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1.
A theory which describes the constant f-plane flow of a steady inviscid baroclinic boundary current over a continental margin with a bathymetry that varies slowly in the alongshore but rapidly in the offshore directions is developed in the parameter regime (LD/L)2 ≤ Ro 1, where LD is the internal deformation radius, L the horizontal length scale, and Ro the Rossby number. To lowest order in the Rossby number the flow is along isobaths with speed qo = Vu(h,z)|Vh|/α, where Vu(h,z) is the upstream speed, α the upstream bottom slope at depth h, and Vh the bottom slope downstream at depth h. The lowest order flow produces a variation in the vertical component of relative vorticity along the isobath as the magnitude and direction of Vh vary in the downstream direction. The variation of vorticity requires a vertical as well as a cross-isobath flow at first order in the Rossby number. The first order vertical velocity is computed from the vorticity equation in terms of upstream conditions and downstream variations of the bathymetry. The density, pressure, and cross-isobath flow at first order in the Rossby number are then calculated. It is shown that in the cyclonic region of current (d/dh(Vu/α) > 0), if the isobaths diverge in the downstream direction ((∂/∂s)|Vh| < 0), then upwelling and onshore flow occur. The theory is applied to the northeastern Florida shelf to explain bottom temperature observations.  相似文献   

2.
The results of a series of high-resolution numerical experiments are used to test and compare three nonlinear models for high-concentration-gradient dispersion. Gravity stable miscible displacement is considered. The first model, introduced by Hassanizadeh, is a modification of Fick’s law which involves a second-order term in the dispersive flux equation and an additional dispersion parameter β. The numerical experiments confirm the dependency of β on the flow rate. In addition, a dependency on travelled distance is observed. The model can successfully be applied to nearly homogeneous media (σ2 = 0.1), but additional fitting is required for more heterogeneous media.The second and third models are based on homogenization of the local scale equations describing density-dependent transport. Egorov considers media that are heterogeneous on the Darcy scale, whereas Demidov starts at the pore-scale level. Both approaches result in a macroscopic balance equation in which the dispersion coefficient is a function of the dimensionless density gradient. In addition, an expression for the concentration variance is derived. For small σ2, Egorov’s model predictions are in satisfactory agreement with the numerical experiments without the introduction of any new parameters. Demidov’s model involves an additional fitting parameter, but can be applied to more heterogeneous media as well.  相似文献   

