摘要:

Two cases of the buckling of hard‐pack snow on a hillside of constant slope are investigated. One model is based on a linear viscoelastic surface slab above a similar viscoelastic sublayer. The second model is of a viscoelastic slab resting on a rigid base. Questions resolved from the analysis of these models are the rise times for order of magnitude changes in buckling mode amplitude, the overburden conditions necessary for the formation of buckling modes, and the effect of subsurface imperfection size on buckle formation. It is suggested in field observations of avalanche‐sensitive slopes that consideration of buckle mode formation be included in physical measureme

ISSN:0148-0227    

DOI:10.1029/JB078i002p00339

年代:1973

数据来源: WILEY

摘要:

The normalized bulk compressibility β/β0of a porous medium is expressed directly in terms of pore strains. The derived expression holds over all porosity and allows for direct substitution of both different pore geometries and pore‐pore interactions into the strain term. Pores are assumed to be open. The parent (matrix forming) material is assumed to be homogeneous and isotropic. Pore fluids may be admitted. A simple pore‐pore interaction term is introduced. Upper‐bound stiffness equations (i.e., equations ignoring pore‐pore interactions) are derived for media with oblate spheroidal pores. Effective stress is introduced into the general equation

ISSN:0148-0227    

DOI:10.1029/JB078i002p00352

年代:1973

数据来源: WILEY

摘要:

Metallic spheroids approximately 1 mm in diameter and having a dendritic structure appropriate to a rapidly solidified liquid alloy are encountered in conjunction with Canyon Diablo meteorites in the vicinity of the Barringer crater, Arizona. Compositionally and structurally similar particles have been encountered in lunar soils returned from Apollo 11, 12, 14, and 15 expeditions. The present study is devoted entirely to Canyon Diablo spheroids, which are shown by means of electron microprobe techniques to be enriched in Ni and considerably enriched in S and P relative to the metallic phases of Canyon Diablo meteorites. In contrast to earlier theories that considered only selective oxidation, a process of formation is now put forward involving the earlier stage of the shock‐induced melting of sulphide‐rich areas in the meteoritic projectile when it hits the earth. This process is also applicable to metallic spheroids formed on the moon, where oxidation processes will be minimal. Measuring the interarm spacing of the dendrites leads to estimates of 500°–30,000°C/sec for the rates at which these spheroids cooled through the solidification range. The breakup of the Canyon Diablo iron meteorite projectile is described by a series of events involving increasing shock pr

ISSN:0148-0227    

DOI:10.1029/JB078i002p00363

年代:1973

数据来源: WILEY

摘要:

Shock wave Hugoniot data have been obtained for almandine‐garnet of composition (Fe0.79, Mg0.14, Ca0.04, Mn0.03) Al2Si3O12to pressures of>650 kb. The Hugoniot data indicate the onset of a high‐pressure phase at 195 ± 20 kb. Equation‐of‐state systematics and crystal chemical data (stemming largely from analog compounds) suggest that the high‐pressure phase occurs in an ‘ilmenitelike’ structure with an initial density of 4.44 ± 0.04 g/cm3. This value represents an increase of about 6% over the initial garnet density of 4.180 ± 0.005 g/cm3. The adiabatic bulk modulus K0sand its first pressure derivative (∂Ks/∂P)Twere calculated for the high‐pressure phase and found to be 3.19 ± 0.39 Mb and 2.6 ± 0.7, respectively. The major source of probable error in these values results from the indicated uncertainty in the initial density of the high‐pressure phase. These results strongly suggest that upper mantle minerals are likely to occur in the ilmenite structure over a substantia

ISSN:0148-0227    

DOI:10.1029/JB078i002p00375

年代:1973

数据来源: WILEY

摘要:

The scattered fields for a line source located over a nonuniform stratified earth are computed on the basis of a full wave analysis. It is shown that the radiation pattern is strongly dependent upon the gradient of the overburden depth and that the relative amplitudes of its principal lobes are sensitive to the substratum surface impedance. The frequency of excitation, the angle of incidence, the complex permittivity of the overburden, and the roughness of overburden‐substratum interface are other variable parameters considered in this paper. The relationship between the full wave and geometrical‐optical solutions is also discus

ISSN:0148-0227    

DOI:10.1029/JB078i002p00393

年代:1973

数据来源: WILEY

摘要:

Snis a short‐period shear wave that propagates in the lithosphere. For long paths, the wave may travel well below the M discontinuity as it seeks a least‐time path. It cannot penetrate the partially molten asthenosphere. More than 130Snphases from earthquakes in the North Atlantic, recorded by stations on islands and surrounding coasts, have been analyzed by regression to obtain regionalized velocities corresponding to different age zones of the Atlantic lithosphere. The highest velocity, 4.71 ± 0.01 km/sec, was found for sea floor older than 50 m.y. The average velocity for younger sea floor, age 0 to 50 m.y., was 4.58 ± 0.02 km/sec. For continental paths,Snvelocity was 4.61 ± 0.02 km/sec. These velocities are interpreted in terms of a lithosphere evolving into a colder, denser mineral assemblage as part of the spreading process. Rocks with elastic velocity higher than that of peridotite must be present in the suboceanic lithosphere to account for the high value of 4.71 ± 0.01 km/sec found in thi

ISSN:0148-0227    

DOI:10.1029/JB078i002p00407

年代:1973

数据来源: WILEY

摘要:

Functional relations expressing liquidus phase boundaries in a six‐component system are obtained for the basalt‐peridotite system. The compositions of liquids coexisting with two of four minerals (olivine, orthopyroxene, clinopyroxene and plagioclase) are formulated as linear equations by using a least‐squares fit to experimental data on simple silicate systems and natural rocks at 1 atm and 8, 11, 14, 17, 21, and 30 kb. The functional liquidus phase relations, combined with distribution coefficients of MgO, FeO, Al2O3, and Na2O between minerals and liquid, are used to compute compositions of liquids formed from plausible source rocks of basalts at various pressures and degrees of partial melting. Permissible compositions for primary liquids of abyssal basalts are estimated from the compositions of abyssal basalts themselves and from those extending from these basalts toward a Mg‐rich olivine. A computer program is made to select source rock compositions by using the constraint that source rock must be able to produce a liquid with a permissible composition of a primary liquid at some pressure and degree of melting. A Hawaiian eclogite satisfies the constraint when it melts at 4 kb. Peridotites are required to melt at higher pressures. Some interpretations are di

ISSN:0148-0227    

DOI:10.1029/JB078i002p00412

年代:1973

数据来源: WILEY

摘要:

Seismic reflection and total magnetic field intensity observations were made off the western coast of India as part of the 1967 global scientific expedition of the USSOceanographer. Linear fault block fragments appear to form the base of the northern segment of the platform that comprises the Laccadive‐Maldive‐Chagos trend. The NW continuation of these linear fault block fragments creates a basement ridge that extends to at least 20°N and is interpreted to be the NW continuation of the main Laccadive structural trend. This basement ridge may be a relict margin of the Indian continent. No obvious magnetic lineations were found in the study area. Short‐wavelength variations of the magnetic field along the Laccadive trend suggest a relatively shallow source. Long‐wavelength high‐amplitude magnetic anomalies suggest the presence of a broad ridge composed of relatively high magnetic material near the western shelf edge of the Indian

ISSN:0148-0227    

DOI:10.1029/JB078i002p00432

年代:1973

数据来源: WILEY

摘要:

Twenty‐six new heat flow determinations in the north central United States range from 0.90 to 2.2 HFU (μcal/cm2sec). Two distinct provinces are characterized on the basis of both heat flow and physiography, although all the stations are located in the stable continental interior. The Interior Lowlands are characterized by a regional mean value of 1.4 HFU, whereas the regional value for the northern Great Plains is about 2.0 HFU. Local variations of heat flow in the Interior Lowlands are attributed to differences in basement rock type and the attendant contrasts in radiogenic heat production and thermal conductivity, Because basement lithologies and crustal thicknesses are quite similar in the Interior Lowlands and the northern Great Plains, most regional deviations in heat flow must be attributed to temperature differences in the upper mantle. The lower heat flow values (≤1.5 HFU) are associated with negative seismic travel time anomalies, whereas the high values (≥1.8 HFU) are related to positive station residuals. LowerPnvelocities are also associated with high heat flux in the northern Great Plains. These correlations support the conclusion that difference in regional heat flux can be attributed to differences in the temperature structure in the upper

ISSN:0148-0227    

DOI:10.1029/JB078i002p00441

年代:1973

数据来源: WILEY

摘要:

Four pairs of ScPand ScSphases recorded at the station Dumont d'Urville, Adelie Land, at the epicentral distance of about 50°, have been frequency analyzed. The slope of spectral ratio has been utilized to calculate the average value ofQβin the mantle between the Tasman Sea and the station. WithQα/Qβ= 1.9, we estimate the average value 〈Qβ〉 = 380. This is much higher than the estimation by H. Kanamori of 230 for the mantle beneath southern Arizona and Ne

ISSN:0148-0227    

DOI:10.1029/JB078i002p00462

年代:1973

数据来源: WILEY