摘要:

The Apollo 16 rocks are classified in three broad intergradational groups: (1) crystalline rocks, subdivided into igneous rocks (C1) and metaclastic rocks (C2), (2) glass, and (3) breccias, which are subdivided into five groups (B1–B5) on the basis of clast and matrix colors. Most of the rocks were derived by impact brecciation of an anorthosite‐norite suite but may represent ejecta from more than one major basin. First‐cycle breccias are believed to have consisted of clasts of crushed anorthosite‐norite in a fine‐grained partly fused matrix (resembling some rocks in ourB4class) with a chemical composition similar to that of the clasts. Most of the other recognized breccia types could have been produced by rebrecciation of first‐cycle breccias. These rocks resemble Apollo 15 Apennine front breccias, but most of them lack the multiple brecciation metamorphism that characterizes rocks of the Fra Mauro formation (Apollo 14). Like the Apollo 15 breccias, most Apollo 16 rocks appear to have been derived from levels of the lunar crust less reworked than the level of Fra Mauro breccias. The nearest potential source for rocks of this sort is the Nectaris basin, but Nectaris ejecta may be overlain by ejecta from younger basins. Common preservation of preimpact lithologies suggests that most of the rocks are exposed as a consequence of one major impact and have been reworked only by much smal

ISSN:0148-0227    

DOI:10.1029/JB078i014p02379

年代:1973

数据来源: WILEY

摘要:

At least three paramagnetic and one ferromagnetic components have been resolved in the electron magnetic resonance spectra of plagioclase fractions of two lunar samples, 14053‐47 and 14321‐166. Measurements were made at 9 and 35 GHz and at 346° 300°, and 130°K. One of the paramagnetic components is attributed to Fe3+in crystal sites of low symmetries for which the axial termsDare 0.4 ≤D≤ 0.6 cm−1and the ratio of rhombicEto axial terms is 0.2430 and 3, respectively. The absolute concentration η(Ti3+) in 14053‐47 and 14321–166 is ∼3 × 1017and ∼6 × 1017g−1, respectively. The concentrations of Fe3+and Ti3+are inversely correlated. The ferromagnetic resonance is attributed to single‐domain iron particles on the basis of comparison with many lunar samples. A plagioclase fraction from Stillwater specimens was measured for purposes of comparison. The spectrum of Fe3+in this material was quite similar to the two lunar plagioclases in shape,geffvalues, and relative proportions in various crystal sites. The concentration was approximately five times greater than that in the sample from 14053‐47. A spectral component attributable to Ti3+was not observed, nor was a ferromagnetic c

ISSN:0148-0227    

DOI:10.1029/JB078i014p02393

年代:1973

数据来源: WILEY

摘要:

Brittle fracture tests of 105 fine‐grained quartz arenites were conducted at 25°C, 1.0‐kb confining pressure, a constant strain rate of 6.5 × 10−5/sec, and pore pressure ranging from 0 to 750 bars. Orientation of planar anisotropy (bedding or cross‐bedding) with respect to principal stresses has little influence on the fracture strength. The Donath orientation effect depends on rock type. Strong dependence of fracture strength on porosity is of the formy=axb(whereyequals stress difference at failure,xequals porosity, anda>0>b; in our samples, values foraranged between 16 and 25 kb, andbbetween −0.8 and −1.0). Through‐going shear fractures result from coalescence of grain boundary cracks, extension fractures within grains, and void space. Rocks with low porosity develop through‐going shears only after many grains are extension fractured. The functional relationship between porosity and fracture strength derives from the lower energy required for propagating cracks to use void space rather than forming ex

ISSN:0148-0227    

DOI:10.1029/JB078i014p02403

年代:1973

数据来源: WILEY

摘要:

The pressure dependence of the single‐crystal elastic constants of synthetic stoichiometric spinel (MgAl2O4) has been measured by using the ultrasonic pulse superposition method. A quadratic pressure dependence of all three elastic constants was observed in the range from 0 to 10 kb. The zero‐pressure values and the first pressure derivatives of the elastic constants agree remarkably closely with the data of Schreiber for a nonstoichiometric spinel MgO·2.6Al2O3). The valueKT(∂2Ks/∂P2)T= −94 of the dimensionless second pressure derivative of the adiabatic bulk modulusKsis about ten times larger than that for alkali halides and would give rise to markedly nonlinear pressure dependence of theP‐wave velocities in the range up to 100 kb. The isothermal equation of state calculated from the elastic data on the basis of the first‐order Birch equation of state agrees up to about 200 kb within experimental error with the X‐ray data of Mao et al. for (FexMg1−x)2SiO4spinel solid solutions. The orientation dependence of the microscopic first and second Grueneisen parameters (mode gammas) is calculated on the basis of the anisotropic elastic continuum model and is found to be almost isotropic for the first, but very anisotropic for the second mode gammas. The macroscopic first Grueneisen parameter, its first pressure derivative, and the Anderson‐Grueneisen parameter calculated from the elastic data on the basis of the anisotropic continuum model do not agree with the coresponding thermal data. This fact is attributed to the neglect of optical modes and of dispersion in the anisotr

ISSN:0148-0227    

DOI:10.1029/JB078i014p02418

年代:1973

数据来源: WILEY

摘要:

When a pore pressurePpand a confining pressurePcare applied to a porous solid, various physical properties are affected. When dealing with these properties, the concept of effective pressure is often used. On the basis of the examples of pore volume and of bulk volumetric strain for several elastic solids, we emphasize that (1) there is no unique law of effective pressure, (2) effective pressure may not be a very useful concept, unless it has the simple formPe=Pc−Pp, and (3) when a property does not vary linearly with pore or confining pressure, effective pressure does not in general have any simple analytic expression, unless again it reduces toPe=Pc

ISSN:0148-0227    

DOI:10.1029/JB078i014p02434

年代:1973

数据来源: WILEY

摘要:

Examination of the geometrical properties of theI1,I2D½,I3D⅓space shows that in this space the failure surface of a material can be clearly and easily displayed. We developed a systematic way of describing material behavior, for organizing the bulk of experimental data into units of comprehensible proportions so that the underlying physics can appear. This same description provides a very convenient format for the description of rock mechanics failure in a continuum mechanics computer calculation. The applicability of the procedure is presently limited by a lack of experimental da

ISSN:0148-0227    

DOI:10.1029/JB078i014p02438

年代:1973

数据来源: WILEY

摘要:

The mathematical framework for describing plane waves in elastic and linear anelastic media is presented. Theoretical results suggest that the nature of plane waves in anelastic materials is distinctly different from the nature of plane waves in elastic materials. In elastic media the only type of inhomogeneous plane wave (PorS) that can propagate is one for which planes of constant phase are perpendicular to planes of constant amplitude. However, in anelastic media this is the only type of inhomogeneous wave that cannot propagate. For an inhomogeneousPorSplane wave the particle motion is elliptical, the velocity is less than that of a corresponding homogeneous wave, the maximum attenuation is greater than that of a corresponding homogeneous wave, and the direction of maximum energy flow is not the direction of phase propagation. Expressions for the energy flux, energy densities, dissipated energy, stored energy, andQ−1are derived from an explicit energy conservation relation, valid for an arbitrary steady state viscoelastic radiation field. Each energy expression is valid for homogeneous or inhomogeneousPorSplane waves in elastic or linear anelastic medi

ISSN:0148-0227    

DOI:10.1029/JB078i014p02442

年代:1973

数据来源: WILEY

摘要:

The finite difference iterative method yields the full wave solution to problems without exact solution that involve the scattering of elastic surface waves at vertical discontinuities in homogeneous media. The technique successfully predicts the results for a problem for which an analytical solution does exist, that of a Rayleigh wavelet propagating on a homogeneous, isotropic, semi‐infinite half space. For a Rayleigh wave of unit amplitude incident normally at a 90° corner in a homogeneous medium of Poisson's ratio σ = 0.245, the amplitude coefficients for transmission and reflection were found to be 0.64 ± 0.02 and 0.36 ± 0.02, respectively, whereas the corresponding phase shifts were −79 ± 5° and 38 ± 5°. About 45% of the incident energy is converted into body waves at the corner, and more than 90% of this energy is radiated back into a sector of the plane included between lines making angles of 15° with the two free surfaces. All these results, which are independent of wavelength, agree well with other published data. In the related problem of Rayleigh wave scattering at a downward step discontinuity, the dependence on step height of the transmission and reflection coefficients and of the phase shifts for a given wavelength component has also been investigated. Results show good agreement with both experimental curves and earlier theoretical work. This type of numerical simulation may be applied to other two‐dimensional geometries, including layered

ISSN:0148-0227    

DOI:10.1029/JB078i014p02454

年代:1973

数据来源: WILEY

摘要:

Relative shear‐wave excitation equivalent to large Nevada Test Site underground explosions was detected for the Amchitka Island test Milrow. Use of Milrow Love waves as match filters enabled detection of these waves on Longshot and Milrow collapse recordings as well. Mechanisms other than tectonic strain release must have produced the Love waves. The Rayleigh waves from the collapse were oppositely polarized relative to Milrow and were delayed by a time increment approximately equal to the expected free‐fall time through the postexplosion cavity. A small delay (1 to 2 sec) in the initial phase of long‐period components of the source function was detected for Milrow relative to Longshot. A Rayleigh‐wave amplitude ratio for Milrow and Longshot was precisely determined by match filtering; this ratio agreed almost exactly with amplitude scaling proportional to the cube root o

ISSN:0148-0227    

DOI:10.1029/JB078i014p02467

年代:1973

数据来源: WILEY

摘要:

Underground nuclear explosions, even though they are thoroughly contained, invariably produce spallation. This mass of earth and rock, kicked up by the initial shock wave, falls back within a second or two. It is possible that the surface waves observed from explosions originate from the impact of this material. This hypothesis has been investigated, first, by estimating the spall impulse from accelerometer data, computing the surface wave amplitudes consistent with this impulse, and comparing the results with observed amplitudes and, second, by performing computer explosion simulation experiments with and without spallation and comparing the amplitudes of the resulting surface waves. The comparison of the amplitudes consistent with the spall momentum with the observed Rayleigh amplitudes at ranges of 50–500 km indicates that the spall has sufficient impulse to account for these waves. The computer simulation experiments show that the Rayleigh amplitudes corresponding to realistic inelastic spallation have several times the amplitude of Rayleigh waves computed from purely elastic behavior. The surface wave for the spallation case is also delayed relative to the wave from the elastic sourc

ISSN:0148-0227    

DOI:10.1029/JB078i014p02475

年代:1973

数据来源: WILEY