Azimuth-dependent AVO in reservoirs containing non-orthogonal fracture sets   总被引：1，自引：0，他引：1  

Colin M. Sayers  Simon Dean 《Geophysical Prospecting》2001,49(1):100-106

Azimuthal anisotropy in rocks can result from the presence of one or more sets of partially aligned fractures with orientations determined by the stress history of the rock. The symmetry of a rock with horizontal bedding that contains two or more non-orthogonal sets of vertical fractures may be approximated as monoclinic with a horizontal plane of mirror symmetry. For offsets that are small compared with the depth of the reflector, the azimuthal variation in P-wave AVO gradient for such a medium varies with azimuth as     where φ is the azimuth measured with respect to the fast polarization direction for a vertically polarized shear wave. φ ₂ depends on both the normal compliance B _N and the shear compliance B _T of the fractures and may differ from zero if B _N B _T varies significantly between fracture sets. If B _N B _T is the same for all fractures,     and the principal axes of the azimuthal variation in P-wave AVO for fixed offset are determined by the polarization directions of a vertically propagating shear wave. At larger offsets, terms in     and     are required to describe the azimuthal variation in AVO accurately. φ ₄ and φ ₆ also depend on B _N B _T. For gas-filled open fractures     but a lower value of B _N B _T may result from the presence of a fluid with non-zero bulk modulus.  相似文献   

Submarine canyons and Deep-Sea Fans: J. H. McD. Whitaker,Editor. Benchmark Papers in Geology,Vol. 24, 1976, Dowden,Hutchinson and Ross,Stroudsburg, Pa., 460 pp     

Dean A. McManus 《Quaternary Research》1977,7(1):147

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The abundance of estuarine larval and juvenile fish in a South Carolina intertidal creek     

Earl L. Bozeman  John Mark Dean 《Estuaries and Coasts》1980,3(2):89-97

The fall and winter population of larval fish in a small intertidal creek was measured. The creek was blocked at high tide, and the immature fish were captured in a channel net designed for consistent quantitative sampling as they left with the ebbing tide. A total of 573,739 individuals with a biomass (preserved wet weight) of 66.1 kg were captured during the eight month sampling period (October 1974–May 1975). Twelve families, 13 genera, and 16 species were represented, with five species comprising 99.3% of the fish captured. The five species were:Leiostomus xanthurus (53.5%),Lagodon rhomboides (31.7%),Brevoortia tyrannus (11.9%),Micropogon undulatus (1.7%), andMyrophis punctatus (0.5%). The net was efficient, the catch was seasonal, and the greatest larval abundance occurred in February and March.  相似文献   

Temporal variation in the utilization of an intertidal creek by the bay anchovy (Anchoa mitchilli)     

Richard R. Reis  John Mark Dean 《Estuaries and Coasts》1981,4(1):16-23

A brackish-water, intertidal creek was sampled 19 times during the summer of 1976. Samples were analyzed to determine occurrence, abundance, and diversity of fish species present and to determine patterns of daily fish movement and utilization of intertidal creeks in an old rice field. Samples were collected from the primary station on the ebbing tide with a channel net. Three secondary stations were each sampled twice for comparative results and total biomass and average length per species calculated for each sample. We collected 125,579 individuals with a total biomass of 11.7 kg which represented 23 families and 37 species. Anchoa mitchilli was the dominant species and comprised 96.3% of the total numbers of individuals caught. The next two most abundant fish, Menidia menidia and Fundulus heteroclitus, represented 2.5% and 0.4% of the total numbers caught. The data from the nineteen sample collections were ordered by time of day and the resultant time series sequence of collections simulated a sample collection taken about once every 1.5 hours over 24 hours. A pattern of occurrence was noted for A. mitchilli as increased fish numbers occurred when the creek flooded during the daylight hours and there were significantly reduced numbers when the creek flooded during the early evening or at night. A relationship between light intensity, feeding, and predator avoidance is proposed to explain the creek loading pattern of A. mitchilli.  相似文献   

Spatial Variability of Turbulent Fluxes in the Roughness Sublayer of an Even-Aged Pine Forest   总被引：1，自引：1，他引：0  

