Bayesian updating revisited     

Allan D. Woodbury 《Mathematical Geosciences》1989,21(3):285-308

Bayesian updating methods provide an alternate philosophy to the characterization of the input variables of a stochastic mathematical model. Here, a priori values of statistical parameters are assumed on subjective grounds or by analysis of a data base from a geologically similar area. As measurements become available during site investigations, updated estimates of parameters characterizing spatial variability are generated. However, in solving the traditional updating equations, an updated covariance matrix may be generated that is not positive-definite, particularly when observed data errors are small. In addition, measurements may indicate that initial estimates of the statistical parameters are poor. The traditional procedure does not have a facility to revise the parameter estimates before the update is carried out. alternatively, Bayesian updating can be viewed as a linear inverse problem that minimizes a weighted combination of solution simplicity and data misfit. Depending on the weight given to the a priori information, a different solution is generated. A Bayesian updating procedure for log-conductivity interpolation that uses a singular value decomposition (SVD) is presented. An efficient and stable algorithm is outlined that computes the updated log-conductivity field and the a posteriori covariance of the estimated values (estimation errors). In addition, an information density matrix is constructed that indicates how well predicted data match observations. Analysis of this matrix indicates the relative importance of the observed data. The SVD updating procedure is used to interpolate the log-conductivity fields of a series of hypothetical aquifers to demonstrate pitfalls and possibilities of the method.  相似文献   

Use of an Annelid Pollution Index for monitoring a moderately polluted littoral zone     

G  rard Bellan  Gaston Desrosiers  Allan Willsie 《Marine pollution bulletin》1988,19(12):662-665

After two sampling surveys, in 1974–1975 and 1984, and with the use of an Annelid Pollution Index, the existence of a degraded Cystoseira stricta community has been established. The community studied was present on superficial rocky substrates on the French Mediterranean coast in unpolluted or moderately polluted zones although, for the latter, pollution reduction measures had been put into effect. The most polluted station in 1984 was close to the effluent of a coastal village sewage treatment plant.  相似文献   

Introduction     

Allan R. Chivas 《Journal of Paleolimnology》1994,12(3):189-189

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Book reviews     

Kacper R. Rybicki  Brian J. Mitchell  Louise H. Kellogg  Andrea Borgia  Allan M. Rubin  Douglas R. Schmitt  Douglas R. Schmitt  Edo Nyland  Zbigniew Fajklewicz  David Stevenson  Janusz L. Borkowski 《Pure and Applied Geophysics》1990,133(1):179-180

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Geochemical characteristics of Cocos Plate seamount lavas     

James F. Allan  Rodey Batiza  Richard O. Sack 《Contributions to Mineralogy and Petrology》1994,116(1-2):47-61

A wide compositional continuum of basalts has been erupted from near-ridge seamounts constructed on the Cocos Plate between the Clipperton and Orozco Francture Zones. They range from highly evolved to moderately primitive (3.0–7.8% MgO), LREE-enriched alkali basalts, to moderately evolved to near-primary (5.2–9.5% MgO) tholeiites indistinguishable from N-type MORB. The data set of 159 quench glass analyses exhibits a remarkably consistent variation in both major and trace element composition that is keyed to variations in (La/Sm). Modeling of potential liquid lines of descent at pressures ranging from 1 bar to 8 kbar shows that this covariation is partially due to systematic differences in liquid lines of descent, where the alkaline lavas have undergone substantially more high pressure clinopyroxene fractionation and substantially less low pressure plagioclase fractionation than the tholeiites. In addition, systematic variation in the composition of the more primitive glasses indicates that they were derived from mixing of discrete enriched and depleted melts in the heterogenous seamount mantle source at pressures of 8–10 kbar and greater, and that clinopyroxene may be a residual phase during partial melting. These results show that porous media flow in the seamount mantle source is minor and that melt transport is accomplished primarily through cracking and diking. This study supports suggestions that the general homogeneity of basalt along the EPR is due to mixing in sub-axial magma chambers and mush zones, with additional mixing during partial mantle melting and melt segregation.  相似文献   

Atmospheric boundary-layer measurements of concentration statistics from isolated and multiple sources     

B. L. Sawford  C. C. Frost  T. C. Allan 《Boundary-Layer Meteorology》1985,31(3):249-268

Atmospheric tracer dispersion experiments have been carried out to measure the statistical characteristics (variance, frequency distribution, spectrum) of the concentration downwind of a pair of partly overlapping plumes. By releasing different tracer substances from each source, it was possible to identify the contributions of the two sources at a given measurement point, both separately and jointly, and thus to compare and interpret the joint statistics in terms of those from the individual sources.Statistics for the individual sources agree well with, and support, existing wind tunnel and theoretical results. Nondimensionalization of the data using the mean concentration and the lateral width of the plume as concentration and length scales successfully removes much of the variation due to changes in atmospheric and surface conditions.Measurements of the correlation between the concentration contributions from separated sources are consistent with recent wind tunnel measurements. Entirely new measurements of the frequency distribution of the combined concentration from a pair of sources show that in many situations, high concentrations relative to the mean occur much less frequently than for an isolated source. Generally the extent of the reduction in frequency of occurrence is inversely related to the degree of correlation between concentrations from the two sources.  相似文献   

