摘要:

To investigate the presence and nature of the lateral heterogeneities in the earth's mantle, geophysical data with global distribution are analyzed and correlated. Surface heat flow, seismic travel‐time residuals, and crustal thickness data are expanded in spherical harmonics. Using these, and the coefficients of similar expansions of surface topography of the earth, and the gravitational potential variations as revealed by satellite data, both total and degree correlation coefficients are obtained. From the interpretation of these results, jointly with available laboratory data on velocity‐density relationships and the temperature coefficient of velocity, the following are concluded: (1) Lateral mass anomalies and/or density variations in the earth's mantle are larger by at least an order of magnitude from what is required to explain the satellite data. Earth's surface topography and crustal structure introduce loads which are compensated in the upper, and perhaps lower, mantle giving rise to lateral density anomalies in the mantle. (2) Surface heat flow variations are controlled primarily by the shallow structure and tectonic features of the earth. (3) At long wavelengths (n ≤ 6), gravitational, heat flow, and seismic travel‐time variations are not correlated with topographic ele

ISSN:0148-0227    

DOI:10.1029/JB074i015p03751

年代:1969

数据来源: WILEY

摘要:

A procedure for constructing lunar models has been developed in which pressure, temperature, and compositional effects are taken into account. Pertinent lattice‐dynamical relations are also incorporated. By using this procedure, a series of lunar models have been constructed based on the latest measurements on the physical properties of rock‐forming minerals. Chemically homogeneous models thus constructed are found to have too high a density at the surface and probably too large a moment of inertia. We conclude that (1) there must be a concentration of lighter material near the surface of the moon, and (2) the deep interior of the moon is more likely to be chemically heterogeneous than to be homogeneous throughout although the possibility of chemical homogeneity cannot be ruled out judging from the current range of uncertainty of the moment of inertia of the m

ISSN:0148-0227    

DOI:10.1029/JB074i015p03771

年代:1969

数据来源: WILEY

摘要:

In order to assess the influence of internal stress on magnetic properties of interest in paleomagnetic research, experiments were made on six strained samples from a nickel single crystal. The samples were (100) disks 7.5 mm in diameter and 2.5 mm thick that were cold rolled to produce dislocation densities between 108and 1011cm2. The intensities of weak field thermoremanent magnetization (TRM) produced in the samples were proportional to their dislocation densities. Direct control of magnetization by stress fields near dislocations is shown to be energetically unfavorable, and a model is developed to explain relationships between remanence and dislocation density based on the pinning of domain walls. Some of the remanence remains after alternating field demagnetization in 400 oe, but possible higher stabilities are masked by a significant viscous component.

ISSN:0148-0227    

DOI:10.1029/JB074i015p03781

年代:1969

数据来源: WILEY

摘要:

The weak ferromagnetism of cassiterite (SnO2) can be attributed to its 1% iron impurity content. Previous workers have postulated two hypothetical iron‐tin compounds to explain the magnetism, namely, Fe4/3;Sn2/3O3and single‐phase magnetic Sn1−xFexO2. Our saturation magnetization measurements on large single crystals as a function of temperature show super‐paramagnetic Fe2O3or Fe2−xSnxO3impurities to be responsible for the weak ferromagnetism. Thermomagnetic curves confirm this interpretation. Contrary to the results of previous workers, no correlation was found between magnetism and the Fe2+/Fe3+ratio, and the observed variability of Curie points is attributed by us to a range of blocking temperatures. More importantly, we suggest that the NRM in cassiterite may be CRM, and hence these crystals are liable to yield incorrect paleointensity values of the geomagne

ISSN:0148-0227    

DOI:10.1029/JB074i015p03789

年代:1969

数据来源: WILEY

摘要:

The solution of the geodetic boundary value problem for a reference ellipsoid is given with a relative error of the order of the square of the earth's flattening. The solution is obtained by representing the disturbing potential at the earth's surface as the potential of a simple layer. If the earth's topography is neglected in the derived solution, a new solution of Stokes' problem for a reference ellipsoid is obtained.