3.
The Long Valley Exploratory Well, at the center of the Resurgent Dome of Long Valley caldera, penetrated pre-caldera basement rocks at a depth of 2101.72–2313.0 m, beneath the caldera-forming Bishop Tuff and post-caldera Early Rhyolite. The basement rocks contain prominent quartzites, with ubiquitous milky white quartz veins (with minor calcite and pyrite) and fractures of varied orientation and geometry. The other members of the basement sequence are very fine-grained quartz-rich graphitic pelites with calcite veins, spotted hornfels, and shallow intrusive rocks. Previous studies established the presence of a post-caldera, paleohydrothermal system (500–100 ka) to a depth of 2000 m that affected the Bishop Tuff and a recent (40 ka to present) hydrothermal system at shallow depth (<1 km). The deeper extent of these hydrothermal activities is established in this paper by a detailed oxygen isotope analysis of the drill core samples. 238 analyses of δ18O in 50 quartz veins within the 163.57 m depth interval of basement rocks reveal extreme heterogeneity in δ18O values (8–19.5‰). Majorities of the 84 bulk analyses of quartzites show variation of δ18O within a narrow range of 14–16‰. However, certain samples of these quartzites near the contacts with veins and fractures exhibit sharp drops in δ18O. The interbedded pelitic rocks and spotted hornfels have whole-rock δ18O ranging from 2.2 to 11.8‰. Clear, euhedral vuggy quartz that partially fills earlier open fractures in both the quartzites and quartz veins, has distinctive δ18O, ranging between −3.2 and +8.4‰. Low values of δ18O are also found in the hydrothermal minerals and whole rocks adjacent to the thin veins, clearly indicating infiltration of meteoric water. Three distinct observed patterns of fractionation in δ18O between veins and host quartzites are analyzed with the principles of mass balance, equilibrium oxygen isotope fractionation in closed system, and kinetically controlled oxygen isotope exchange in an open system. This analysis suggests that the early quartz veins formed due to a magmatic-hydrothermal activity with no influx of external water once the system comprising the sedimentary envelope and a magmatic-hydrothermal fluid phase became closed. Two-stage isotopic exchange processes caused fractionation in the δ values that originally formed arrays with slope 1 in a δvein quartz–δhost quartzite space. Another array in the same space, with near zero slope was also formed due to variation in temperature, initial isotopic compositions of the quartzite sequence and the fluid phase. Variation in temperature was mostly in the range of 300–400°C giving Δ (=δvein quartz–δhost quartzite)≈−2.8 to +2.8. The δ18O of the fluid could range from −5 to +10; however a narrower range of +5 to +10 can explain the data. This episode of hydrothermal activity could take place either as a single pulse or in multiple pulses but each as a closed system. A later, fracture-controlled, meteoric water (δ18O−0.46 to −12.13) flow and interaction (at 250°C) is interpreted from the analysis of δ18O values of the coexisting quartz and calcite pairs and existence of markedly 18O-depleted pelitic horizons interbedded with 18O-enriched quartzite layers. Thus, the interpreted earlier magmatic-hydrothermal activity was overprinted by a later meteoric-hydrothermal activity that resulted in steep arrays of δ18O values in the δvein quartz–δhost quartzite space. Calculations show that the likely life span of the post-caldera, hydrothermal activity in the depth range of 2.1–2.3 km beneath Long Valley was 0.08–0.12 Ma. Diffusive ±advective transport of oxygen isotopes from fracture-channelized meteoric water to nearly impermeable wall rocks caused a lowering of δ18O values in the quartz over short distances and in calcites over greater distances. Thus, the hydrothermal activity appears pervasive even though the meteoric water flow was primarily controlled by fractures.  相似文献   

4.
A 23-m.y.-old, fossil meteoric-hydrothermal system in the Lake City caldera (11 × 14 km) has been mapped out by measuring δ 18O values of 300 rock and mineral samples. δ 18O varies systematically throughout the caldera, reaching values as low as −2. Great topographic relief, regional tilting, and variable degrees of erosion within the caldera all combine to give us a very complete section through the hydrothermal system, from the surface down to a depth of more than 2000 m. The initial δ 18O value of the caldera-fill Sunshine Peak Tuff was very uniform (+7.2 ± 0.1), making it easy to determine the exact amount of 18O depletion experienced by each sample during hydrothermal alteration. Also, we have excellent stratigraphic control on depths beneath the mid-Tertiary surface, quantitative information on mineralogical alteration products, and accurate data on the shape of the central resurgent intrusion, which was the principal ‘heat engine’ that drove the hydrothermal circulation. Major conclusions are: (1) Although pristine mid-Tertiary meteoric waters in this area had δ 18O −14, these fluids were 18O-shifted upward to about δ18O = −8 to −5 prior to entering the shallow convective system associated with the resurgent intrusive rocks. Although there was undoubtedly radial inflow toward the caldera from all directions, the highly fractured Eureka Graben, southwest of the caldera, was probably the principal source of recharge groundwater for the Lake City system. (2) Fluid flow within the caldera was dominated by three major categories of permeable zones: the porous megabreccia units (which dip outward from the resurgent dome), vertical fractures and faults related to resurgence, and the caldera ring fault itself. All of these zones exhibit marked 18O depletions, and they are also typically intensely mineralogically altered. (3) The resurgent intrusive stock and its contact metamorphic aureole of hornfels both experienced water/rock ratios lower than the permeable zones; however, they have similarly low δ 18O values because they were altered at higher temperatures. (4) Throughout the caldera, the δ 18O of Sunshine Peak Tuff decreases with increasing depth (about 6 per mil/km), indicative of a shallow thermal gradient, typical of a convective hydrothermal system. The near-surface portion of this gradient was controlled by the temperature drop associated with boiling in the uprising fluid. (5) Deeply circulating meteoric water rose along permeable ring fractures 3 to 5 km beneath the mid-Tertiary surface. These fluids were drawn into the shallow convective system through the lower, porous, megabreccia units. Near the resurgent intrusions, fluid flow was again directed upward where resurgence-related, near-vertical fractures intersect the megabreccia units.  相似文献   

