共查询到20条相似文献，搜索用时 15 毫秒
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R.W. Readman 《Physics of the Earth and Planetary Interiors》1978,16(3):196-199
Magnetisation measurements on ulvöspinel have shown that there is a transition from the weakly ferromagnetic state to an essentially antiferromagnetic one at T ～ 60–100 K when moderate measuring fields (24 kOe) are used. Cooling from above 100 K in the presence of a magnetic field of several kilooersteds produces a reversed remanence for and the resulting thermomagnetic curve is Néel N-type. Magnetisation in 80 kOe produces a spontaneous moment extrapolated to 0 K of 0.015 μB, although this may not be completely saturated. An explanation for the magnetic transition is suggested in terms of an increased anisotropy possibly associated with a crystal transition. 相似文献
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The dependence of bulk sound speed Vφ upon mean atomic weight and density ρ can be expressed in a single equation: Here B is an empirically determined “universal” parameter equal to 1.42, , a reference mean atomic weight for which well-determined elastic properties exist, and λ = 1.25 is a semi empirical parameter equal to where γ is a Grüneisen parameter. The constant c = (? ln VM/? ln , where VM is molar volume, is in general different for different crystal structure series and different cation substitutions. However, it is possible to use cFe = 0.14 for Fe2+Mg2+ and GeSi substitutions and cCa ? 1.3 for CaMg substitutional series. With these values it is pos to deduce from the above equation Birch's law, its modifications introduced by Simmons to account for Ca-bearing minerals, variations in the seismic equation of state observed by D.L. Anderson, and the apparent proportionality of bulk modulus K to VM?4. 相似文献
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George Purcaru 《Physics of the Earth and Planetary Interiors》1979,18(4):274-287
The available data on the destructive intermediate earthquakes () in the Vrancea, Romania, region have been examined with the aim of revealing some time-magnitude regularities. The basic idea is that the total sequence (? 1100–1973 yr.), which appears as random, could be decomposed in some regular source-components which, by extrapolation, are superimposed to predict the future total sequence.The common nature of faulting (reverse dip-slip) and inferred regularities in the time-magnitude pattern of destructive Romanian earthquakes — (a) three active (seismic) time-bands alternating with quiet periods, the existence of (b) “quasicycles” and of (c) “supercycles” — led to the following predictions: (1) the occurrence of a shock with in 1980 ± 13 years; and (2) later earthquakes are predicted in 2005, in 2030–2040 (), and one with nearly maximum magnitude () in 2070–2090.In every century, about 40 years represent a time interval of high seismic danger for Romania and, according to the proposed long-term time-magnitude model, three destructive earthquakes arc to occur in (and/or near) the evidenced seismic periods P1, P2 and P3.It is shown that, taking into account the actual difficulties involved in the earthquake prediction, the Vrancea destructive earthquake of March 4, 1977 (M = 7.1) was quite successfully predicted. 相似文献
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Adam Zsolnay 《Marine pollution bulletin》1979,10(4):107-108
The average hydrocarbon content found in 14 water samples from the euphotic zone off Northwest Africa was 4.4 μg l.?1 with no extreme values. The average chlorophyll content was 1.9 μg l.?1. The data fit a model proposed in a previous paper (Zsolnay, 1977). The resulting equation was and could explain 59% of the variance in the hydrocarbon distribution. This indicates a correlation that is significant at the 0.002 level. 相似文献
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Shock recovery experiments on olivine single crystals (mineralogical composition: forsterite～80) have been carried out in a pressure range from～200up to～ 575kbar. Infrared spectroscopic investigations indicate a transformation of the mineral within a pressure interval from～420to～575kbar. Exposure to dynamic pressures of～575kbar yielded complete decomposition of the former olivine into an X-ray amorphous material upon pressure release. The infrared investigations suggest the post-shock products to consist essentially out of short-range-ordered (Mg,Fe)O and SiO2. 相似文献
