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131.
Melt–water Accumulation on the Surface of the Greenland Ice Sheet: Effect on Albedo and Mass Balance
Wouter Greuell 《Geografiska Annaler: Series A, Physical Geography》2000,82(4):489-498
Satellite–derived albedo maps of the western part of the Greenland ice sheet (between 64.5 and 70.5 ∘ N) reveal a north–south extending zone with relatively low albedos at some distance from the ice margin. In the literature it has been hypothesized that this "dark zone" is due to a local maximum in melt–water accumulation on the ice–covered surface. A plausible explanation for this maximum in melt–water accumulation is thatrelative to the situation within the "dark zone", melt–water accumulation is reduced at higher elevations by a smaller melt–water production rate whereas runoff occurs more easily at lower elevations where slopes are generally steeper. For the present paper AVHRR images from eight years (1990–1997) were analysed. The following indications confirming the "melt–water accumulation hypothesis" were found: (1) there is a significant correlation between the annual mean albedo lowering within the "dark zone" and the annual amount of melt as inferred from local mass–balance measurements; and (2) within each summer season the albedo lowering within the "dark zone" seems to respond to the melt–water production rate as inferred from local temperature measurements. The effect of melt–water accumulation on the albedo implies a positive feedback between the albedo and the amount of melt. It is estimated that approximately 40% of the interannual mass–balance variations in the "dark zone" are due to this feedback. 相似文献
132.
在科尔沁沙地选择不同类型沙地优势植物,测定了其在自然脱水、高温处理及复水后叶可溶性糖、可溶性蛋白质和脯氨酸含量的变化。结果表明,在胁迫过程中流动沙地上的沙米、欧亚旋覆花,叶片内可溶性糖积累,尤其是脯氨酸积累较高,处理12h较处理前分别增加了92.87%、10.28倍,可溶性蛋白质含量下降,在胁迫处理后植株枯死;半固定沙地上的差不嘎蒿可溶性糖增加41.57%、脯氨酸含量增加8.95倍、可溶性蛋白质下降15.04%,在两种胁迫处理后依然存活并恢复生长;固定沙地的白草和狗尾草可溶性糖增加89.82%和89.43%,脯氨酸增加2.49倍和2.53倍、可溶性蛋白质增加。因此,如果把胁迫中叶内积累的脯氨酸与胁迫后植株的存活结合起来看,两种胁迫中差不嘎蒿、狗尾草、白草体内积累的脯氨酸起保护性反应,而沙米、欧亚旋覆花的则是受害症状。 相似文献
133.
The coupled heat-fluid-stress problem of circular wellbore or spherical cavity subjected to a constant temperature change and a constant fluid flow rate is considered. Transient analytical solutions for temperature, pore pressure and stress are developed by coupling conductive heat transfer with Darcy fluid flow in a poroelastic medium. They are applicable to low permeability porous media suitable for liquid-waste disposal and also simulating reservoir for enhanced oil recovery, where conduction dominates the heat transfer process. A full range of solutions is presented showing separately the effects of temperature and fluid flow on pore pressure and stress development. It is shown that injection of warm fluid can be used to restrict fracture development around wellbores and cavities and generally to optimize a fluid injection operation. Both the limitations of the solutions and the convective flow effect are addressed. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
134.
Andrei Petriaev 《寒旱区科学》2015,7(4):348-353
The article presents the field measurement results of the stress states of roadbed thawed soil subgrade during the passage of trains. The dependences of the vertical and horizontal stresses on the velocity of the rolling stock motion, the axle load, and the distance from the sleeper sole have been obtained. 相似文献
135.
Analyses of bathymetry, gravity and seismic reflection data of the diffusive plate boundary in the central Indian Ocean reveal
a new kind of deformed structure besides the well-reported structures of long-wavelength anticlinal basement rises and high-angle
reverse faults. The structure (basement trough) has a length of about 150 km and deepens by up to 1 km from its regional trend
(northward dipping). The basement trough includes a rise at its center with a height of about 1.5km. The rise is about 10
km wide with rounded upper surface and bounded by vertical faults. A broad freeair gravity low of about 20 mGal and a local
high of 8 mGal in its center are associated with the identified basement trough and rise structure respectively. Seismic results
reveal that the horizontal crustal compression prevailing in the diffusive plate boundary might have formed the basement trough
possibly in early Pliocene time. Differential loading stresses have been generated from unequal crust/sediment thickness on
lower crustal and upper mantle rocks. A thin semi-ductile serpentinite layer existing near the base of the crust that is interpreted
to have been formed at mid-ocean ridge and become part of the lithosphere, may have responded to the downward loading stresses
generated by the sediments and crustal rocks to inject the serpentinites into the overlying strata to form a classic diapiric
structure. 相似文献
136.