5.
Water samples were collected from Baffin Bay and surrounding areas in order to evaluate this region as a potential source of Nd from old continental material to Atlantic water. The isotopic data ranged from εNd(0) = −9.0 to −26 with most of the data around εNd(0) = −20 compared with values of North Atlantic Deep Water (NADW) with εNd(0) = −13.5. The concentration of Nd in Baffin Bay waters was as high as 6 × 10−12 g/g compared with 2.5 × 10−12 g/g for NADW. The combination of low εNd and high Nd concentration indicates that Baffin Bay may be a significant source of Nd from very old crustal material. A simple box model was used to evaluate the contribution to the Nd budget of NADW and it was concluded that a substantial fraction of the Nd from ancient crustal sources that is required to maintain the isotopic composition of NADW could be supplied by Baffin Bay outflow.  相似文献   

6.
This study compares the Isis II satellite measurements of the electron density and temperature, the integral airglow intensity and volume emission rate at 630 nm in the SAR arc region, observed at dusk on 4 August, 1972, in the Southern Hemisphere, during the main phase of the geomagnetic storm. The model results were obtained using the time dependent one-dimensional mathematical model of the Earth’s ionosphere and plasmasphere (the IZMIRAN model). The major enhancement to the IZMIRAN model developed in this study to explain the two component 630 nm emission observed is the analytical yield spectrum approach to calculate the fluxes of precipitating electrons and the additional production rates of N+2, O+2, O+(4S), O+(2D), O(2P), and O+(2P) ions, and O(1D) in the SAR arc regions in the Northern and Southern Hemispheres. In order to bring the measured and modelled electron temperatures into agreement, the additional heating electron rate of 1.05 eV cm−3 s−1 was added in the energy balance equation of electrons at altitudes above 5000 km during the main phase of the geomagnetic storm. This additional heating electron rate determines the thermally excited 630 nm emission observed. The IZMIRAN model calculates a 630 nm integral intensity above 350 km of 4.1 kR and a total 630 nm integral intensity of 8.1 kR, values which are slightly lower compared to the observed 4.7 kR and 10.6 kR. We conclude that the 630 nm emission observed can be explained considering both the soft energy electron excited component and the thermally excited component. It is found that the inclusion of N2(v > 0) and O2(v > 0) in the calculations of the O+(4S) loss rate improves the agreement between the calculated Ne and the data on 4 August, 1972. The N2(v > 0) and O2(v > 0) effects are enough to explain the electron density depression in the SAR arc F-region and above F2 peak altitude. Our calculations show that the increase in the O+ + N2 rate factor due to the vibrationally excited nitrogen produces the 5–19% reductions in the calculated quiet daytime peak density and the 16–24% decrease in NmF2 in the SAR arc region. The increase in the O+ + N2 loss rate due to vibrationally excited O2 produces the 7–26% decrease in the calculated quiet daytime peak density and the 12–26% decrease in NmF2 in the SAR arc region. We evaluated the role of the electron cooling rates by low-lying electronic excitation of O2(a1δg) and O2(b1σg+), and rotational excitation of O2, and found that the effect of these cooling rates on Te can be considered negligible during the quiet and geomagnetic storm period 3–4 August, 1972. The energy exchange between electron and ion gases, the cooling rate in collisions of O(3P) with thermal electrons with excitation of O(1D), and the electron cooling rates by vibrational excitation of O2 and N2 are the largest cooling rates above 200 km in the SAR arc region on 4 August, 1972. The enhanced IZMIRAN model calculates also number densities of N2(B3πg+), N2(C3πu), and N2(A3σu+) at several vibrational levels, O(1S), and the volume emission rate and integral intensity at 557.7 nm in the region between 120 and 1000 km. We found from the model that the integral integral intensity at 557.7 nm is much less than the integral intensity at 630 nm.  相似文献   