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The correlation discovered by Hide and Malin between the variable parts of the Earth's gravitational field and magnetic field (suitably displaced in longitude) was tentatively and qualitatively explained by them in terms of the influence on both fields of irregularities (or “surface bumps”) at the core-mantle interface. In this paper, a quantitative analysis of this phenomenon is developed, through study of an idealised problem in which conducting fluid occupying the region z < η(x) flows over the surface z = η(x) in the presence of a magnetic field (B0,0,0), the whole system rotating with angular velocity (0,0,Ω). It is assumed that so that perturbation methods are applicable. Determination of the magnetic potential in the “mantle” region z < η(x) requires solution of the full hydromagnetic problem in the fluid. It is shown that three wave modes are excited, two of which (for values of the parameters of the problem of geophysical interest) have a boundary layer character. Phase interactions between these modes lead to a shift and a distortion of the magnetic pattern relative to the gravitational pattern. The correlation between the gravitational potential and the magnetic potential (shifted by a distance x0) is determined on the plane as a function of x0/d and the curves obtained are qualitatively similar to that based on the observed data; the maximum correlation obtained varies between 0.67 and 1, depending on values of the parameters of the problem, and is about 0.72 for reasonable estimates of these parameters in the geophysical context. 相似文献
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L.C. Ming M.H. Manghnani T. Matsui J.C. Jamieson 《Physics of the Earth and Planetary Interiors》1980,23(4):276-285
Pressure-induced phase transformations in each of the rutile-structured difluorides (NiF2, MgF2, CoF2, ZnF2, FeF2 and MnF2) exhibit unique behavior; however, a general trend is found in the major structural changes: rutile phase → “distorted fluorite” phase → post-“distorted fluorite” phase with volume changes of about 5–10%. For a given phase transformation sequence found commonly in two or more difluorides, the phase transformation pressure is related inversely to the unit cell volume and thus inversely to the mean cation-anion bond length. The relationship in oxides (SnO2, TiO2 and GeO2) is much less systematic. It is therefore not possible to predict without uncertainty the post-stishovite phases in the lower mantle.Velocity-density systematics in the difluorides and oxides are governed, to a large extent, by cationic radius. The pressure dependence of shear elastic constant CS = (C11 ? C12)/2 is negative in all of the nine difluorides and oxides. However, the CS mode does not vanish at the initial phase transformation pressure; rather, the ratios of are 0.10 and 0.04 to 0.10 for transitions of rutile → orthorhombic and of rutile → “distorted fluorite”, respectively, and are in agreement with the approach of Demarest et al. 相似文献
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Eiji Ohtani 《Physics of the Earth and Planetary Interiors》1983,33(1):12-25
The melting curve of perovskite MgSiO3 and the liquidus and solidus curves of the lower mantle were estimated from thermodynamic data and the results of experiments on phase changes and melting in silicates.The initial slope of the melting curve of perovskite MgSiO3 was obtained as at 23 GPa. The melting curve of perovskite was expressed by the Kraut-Kennedy equation as , where Tm?2900 K and P?23 GPa; and by the Simon equation, .The liquidus curve of the lower mantle was estimated as (perovskite) and this gives the liquidus temperature Tliq=7000 ±500 K at the mantle-core boundary. The solidus curve of the lower mantle was also estimated by extrapolating the solidus curve of dry peridotite using the slope of the solidus curve of magnesiowüstite at high pressures. The solidus temperature is ～ 5000 K at the base of the lower mantle. If the temperature distribution of the mantle was 1.5 times higher than that given by the present geotherm in the early stage of the Earth's history, partial melting would have proceeded into the deep interior of the lower mantle.Estimation of the density of melts in the MgOFeOSiO2 system for lower mantle conditions indicates that the initial melt formed by partial fusion of the lower mantle would be denser than the residual solid because of high concentration of iron into the melt. Thus, the melt generated in the lower mantle would tend to move downward toward the mantle-core boundary. This downward transportation of the melt in the lower mantle might have affected the chemistry of the lower mantle, such as in the D″ layer, and the distribution of the radioactive elements between mantle and core. 相似文献
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High pressure polymorphs of olivine (Mg, Fe)2SiO4 have been observed by transmission electron microscopy in the shocked Tenham and Catherwood meteorites. Planar defects are characterized in β and γ polymorphs and their possible role in polymorphic transitions is assessed and discussed in relation with the published literature. The stacking fault observed in the β-phase can produce a shear transformation to the γ-phase if it occurs on every other (010) plane. Conversely, the stacking fault observed in the γ-phase can be transformed to the β-phase if it is repeated on every other (110) plane and to an intermediate, yet unobserved, ε1-phase if it is repeated on every (110) plane. Shear transformation between olivine and γ-spinel could involve the ε1-phase as an intermediate stage. 相似文献
