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  • 1935-1939  (96)
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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The propagation of Rayleigh waves in the Earth is investigated in the whole range of periods T from about 10s up to one hour. Three methods are necessary in order to cover this range of periods effectively. The standard flat Earth method, with neglect of gravity, gives values for the phase velocity C correct to within I per cent up to T= 50s only, and for the group velocity U up to T= 250s. The method of the flattening of the Earth, with neglect of gravity, has the I per cent accuracy limits for C and U at 300 and 400, respectively. Inclusion of gravity effects in the flattening of the Earth approximation does not alter the above limits. For T 〉 300 (n 〈 25) one must determine the period T(n) of free oscillation of the Earth as a function of the order of the spherical harmonic n. This involves the solution of a system of differential equations of the sixth order, in which the gravitational effects are included. The wave penetrates appreciably into the core already at T= 600. Using the above three methods in their respective ranges of validity, we have evaluated C(T) and U(T) for (I) Bullen's Model B, (2) the Jeffreys-Bullen Model, as modified by Dorman, Ewing and Oliver, and (3) the Gutenberg Model. The observed Rayleigh group velocity data of Ewing and Press for T 〈 380s and the phase velocity data of Nafe and Brune for T 〈 300s agree with the values computed for the Gutenberg model, but not for the other models. This substantiates a previous conclusion reached by Takeuchi, Press and Kobayashi and by Dorman, Ewing and Oliver that the observed Rayleigh wave data provide evidence in support of Gutenberg's lowvelocity layer. The few observed Rayleigh group velocities between T= 400 and 600 are substantially lower than the theoretical values for all the three models.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Making use of the variational calculus method developed in a previous paper, we calculate the free periods of torsional oscillations for two Earth models. In the Model, the Earth is assumed to be composed of homogeneous mantle and core. In the Model 2, we use the mantle structure model by Jeffreys and Bullen. In order to see the dependence of the periods on the core rigidity, we calculate the periods when the core is fluid or perfectly rigid. In the fluid core model, we work out the periods when the coupling between the mantle and core is perfect or zero. The present study will show that in order to get useful information on the rigidity of the core or the strength of coupling between the mantle and core by this kind of study, we must make the observations of free periods with an accuracy of several ten seconds.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A number of thermal problems connected with the Earth are discussed–the early thermal history of the Earth and some of its consequences, the formation and state of the inner core, convection in the core and its relation to the Earth's magnetic field, and conditions in the upper mantle.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: It is shown that the heat necessary to maintain convection in the core may come from slow cooling and crystallization of the core with corresponding growth of the solid inner core. The present rate of cooling would be of the order of 10–45 degrees per 109 years, depending on temperature.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Fifteen measurements of the heat flow through the ocean floor have been made in the Atlantic and one in the Mediterranean. One measurement in the central valley of the Mid-Atlantic Ridge gives a heat flow of 6.5 μcal/cm2s. Similar very high values have been found by others on the crest of the East Pacific Rise. The possibility that these high values represent the rising limb of a convection current is discussed. The mean of the remaining fifteen values and of five from a previous investigation, give a mean heat flow of 1.06 ± 0.055 μcal/cm2 s which is very close to the mean for all measurements in the Pacific excluding those on the East Pacific Rise.The equipment has been modified so that the temperature gradients in the whole probe and in its lower half can be determined separately. The lower half gives a value 8.8 per cent above that for the whole probe, the reason for this is not known.The thermal resistivity of ocean sediment, R, is found to be a linear function of the water content, ω (in per cent water of the wet weight). At the temperature of the ocean floor the relation is R(cms deg C/cal) = (168 ± 14)+(6.78 ± 0.31)ω.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Type of Medium: Electronic Resource
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