Dynamic modeling suggests terrace zone asymmetry in the Chicxulub crater is caused by target heterogeneity     

Gareth S. Collins  Joanna Morgan  Penny Barton  Gail L. Christeson  Sean Gulick  Jaime Urrutia  Michael Warner  Kai Wünnemann 《Earth and Planetary Science Letters》2008,270(3-4):221-230

We investigate the cause of terrace zone asymmetry in the Chicxulub impact crater using dynamic models of crater formation. Marine seismic data acquired across the crater show that the geometry of the crater's terrace zone, a series of sedimentary megablocks that slumped into the crater from the crater rim, varies significantly around the offshore half of the crater. The seismic data also reveal that, at the time of impact, both the water depth and sediment thickness varied with azimuth around the impact site. To test whether the observed heterogeneity in the pre-impact target might have affected terrace zone geometry we constructed two end-member models of upper-target structure at Chicxulub, based on the seismic data at different azimuths. One model, representing the northwest sector, had no water layer and a 3-km thick sediment layer; the other model, representing the northeast sector, had a 2-km water layer above a 4-km sediment layer. Numerical models of vertical impacts into these two targets produced final craters that differ substantially in terrace zone geometry, suggesting that the initial water depth and sediment thickness variations affected the structure of the terrace zone at Chicxulub. Moreover, the differences in terrace zone geometry between the two numerical models are consistent with the observed differences in the geometry of the terrace zone at different azimuths around the Chicxulub crater. We conclude that asymmetry in the pre-impact target rocks at Chicxulub is likely to be the primary cause of asymmetry in the terrace zone.  相似文献   

An experimental investigation of geochromatography during secondary migration of petroleum performed under subsurface conditions with a real rock     

Steve Larter  Berni Bowler  Ed Clarke  Colin Wilson  Brian Moffatt  Barry Bennett  Gareth Yardley  Dan Carruthers 《Geochemical transactions》2000,1(1):54-7

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Shallow water hydrodynamic models for hyperconcentrated sediment-laden floods over erodible bed     

Zhixian Cao  Gareth Pender  Paul Carling 《Advances in water resources》2006

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Utilizing spectral decomposition to determine the distribution of injected CO2 at the Snøhvit Field          下载免费PDF全文

Gareth A. Williams  Sissel Grude  R. Andrew Chadwick 《Geophysical Prospecting》2015,63(5):1213-1223

Time‐lapse 3D seismic reflection data, covering the CO₂ storage operation at the Snøhvit gas field in the Barents Sea, show clear amplitude and time‐delay differences following injection. The nature and extent of these changes suggest that increased pore fluid pressure contributes to the observed seismic response, in addition to a saturation effect. Spectral decomposition using the smoothed pseudo‐Wigner–Ville distribution has been used to derive discrete‐frequency reflection amplitudes from around the base of the CO₂ storage reservoir. These are utilized to determine the lateral variation in peak tuning frequency across the seismic anomaly as this provides a direct proxy for the thickness of the causative feature. Under the assumption that the lateral and vertical extents of the respective saturation and pressure changes following CO₂ injection will be significantly different, discrete spectral amplitudes are used to distinguish between the two effects. A clear spatial separation is observed in the distribution of low‐ and high‐frequency tuning. This is used to discriminate between direct fluid substitution of CO₂, as a thin layer, and pressure changes that are distributed across a greater thickness of the storage reservoir. The results reveal a striking correlation with findings derived from pressure and saturation discrimination algorithms based on amplitude versus offset analysis.  相似文献   

Reflections on interviewing elites   总被引：1，自引：0，他引：1  

Gareth Rice 《Area》2010,42(1):70-75

This paper presents one case of the particularities of power. Drawing upon interviews with UK-based elites, I unpack the general with the specific through discussing how I experienced power as a relational effect of social interaction. Within the parameters of a collaborative research project, this involved the challenge of gaining access to and interviewing elites as means to explore the role of a flagship shopping mall as part of a wider urban regeneration agenda. I conclude with some recommendations on how to negotiate the unequal power relations between elites and researchers.  相似文献   