7.
Cave air PCO2 at two Irish sites varied dramatically on daily to seasonal timescales, potentially affecting the timing of calcite deposition and consequently climate proxy records derived from stalagmites collected at the same sites. Temperature-dependent biochemical processes in the soil control CO2 production, resulting in high summer PCO2 values and low winter values at both sites. Large Large-amplitude, high-frequency variations superimposed on this seasonal cycle reflect cave air circulation. Here we model stalagmite growth rates, which are controlled partly by CO2 degassing rates from drip water, by considering both the seasonal and high-frequency cave air PCO2 variations. Modeled hourly growth rates for stalagmite CC-Bil from Crag Cave in SW Ireland reach maxima in late December (0.063 μm h− 1) and minima in late June/early July (0.033 μm h− 1). For well-mixed ‘diffuse flow’ cave drips such as those that feed CC-Bil, high summer cave air PCO2 depresses summer calcite deposition, while low winter PCO2 promotes degassing and enhances deposition rates. In stalagmites fed by well-mixed drips lacking seasonal variations in δ18O, integrated annual stalagmite calcite δ18O is unaffected; however, seasonality in cave air PCO2 may influence non-conservative geochemical climate proxies (e.g., δ13C, Sr/Ca). Stalagmites fed by ‘seasonal’ drips whose hydrochemical properties vary in response to seasonality may have higher growth rates in summer because soil air PCO2 may increase relative to cave air PCO2 due to higher soil temperatures. This in turn may bias stalagmite calcite δ18O records towards isotopically heavier summer drip water δ18O values, resulting in elevated calcite δ18O values compared to the ‘equilibrium’ values predicted by calcite–water isotope fractionation equations. Interpretations of stalagmite-based paleoclimate proxies should therefore consider the consequences of cave air PCO2 variability and the resulting intra-annual variability in calcite deposition rates.  相似文献   

8.
Emf measurements were made on the cell Pt|Fe,(Fe,Mg)xSi2O6,SiO2|(ZrO2)0.85(CaO)0.15|Fe,FeO|Pt at 1000 K. Using the present data, the standard free energy of formation of ferrosilite (compound FeSiO3), from the component oxides FeO and SiO2, is calculated to be −6.35 ± 0.80 kJ/mol. The activity-composition relation for pyroxene solid solution shows that it has a positive deviation from ideality at 1000 K. The present results are compared with the results of other workers.ΔGmix andΔGex are calculated and plotted againstNFeSiO3.  相似文献   

9.
Millstone Hill ionospheric storm time measurements of the electron density and temperature during the ionospheric storms (15-16 June 1965; 29–30 September 1969 and 17–18 August 1970) are compared with model results. The model of the Earth’s ionosphere and plasmasphere includes interhemispheric coupling, the H+, O+(4S), O+(2D), O+(2P), NO+, O+2 and N+2 ions, electrons, photoelectrons, the electron and ion temperature, vibrationally excited N2 and the components of thermospheric wind.In order to model the electron temperature at the time of the 16 June 1965 negative storm, the heating rate of the electron gas by photoelectrons in the energy balance equation was multiplied by the factors 5–30 at he altitude above 700 km for the period 4.50-12.00 LT, 16 June 1965. The [O]/[N2] MSIS-86 decrease and vibrationally excited N2 effects are enough to account for the electron density depressions at Millstone Hill during the three storms. The factor of 2 (for 27–30 September 1969 magnetic storm) and the & actor 2.7 (for 16–18 August 1970 magnetic storm) reduction in the daytime peak density due to enhanced vibrationally excited N2 is brought about by the increase in the O++N2 rate factor.  相似文献   

