摘要:

Reduction of 2½ days of Lunar Orbiter 4 radio tracking data has provided an independent estimate of the low‐degree spherical harmonic coefficients in the lunar potential model. The estimate is in good agreement with previous results and confirms that the moon is essentially homogeneous. These Doppler data, never incorporated in other gravity estimates, were obtained at relatively high spacecraft altitudes (2700–6000 km). This high‐altitude data allowed the model to fit to the noise level of 1 mm/sec, unlike previous results, where systematic residuals of tens of millimeters per second occurred, owing to local gravity anomalies detectable at low spacecraft altitudes (

ISSN:0148-0227    

DOI:10.1029/JB076i029p07021

年代:1971

数据来源: WILEY

摘要:

Frequency variations from 5.4 to 2.35 Hz in air‐coupled surface waves have been observed repeatedly during various Saturn 5 launches. Signals obtained with low‐frequency microphones are used to compute the apparent phase velocity experienced by the ground at a particular seismograph site. The change of the apparent phase velocity during flight of the rocket is compared with the frequency variations of the seismic signal. The close agreement between these two quantities implies that (a) resonance due to phase‐velocity matching exists at the atmosphere‐ground interface, which results in generation of relatively large‐amplitude (50 μ) seismic waves; (b) contrary to previous observations on explosions and certain cases of sonic booms (aircraft in level flight and at constant speed), rocket‐generated surface waves are not constant‐frequency wave trains but vary in frequency; therefore they are physical proof that the air‐coupled surface waves cannot always be identified as constant‐frequency wave trains; and (c) the Saturn 5 rocket is a unique source of air‐coupled surface waves, and thus certain studies not possibl

ISSN:0148-0227    

DOI:10.1029/JB076i029p07027

年代:1971

数据来源: WILEY

摘要:

Three titanomagnetite samples, of compositionx=0.7, 0.9, and 1.0 (wherexis the ulvöspinel molecular fraction), were oxidized according to the method of Sakamoto et al., namely, wetgrinding followed by heating to 200–300°C. Like the samples of Sakamoto et al., our samples showed reversal of saturation magnetization during alteration of titanomagnetite to titanomaghemite. Our experimental results seem to be compatible neither with the ionic model of Verhoogen nor with the model of O'Reilly and Banerjee. The Curie point gradually increased and the lattice parameter decreased during low‐temperature oxidation (titanomaghemitization). On heating above 300°C, the γ‐titanomaghemites underwent high‐temperature oxidation (unmixing into magnetite, pseudobrookite, which is formed only during heating to 600°C, and rutile phases). The unmixing results in a sudden increase in Curie point and decrease in lattice parameter and saturation magnetization. On further heating, the saturation magnetization reverses for a second time. Therefore, double self‐reversal of remanent magnetization in naturally oxidized rocks is considered a re

ISSN:0148-0227    

DOI:10.1029/JB076i029p07035

年代:1971

数据来源: WILEY

摘要:

A new steady‐state absolute method for determining the thermal conductivity of rock specimens is presented. The technique involves putting a known quantity of heat into a specimen with an ohmic heater and determining the thermal gradient across the specimen with thermocouples. It follows from the steady‐state conduction equation that the thermal conductivity can be calculated from the expressionK=q/(ΔT/Δz). The heating element and the sample are insulated with polyurethane to reduce thermal losses. The bottom of the specimen is placed in contact with a massive aluminum block that serves as a thermal sink and remains essentially an isotherm for the duration of an experiment. Thermal‐conductivity values for fused and crystalline quartz determined by the new apparatus agree with Ratcliffe's data to within 1.5% for fused quartz and to within 2% for crystalline quartz. Thermal‐conductivity values of rock specimens measured on our apparatus agree to within 3.5% with the thermal‐conductivity values of the same specimens determined on a divided‐bar apparatus. It is estimated that the system has an absolute accuracy of ±4%. The apparatus is easier and less expensive to construct than many other thermal‐conductivity systems. The apparatus should also be applicable to measuring thermal diffusivity by a variation on

ISSN:0148-0227    

DOI:10.1029/JB076i029p07047

年代:1971

数据来源: WILEY

摘要:

The elastic moduli of pressure‐sintered nickel oxide near theoretical density have been measured by three different techniques. The values of Young's modulus and the shear modulus at room temperature determined by the resonant sphere method were 9.58×1011dynes/cm2and 3.38×1011dynes/cm2, respectively. The value of Young's modulus determined by a three‐part composite oscillator technique was 9.56×1011dynes/cm2, in good agreement with the resonant sphere measurements. Measurements of Young's modulus and shear modulus by the pulse‐transmission method were subject to fairly large end effects, which gave lower values. The temperature of the anomalous increase in Young's modulus and in relative acoustic loss was found to be 250°C±1/2°C, in excellent agreement with previously reported measurements for the Néel temperature of

ISSN:0148-0227    

DOI:10.1029/JB076i029p07052

年代:1971

数据来源: WILEY

摘要:

The constitutive laws required in a finite deformation (mechanical) theory of plasticity to describe elastic response, yield, and plastic flow are discussed. Even strong restrictions on the history dependence and the assumption of material isotropy leave a model considerably more general than the customary extensions of infinitesimal strain theory. The absence of rotation in triaxial stress systems provides further simplification, and the material functions which, in principle, could be inferred by a complete program of triaxial stress tests are described, together with a reduced set determined by biaxial tests. Equations of motion for uniaxial strain and for polar symmetry are derived, and matching conditions at an elastic‐plastic interface are obtained for the six distinct ranges of propagation spee