S. Vinciguerra C. Trovato P.G. Meredith P.M. Benson C. Troise G. De Natale 《Pure and Applied Geophysics》2006,163(10):2205-2221
We report laboratory measurements of P- and S-wave velocities on samples of tuff from Campi Flegrei (Italy), and a new tomographic
velocity map of the Campi Flegrei caldera. Laboratory measurements were made in a hydrostatic pressure vessel during both
increasing and decreasing effective pressure cycles. Selected samples were also thermally stressed at temperatures up to 600°C
to induce thermal crack damage. Acoustic emission output was recorded throughout each thermal stressing experiment, and velocities
were measured after thermal stressing. Laboratory P- and S-wave velocities are initially low for the tuff, which has an initial
porosity of ~45%, but both increase by between 25 and 50% over the effective pressure range of 5 to 80 MPa, corresponding
to a decrease of porosity of ~70%. Marked velocity hysteresis, due to inelastic damage processes, is also observed in samples
subjected to a pressurization-depressurization cycle. Tomographic seismic velocity distributions obtained from field recordings
are in general agreement with the laboratory measurements. Integration of the laboratory ultrasonic and seismic tomography
data indicates that the tuffs of the Campi Flegrei caldera can be water or gas saturated, and shows that inelastic pore collapse
and cracking produced by mechanical and thermal stress can significantly change the velocity properties of Campi Flegrei tuffs
at depth. These changes need to be taken into account in accurately interpreting the crustal structure from tomographic data. 相似文献
137.
Roman Teisseyre 《Acta Geophysica》2006,54(3):225-238
We present a relation between stress moments and antisymmetric part of stresses and the related constitutive law joining those
stresses with the particle/point rotations. Correspondence of the asymmetric continuum theory to the micromorphic theory is
considered. An extension of the asymmetric continuum theory for the case of 2D anisotropy for antisymmetric stresses leads
us to the problems of friction anisotropy and fracture pattern. 相似文献
138.
Mechanism of wave–seabed interaction has been extensively studied by coastal geotechnical engineers in recent years. Numerous poro-elastic models have been proposed to investigate the mechanism of wave propagation on a seabed in the past. The existing poro-elastic models include drained model, consolidation model, Coulomb-damping model, and full dynamic model. However, to date, the difference between the existing models is unclear. In this paper, the fully dynamic poro-elastic model for the wave–seabed interaction will be derived first. Then, the existing models will be reduced from the proposed fully dynamic model. Based on the numerical comparisons, the applicable range of each model is also clarified for the engineering practice. 相似文献
139.
An Integrated Approach to Fatigue Life Prediction of Whole System for Offshore Platforms 总被引:3,自引:0,他引:3
FANG Huacan 《中国海洋工程》2001,(2):177-184
The failure of one or even more components usually does not lead to the collapse of the whole structure. Most of the analysis of fatigue is centered on only a single component which the researchers are interested in or much attention should be paid to. However, the collapse of a structure is the result of failure of a series of components in a specific order or path. This paper proposes an integrated approach to fatigue life prediction of whole structural system for offshore platforms, mainly describing the basic principles and prediction method. A method is presented for determining the failure path of the whole structure system and calculating the fatigue life in the determined failure path. The corresponding final collapse criteria for the whole structure system are discussed. A simple method of equivalent fatigue stress range calculation and a mathematical model of structural component fatigue life estimation in consideration of sea wave and sea ice loads are provided. As an application of the propo 相似文献
140.
We characterized natural fractures and in-situ stresses for exploration and prospect evaluation in nine periclinal structural traps, in the Eastern Province of Saudi Arabia, where several major gas discoveries were made in the deeply buried, Permian–Triassic Khuff Formation. Borehole image logs, oriented cores, seismic, gravity-magnetic data, and dynamic observations were used in the study. Two fracture systems were identified: a younger, major system, which enhances reservoir permeability and an older, minor, fully mineralized system. The older system consists of subordinate northerly striking extensional mesofractures, including joints and faults, which are fully mineralized by anhydrite and calcite. This mineralization occurred during an early diagenetic-phase. This system acted as paleo-fluid conduits, facilitating the occlusion of matrix porosity and deteriorating the reservoir quality in the immediate vicinity of the fractures. The younger system is regionally dominant, and includes mesofractures with persistent strike ranging from NE–SW to ESE–WNW irrespective of local structure. These younger fractures are nearly parallel to the present day maximum horizontal in-situ stress and perpendicular to the minimum horizontal in-situ stress, which are dominated by the Zagros plate tectonics. The development of this system commenced during the convergence of the Arabian and Eurasian plates (Late Cretaceous to Cenozoic) and culminated during the continental collision. The fractures are predominantly extension joints and hybrid (extensional-shear) fractures, and were facilitated by increases in pore pressure due to the oil placement and the subsequent cracking of this oil into gas. Hydrocarbon migration into the Khuff reservoirs was crucial in slowing down diagenesis and preserving both fracture apertures and matrix porosity. Therefore, most of the fractures in this system tend to be partly mineralized, mainly by carbonates, and/or coated with hydrocarbons. These fractures show channel-type apertures that enhance permeability and productivity of the Khuff by up to two fold. The channel apertures can endure operational changes in reservoir pressure with little or no reduction of their permeability. Critically stressed open fractures have no major role. Geomechanical analyses show that they are estimated to occur under the upper limits of differential stresses, within the margin of error of stress estimates. The static and dynamic observations show the permeability and productivity enhancement follows mechanical layering patterns. Production and pressure profiles in individual wells indicate lack of vertical communication (seal breach) across the different reservoir units. Similar pre-production pressure and hydrocarbons across the Khuff reservoir units is the result of normalization over geological time. Hydrocarbon migration across the anhydrite seals happened via episodic paleoseismic pumping along faults with no sufficient vertical offset to permanently breach the reservoir seals. 相似文献