摘要:

Appendix 2, along with the entire paper, is available in microfiche. Order from the American Geophysical Union, 1707 L Street; N.W., Washington, D.C. 20036. Document J72‐002; $1.00. Payment must accompany order.During the 1969 opposition an IR (λλ 0.60–2.27 μm) mapping program of the surface of Mars was carried out at a spatial resolution of 300–500 km. Spectral albedo curves were obtained for 150 mare and desert areas. These curves fall into two well‐defined and fairly uniform color‐albedo groups corresponding to mare and desert units. The lack of areas with color and albedo that are distinctively different from those of these groups is interpreted as an indication that the surface of Mars consists of basically only two types of materials. Laboratory comparison data support a model of the Martian regolith that suggests that the general color of these surface units is due to a limonite stain coating the particles of lithic soils. Color differences between the two units in the 1‐μm region are interpreted as an indication that the proposed lithic soils of the maria are richer in pyroxene, olivine, or both than the lithic soils of the deserts. Features in the spectral albedo curves at 1.6 and 2.1 μm are interpreted as being due to the H2O ice on the surface or in the Martian atmosphere. The data are also used to show that the photometric properties of the Martian deserts can be described empirically by using the Minnaert function, at least for wavelengths between 0.60 and 2.27 μm and for phase angles up to ∼20°. Values ofk, the limb‐darkening coefficient of the Minnaert function, are given for those ranges of wavele

ISSN:0148-0227    

DOI:10.1029/JB077i017p03005

年代:1972

数据来源: WILEY

摘要:

A computer model is presented that simulates the data from a flight of an air‐borne gamma‐ray spectrometer over a surface containing gamma‐ray sources of arbitrary horizontal dimension and coordinates. The mathematical formalism is given, together with a discussion of the assumptions or approximations that are made. Representative computational results are shown for simulated flights over circular sources and across linear so

ISSN:0148-0227    

DOI:10.1029/JB077i017p03021

年代:1972

数据来源: WILEY

摘要:

Helium and argon determinations on minerals contained in ultramafic xenoliths from Salt Lake crater, Oahu, Hawaii, show low values for the ratios of these radiogenic gases, incompatible with the radioactive parent (uranium‐thorium and potassium) content. It is suggested that the gas content has been altered by diffusion during ascent of the xenoliths in the erupting lava. The diffusion of helium and argon contained in the augite of a pyroxenite (‘eclogite’) and in the olivine, enstatite, and chrome diopside of lherzolite nodules was measured at 1100°C. The4He/40Ar ratio of the inert gases released from the minerals varied linearly with the square root of the heating time. Extrapolation of the ratio backward in time to the point where the minerals of the lherzolite nodules contained the same inert‐gas ratio gave a value of 1.2 ± 0.2, which would be the gas ratio in the environment from which the gases were trapped. From this it was possible to estimate the time of exposure of the nodules to the high temperatures of the erupting lavas, which gave values between 6500 hours and 8000 hours. The possible use of such data to estimate the depth of the source of the nodules is pointed out. The4He/40Ar ratio indicates gas accumulation for at least 3.5 b.y. from a material with the same U‐Th/K ratio as the host lava of the ultramafics or as the garnet pyroxenite type o

ISSN:0148-0227    

DOI:10.1029/JB077i017p03032

年代:1972

数据来源: WILEY

摘要:

Results of the analysis of Aouelloul crater glass for cosmogenic26Al place severe constraints on the possibility that the Aouelloul crater was formed by a glassy body that was also the source of the Aouelloul glass. The size of such a body, calculated from the26Al upper limit of 4.3 dpm/kg at time of formation, is much too large to have produced either the observed crater or the distribution of Aouelloul glass around it. Analyses of the glass and the local Zli sandstone for K, U, Th, Rb, Sr, and87Sr/86Sr demonstrate that the general chemical similarity between the two materials already established for major elements also applies to these minor and trace elements. The existence of strong similarities between Aouelloul glass and Zli sand‐stone and the dissimilarities (especially in Rb versus Sr, U versus Th, and87Sr/86Sr versus Rb/Sr) between Aouelloul glass and tektites or other impactite glasses strongly support terrestrial derivation of Aouelloul glass by fusion of the Zli sandstone during impact formation of the Aouelloul crate

ISSN:0148-0227    

DOI:10.1029/JB077i017p03043

年代:1972

数据来源: WILEY

摘要:

A method for determining directly the rate of radon and thoron exhalation from the ground was studied. Radon and thoron gases are directly adsorbed on a layer of granular activated charcoal distributed over the ground surface, and the charcoal is subjected to γ‐ray spectrometry. The radon quantity is determined from the area of the photopeak due to 0.61‐Mev γ rays of214Bi and the thoron quantity from the area of the photopeak due to 2.61‐Mev γ rays of208Tl. Some results of measurements obtained by this method are p

ISSN:0148-0227    

DOI:10.1029/JB077i017p03052

年代:1972

数据来源: WILEY

摘要:

Equilibrium constants for oxygen isotope exchange between quartz and water have been measured from 195°C (1000 ln α = 12.0) to 750°C (1000 ln α = 0.4). Over limited temperature ranges the behavior of fractionation with temperature can be approximated by 1000 ln α = 3.38 (106T−2) − 3.40 for 200°–500°C and by 1000 ln α = 2.51 (106T−2) − 1.96 for 500°–750°C. The results of measurements in the quartz‐water system can be combined with analogous results from other mineral systems to make mineral‐pair isotopic thermometers for application to

