. The computed amplification function is shown to significantly depend on the modelling of the fluid phase and the soil permeability. Subsequently, a ground profile corresponding to a downhole array in Dahan (Taiwan) is examined assuming undrained, drained and coupled consolidation behaviour. The numerical predictions are compared with the vertical recorded response during the 1999 Chi-Chi earthquake demonstrating a very good agreement for the coupled consolidation analysis and highlighting the limitations of the other two approaches (i.e. drained and undrained analyses).
-
Journal articlePapaspiliou M, Kontoe S, 2013,
Sensitivity of site response analysis on the number of ground motion records and implications for PSHA
, Bulletin of Earthquake Engineering, Vol: available online, ISSN: 1573-1456This paper investigates issues related to the number of ground-motion records required for the performance of site response analysis and the inclusion of the site-specific amplification function within probabilistic seismic hazard calculations (PSHA). It explores the minimum number of records required for a robust estimation of the median and standard deviation of the site amplification function, as well as the impact of the selected ground-motion suites on the results of PSHA. Site response analyses are performed using both equivalent linear and nonlinear methodologies. Although the median amplification was observed to be relatively easy to capture, the standard deviation was seen to fluctuate considerably, especially when suites of few records were used. It was observed that in the case of the nonlinear site response analysis 10 records provide relatively stable estimates of the hazard curves for the majority of periods, while in the case of the equivalent linear analysis 20 records or more are required to achieve a similar level of accuracy.
-
Journal articleMagee C, Hunt-Stewart E, Jackson CAL, 2013,
Volcano growth mechanisms and the role of sub-volcanic intrusions: Insights from 2D seismic reflection data
, Earth and Planetary Science Letters, Vol: 373, Pages: 41-53Temporal and spatial changes in volcano morphology and internal architecture can determine eruption style and location. However, the relationship between the external and internal characteristics of volcanoes and sub-volcanic intrusions is often difficult to observe at outcrop or interpret uniquely from geophysical and geodetic data. We use high-quality 2D seismic reflection data from the Ceduna Sub-basin, offshore southern Australia, to quantitatively analyse 56, pristinely-preserved, Eocene-age volcanogenic mounds, and a genetically-related network of sub-volcanic sills and laccoliths. Detailed seismic mapping has allowed the 3D geometry of each mound to be reconstructed and distinct seismic facies within them to be recognised. Forty-six continental, basaltic shield volcanoes have been identified that have average flank dips of <10.31, basal diameters of 1.94–18.89 km, central summits that are 0.02–1 km high and volumes that range from 0.06 to 57.21 km3. Parallel seismic reflections within the shield volcanoes are interpreted to represent interbedded volcanic and clastic material, suggesting that a series of temporally separate eruptions emanated from a central vent. The shield volcanoes typically overlie the lateral tips of sills and we suggest that the intermittent eruption phases correspond to the incremental emplacement of discrete magma pulses within the laterally extensive sill-complex. Eight volcanogenic hydrothermal vents, which are also associated with the lateral tips of sills, were also recognised, and these appear to have formed from the seepage of intrusion-related hydrothermal fluids onto the seafloor via emplacement-induced fractures. This work highlights that deformation patterns preceding volcanic eruptions may (i) be offset from the eruption site; (ii) attributed to intrusions with complex morphologies; and/or (iii) reflect magma movement along pre-existing fracture systems. These complexities should therefore be considered in erupt
-
Journal articleCamara A, Ruiz-Teran AM, Stafford PJ, 2013,
Structural behaviour and design criteria of under-deck cable-stayed bridges subjected to seismic action
, Earthquake Engineering and Structural Dynamics, Vol: 42, Pages: 891-912, ISSN: 0098-8847Under‐deck cable‐stayed bridges are very effective structural systems for which the strong contribution of the stay cables under live loading allows for the design of very slender decks for persistent and transient loading scenarios. Their behaviour when subjected to seismic excitation is investigated herein and a set of design criteria are presented that relate to the type and arrangement of bearings, the number and configuration of struts, and the transverse distribution of stay cables. The nonlinear behaviour of these bridges when subject to both near‐field and far‐field accelerograms has been thoroughly investigated through the use of incremental dynamic analyses. An intensity measure that reflects the pertinent contributions to response when several vibration modes are activated was proposed and is shown to be effective for the analysis of this structural type. The under‐deck cable‐stay system contributes in a very positive manner to reducing the response when the bridges are subject to very strong seismic excitation. For such scenarios, the reduction in the stiffness of the deck because of crack formation, when prestressed concrete decks are used, mobilises the cable system and enhances the overall performance of the system. Sets of natural accelerograms that are compliant with the prescriptions of Eurocode 8 were also applied to propose a set of design criteria for this bridge type in areas prone to earthquakes. Particular attention is given to outlining the optimal strategies for the deployment of bearings.