Cavity expansion in sands under drained loading conditions     

I. F. Collins  M. J. Pender  Wang Yan 《国际地质力学数值与分析法杂志》1992,16(1):3-23

Solutions for the expansion of cylindrical and spherical cavities in sands are presented. The sand is modelled using recently proposed critical-state models in which the values of the friction and dilation angles depend on the deformation history. Similarity solutions are obtained which enable the limit pressure to be calculated as a function of the initial conditions. Comparisons with existing perfectly plastic theories are made and consequences for the interpretation of cone penetrometer measurements are indicated.  相似文献   

Slope stability analyses for materials with a non-linear failure envelope     

I. F. Collins  C. I. M. Gunn  M. J. Pender  Wang Yan 《国际地质力学数值与分析法杂志》1988,12(5):533-550

Upper bound techniques are used to analyse the stability of slopes of material failing according to a non-linear failure criterion, such as closely jointed rocks. The global, extremal nature of upper bound calculations is discussed, as is the inverse use of such procedures for obtaining safe lower bound estimates for material strength properties in back analyses. Specific results are presented for the material model proposed by Hoek and Brown.  相似文献   

New proxy for reconnection     

Gareth Chisham 《Astronomy& Geophysics》2005,46(4):4.23-4.23

Gareth Chisham describes a new method for remotely sensing reconnection in the magnetosphere. This article is based on his poster, which won a 2005 Rishbeth Prize.  相似文献   

Numerical Analysis of Adaptation-to-capacity Length for Fluvial Sediment Transport     

LI Zhi-jing  CAO Zhi-xian  Gareth PENDER  HU Peng 《山地科学学报》2014,(6):1491-1498

Over the last several decades,various sediment transport capacity formulations have been used by geomorphologists and engineers to calculate fluvial morphological changes.However,it remains poorly understood if the adaptation to capacity could be fulfilled instantly in response to differing inflow discharges and sediment supplies,and thus if the calculation of morphological changes in rivers based on the assumed capacity status is fully justified.Here we present a numerical investigation on this issue.The distance required for sediment transport to adapt to capacity（i.e.,adaptation-to-capacity length） of both bed load and suspended sediment transport is computationally studied using a coupled shallow water hydrodynamic model,in line with varied inlet sediment concentrations.It is found that the adaptation-to-capacity length generally decreases as the Rouse number increases,irrespective of whether the inlet sediment concentration increases or reduces.For cases with vanishing inlet sediment concentration a unified relationship is found between the adaptation-to-capacity length and the Rouse number.Quantitatively,the adaptation-to-capacity length of bed load sediment is limited to tens of times of the flow depth,whilst that of suspended sediment increases substantially with decreasing Rouse number and can be up to hundreds of times of the flow depth.The present finding concurs that bed load sediment transport can adapt to capacity much more rapidly than suspended sediment transport,and it facilitates a quantitative criterion on which the applicability of bed load or suspended sediment transport capacity for natural rivers can be readily assessed.  相似文献   

Facies and flow regimes of sandstone‐hosted columnar intrusions: Insights from the pipes of Kodachrome Basin State Park     

Jessica A. Ross  Jeff Peakall  Gareth M. Keevil 《Sedimentology》2014,61(6):1764-1792

Sandstone‐hosted intrusions are found in a wide variety of environments, but remain poorly understood compared with their mudstone‐hosted counterparts. In particular, they remain largely unrecognized in the subsurface, in part because they are problematic to image in seismic data. This study reports on the facies and fluid flow associated with a 20 000 km³ sandstone intrusion province in Utah, USA. Forming a small portion of this intrusion province, the intrusions cropping out in Kodachrome Basin State Park display a very wide array of facies and morphologies, factors which would make their identification in core a significant challenge. Remobilized sediment is shown to have been injected at least 200 m vertically from its source, with flow prolonged enough to concentrate heavy minerals in placer‐style deposits at the pipe margins. Evidence for lateral pipe migration and for associated broader fluidization regions is also presented. A new approach to estimating flow parameters in injectites is implemented herein, and indicates that previous work has overestimated velocities and flow Reynolds numbers by up to two orders of magnitude. Flow modelling suggests turbulent flow in the pipes that is consistent with field observations of erosive margins and chaotic internal structures. Post‐emplacement, these pipes remained as long‐term fluid conduits, as revealed by their diagenetic history, focussing and facilitating flow of extraformational fluids, despite the relatively high porosity and permeability of the aeolian host strata.  相似文献