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The second order theory of elasticity, in which terms to second order in strain are retained in calculating atomic bond length changes and elastic moduli, is extended to describe thermal vibration of a face-centred cubic crystal. Coupled with equations relating the pressure dependences of elastic constants, this yields a new formulation of the thermal Grüneisen parameter γ in terms of pressure P, incompressibility K and rigidity, μ where f = 24 (3 K ? 2 P)/(3 K + 115 μ + 90 P). The factor f arises from bond interactions and the case f = 1, representing independent bonds (no interactions), yields the free-volume γ- Since we have shown earlier that the second order elasticity theory provides a convincing explanation of the elasticity of the inner core, we believe that the new formula is appropriate for the inner core. It is, however, inadequate to describe the lower mantle γ, in which atomic bond angle rigidity, not considered here, may be appreciable. 相似文献
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We developed an objective method to define the aftershock areas of large earthquakes as a function of time after the main shock. The definition is based upon the amount of energy released by aftershocks, the spatial distribution of the energy release is first determined and is contoured. The 1-day aftershock area is defined by a contour line corresponding to the energy release level of 1015.6 ergs/(100 km2 · day). The 10-day, 100-day and 1-y aftershock areas are similarly defined by contour lines corresponding to 1014.8, 1014.0, and 1013.5 ergs/(100 km2 · day), respectively. We also define the expansion ratios at time t by the ratio of the aftershock area at t to that at 1 day.Using this method we study the aftershock area expansion patterns of 44 large (Ms ? 7.5) and five moderate shallow earthquakes which occurred from 1963 to 1980. Each aftershock sequence is examined at four different times, i.e., 1 day, 10 days, 100 days, and 1 y after the main event. We define the aftershock area expansion ratios η and ηe by , respectively: here S(t) and L(t) are the area and the length of the aftershock area, respectively, at time t. Our study suggests that a distinct regional variation of aftershock area expansion patterns is present; it is strongly correlated with the tectonic environment. In general, the subduction zones of the “Mariana” type have large expansion ratios, and those of the “Chilean” type have small expansion ratios. Some earthquakes that occurred in the areas of complex bathymetry such as aseismic ridges tend to have large expansion ratios.These results can be explained in terms of an asperity model of fault zones in which a fault plane is represented by a distribution of strong spots, called the asperities, and weak zones surrounding the asperities. The rupture immediately after the main shock mostly involves asperities. After the main rupture is completed, the stress change caused by the main shock gradually propagates outward into the surrounding weak zones. This stress propagation manifests itself as expansion of aftershock activity. In this simple picture, if the fault zone is represented by relatively large asperities separated by small weak zones (“Chilean” type), then little expansion of aftershock activity would be expected. On the other hand, if relatively small asperities are sparsely distributed (“Mariana” type), significant expansion occurs. The actual distribution of asperities is likely to be more complex than the two cases described above. However, we would expect that the expansion ratio is in general proportional to the spatial ratio of the total asperity area to the fault area. 相似文献
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L.G. Parry 《Physics of the Earth and Planetary Interiors》1982,28(3):230-241
The magnetic properties of specimens containing dispersed magnetic particles, at low concentrations, containing two distinct size ranges, have been measured. The results have been used to evaluate the effectiveness of several parameters which have been used to discriminate the type of particles in a dispersion. The location of the point representing the properties of a specimen on a graph of and indicates a possible particle dispersion which would produce a model with equivalent magnetic properties. The behaviour of dispersions of titomagnetic is also considered and these produce ambiguities in the interpretation of the graph. The possibility of modelling a dispersion which has equivalent properties to specimens from a single lava is considered. 相似文献
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D.J. Stevenson 《Physics of the Earth and Planetary Interiors》1980,22(1):42-52
