摘要:

The earth's lithosphere and asthenosphere are modeled as a thin elastic sheet and a fluid substratum, respectively; the physical principles involved are briefly described. The flexural rigidity of the lithosphere is deduced from observations of the wavelength and amplitude of bending in the vicinity of supercrustal loads. Data from Lake Bonneville given by M. D. Crittenden, Jr., are reinterpreted to give a value for the flexural rigidity of the lithosphere in the Basin and Range province of the western United States of 5×1022Newton meters. Observations of loading in Canada give values for the flexural rigidity of greater than 3×1020N m for the Caribou Mountains in Northern Alberta; about 4×1023N m for the topography over the Interior Plains; about 1023N m for the Boothia uplift in arctic Canada; and about 1025N m for the bending of the beaches of Pleistocene Lakes Agassiz and Algonquin. The flexure of the lithosphere at Hawaii and the bending of the oceanic lithosphere near island arcs give values of about 2×1023N m. For short‐term loads (103–104years) the flexural rigidity of the continental lithosphere is almost two orders of magnitude larger than for long‐term loads, indicating nonelastic behavior of the lithosphere with a viscous (about 1023N sec m−2) as well as an elastic response to stress. From the values of the flexural rigidity, the thickness of the continental lithosphere is inferred to be about 110 km and that of the oceanic lithosphere about 75 km or more. The anomalously low flexural rigidity of the lithosphere of the Basin and Range province may be due to a very thin lithosphere, only about 20 km thick, with hot, lower crustal material acting as an as

ISSN:0148-0227    

DOI:10.1029/JB075i020p03941

年代:1970

数据来源: WILEY

摘要:

Model studies show that the low anomaly amplitudes in the 400‐km‐wide magnetic smooth zones bordering the North Atlantic can be explained by sea‐floor spreading during the Early Triassic. At that time the northern mid‐Atlantic ridge was crossed at a fairly high angle by the magnetic equator, and low anomaly amplitudes should result in these circumstances. The 100‐km‐wide transition between the low‐amplitude zones and correctable 200‐gamma anomalies toward the ridge crest can be explained in terms of rapid polar wandering (25 cm/yr), independently established for the Late Triassic, and simultaneous sea‐floor spreading of 1 cm/yr. An alternate theory for the smooth zone follows from the low anomaly amplitudes being created by the Tertiary arctic extension of the mid‐Atlantic Ridge. While the rift is still close to terrestrial sediment sources, new sea floor is kept inundated by sediment, which gains access to the rift valley by utilizing transverse fracture valleys. In place of highly magnetized, rapidly quenched pillow basalts, the magma forms less magnetic dolerite sills at the basement‐sediment interface. Any magnetized pillows buried by sediment may be heated while st

ISSN:0148-0227    

DOI:10.1029/JB075i020p03955

年代:1970

数据来源: WILEY

摘要:

A platinum temperature transducer moving at a constant speed in a drill hole gives a temperature that is the convolution of the true temperature and the impulse response of the transducer. The true temperature function appearing in the convolution integral can be determined by inverse filtering, and accurate thermal gradients can be obtained by using moving probes that are not in thermal equilibrium. Layered sections composed of layers from 1 to 15 meters thick, with thermal conductivities varying from 5 mcal/cm sec °C to 15 mcal/cm sec °C were synthesized. Large apparent heat‐flow anomalies associated with a probe not in equilibrium and moving through the layered media at a constant speed of 0.5 meter/sec were examined. From a laboratory determination of the time response of the probe to a step change in temperature, an inverse filter can be designed that, when convolved with the measured temperature profile, gives the true temperature and thus gives correct thermal gradients. The proposed method of recovering the true temperature gradient would result in a continuous equilibrium temperature gradient with greater resolution and with no sacrifice in logging time. Small variations in a continuous log of thermal conductivity, especially in sedimentary sections, can be of value in stratigraphic correlation and interpretat

ISSN:0148-0227    

DOI:10.1029/JB075i020p03967

年代:1970

数据来源: WILEY

摘要:

The collection efficiency for inertial impaction on simple collecting configurations was examined using a worst‐case approach. The shock standoff distance was assumed constant across the collector, and the air mass behind the shock wave was assumed to be moving parallel to the collecting surface with a constant velocity. This velocity was calculated from the conservation of mass flow. The drag force on the particle was taken as the experimentally determined Millikan drag force with the modifications suggested by Kornblum. Sampling configurations examined were a disk, a square plate, and a ribbon. Shock‐wave standoff distances were taken from the experimental measurements of J. M. Kendall, Jr., for disks and from the theoretical calculations of A. P. Bazzhin for ribbons and were extrapolated to Mach numbers between 1 and 5 where necessary. We have derived a simple formula for the collection efficiency that depends on a parameterqdefined asRcρ1/rρpwhereRcis the collector half‐width,p1is the atmosphere density,ris the radius of the particle impacting, andPPis the density of the particle. The value ofq, which yields around 90% collection efficiency for Mach numbers greater than 2, is 0.17 for a disk collector and 0.10 for a ribbon collector. As the value ofqdecreases, the collection efficiency increases. For Mach numbers greater than 2, doubling the value ofq, which gives a 90% collection efficiency, results in the collection efficiency dropping to zero. Thus for values ofqgreater than 0.34 for a disk collector and 0.20 for a ribbon collector, the collection efficiency is zero. The above results are valid for altitudes and particle sizes such thatrλ1/5 can also be treated by changing the value of a coefficientC, which appears in the drag force. The general method presented is applicable to all atmospheric conditions, but the results were examined in detail only for those conditions that are applicable to rocket collections of meteoric dust. Special attention was given to the Luster rocket sampling instrument configuration. The collecting surface of the Luster rocket approximates a ribbon configuration of half‐width 0.15 meter. It is found that at altitudes of 80 km and above the Luster rocket should collect with greater than 90% efficiency stony particles (ρ = 3.4 g/cm3) of radius greater than 0.01μ and ice particles of radius gre