Lamprophyric lavas in the Colima graben,SW Mexico   总被引：2，自引：3，他引：2  

J. F. Allan  I. S. E. Carmichael 《Contributions to Mineralogy and Petrology》1984,88(3):203-216

The Colima graben, located in SW Mexico, is one of three grabens which intersect about 50 km SSW of Guadalajara, forming a triple junction. The 90 km long, 20–60 km wide Colima graben represents a N-S rift of the E-W trending Mexican Volcanic Belt. Since the Early Pliocene, the Colima graben has served as a locus for the eruption of alkaline lavas, the most recent of which are basanites and minettes erupted from Late Pleistocene cinder cones (Luhr and Carmichael 1981). In this paper, we report on older alkaline lavas which crop out in the graben's walls. These rocks include phlogopite- and hornblende-bearing lamprophyres, a phlogopite-kalsilite-ankaratrite, and high-K andesites. These lavas crop out throughout the Colima graben area, and are intimately associated with calc-alkaline lavas in the field. Compared to these, the alkaline rocks are strikingly enriched in the incompatible elements, particularly Ba, Sr, P, and the LREE. Unlike the younger Late Pleistocene alkaline cinder cone lavas, most of the graben wall lamprophyres and the high-K andesites represent magmas that appear to have undergone significant evolution since their generation, including fractionation, crustal contamination, and possible magma mixing. Least-squares modeling indicates that the cinder cone minettes represent reasonable parental magmas for the graben lamprophyres. The occurrence of these alkaline lavas in an active calc-alkaline volcanic arc is unusual, and we suggest that they are a manifestation of the rifting processes which produced the Colima graben.  相似文献   

Uplift and submarine formation of some Melanesian porphyry copper deposits: Stable isotope evidence     

Allan R. Chivas  James R. O&#x;Neil  George Katchan 《Earth and Planetary Science Letters》1984,68(2):326-334

Hydrogen and oxygen isotope analyses of sericites and kaolinites from four young porphyry copper deposits (Ok Tedi (1.2 Ma) and Yandera (6.5 Ma), Papua New Guinea; Koloula (1.5 Ma), Solomon Islands; and Waisoi (<5 Ma), Fiji) indicate that the fluids from which these minerals precipitated were of mixed magmatic and non-magmatic sources. The non-magmatic component of the fluid from the island arc deposits (Koloula, Waisoi) was ocean water.For Ok Tedi, the non-magmatic component was a meteoric water with an isotopic composition different from that of the present meteoric water in the region. The isotopic signature of the former meteoric water is consistent with a surface elevation of 200 m a.s.l. or less at the time of mineralization. The deposit was later exposed and supergene kaolinitization commenced at approximately 1200 m a.s.l. Uplift and erosion has continued to the present at which time the elevation of the exposed deposit is 1800 m a.s.l. This rate of uplift is consistent with that known from other geological evidence. If the rate of uplift were approximately constant during the last 1.2 Ma, the age of supergene enrichment can be dated at approximately 0.4 Ma B.P.Similarly, influx of meteoric water at Yandera occurred when the ground surface above the deposit was at an elevation of approximately 600 m a.s.l. The deposit's present elevation is 1600 m a.s.l. In this case a total uplift of approximately 2.2 km is indicated, with removal of 1.2 km of overburden by erosion.  相似文献   

Oxygen isotope fractionation and disequilibrium displayed by some granulite facies rocks from the Fraser Range,Western Australia     

Allan F. Wilson  Ajoy K. Baksi 《Geochimica et cosmochimica acta》1984,48(3):423-432

The granulites of the Fraser Range are assumed to have formed in a carbon-rich fluid, and are generally devoid of hornblende, and lack obvious hydrous retrograde features. In these granulites, pyroxene, garnet, plagioclase and quartz are the minerals most likely to retain the oxygen isotope ratios fixed at an early stage of initial granulite metamorphism. Temperature estimates using these minerals commonly suggest that oxygen isotopic exchange ceased in the range 600 to 680°C. The peak metamorphic temperature was probably ～ 850°C as based on the stability fields of the coexisting minerals and some cation temperatures from coexisting pyroxenes in these rocks. Ilmenite may be slightly out of isotopic equilibrium with the other minerals. Thus, grains of quartz, feldspar, pyroxene and ilmenite have suffered considerable oxygen isotopic exchange during the retrogressive phase of the metamorphism, in spite of the fact that very little water was present in these granulites. The observed deviation from the peak metamorphic temperatures can be explained by essentially closed system solid-state diffusion (on at least a scale of centimetres) during slow cooling of the rocks from ~850 to 650°C, followed by more rapid cooling down to ～ 300°C. Such an explanation is not at variance with the radiometric data available for rocks from the area, which suggest that the latter phase could have involved uplift rates of ?0.5 mm/yr for a period of about 40 Ma. Wholerock δ¹⁸O values on non-quartzose mafic granulites, about 7.2%., fall within the range of basalts affected by seafloor weathering.  相似文献   

Macroinvertebrate associations on the egg masses of the sea hare,Aplysia brasiliana rang (Gastropoda: Opisthobranchia)     

J. R. Rey  Allan W. Stoner 《Estuaries and Coasts》1984,7(2):158-164

We examined the assemblage of macroinvertebrates that inhabits the egg masses of the sea hareAplysia brasiliana Rang. A total of 3,721 individuals belonging to 31 invertebrate species was recovered from 107 egg masses collected in the Indian River Lagoon in east-central Florida. The egg mass associates appeared to be a subset of the surrounding faunal assemblage. Amphipods, polychaetes, and molluscs comprised the majority of the egg mass fauna. Of these, approximately 10 species were abundant, and were collected with high frequency in the egg masses examined. Association analysis of the distribution patterns of the more common species indicates that only positive first order effects and second order interactions were potentially important in this assemblage.  相似文献