10.
The structure of macroporous or aggregated soils and fractured rocks is generally so complex that it is impractical to measure the geometry at the microscale (i.e., the size and the shape of soil aggregates or rock matrix blocks, and the myriad of fissures or fractures), and use such data in geometry-dependent macroscale flow and transport models. This paper analyzes a first-order type dual-porosity model which contains a geometry-dependent coefficient, β, in the mass transfer term to macroscopically represent the size and shape of soil or rock matrix blocks. As a reference, one- and two-dimensional geometry-based diffusion models were used to simulate mass transport into and out of porous blocks of defined shapes. Estimates for β were obtained analytically for four different matrix block geometries. Values for β were also calculated by directly matching analytical solutions of the diffusion models for a number of selected matrix block geometries to results obtained with the first-order model assuming standard boundary conditions. Direct matching improved previous results for cylindrical macropore geometries, especially when relatively small ratios between the outer soil mantle and the radius of the inner cylinder were used. Results of our analysis show that β is closely related to the ratio of the effective surface area available for mass transfer, and the soil matrix volume normalized by the effective characteristic length of the matrix system. Using values of β obtained by direct matching, an empirical function is derived to estimate macroscopic geometry coefficients from medium properties which in principle are measurable. The method permits independent estimates of β, thus allowing the dual-porosity approach eventually to be applied to media with complex and mixed types of structural geometry.  相似文献   

11.
The Boussinesq equation appears as the zeroth-order term in the shallow water flow expansion of the non-linear equation describing the flow of fluid in an unconfined aquifer. One-dimensional models based on the Boussinesq equation have been used to analyse tide-induced water table fluctuations in coastal aquifers. Previous analytical solutions for a sloping beach are based on the perturbation parameter, N=αcotβ (in which β is the beach slope, α is the amplitude parameter and is the shallow water parameter) and are limited to tan−1(α)βπ/2. In this paper, a new higher-order solution to the non-linear boundary value problem is derived. The results demonstrate the significant influence of the higher-order components and beach slope on the water table fluctuations. The relative difference between the linear solution and the present solution increases as and α increase, and reaches 7% of the linear solution.  相似文献   

12.
The morphology and composition of spinel in rapidly quenched Pu’u ’O’o vent and lava tube samples are described. These samples contain glass, olivine phenocrysts (3–5 vol.%) and microphenocrysts of spinel (0.05 vol.%). The spinel surrounded by glass occurs as idiomorphic octahedra 5–50 μm in diameter and as chains of octahedra that are oriented with respect to each other. Spinel enclosed by olivine phenocrysts is sometimes rounded and does not generally form chains. The temperature before quenching was calculated from the MgO content of the glass and ranges from 1150°C to 1180°C. The oxygen fugacity before quenching was calculated by two independent methods and the log fO2 ranged from −9.2 to −9.9 (delta QFM=−1). The spinel in the Pu’u ’O’o samples has a narrow range in composition with Cr/(Cr+Al)=0.61 to 0.73 and Fe2+/(Fe2++Mg)=0.46 to 0.56. The lower the calculated temperature for the samples, the higher the average Fe2+/(Fe2++Mg), Fe3+ and Ti in the spinel. Most zoned spinel crystals decrease in Cr/(Cr+Al) from core to rim and, in the chains, the Cr/(Cr+Al) is greater in the core of larger crystals than in the core of smaller crystals. The occurrence of chains and hopper crystals and the presence of Cr/(Cr+Al) zoning from core to rim of the spinel suggest diffusion-controlled growth of the crystals. Some of the spinel crystals may have grown rapidly under the turbulent conditions of the summit reservoir and in the flowing lava, and the crystals may have remained in suspension for a considerable period. The rapid growth may have caused very local (μm) gradients of Cr in the melt ahead of the spinel crystal faces. The crystals seem to have retained the Cr/(Cr+Al) ratio that developed during the original growth of the crystal, but the Fe2+/(Fe2++Mg) ratio may have equilibrated fairly rapidly with the changing melt composition due to olivine crystallization. Six of the samples were collected on the same day at various locations along a 10-km lava tube and the calculated pre-collection temperatures of the samples show a 5°C drop with distance from the vent. The average Fe2+/(Fe2++Mg) of the spinel in these samples shows a weak positive correlation with decreasing MgO in the glass of these samples. The range in Cr2O3 (0.041–0.045 wt.%) of the glass for these six samples is too small to distinguish a consistent change along the lava tube. The spinel in the Pu’u ’O’o samples shows a zoning trend in a Cr–Al–Fe3+ diagram almost directly away from the Cr apex. This compares with a zoning trend in rapidly quenched MORB samples away from Cr coupled with decreasing Fe3+. The trend away from Cr displayed by spinel in rapidly quenched samples is in marked contrast to the trend of increasing Fe3+ shown by spinel in slowly cooled lava.  相似文献   

