摘要:

The method of layer matrices is applied to solve the problem of the static deformation of a multilayered elastic half‐space by buried sources. Each layer of the multilayered medium is assumed to be homogeneous and isotropic, and the interfaces are assumed to be in welded contact. The point source ia represented as a discontinuity in thez‐dependent coefficients of the displacement and stress integrands at the source level. Source functions are obtained for the six elementary displacement dislocations. Explicit expressions for the surface displacements are calculated for a vertical strike‐slip and a vertical dip‐sli

ISSN:0148-0227    

DOI:10.1029/JB075i017p03257

年代:1970

数据来源: WILEY

摘要:

Available experimental data for some rock‐forming minerals indicate that, for the prediction of density in the upper mantle, it may be preferable to use an empirical relation between bulk sound velocity and density rather than Birch's relation between the velocity of compressional waves and density. An empirical relation between bulk sound velocity and density is applied to the prediction of density distribution in the mantle to a depth of 1000 km. In the lower mantle and the core, the density changes are computed by the use of the Adams‐Williamson relation. One of the models generated this way is modified in order to fit the relevant geophysical data, which include the periods of earth's free oscillations, phase and group velocities of Rayleigh and Love waves along great‐circle paths, and the total mass and moment of inertia of the earth. A model that satisfies all these data well within the observational uncertainties is found. Density in the upper 170 km of the mantle is about 3.3 g/cm3; this density distribution lends support to the current petrological theory that the upper mantle may be composed of some varieties of peridotite. The mean atomic weight for the lower mantle is about 21.3–21.5, suggesting the possibility that the entire mantle may have a uniform iron

ISSN:0148-0227    

DOI:10.1029/JB075i017p03264

年代:1970

数据来源: WILEY

摘要:

Slip rates associated with fracture zones were calculated from earthquakes on the Eastern Pacific rise. A total of 2465 earthquakes located by theT‐phase network during the period December 1964 through July 1967 were selected for study. Seismic moment was calculated for each earthquake, summed over 1° squares, plotted, and contoured. Comparison of this plot with bathymetric charts of the area shows that: (1) Zones of high seismic moment are associated with, but not restricted to, transverse fracture zones; (2) Areas of high slip rate are associated with zones of low sea‐floor spreading rate; and (3) The Eastern Pacific rise appears to be aseismic between 35°S and 55°S, except near 47°S

ISSN:0148-0227    

DOI:10.1029/JB075i017p03285

年代:1970

数据来源: WILEY

摘要:

The surprising linear relation between surface heat flow and heat production in plutons is easily explained in terms of an exponential decrease of heat production with depth in the crust. If the linear relation is assumed to be true in a mathematical sense, it can be shown that this is the only possible explanation, provided that three other assumptions that seem geologically reasonable are made. The decrementDof the exponential function is determined empirically from surface observations since theory requires that it be equal to the slope parameter of the linear relation. Recently published heat‐flow results indicate thatDvaries little from one province to another, and this suggests a model in whichDis a general geochemical property of the crust beneath plutons. The outer layer of variable heat production, suggested by the linear relation, is identified with a zone of partial melting in which the heat‐producing elements were redistributed exponentially during the plutonic process. The analysis suggests that this zone typically includes a substantial portion of the crust, and that the upward concentration of crustal heat production and heat flow from much of the continental mantle are both somewhat greater than has generally been supposed. The model leads to simple estimates of crustal temperatures beneath plut

ISSN:0148-0227    

DOI:10.1029/JB075i017p03291

年代:1970

数据来源: WILEY

摘要:

Constraints on the atmospheric conditions at the surface of Venus are determined from the radar angular scattering law, radar cross section, and microwave brightness spectrum. These constraints are satisfied by the conditions [T(surface) = 750 ± 50°K,P(surface) = 110 ± 30 atm] inferred from extrapolation of the Mariner 5 pressure and temperature profiles to the surface given by the radar radius. Refraction by such a dense atmosphere will complicate radar mapping of the surface (especially near the limbs of the planet where the distortion of the apparent surface is not negligible). A rigorous derivation, considering refraction effects, is given for the relationship between delay‐Doppler coordinates and spherical coordinates on the planet's sur

