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81.
Jay Parker Gregory Lyzenga Charles Norton Cinzia Zuffada Margaret Glasscoe John Lou Andrea Donnellan 《Pure and Applied Geophysics》2008,165(3-4):497-521
GeoFEST (Geophysical Finite Element Simulation Tool) is a two- and three-dimensional finite element software package for the modeling of solid stress and strain in geophysical and other continuum domain applications. It is one of the featured high-performance applications of the NASA QuakeSim project. The program is targeted to be compiled and run on UNIX systems, and is running on diverse systems including sequential and message-passing parallel systems. Solution to the elliptical partial differential equations is obtained by finite element basis sampling, resulting in a sparse linear system primarily solved by conjugate gradient iteration to a tolerance level; on sequential systems a Crout factorization for the direct inversion of the linear system is also supported. The physics models supported include isotropic linear elasticity and both Newtonian and power-law viscoelasticity, via implicit quasi-static time stepping. In addition to triangular, quadrilateral, tetrahedral and hexahedral continuum elements, GeoFEST supports split-node faulting, body forces, and surface tractions. This software and related mesh refinement strategies have been validated on a variety of test cases with rigorous comparison to analytical solutions. These include a box-shaped domain with imposed motion on one surface, a pair of strike slip faults in stepover arrangement, and two community-agreed benchmark cases: a strike slip fault in an enclosing box, and a quarter-domain circular fault problem. Scientific applications of the code include the modeling of static and transient co- and post-seismic earth deformation, Earth response to glacial, atmospheric and hydrological loading, and other scenarios involving the bulk deformation of geologic media. 相似文献
82.
Three major rhyolite systems in the northeastern Davis and adjacent Barrilla Mountains include lava units that bracketed a
large pantelleritic ignimbrite (Gomez Tuff) in rapid eruptions spanning 300,000 years. Extensive silicic lavas formed the
shields of the Star Mountain Formation (37.2 Ma-K/Ar; 36.84 Ma 39Ar/40Ar), and the Adobe Canyon Formation (37.1 Ma-K/Ar; 36.51-39Ar/40Ar). The Gomez Tuff (36.6 Ma-K/Ar; 36.74-39Ar/40Ar) blanketed a large region around the 18×24 km diameter Buckhorn caldera, within which it ponded, forming sections up to
500 m thick. Gomez eruption was preceded by pantelleritic rhyolite domes (36.87, 36.91 Ma-39Ar/40Ar), some of which blocked movement of Star Mountain lava flows. Following collapse, the Buckhorn caldera was filled by trachyte
lava. Adobe Canyon rhyolite lavas then covered much of the region. Star Mountain Formation (~220 km3) is composed of multiple flows ranging from quartz trachyte to mildly peralkalic rhyolite; three major types form a total
of at least six major flows in the northeastern Davis Mountains. Adobe Canyon Formation (~125 km3) contains fewer flows, some up to 180 m thick, of chemically homogenous, mildly peralkalic comendite, extending up to 40 km.
Gomez Tuff (~220 km3) may represent the largest known pantellerite. It is typically less than 100 m thick in extra-caldera sections, where it
shows a pyroclastic base and top, although interiors are commonly rheomorphic, containing flow banding and ramp structures.
Most sections contain one cooling unit; two sections contain a smaller, upper cooling unit. Chemically, the tuff is fairly
homogeneous, but is more evolved than early pantelleritic domes. Overall, although Davis Mountains silicic units were generated
through open system processes, the pantellerites appear to have evolved by processes dominated by extensive fractional crystallization
from parental trachytes similar to that erupted in pre- and post-caldera lavas. Comparison with the Pantelleria volcano suggests
that the most likely parental magma for the Buckhorn series is transitional basalt, similar to that erupted in minor, younger
Basin and Range volcanism after about 24 Ma. Roughly contemporaneous mafic lavas associated with the Buckhorn caldera appear
to have assimilated or mixed with crustal melts, and, generally, may not be regarded as mafic precursors of the Buckhorn silicic
rocks, They thus form a false Daly Gap as opposed to the true basalt/trachyte Daly gap of Pantelleria.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic
rhyolites. 相似文献
83.
84.