13.
Gas concentrations and isotopic compositions of water have been measured in hydrothermal waters from 13°N on the East Pacific Rise. In the most Mg-depleted samples ( 5 × 10−3 moles/kg) the gas concentrations are: 3–4.5 × 10−5 cm3 STP/kg helium, 0.62–1.24 cm3 STP/kg CH4, 10.80–16.71 × 10−3 moles/kg CO2. The samples contain large quantities (95–126 cm3/kg) of H2 and some carbon monoxide (0.26–0.36 cm3/kg) which result from reaction with the titanium sampling bottles. δ13C in methane and CO2 (−16.6 to −19.5 and −4.1 to −5.5 respectively) indicate temperatures between 475 and 550°C, whereas δ13CCO is compatible with formation by reduction of CO2 on Ti at 350°C close to the sampling temperature.3He/4He are very homogeneous at (7.5 ± 0.1)RA(3He/4He = 1.0 × 10−5) and very similar to already published data as well as CH4/3He ratios between 1.4 and 2.1 × 106.18O and D in water show enrichments from 0.39 to 0.69‰ and from 0.62 to 1.49‰ respectively. These values correspond to W/R ratios of 0.4–7. The distinct18O enrichments indicate that the isotopic composition of the oceans is not completely buffered by the hydrothermal circulations. The3He-enthalpy relationship is discussed in terms of both hydrothermal heat flux and3He mantle flux.  相似文献   

14.
Quaternary lavas from the Northern Mariana Islands have respective O- and S-isotope ranges ofδ18O = +5.7 to +6.6 (‰ SMOW) andδ34S = +2.0to+20.7 (‰ CDT). Chemically evolved andesites and dacites with meanδ18O = +6.3 ± 0.2 are slightly enriched in18O with respect to unfractionated basalts of<53%SiO2 with meanδ18O = +6.0 ± 0.1. This18O enrichment can be explained in terms of differentiation of parental mafic magmas havingδ18O values between +5.7 to +6.2‰ through closed-system crystal fractionation because the lavas from all nine islands of the arc define a coherentδ18OSiO2 trend. The S-isotope composition of oxidized magmas is not modified extensively through the degassing of SO2; therefore, the meanδ34S value of ca. +11‰ for the Mariana lavas is considered to be representative of their source region.The enrichment of18O and34S in Mariana Arc parental magmas relative to ocean floor basalts withδ18O ca. + 5.7‰ andδ34S = ca.0.3‰ is attributed to the recycling of18O- and34S-rich crustal components (sediment withδ18O = ca. + 25‰ and seawater sulfate withδ34S = ca. +20‰ into the upper mantle source region for these arc magmas. This interpretation is consistent with enrichments of radiogenic Sr and Pb in the same lavas relative to ocean-floor basalts erupted either side of the arc, which are presumed to share a common upper mantle source. This enrichment is considered to reflect the mixing of two components, one having a typical upper mantle composition and the other having a more radiogenic character similar to that of western Pacific pelagic sediments.  相似文献   