Gabriel Katul  Cheng-I Hsieh  David Bowling  Kenneth Clark  Narasinha Shurpali  Andrew Turnipseed  John Albertson  Kevin Tu  Dave Hollinger  Bob Evans  Brian Offerle  Dean Anderson  David Ellsworth  Chris Vogel  Ram Oren 《Boundary-Layer Meteorology》1999,93(1):1-28

The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (_u, _w) and temperature (_T) are more planar homogeneous than their vertical flux of momentum (u_* ²) and sensible heat (H) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO₂ and water vapour. While the spatial variability in fluxes was significant (>15 %), this unique data set confirmed that single tower measurements represent the canonical structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the moving-equilibrium hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u_*, especially when u_* was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (I_w) and the arrival frequency of organized structures (/h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed.  相似文献   

Vibration tests and analysis of a model arch dam     

Jimmy P. Balsara  C. Dean Norman 《地震工程与结构动力学》1975,4(2):163-177

Vibration tests were conducted on a 1/24-scale model of the North Fork Dam, a double-curvature arch dam, to determine natural frequencies, mode shapes and hydrodynamic pressures. The mode shapes and natural frequencies were determined from tests using two vibrators mounted on the crest of the dam. Hydrodynamic pressures at the dam/reservoir interface were determined from tests in which the vibrator was attached to the downstream foundation of the dam. The hydrodynamic pressures calculated using Westergaard's theory and a theory for arch dams developed by Perumalswami and Kar accurately predicted the measured pressure at frequencies below the first mode frequency of the dam. The differences in the two theories were insignificant. The Structural Analysis Program (SAP), a linear three-dimensional (3-D) finite element code, was used to compute mode shapes and frequencies for the dam with its base fixed and with a foundation. Numerical solution schemes used in the finite element analysis consisted of a Ritz analysis and a subspace iteration method. Calculations were conducted for both full and empty reservoir conditions. The accuracy of the Ritz analysis improved considerably as more nodes in flexible regions of the dam were loaded. However, the lowest eigenvalues were computed using the subspace iteration method. For the full reservoir, the natural frequencies decreased by 20-30 per cent when the foundation was included in the finite element model. The difference was less when the reservoir was empty. The calculations using the subspace iteration scheme and including the foundation agreed closely with experimental mode shapes and corresponding natural frequencies.  相似文献   

Time delays in large and small loop thermal models for hard X-ray bursts     

Dean F. Smith  Lorant A. Muth 《Solar physics》1984,90(1):83-96

The time histories of the emission at 10, 30, and 100 keV averaged over the loop from small and large loop thermal models of hard X-ray emission are studied. The small (15000 km) loop cases show a characteristic delay in the peak of the 100 keV emission relative to the 30 keV emission of about 1.5 s which should be detectable. The large (47 000 km) loop cases show no delay, but in the case of a continuous energy input, the 30 keV emission has a peak at 9.5 s whereas the 100 keV emission rises monotonically. Again, this difference should be detectable to the extent that it is not washed out by a dominant beam or escaping tail component which is not considered in this paper. A large loop case where only classical and saturated heat conduction are allowed is considered. The 30 keV emission has a peak at 7.5 s whereas the 100 keV emission rises monotonically. The peak temperature reached is 8 × 10⁷ K and the probability of finding examples in the data uncontaminated by a dominant beam or escaping tail component should be considerably higher than in the cases with higher rates of energy input.  相似文献   

A 1500-year record of climatic and environmental change in ElkLake, Clearwater County, Minnesota II: geochemistry, mineralogy, and stableisotopes     