ISSN:0148-0227    

DOI:10.1029/JB074i015p03796

年代:1969

数据来源: WILEY

摘要:

A symmetric matrix is introduced to specify a set of variable densities. An iterative process is generated by means of such a matrix formulation, which leads to an elegant and rapid method for calculating the configuration of two‐dimensional subsurface mass deficiencies, such as sedimentary basins and isostatic structures below the mountains. Applications are illustrated for Godavari Basin (India) and the Rocky Mountains (United States

ISSN:0148-0227    

DOI:10.1029/JB074i015p03804

年代:1969

数据来源: WILEY

摘要:

The results of a search of records of the University of Nevada seismographic station network for grossly observable effects of underground nuclear tests on regional seismicity are presented. Most of the data were obtained at the Tonopah station, 100–150 km from the explosions studied. Periods of time before and after 21 explosions were examined. In all cases of explosions with magnitudemb; ≥ 5.0, an increase in seismicity was observed for at least one day following the test. The decay of post‐shot activity and its relationships to the equivalent magnitude of the explosion provide confirmation of the determinative role of the nuclear event. For the most part, this activity was confined to the test site, and was probably located within 20km of the shotpoint. In one case, however, earthquake activity following the Faultless test in January 1968 may have extended to 40 km from the site of the explosion. One or two of the earlier tests studied may have influenced seismicity at larger distances. Most of the events studied had very small magnitudes, and all earthquakes related to underground tests had magnitudes lower by at least one magnitude unit, than those of the associated blasts. Attempts to determine the extent to which underground tests influence seismicity in active areas distant from the test site have indicated that, if such effects exist, they are probably minor compared with normal variations in seism

ISSN:0148-0227    

DOI:10.1029/JB074i015p03808

年代:1969

数据来源: WILEY

摘要:

The absence of a heat flow anomaly greater than ∼0.3 µcal/cm2/sec associated with the San Andreas fault is used to estimate the upper limit for the steady state or initial shear stress. Under the assumption that the long‐term rate of motion along the fault is 5 cm/yr and occurs primarily in the form of creep, this upper limit is about 100 bars. If the motion is primarily accomplished by faulting during large earthquakes and if the frictional stress is equal to the final stress as suggested by E. Orowan (1960), the upper limit is estimated to be about 200 bars. Without Orowan's assumption, the estimation of the upper limit is about 250 bars, based on earthquake energy‐magnitude‐moment relations. If the long‐term rate of motion along the San Andreas fault is only ∼2 cm/yr, these results are increased to 250, 350, and 400 bars,

ISSN:0148-0227    

DOI:10.1029/JB074i015p03821

年代:1969

数据来源: WILEY

摘要:

Criteria for achieving an order of magnitude discrimination between underground explosions and shallow‐focus continental earthquakes are presented. The basis of all these criteria is the gross difference between earthquakes and explosions as regards their relative generation of short‐ and long‐period waves. It is also shown that depth of focus of small events can be accurately determined either by use of master‐controlled travel‐time corrections or by determination of time of origin (Pg,S‐P, etc.). Therefore, the basic problem for differentiating earthquakes and underground explosions of magnitude 4¾ or greater by seismic criteria has been solved. The remaining problems are the detection of long‐period waves at low signal‐to‐noise ratios and the evaluation of the applicability of long‐period identification criteria for

ISSN:0148-0227    

DOI:10.1029/JB074i015p03828

年代:1969

数据来源: WILEY

摘要:

The elastic constants of crystals show a general tendency to increase as the mean molar volume 〈V〉 = 〈M〉/ρ decreases. The role of other factors, such as cation radius, crystal field effects, and anion‐cation coordination, can now be discussed with available elastic constant data. For a given coordination the parameter ψ0= (ρ0/〈M〉) Φ0−⅓(where ρ0is the zero‐pressure density, 〈M〉 is the mean atomic weight, and Φ0is the ratio of the zero‐pressure bulk modulus to the density) decreases with increasing cation radius and with cell volume per oxygen atom unless a nonspherical transition element ion, such as Fe++, substitutes for a nontransition ion, such as Mg++. The calcium effect discovered by G. Simmons is a special case of the cation radius effect. The elastic ratio Φ0for complex oxides is approximately a molar average of the Φ0of the component simple oxides. For silicates it appears that an empirical table of Φ0(SiO2) can be constructed for various mineral groups. Tentatively, Φ0(SiO2) is roughly that of α quartz for the feldspars, β quartz for olivines and pyroxenes, coesite fo

ISSN:0148-0227    

DOI:10.1029/JB074i015p03857

年代:1969

数据来源: WILEY