15.
Between December 1997 and March 1998 Equator-S made a number of excursions into the dawn-side magnetosheath, over a range of local times between 6:00 and 10:40 LT. Clear mirror-like structures, characterised by compressive fluctuations in |B| on occasion lasting for up to 5 h, were observed during a significant fraction of these orbits. During most of these passes the satellite appeared to remain close to the magnetopause (within 1–2 Re), during sustained compressions of the magnetosphere, and so the characteristics of the mirror structures are used as a diagnostic of magnetosheath structure close to the magnetopause during these orbits. It is found that in the majority of cases mirror-like activity persists, undamped, to within a few minutes of the magnetopause, with no observable ramp in |B|, irrespective of the magnetic shear across the boundary. This suggests that any plasma depletion layer is typically of narrow extent or absent at the location of the satellite, at least during the subset of orbits containing strong magnetosheath mirror-mode signatures. Power spectra for the mirror signatures show predominately field aligned power, a well defined shoulder at around 3–10 × 10−2 Hz and decreasing power at higher frequencies. On occasions the fluctuations are more sinusoidal, leading to peaked spectra instead of a shoulder. In all cases mirror structures are found to lie approximately parallel to the observed magnetopause boundary. There is some indication that the amplitude of the compressional fluctuations tends to be greater closer to the magnetopause. This has not been previously reported in the Earth’s magnetosphere, but has been suggested in the case of other planets.  相似文献   

16.
Flow liquefaction and cyclic mobility are two different phenomena that are encountered during strong earthquakes. Flow liquefaction is associated with the contractive behavior of loose granular materials and cyclic mobility is associated with the dilative response of both loose and dense granular materials at low confining stresses. These two types of response pertain to the same material and therefore should be modeled in a consistent manner. Whether a soil in a given state exhibits contractive or dilative behavior is dependent on its dilatancy, d=dvp/dqp. A form of the dilatancy d=d(η,ψ,C) is proposed, where η=q/p is the stress ratio, and ψ and C denote the internal state variables and the intrinsic properties, respectively. It has been shown that such a state-dependent dilatancy is effective in describing both the contractive and dilative behavior. This allows the soil behavior associated with flow liquefaction and cyclic mobility during earthquakes to be modeled in a unified way.  相似文献   

17.
We report small but significant variations in the 58Ni/61Ni-normalised 60Ni/61Ni and 62Ni/61Ni ratios (expressed as ε60Ni and ε62Ni) of bulk iron and chondritic meteorites. Carbonaceous chondrites have variable, positive ε62Ni (0.05 to 0.25), whereas ordinary chondrites have negative ε62Ni (− 0.04 to − 0.09). The Ni isotope compositions of iron meteorites overlap with those of chondrites, and define an array with negative slope in the ε60Ni versus ε62Ni diagram. The Ni isotope compositions of the volatile-depleted Group IVB irons are similar to those of the refractory CO, CV carbonaceous chondrites, whereas the other common magmatic iron groups have Ni isotope compositions similar to ordinary chondrites. Only enstatite chondrites have identical Ni isotope compositions to Earth and so appear to represent the most appropriate terrestrial building material. Differences in ε62Ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed, but some of the ε60Ni variability could reflect a radiogenic component from the decay of 60Fe. Comparison of the ε60Ni of iron and chondritic meteorites with the same ε62Ni allows us to place upper limits on the 60Fe/56Fe of planetesimals during core segregation. We estimate that carbonaceous chondrites had initial 60Fe/56Fe < 1 × 10− 7. Our data place less good constraints on initial 60Fe/56Fe ratios of ordinary chondrites but our results are not incompatible with values as high as 3 × 10− 7 as determined by in-situ measurements. We suggest that the Ni isotope variations and apparently heterogeneous initial 60Fe/56Fe results from physical sorting within the protosolar nebula of different phases (silicate, metal and sulphide) that carry different isotopic signatures.  相似文献   