-
Journal articleGoes S, 2013,
EARTH SCIENCE Western North America's jigsaw
, NATURE, Vol: 496, Pages: 35-37, ISSN: 0028-0836- Author Web Link
- Cite
- Citations: 3
-
Journal articleRefsnider KA, Miller GH, Fréchette B, et al., 2013,
A chronological framework for the Clyde Foreland Formation, Eastern Canadian Arctic, derived from amino acid racemization and cosmogenic radionuclides
, Quaternary Geochronology, Vol: 16, Pages: 21-34, ISSN: 1871-1014The most extensive terrestrial outcrops of glacial and glaciomarine deposits in the Eastern Canadian Arctic are exposed in sea cliffs along the Clyde Foreland and Qivitu Peninsula of Baffin Island. Collectively known as the Clyde Foreland Formation (CFF), these stacked deposits record at least seven glacial advances. Despite having been the focus of numerous investigations spanning nearly 50 years, no numerical chronological framework for the age of the deposits has been established. Previous studies relied on biostratigraphy and amino acid racemization (AAR) geochronology and postulated that the oldest units were Late Pliocene to Mid-Pleistocene in age. In this paper, we use a cosmogenic radionuclide isochron approach to determine a minimum age for the burial of a paleosol preserved within the CFF. Abundant palynomorphs in the paleosol are dominated by cool-climate taxa. Combining the paleosol burial age with a compilation of published and new CFF AAR data for marine bivalves Hiatella arctica and Mya truncata, we statistically define seven CFF aminozones and develop a piecewise isoleucine AAR calibration model for Baffin Island. From this, we estimate the minimum age of each aminozone, although the propagation of errors through all calculations produces large uncertainties for each age estimate. The youngest three CFF units, known as the Kogalu, Kuvinilk, and Cape Christian members, were most likely deposited during glaciations in the Mid- to Late-Pleistocene. The paleosol formed prior to 1.15 ± 0.20 Ma, and the underlying aminozones represent sedimentation during Early Pleistocene or latest Pliocene glaciations and record early advances of Laurentide ice across Baffin Island. © 2012 Elsevier B.V.
-
Journal articleMagee C, Jackson CAL, Schofield N, 2013,
The influence of normal fault geometry on igneous sill emplacement and morphology
, Geology, Vol: 41, Pages: 407-410Magma flow within the subsurface is heavily influenced by the pre-existing structure of the upper crust. During continental rifting, normal faults modify the geometry of igneous networks by providing preferential pathways for the intrusion of magma. However, the mechanisms by which magma intrudes into fault planes is poorly understood. Here, we quantitatively document the relationship between fault architecture and intrusion distribution and geometry using 3D seismic reflection data from the Exmouth Sub-basin, offshore NW Australia. Inclined segments of saucer-shaped sills are observed to specifically intrude faults along positive fault-plane corrugations (i.e., convex-into-the-hangingwall). We suggest that stress field variations associated with the positive corrugations provide suitable conditions for fault reactivation as magma conduits. Pre-existing faults also modify sill geometries through the offset of stratigraphic horizons that may be preferentially intruded, potentially resulting in the formation of a new sill or the development of minor intrusive steps. This work emphasizes the importance of the pre-existing structural template in controlling the growth and final geometry of intrusive networks and, implicitly, the distribution of eruptive volcanic centers.
-
Journal articleBoroda R, Matmon A, Amit R, et al., 2013,
Long-term talus flatirons formation in the hyperarid northeastern Negev, Israel
, Quaternary Research (United States), Vol: 79, Pages: 256-267, ISSN: 0033-5894Colluvial sediments of talus relicts ("talus flatirons") around mesas preserve a record that sheds light on slope-forming processes at temporal scales >103yr. The sedimentology and soil stratigraphy of two groups of talus flatirons in the northeastern hyperarid Negev desert reveal four deposition events in the younger talus and at least two in the older one. Numerical modeling of high-resolution 10Be depth profiles suggests that these taluses were deposited during the middle Pleistocene; the younger talus group first depositional event occurred at 551 -142+80ka and its abandonment occurred at 270 -38+17ka. The abandonment of the older talus group and stabilization of its surface occurred at 497 -114+176ka. These ages indicate that the development of the studied talus sequence is not specifically associated with Pleistocene glacial-interglacial cycles. The 10Be modeled concentrations indicate significant differences in the average inheritance of talus flatirons of different groups. These differences can be attributed to variability in the transport distance and duration of gravel exposure during transport but could also reflect some temporal variability in cliff retreat. Our results also demonstrate that talus slopes in hyperarid areas, despite their steepness, can store sediment for long periods (~500ka) and thus constitute a valuable archive. © 2012 University of Washington.