ISSN:0148-0227    

DOI:10.1029/JB077i017p03057

年代:1972

数据来源: WILEY

摘要:

We have applied the Backus‐Gilbert inversion technique to the isostatic Green function for the continental United States, which we measured earlier. A two‐level compensation mechanism (overcompensation beneath the crust with the resulting mass deficiency compensated deeper in the mantle) is indicated at about the 80% confidence level. This model is consistent with seismic refraction and surface‐wave

ISSN:0148-0227    

DOI:10.1029/JB077i017p03068

年代:1972

数据来源: WILEY

摘要:

A simple elastic stiffness figure called theQellipsoid is derived from the basic equations for elastic waves in anisotropic media. HereQis the sum of the squares of three velocities for a given direction multiplied by the density. This surface can be used (1) to show that only 18 independent elastic constants are necessary to describe the most general anisotropic case (triclinic), (2) to orient sonically a material through a least‐squares fit of the seismic data, (3) to test statistically for velocity anisotropy, (4) to provide a constraint on velocity measurements, and (5) perhaps to estimate the variation in directional properties of second‐rank tensor properties, such as thermal and electromagnetic properties. In general the measurement of velocity anisotropy may provide a means of estimating petrofabric and structural patterns in the crust and upper mantle and act as a constraint on petrologic models. The method requires measurement of the pseudocompressional velocity and two pseudo shear‐wave phase veloc

ISSN:0148-0227    

DOI:10.1029/JB077i017p03078

年代:1972

数据来源: WILEY

摘要:

A step‐by‐step display of the theoreticalP‐wave amplitude spectrum of shallow (focal depth ≤ 40 km) earthquakes withmbvalues ranging from 5.9 to 6.3 and underground explosions of comparable magnitudes as the signal propagates from source to receiver indicates that the factors most influential in shaping the respective spectra are the source crust transfer function, which includes the focal depth effect, and the source function. The results, although not unequivocal, favor a peak in the amplitude spectrum of the teleseismicPcoda of earthquakes rather than a flat spectrum at low frequencies. The effect of focal depth appears to have more influence than the effect of source parameters on the peak frequencyf0in the spectra of earthquakes, whereas the source function is the important parameter for shallow underground nuclear explosions. For shallow seismic events of comparablembthef0of earthquake spectra is smaller than thef0of explosion spectra by approximately an order of magnitude. The pronounced minimum (hole) at about 0.1 Hz in the long‐period spectrum of earthquakes is associated with the focal depth effect and can be identified for several events. However, theoretically predicted holes starting at about 0.5 Hz in the short‐period spectrum of assumed unilateral faulting earthquakes are due to the extended source effect and are not identifiable on any of the experimental spectra. For short‐period records of Longshot and Milrow, Haskell's analytic formulation of the Werth and Herbst displacement potential, in conjunction with the outlined theory, predicts fairly accurately the increase (approximately 0.15 sec) in the duration of the first half‐cycle with increasing yield. For the corresponding long‐period records of Milrow his formulation predicts a value smaller than a mean of the measured values by about 15% (0.32 sec). Haskell's equations, together with the rest of the theory, appear to predict fairly accurately the variation inmbwith yield for these two events when amplitude measurements are restricted to the

ISSN:0148-0227    

DOI:10.1029/JB077i017p03081

年代:1972

数据来源: WILEY

摘要:

Excitation of tsunamis by submarine faults is studied with the purpose of revealing the relations that exist between seismic and tsunamigenic source parameters. Evidence is produced to show that the far‐field deep‐water wave amplitudes are determined by the relationε(r,ϕ,t)=[S0u0sinλsinδTs(ϒ)F(ϕ;ξ0;η0)]/[π3/2(αrt)1/2H]where δ and λ are the dip and slip angles, respectively,S0= η0ξ0is the tsunamigenic area,u0is the fault dislocation, α is the group velocity of long gravity waves, andTs(ϒ) is a calculable wave function that depends on the epicentral distancer, the mean ocean depthH, and the timet. The dependence of ε on the azimuth angle ϕ and on the linear dimensions of the source is embodied inF.We have applied the above relation to four North Pacific earthquakes for which the seismic source parameters were derived from analyses of 236 signals of mantle Love and Rayleigh waves. The corresponding values of ε were taken from observations of W. G. Van Dorn (1965). Solving for η0andS0, we obtain, for example, a width of 20 km and a tsunamigenic area of about 1.2 × 104km2for the Alaskan earthquake of March 28, 1964. Conversely, the above equation can be used to estimateu0, provided that ε andS0are known. Deep‐water radiation patterns are derived: wave amplitudes in a direction normal to the fault exceed corresponding amplitudes in the fault's direction. Typical values for the ratioF(84°)/F(0°) are 2 : 1 for earthquakes with magnitudeM∼7¼, 5 : 1 forM∼8, and 14 : 1 for M ∼8½. Observ

ISSN:0148-0227    

DOI:10.1029/JB077i017p03097

年代:1972

数据来源: WILEY