ISSN:0148-0227    

DOI:10.1029/JB075i020p03976

年代:1970

数据来源: WILEY

摘要:

Aluminum spheres were fired vertically into dry quartz sand in the light‐gas gun facility at the NASA Ames Research Center. A velocity of 6.37 km/sec and a chamber pressure of 150 μ were used for all shots. Using an estimated impact pressure of 500 kb, heating of the target was computed to be 26% of the initial projectile kinetic energy, while ejecta absorbed 53%, both figures being very similar to those found earlier for basalt. Energy lost to compaction was 20% of the total initial energy, whereas in basalt it is negligible. Comminution in the already granular sand used about 8% of the energy, whereas for basalt this ranges from 10 to 24%. No observed ejecta velocities exceeded that of the impacting projectile. Most of the fused material, if any, was ejected, and there was an increase in density at the bottom of the crater due to compaction. The final shape of craters in sand emphasizes the importance of target strength at low stress leve

ISSN:0148-0227    

DOI:10.1029/JB075i020p03987

年代:1970

数据来源: WILEY

摘要:

Detailed paleomagnetic measurements have been made on a lava sequence exposed between altitudes of 700 to 1000 meters in the Amarkantak‐Dindori tract on the eastern margin of the Deccan traps. The variation in the direction of remanent magnetism with altitude has been studied. The paleomagnetic data reveal the occurrence of a reversal of the earth's magnetic field at an altitude of about 975 meters at Amarkantak as well as the unstable behavior of the geomagnetic field near the polarity transition. These data are at variance with the observation of the same reversal of magnetic field at an altitude of about 625 meters in the paleomagnetic study of several other vertical sequences in the Deccan traps. The variance is interpreted in terms of an uplift of the Amarkantak region by about 350 meter

ISSN:0148-0227    

DOI:10.1029/JB075i020p04000

年代:1970

数据来源: WILEY

摘要:

Proton magnetometer measurements were made from the USSR satellite Cosmos 49 during the period October 24 to November 3, 1964. A selected number of the 18,000 observations were fitted to a special field model; residual anomalies were less than 100 gammas and appear to be consistent with belts of broad anomalies that are known from surface and near‐surface magnetic measurements. Correlation of the residual anomalies with broad geologic provinces is good. A series of magnetic lows across the continental United States agrees in position with a proposed rift extending from the Cape Mendocino fracture off the west coast to the wrench fault system proposed by C. L. Drake and H. P. Woodward in the east coast area. In the western United States, large‐amplitude magnetic lows are associated with the Basin and Range province and the northern Rocky Mountains; both regions are characterized by high heat flow and similar crustal structure and Cenozoic geologic history. Most of central Wyoming, central Montana, and the area of the Colorado plateau is characterized by normal heat flow and generally positive magnetic anomal

ISSN:0148-0227    

DOI:10.1029/JB075i020p04007

年代:1970

数据来源: WILEY

摘要:

In general, vertical deflections are obtained either by astrogeodetic methods or by gravimetric methods. In the latter approach, gravity anomaly measurements are processed by using the so‐called Vening Meinesz equations to yield the vertical deflections. These calculated values of vertical deflections differ from the true values for two reasons: the measurements of the gravity anomalies are subject to error, and a numerical algorithm must be used to approximate the Vening Meinesz equations. In this paper, the autocorrelation functions of the deflection errors arising from these two sources are determined under the assumption that the anomalies and the error in measuring the anomalies are random processe

ISSN:0148-0227    

DOI:10.1029/JB075i020p04017

年代:1970

数据来源: WILEY

摘要:

Substitution of 3d‐transition elements for Mg and Al in the olivine, spinel, and corundum lattices causes a systematic decrease in the compressional wave velocity υpfor oxides and silicates crystallizing in these structures at low pressures. The new measurements of υpfor Fe2SiO4spinel by H. Mizutani, Y. Hamano, Y. Ida, and S. I. Akimoto fit the line for spinel compounds, which indicates that the velocity is controlled only by the densitypand the crystallographic structure and not by compositional details. In particular, the relationship for spinel compounds is υp= 15.66 ‐ 1.59pwhere υpis in km/sec andpis in g/cm3. By analogy, the equation for the shear wave velocity υsis υs= 9.88 ‐1.17p. These velocity‐density systematics suggest that the isotropic elastic properties of the Mg2SiO4‐Fe2SiO4spinel series may be predicted from a knowledge of only the density or

ISSN:0148-0227    

DOI:10.1029/JB075i020p04029

年代:1970

数据来源: WILEY

摘要:

The state of stress in a porous medium is defined. The nature of the stress‐strain relationship for each component is analyzed. The assumptions necessary to achieve symmetry of the partial stresses are discussed. The role of the soil‐water interaction coefficient is developed. We show that this coefficient is the coupling term relating soil‐skeleton and pore‐fluid defor

ISSN:0148-0227    

DOI:10.1029/JB075i020p04035

年代:1970

数据来源: WILEY