-
Journal articleGoes S, Eakin CM, Ritsema J, 2013,
Lithospheric cooling trends and deviations in oceanic <i>PP</i>-<i>P</i> and <i>SS</i>-<i>S</i> differential traveltimes
, JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, Vol: 118, Pages: 996-1007, ISSN: 2169-9313- Author Web Link
- Cite
- Citations: 13
-
Book chapterMian J, Kontoe S, Free M, 2013,
Assessment and Management of Risks Related to Earthquake-Induced Liquefaction
, Seismic risk analysis and management of civil infrastructure systems, Editors: Tesfamariam, Goda, Cambridge, UK, Publisher: Woodhead Publishing Ltd -
Journal articleTsiampousi A, Zdravkovic L, Potts DM, 2013,
A new Hvorslev surface for critical state type unsaturated and saturated constitutive models
, Computers and Geotechnics, Vol: 48, Pages: 156-166 -
Journal articleTsiampousi A, Zdravkovic L, Potts DM, 2013,
Variation with time of the factor of safety of slopes excavated in unsaturated soils
, Computers and Geotechnics, Vol: 48, Pages: 167-178 -
Journal articleTsiampousi A, Zdravkovic L, Potts DM, 2013,
A three-dimensional hysteretic soil-water retention curve
, Geotechnique, Vol: 63, Pages: 155-164, ISSN: 0016-8505One of the most important features in unsaturated soil mechanics is the soil-water retention curve and its coupling to the mechanical component of soil behaviour. It has long been recognised that the retention curve exhibits significant hysteresis, and that it is affected by the specific volume. Several attempts have been made in the past to model this behaviour. A novel approach is proposed herein, which accounts for both the hydraulic hysteresis and the specific volume dependence of the retention relationship in a three-dimensional formulation. The primary and the scanning paths are simple geometric curves, which have a common tangent at the point of intersection, ensuring a smooth transition from scanning to primary paths. A small number of parameters are required to define the primary paths, and no fitting parameters are necessary for generation of the scanning paths. As knowledge of the specific volume and its variation is required, the retention model needs to be employed in conjunction with a constitutive model capable of reproducing the complex behaviour of unsaturated soils. To guarantee consistency with the retention model, the degree of saturation needs to be incorporated in the specific volume–suction relationship adopted within the constitutive model. To accommodate such a feature when absent, a new expression for the soil compressibility with suction as a function of the degree of saturation is proposed. Simulations of laboratory experiments on unsaturated soils, involving cyclic changes of applied suction, demonstrate the effectiveness of the proposed modelling approach.
-
Journal articleHidy AJ, Gosse JC, Froese DG, et al., 2013,
A latest Pliocene age for the earliest and most extensive Cordilleran Ice Sheet in northwestern Canada
, Quaternary Science Reviews, Vol: 61, Pages: 77-84, ISSN: 0277-3791The Klondike gravel is a widespread glaciofluvial gravel marking the earliest and most extensive Cordilleran Ice Sheet (CIS) in NW North America. New terrestrial cosmogenic nuclide (TCN) burial ages indicate this gravel was emplaced 2.64+0.20/-0.18 Ma (1σ). Coupled with previously interpreted paleomagnetic stratigraphy, this numerical age constrains the timing of the earliest CIS to the late Gauss Chron and provides a minimum age for the Upper White Channel gravel, a significant placer gold source in the Yukon. This implies the first CIS glacial maximum pre-dates the maximum extent of the Laurentide Ice Sheet, indicating that during the initial stages of northern hemisphere glaciation, the most extensive glaciers were present in the relatively cold and high elevation northern Cordillera. Our results verify the CIS as a likely source of persistent coeval ice-rafted debris in the northern Pacific, and suggest that the first CIS formed as a response to the establishment of the northern Pacific halocline and emergence of the 41 ka obliquity cycle during the Plio-Pliocene transition. © 2012 Elsevier Ltd.