Scott M. Croom A. Ratcliffe Q. A. Parker T. Shanks B. J. Boyle R. J. Smith 《Monthly notices of the Royal Astronomical Society》1999,306(3):592-598
We present results from a continuing campaign to secure deep multi-colour CCD sequences for photometric calibration in UK Schmidt fields with galactic latitudes | b |>50°. In this paper we present UBVR photometry in 12 fields and BR photometry in a further 14 fields observed within UK Schmidt survey fields centred at δ =−30°. Photometric errors are at the 0.05 level at 20.2, 21, 20.5 and 20 mag for UBVR sequences respectively. Our observations were carried out with the 0.9-m telescope at the Cerro-Tololo Inter-American Observatory. These data are not intended for use as highly accurate individual photometric standards, but rather for use as sequences, using a large number of stars to calibrate wide-area data such as photographic plates. The data are available electronically at http://icstar5.ph.ic.ac.uk/~scroom/phot/photom.html . 相似文献
85.
Gavin Parker 《Area》1999,31(1):75-80
Summary Using figures derived from the UK Home Office, this paper analyses and reviews the impact and deployment of Part V of the Criminal Justice and Public Order Act 1994 since its enactment. This is done with special reference to its impact on citizenship and the regulation of 'the environment' and associated rural spaces. It is argued that, notwithstanding the actual use of the public order clauses in Part V of the Act, its underlying meanings are largely of a symbolic nature. Such symbolism is, however, a powerful indication of the defence of particularist constructions of rural space. It can also open out new conditions of possibility, providing a useful 'oppressed' status and media spectacle for a range of protesters and activists. 相似文献
86.
Jack C. Parker Ungtae Kim Alyson Fortune Steffen Griepke James P. Galligan Amber Bonarrigo 《Ground Water Monitoring & Remediation》2017,37(1):51-66
The objective of in situ thermal treatment is typically to reduce the contaminant mass or average soil concentration below a specified value. Evaluation of whether the objective has been met is usually made by averaging soil concentrations from a limited number of soil samples. Results from several field sites indicate large performance uncertainty using this approach, even when the number of samples is large. We propose a method to estimate average soil concentration by fitting a log normal probability model to thermal mass recovery data. A statistical approach is presented for making termination decisions from mass recovery data, soil sample data, or both for an entire treatment volume or for subregions that explicitly considers estimation uncertainty which is coupled to a stochastic optimization algorithm to identify monitoring strategies to meet objectives with minimum expected cost. Early termination of heating in regions that reach cleanup targets sooner enables operating costs to be reduced while ensuring a high likelihood of meeting remediation objectives. Results for an example problem demonstrate that significant performance improvement and cost reductions can be achieved using this approach. 相似文献
87.
Morphodynamics of a bedrock‐alluvial meander bend that incises as it migrates outward: approximate solution of permanent form 下载免费PDF全文
In meandering rivers cut into bedrock, erosion across a channel cross‐section can be strongly asymmetric. At a meander apex, deep undercutting of the outer bank can result in the formation of a hanging cliff (which may drive hillslope failure), whereas the inner bank adjoins a slip‐off slope that connects to the hillslope itself. Here we propose a physically‐based model for predicting channel planform migration and incision, point bar and slip‐off slope formation, bedrock abrasion, the spatial distribution of alluvial cover, and adaptation of channel width in a mixed bedrock‐alluvial channel. We simplify the analysis by considering a numerical model of steady, uniform bend flow satisfying cyclic boundary conditions. Thus in our analysis, ‘sediment supply’, i.e. the total volume of alluvium in the system, is conserved. In our numerical simulations, the migration rate of the outer bank is a specified parameter. Our simulations demonstrate the existence of an approximate state of dynamic equilibrium corresponding to a near‐solution of permanent form in which a bend of constant curvature, width, cross‐sectional shape and alluvial cover distribution migrates diagonally downward at constant speed, leaving a bedrock equivalent of a point bar on the inside of the bend. Channel width is set internally by the processes of migration and incision. We find that equilibrium width increases with increasing sediment supply, but is insensitive to outer bank migration rate. The slope of the bedrock point bar varies inversely with both outer bank migration rate and sediment supply. Although the migration rate of the outer bank is externally imposed here, we discuss a model modification that would allow lateral side‐wall abrasion to be treated in a manner similar to the process of bedrock incision. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
88.