ISSN:0148-0227    

DOI:10.1029/JB076i029p07062

年代:1971

数据来源: WILEY

摘要:

Data from a 3‐km borehole in granitic crystalline rocks include cores, cuttings, velocity survey, formation density log, sonic log, and caliper survey. The borehole and adjacent peaks represent about 4‐km exposure of granitic gneisses from a migmatite terrain typical of deeply eroded Precambrian terrains. Although the rocks are all granitic, they range in composition from quartz monzonite to quartz diorite gneiss. Mean chemical composition of these rocks is close to that of Poldervaart's shield surface rocks, the Canadian Precambrian shield, and the Finnish Precambrian shield. Compositional variations are reflected in distinct chemical variations and in density that ranges from 2.58 to 2.77 g/cm3. Mean density for all the cores is 2.70 g/cm3. Seismic velocities from the velocity survey range from 5.18 to 6.10 km/sec from the top to the bottom of the borehole. The mean velocity is 5.78 km/sec, but is 5.89 km/sec below the upper 0.5 km. Sonic log velocities, which are 6.1 to 6.2 km/sec in relatively unfractured deeper zones, are higher than interval velocities over shorter distances and reach a maximum value of 6.35 km/sec. Maximum temperature is 62°C, and maximum lithostatic pressure is 800 bars. Although pressure and composition are important factors affecting seismic velocity, fractures seem to be the most important factor at these depths. The velocity function,V= 0.16z + 5.58, is suggested for this depth range. Because these rocks are typical for exposed crystalline shields, velocities of 6.1 to 6.2 km/sec or slightly greater should be common; velocities much under 6.0 km/sec would generally be unlikely in the upper c

ISSN:0148-0227    

DOI:10.1029/JB076i029p07079

年代:1971

数据来源: WILEY

摘要:

Analysis based on the theory of dislocations can provide a quantitative description of the inelastic deformation that occurs near the edges of thin tabular excavations (stopes) at deep levels in brittle rock. The stope is modeled as an array of edge dislocations that climb from the center of the stope toward the edges as the stope is enlarged. The dislocations representing the stope interact with dislocations representing inelastic deformation in the surrounding rock and with the virgin stress field. One type of interaction leads to the formation of a zone of fractured rock, represented as an array of dislocations extending ahead of the stope. The continuous migration of dislocations into the plane of the stope results in the production of a ‘fracture zone’ and the continuous convergence of the center of the stope. This process consumes much of the energy released by extending the stope, and also relaxes the intense stress field near the edge of the st

ISSN:0148-0227    

DOI:10.1029/JB076i029p07088

年代:1971

数据来源: WILEY

摘要:

A free‐air gravity map along the east coast of Africa from about 1°S to 7°S is constructed. The most important features of this map are:1. A relative free‐air gravity high that approaches 0 mgal just seaward of Mombasa. This high is flanked to the west by a free‐air low more negative than −100 mgal and to the east by a low more negative than −50 mgal. Isostatic calculations indicate that these anomalies do not arise from ‘edge’ effects, but result from crustal structure. The high extends from Pemba Island and appears to represent a submarine extension of the island. Crustal models indicate thick sediment accumulations on either side of this submarine extension.2. A free‐air gravity low observed throughout the length of the map at water depths ranging from about 2000 to 3500 meters. Landward of this low is a free‐air gravity high that appears to extend onshore at about 2°S. This high is interpreted as representing a continuous basement ridge, somewhat similar to the ridge observed off the east coast of the United States. However, unlike the basement ridge observed off the east coast of the United States, which appears to be generally located at the shelf break, the presumed basement ridge off the east coast of Africa does not follow any particular topographic contour. It is located beneath ocean depths exceeding 2000 meters in the south to possibly onshore in an area farther to the north. Previous refraction measurements taken seaward of the gravity high did not detect the presence of the ridge.The widespread existence of basement ridges on nontectonic continental margins indicate their common origin regardless of how they are expressed. If they are the products of the initial demarcation of the continents, the location of such ridges and, hence, the gravity signature associated with the ridges may define

ISSN:0148-0227    

DOI:10.1029/JB076i029p07107

年代:1971

数据来源: WILEY

摘要:

The results of 57 seismic‐refraction profiles recorded in the South Atlantic Ocean south of 47°S are used to describe the gross structure of the Scotia Sea basins, the Falkland plateau, and, to a lesser extent, the North Scotia and South Sandwich ridges. The Drake passage and Scotia Sea basins have normal or nearly normal oceanic crust. Their floors are covered by 300–1000 meters of sediment, except in a band in the western part, where the sediment cover is thin and nonuniform. There is direct correspondence between the position of the band of thin sediments and the position of a low oceanic ridge, as defined by morphology, seismic refractions, magnetic lineations, and earthquake epicenters; this correspondence suggests that the band may represent young oceanic crust produced by sea‐floor spreading. Scouring or nondeposition due to strong bottom currents may also have reduced accumulation in this band. The Falkland plateau is a southward‐tilted continental block capped by a thick wedge‐shaped body of sediments, the top‐most layers of which continue farther south to form the floor of the adjacent Falkland trough. The section beneath the Falkland trough is similar to a depressed or subsided oceanic crust overlain by 4 km of low‐velocity sediments.A complete set of travel‐time graphs can be ordered from the American Geophysical Union, Suite 435, 2100 Pennsylvania Ave., N.W., Washington, D.C. 20037. Document J71‐001; $1.00 p

ISSN:0148-0227    

DOI:10.1029/JB076i029p07118

年代:1971

数据来源: WILEY