-
Journal articleSomme TO, Jackson CAL, Vaksdal M, 2013,
Source-to-sink analysis of ancient sedimentary systems using a subsurface case study from the Møre-Trøndelag area of southern Norway: Part 1 - depositional setting and fan evolution
, Basin Research, Vol: 25, Pages: 489-511In this study we use seismic reflection, well and core data to investigate the role that basin physiography and sediment routing systems played on the distribution, geometry and stratigraphic architecture of Upper Cretaceous submarine fans offshore Norway. The Late Cretaceous Møre-Trøndelag margin of western Norway was characterised by steep submarine slopes (gradient of ~0,3-3º). Mudstones dominate the Upper Cretaceous slope succession although a few regionally extensive, sandstone-dominated units are developed. We focus on the most regionally extensive sandstone unit, which is of Late Turonian-to-Early Coniacian age. Mapping and visualisation of 2D and 3D seismic reflection data and analysis of well data indicates that the sandstone unit comprises a total of 11 submarine fans, which were fed by sand-rich sediment gravity flows routed through multiple upper slope canyons. Based on the internal organisation of seismic facies, four fan types have been identified: (i) Type Ia fans, which are characterised by <10 erosional channel complexes at their bases and aggradational to landward-stepping lobes in their upper parts; (ii) Type Ib fans, which are characterised by >10 erosional channel complexes at their bases and aggradational to landward-stepping lobe and mass-transport deposits near the fan apex in their upper parts; (iii) Type II fans, which are dominated by aggradational lobe deposits; and (iv) Type III fans, which are dominated by a single channel complex that passes downdip into a small terminal lobe. The different fan types are interpreted to reflect variable stratigraphic responses to source proximity and basin physiography, which is principally related to the degree of local fault reactivation and differential compaction. This variability highlights the diversity of fan types that may occur over short distances along continental margins, and demonstrates the importance of local controls in understanding the internal stratigraphic va
-
Journal articleMiljković K, Collins GS, Mannick S, et al., 2013,
Morphology and population of binary asteroid impact craters
, Earth and Planetary Science Letters, Vol: 363, Pages: 121-132, ISSN: 0012-821XObservational data show that in the Near Earth Asteroid (NEA) region 15% of asteroids are binary. However, the observed number of plausible doublet craters is 2–4% on Earth and 2–3% on Mars. This discrepancy between the percentage of binary asteroids and doublets on Earth and Mars may imply that not all binary systems form a clearly distinguishable doublet crater owing to insufficient separation between the binary components at the point of impact. We simulate the crater morphology formed in close binary asteroid impacts in a planetary environment and the range of possible crater morphologies includes: single (circular or elliptical) craters, overlapping (tear-drop or peanut shaped) craters, as well as clearly distinct, doublet craters. While the majority of binary asteroids impacting Earth or Mars should form a single, circular crater, about one in four are expected to form elongated or overlapping impact craters and one in six are expected to be doublets. This implies that doublets are formed in approximately 2% of all asteroid impacts on Earth and that elongated or overlapping binary impact craters are under-represented in the terrestrial crater record. The classification of a complete range of binary asteroid impact crater structures provides a template for binary asteroid impact crater morphologies, which can help in identifying planetary surface features observed by remote sensing.
-
Journal articleLonergan L, Jamin NH, Jackson CA-L, et al., 2013,
U-shaped slope gully systems and sediment waves on the passive margin of Gabon (West Africa)
, Marine Geology, Vol: 337, Pages: 80-973-D seismic reflection data has enabled the documentation of a system of remarkable modern and buried u-shaped gullies which intimately co-exist with upslope migrating sediment waves along 80 km of the Gabon continental slope. The modern gullies occur on a silty mud-dominated slope in water depths of 150–1500 m on an ~50 km wide slope with a gradient of 4.5° decreasing to 1.5°. The gully sets persist laterally for distances of at least 40 km and extend downslope for distances of up to 60 km. The gullies are u-shaped in crosssection,with a relief of 5–30 m, and widths of 50–400 m. Intriguingly, the gullies become narrower andshallower with distance down the slope, as well as increasing in number down slope. The majority of the gullies appear to be erosional but some appear to have resulted from simultaneous aggradation along inter-gully ridges and non-deposition along the adjacent gully floor. Hence, these gullies are interpreted to have formed mainly inresponse to spatially-variable deposition, rather than erosion. Upslope migrating sediment waves occur in close proximity to the gullies. Gullies cross fields of sediment waves and waves are observed to migrate up-slopelocally within both the erosional and aggradational gullies. Evidence is lacking for any slumping or headward erosion in the headwall region of the gullies, which discounts formation by very local sediment gravity flowsoriginating from shelf-edge collapse, as has been observed in other v-shaped gully systems. Based on our new data, and supported by theoretical studies on the mechanics of turbidity currents, we propose that the gulliesand related sediment waves were formed by diffuse, sheet-like, mud-rich turbidity currents that presumably originated on the shelf. Instabilities in the turbidity currents generated a wave-shaped perturbation in a crossflow direction leading to regularly spaced regions of faster and slower flow. For the non-aggradational and erosional gullies it is
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.