18.
Propagation of electromagnetic (EM) waves from an earthquake focus in the conductive Earth has been investigated using 1/1,000,000 scaling models taking earth-ionosphere and ocean-Moho plane parallel-plate waveguides into account. Microwaves at a frequency, ωm, a million times higher than that of seismic EM signal (SEMS), ω, were generated at the model focus. They are propagated in a salt solution modeling the earth's crust and reflected by ocean, fault planes, ionosphere and Moho plane all made by aluminum. Distribution of EM power was mapped by scanning a detector antenna over the model Earth's surface. The skin depth, δ, calculated by the exact skin depth equation, 1/δ=ω(μ/2)1/2 [(1+(1/ωρ)2)1/2 −1]1/2 where dielectric constant, and permeability, μ are the same but resistivity, ρ, 10−6 times smaller than that of Earth, gave 10−6 times small skin depth validating the model scaling index. Images for evanescent and wave-ripple standing waves disturbed by normal, strike-slip and dip-slip conductive fault planes have been obtained using an aluminum plate. The co-circular contour map above the epicenter due to evanescence was pushed to the north east direction from the epicenter by the presence of ocean for the Loma Prieta earthquake, while to north direction for the Kobe earthquake. The intensity of EM ULF emissions for the Loma Prieta earthquake is discussed quantitatively.  相似文献   

19.
A series of cyclic triaxial tests on clayey sands was carried out and attempts were made to evaluate the strain dependency of shear modulus and damping. Strain dependencies of shear modulus and damping were simply modeled. It was shown that the change in the effective confining stress with loading cycles in the undrained shear test needed to be considered particularly in the large strain range. The consideration could be made by normalizing G with G0=AF(e)(σ′mmr)n, the initial shear modulus for the effective confining stress of that particular loading cycle, instead of using G0. G/G0 was expressed by a function of γ as G/G0=1/(1+bgγ) which was almost stress level independent for clayey sands used in this study. The damping ratio was not much affected by the confining stress. The strain dependency of the damping ratio was modeled by h=ahγ/(1+bhγ). Effects of load irregularity on the shear modulus were also investigated. The excess pore pressure and the residual strain were generated especially when the major peaks in the irregular loading were applied to the specimen. However, G/G0 for the irregular loading could be represented reasonably well by the average curve for the uniform cyclic loading, if the excess pore water pressure and the residual strain were taken into account.  相似文献   

20.
Isotopic compositions were determined for hydrothermal quartz, calcite, and siderite from core samples of the Newberry 2 drill hole, Oregon. The δ15O values for these minerals decrease with increasing temperatures. The values indicate that these hydrothermal minerals precipitated in isotopic equilibrium with water currently present in the reservoirs. The δ18O values of quartz and calcite from the andesite and basalt flows (700–932 m) have isotopic values which require that the equilibrated water δ18O values increase slightly (− 11.3 to −9.2‰) with increasing measured temperatures (150–265°C). The lithic tuffs and brecciated lava flows (300–700 m) contain widespread siderite. Calculated oxygen isotopic compositions of waters in equilibrium with siderite generally increase with increasing temperatures (76–100°C). The δ18O values of siderite probably result from precipitation in water produced by mixing various amounts of the deep hydrothermal water (− 10.5 ‰) with meteoric water (− 15.5 ‰) recharged within the caldera. The δ13C values of calcite and siderite decrease with increasing temperatures and show that these minerals precipitated in isotopic equilibrium with CO2 of about −8 ‰.The δ18O values of weakly altered (<5% alteration of plagioclase) whole-rock samples decrease with increasing temperatures above 100°C, indicating that exchange between water and rock is kinetically controlled. The water/rock mass ratios decrease with decreasing temperatures. The δ18O values of rocks from the bottom of Newberry 2 show about 40% isotopic exchange with the reservoir water.The calculated δ18O and δD values of bottom hole water determined from the fluid produced during the 20 hour flow test are −10.2 and −109‰, respectively. The δD value of the hydrothermal water indicates recharge from outside the caldera.  相似文献   

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