By use of the modern theory of liquids and some guidance from the hard-sphere model of liquid structure, the following new results have been derived for application to the Earth's outer core. (1) dK//K, where K is the incompressibility and P the pressure. This is valid for a high-pressure liquid near its melting point, provided that the pressure is derived primarily from a strongly repulsive pair potential φ. This result is consistent with seismic data, except possibly in the lowermost region of the outer core, and demonstrates the approximate universality of dK/dP proposed by Birch (1939) and Bullen (1949). (2) dlnTM/dlnρ = (γCV ? 1)/( is the melting point, ρ the density, γ the atomic thermodynamic Grüneisen parameter and CV the atomic contribution to the specific heat in units of Boltzmann's constant per atom. This reduces to Lindemann's law for CV = 3 and provides further support for the approximate validity of this law. (3) It follows that the “core paradox” of Higgins and Kennedy can only occur if . However, it is shown that , which cannot be achieved for any strongly repulsive pair potential φ and the corresponding pair distribution function g. It is concluded that and that the core paradox is almost certainly impossible for any conceivable core composition. Approximate calculations suggest that γ ～ 1.3–1.5 in the core. Further work on the thermodynamics of the liquid core must await development of a physically realistic pair potential, since existing pair potentials may be unsatisfactory. 相似文献
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A. Ádám 《Physics of the Earth and Planetary Interiors》1978,17(2):P21-P28
Pollack and Chapman have shown that the surface heat flow in continental regions is dependent not only on the earth's crust below the observation site, but also on the upper mantle there. Therefore heat flow can be used to investigate the role of the thermal conditions in the creation of the electrically conductive zones in both the crust and mantle.Empirical exponential formulas describe the depth to the conductivity increase in the crust corresponding to granitization, the depth to the conductive zone at the top of the asthenosphere (SLVZ), as a function of heat flow. Comparing the latter with temperature estimations in the asthenosphere it is concluded that partial melting of the upper mantle occurs only where .The depth to the conductivity increase corresponding to the mineralogic phase transition in the upper mantle is increased with high temperatures. Such a conductive zone shows that the maximum temperature difference between stable platform areas and active zones is about 1000°C. 相似文献
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By considering high-temperature (classical) thermal oscillations of atoms in certain simple crystal structures with purely central interatomic forces, the treatment of anharmonic oscillations is generalised to random three-dimensional motion, yielding the Vashchenko and Zubarev relationship for the Grüneisen ratio γ at any pressure. If one-dimensional atomic oscillations only are considered the equation reduces to the Dugdale-MacDonald expression. To account for non-central forces additional terms must be introduced, giving: where f = 0 for purely central forces. Calculations of f in terms of the Poisson ratio for different crystal structures have not been made, but for many materials the central-force approximation suffices. This is believed to be true both for the outer core and for the close-packed structures of the lower mantle . For the upper mantle non-central atomic forces are important and we have no estimate of ( independently of laboratory values for plausible minerals which suggest γ ≈ 0.8. 相似文献
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Orson L. Anderson 《Physics of the Earth and Planetary Interiors》1982,29(1):91-104
It is shown that there is linearity between the thermal pressure PTH and T between the Debye temperature θ and some high temperature . has been measured at 1 atm and is reported for several minerals including, for example, MgO (1300 K) and forsterite (1200 K). The change in thermal pressure from room temperature for five solids, so far measured, indicate striking linearity with T at high temperatures.It is further shown that the value of increases greatly as the pressure increases. It is therefore concluded that PTH is probably linear with T for mantle minerals under mantle conditions. The proportionality constant is derived from the measurements of thermal expansivity and bulk modulus at high temperature and zero pressure.The argument is then reversed. Assuming that the thermal pressure is in fact linear with T for the various shells in a planet, the resulting density and temperature profile of the planet is derived. The resulting density profile of the Earth compares favorably with corresponding values of recent seismic profiles. 相似文献