ISSN:0148-0227    

DOI:10.1029/JB075i017p03301

年代:1970

数据来源: WILEY

摘要:

Differential drift scans were made across the 3‐day‐old moon at a wavelength of 22 μ with a beamwidth of 2.4 arc min. Measured cold‐limb brightness temperatures ranged from 102°K in the equatorial region to 84°K in the southern polar regions. Certain scans were processed to reveal the temperature distribution from the cold limb to the sunrise terminator. The portion of the lunar ‘cooling curve’ that was obtained by this method agrees well with the portion measured by previous investigators who made infrared scans from the sunset terminator into unillumin

ISSN:0148-0227    

DOI:10.1029/JB075i017p03319

年代:1970

数据来源: WILEY

摘要:

Quantitative paleontologic data sensitive to the planetary temperature gradient are used with similar data for living organisms to test two possible Permian latitude models for the Northern Hemisphere. The Permian paleontologic data applied to a present‐earth model yield a pattern strikingly similar to that of living organisms on the same model. Permian paleontologic data applied to a Permian paleomagnetic earth model show a pattern which is again strikingly similar to that exhibited by living organisms when plotted on this (for them patently incorrect) framework. The results indicate that the present‐earth latitude model could be correct for the Permian but do not prove that this is so because data are sparse, the noise level is relatively high, and neither North America nor Eurasia contains the equator for this model of the earth. The data show that the Permian paleomagnetic models tested are as inappropriate for the Permian as for the Recent data. The fact that the paleomagnetic models are found inappropriate in this test may be interpreted to indicate that (1) the paleontological data are inadequate, (2) the paleomagnetic model used is not correct because data needed to define it are lacking in large areas, or (3) the Permian magnetic field was not ax

ISSN:0148-0227    

DOI:10.1029/JB075i017p03325

年代:1970

数据来源: WILEY

摘要:

Low‐temperature treatments and alternating‐field demagnetization of magnetite samples are compared. Both theory and experiments show that these treatments affect different parts of the coercive force spectrum of magnetite. Some secondary magnetization can survive low‐temperature ‘cleaning.’ The combination of low‐temperature treatment with af demagnetization may be useful in separating behavior in multidomain regions from that in singledom

ISSN:0148-0227    

DOI:10.1029/JB075i017p03343

年代:1970

数据来源: WILEY

摘要:

Magnetotelluric fields in the equatorial and auroral electrojet zones violate the condition of plane waves because of the concentrated nature of sources in the ionosphere. To test if Cagniard's relation for apparent resistivity is still valid in these areas, a line current is used to simulate an electrojet. The integral expressions for the electromagnetic fields at the surface of a layered earth are numerically integrated for two simple models, one representing an average continent, the other representing an active tectonic area. It is shown that Cagniard's relation is particularly applicable to active tectonic areas where conductivities in the earth may be enhanced as a result of thermal processes. Cagniard's relation is also applicable to average continental areas, provided that the electrojet may be represented by a line current at a height greater than 500 km. This suggests than an electrojet at a height less than 500 km would permit invoking Cagniard's relation if the electro jet is reasonably broad.

ISSN:0148-0227    

DOI:10.1029/JB075i017p03351

年代:1970

数据来源: WILEY

摘要:

In classical isostatic computations, the isostatic reduction is made using the isostatic response function (the response of the earth's gravity field to a point load) derived for an assumed mechanism of compensation, as, for example, in the hypotheses of Pratt, Airy. A method is given here for the computation of this function directly from observational data, eliminating the need for assuming a compensation mechanism. If the earth is linear in its response to the crustal loading of the topography, the response of the earth's gravity field to this loading can be represented as the two‐dimensional convolution of the topography with the earth's isostatic response function. Actually, the topography is more likely to be the result of changes in density at depth than the cause, but the mathematical treatment is the same in both cases. Through transformation into the frequency domain, the convolution becomes multiplication, and one is led directly to the result that the isostatic response function is equal to the inverse transform of the quotient of the transforms of the Bouguer gravity anomaly and the topography. If one assumes local compensation, one can invert the isostatic response function to find the changes in density with depth that result in the uplift of the topograph

ISSN:0148-0227    

DOI:10.1029/JB075i017p03357

年代:1970

数据来源: WILEY