Walter Dean 《Journal of Paleolimnology》2002,27(3):301-319

Most of the sediment components that have accumulated in ElkLake, Clearwater County, northwestern Minnesota, over the past 1500 years areauthigenic or biogenic (CaCO₃, biogenic SiO₂, organicmatter, iron and manganese oxyhydroxides, and iron phosphate) and are deliveredto the sediment–water interface on a seasonal schedule where they are preservedas distinct annual laminae (varves). The annual biogeochemical cycles of thesecomponents are causally linked through the carbon pump, and are recapitulatedin longer-term cycles, most prominently with a periodicity of about 400 years.Organic carbon is fixed in the epilimnion by photosynthetic removal ofCO₂, which also increases the pH, triggering the precipitation ofCaCO₃. The respiration and degradation of fixed organic carbon inthe hypolimnion consumes dissolved oxygen, produces CO₂, and lowersthe pH so that the hypolimnion becomes anoxic and undersaturated with respectto CaCO₃ during the summer. Some of the CaCO₃ produced inthe epilimnion is dissolved in the anoxic, lower pH hypolimnion and sediments.The amount of CaCO₃ that is ultimately incorporated into thesediments is a function of how much is produced in the epilimnion and how muchis consumed in the hypolimnion and the sediments. Iron, manganese, andphosphate accumulate in the anoxic hypolimnion throughout the summer.Sediment-trap studies show that at fall overturn, when iron-, manganese-, andphosphate-rich bottom waters mix with carbonate- and oxygen-rich surfacewaters, precipitation of iron and manganese oxyhydroxides, iron phosphate, andmanganese carbonate begins and continues into the winter months.Detrital clastic material in the sediments of Elk Lake depositedover the last 1500 years is a minor component (<10% by weight) that ismostly wind-borne (eolian). Detailed analyses of the last 1500 years of the ElkLake sediment record show distinct cycles in eolian clastic variables (e.g.aluminum, sodium, potassium, titanium, and quartz), with a periodicity of about400 years. The 400-yr cycle in eolian clastic material does not correspond tothe 400-yr cycles in redox-sensitive authigenic components, suggesting that theclastic component is responding to external forcing (wind) whereas theauthigenic components are responding to internal forcing (productivity),although both may ultimately be forced by climate change. Variations in theoxygen and carbon isotopic composition of CaCO₃ are small but appearto reflect small variations in ground water influx that are also driven byexternal forcing.  相似文献   

Thermal precursors in satellite images of the 1999 eruption of Shishaldin Volcano     

Jonathan Dehn  Kenneson G. Dean  Kevin Engle  Pavel Izbekov 《Bulletin of Volcanology》2002,64(8):525-534

Shishaldin Volcano, Unimak Island Alaska, began showing signs of thermal unrest in satellite images on 9 February 1999. A thermal anomaly and small steam plume were detected at the summit of the volcano in short-wave thermal infrared AVHRR (advanced very high resolution radiometer) satellite data. This was followed by over 2 months of changes in the observed thermal character of the volcano. Initially, the thermal anomaly was only visible when the satellite passed nearly directly over the volcano, suggesting a hot source deep in the central crater obscured from more oblique satellite passes. The "zenith angle" needed to see the anomaly increased with time, presumably as the thermal source rose within the conduit. Based on this change, an ascent rate of ca. 14 m per day for the thermal source was estimated, until it reached the summit on around 21 March. It is thought that Strombolian activity began around this time. The precursory activity culminated in a sub-Plinian eruption on 19 April, ejecting ash to over 45,000 ft. (13,700 m). The thermal energy output through the precursory period was calculated based on geometric constraints unique to Shishaldin. These calculations show fluctuations that can be tied to changes in the eruptive character inferred from seismic records and later geologic studies. The remote location of this volcano made satellite images a necessary observation tool for this eruption. To date, this is the longest thermal precursory activity preceding a sub-Plinian eruption recorded by satellite images in the region. This type of thermal monitoring of remote volcanoes is central in the efforts of the Alaska Volcano Observatory to provide timely warnings of volcanic eruption, and mitigate their associated hazards to air-traffic and local residents.  相似文献   

The Significance of Ground Water to the Accumulation of Iron and Manganese in the Sediments of Two Hydrologically Distinct Lakes in North-Central Minnesota: A Geological Perspective     

Walter E. Dean  Brian P. Neff  Donald O. Rosenberry  Thomas C. Winter  Renee Parkhurst 《Ground water》2003,41(7):951-963

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