We consider the evolution of the hydraulic geometry of sand-bed meandering rivers. We study the difference between the timescale of longitudinal river profile adjustment and that of channel width and depth adjustment. We also study the effect of hydrological regime alteration on the evolution of bankfull channel geometry. To achieve this, a previously developed model for the spatiotemporal co-evolution of bankfull channel characteristics, including bankfull discharge, bankfull width, bankfull depth and down-channel bed slope, is used. In our modelling framework, flow variability is considered in terms of a specified flow duration curve. Taking advantage of this unique feature, we identify the flow range responsible for long-term bankfull channel change within the specified flow duration curve. That is, the relative importance of extremely high short-duration flows compared to moderately high longer duration flows is examined. The Minnesota River, MN, USA, an actively meandering sand-bed stream, is selected for a case study. The longitudinal profile of the study reach has been in adjustment toward equilibrium since the end of the last glaciation, while its bankfull cross-section is rapidly widening due to hydrological regime change in the last several decades. We use the model to demonstrate that the timescale for longitudinal channel profile adjustment is much greater than the timescale for cross-sectional profile adjustment due to a lateral channel shift. We also show that hydrological regime shift is responsible for the recent rapid widening of the Minnesota River. Our analysis suggests that increases in the 5–25% exceedance flows play a more significant role in recent bankfull channel enlargement of the Minnesota River than increase in either the 0.1% exceedance flow or the 90% exceedance flow. © 2020 John Wiley & Sons, Ltd. 相似文献
89.
Slack Tim Parks Vanessa Ayer Lynsay Parker Andrew M. Finucane Melissa L. Ramchand Rajeev 《Natural Hazards》2020,102(3):1207-1224
Natural Hazards - Researchers have traditionally conceptualized hazards that give rise to disasters as “natural” or “technological.” An extensive literature has documented... 相似文献
90.
Frank Dennis John N. Andrews Andrew Parker Jason Poole Manfred Wolf 《Applied Geochemistry》1997,12(6):763-773
The chemical and isotopic composition of groundwater from 52 sites in the London (U.K.) area was determined as part of a project aimed at assessing the spatial variation in the age of Chalk groundwater, and in determining the relationship between fracture and matrix groundwater in this dual porosity system.Systematic changes in groundwater chemistry take place in the downgradient direction in response to several chemical processes. These processes include early concentration by evaporation and congruent dissolution of calcite followed by widespread incongruent dissolution and ion exchange in addition to local oxidation-reduction reactions, gypsum dissolution and saline intrusion. As a result of the above processes, Chalk groundwater follows an evolutionary path from Ca bicarbonate type to Na bicarbonate type.The age of Chalk groundwater was modelled using14C, δ13C,3H, δ2H and δ180. There is a general increase in the groundwater age in a downgradient direction with the oldest water found in N central areas of the basin. Groundwater in the unconfined zones and in areas S of the Greenwich fault is almost entirely of unevolved, modem composition. Carbon-14 modelling suggests that Chalk groundwater in the S basin is generally less than 10000 a old while that in the north is generally between 10000 and 25000 a old. The presence of3H in concentrations of up to 7 TU in groundwater which yields ages of several 1000 a, however, indicates that mechanisms exist for the rapid introduction of recent groundwater to the confined aquifer. Results of palaeorecharge temperature determinations using δ2H, δ180 and noble gas analytical results suggest that significant Devensian recharge did indeed occur in the aquifer.A model of the development of the Chalk recognizes that it is a classic dual porosity aquifer in which groundwater flow occurs predominantly in the fracture system. The upper 50 m of the aquifer was flushed with fresh water during the 2–3 × 106 a of the Quaternary and therefore meteoric water largely replaced the Tertiary and Cretaceous marine water that previously saturated the system. Most processes which control the chemistry of the groundwater occur in the matrix where the surface area is exceptionally high. Although fracture flow dominates the flow regime, diffusion from the matrix into the fracture porosity controls the chemistry of Chalk groundwater. 相似文献