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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Rigorous precision p-wave positron-hydrogen scattering calculation

Rigorous lower-bound p-wave positron-hydrogen phase shifts are calculated below the positronium pickup threshold. The wave function is expanded in terms of the two linearly independent D functions each multiplied by an associated Hilleraas-type radial function with two parameters. Adiabatic and nonadiabatic corrections have been included. The results are found to be larger than Armstead's (1968) in all cases near the upper edge of his estimated uncertainty.

Bhatia, A. K.↗
NASA NTRS1978

Laboratory measurements of p-wave seismic Q on lunar and analog rocks

The longitudinal-wave, internal friction quality factor (Qp) of out-gassed rock subjected to hydrostatic confining pressure was measured by a technique of aerodynamically shaping the sample ends to remove most of the air drag. Q values of about 1000 and 100 were obtained at 100 MPa and in laboratory air, respectively. The temperature dependence of Q in lunar rock 70215.85 and an analog of lunar basalt was investigated over the range -100 to 450 deg C. A systematic increase in Q was observed at 50 Hz, 5 kHz and 50 kHz. When the temperature was lowered to -100 deg C moderate decreases in Q were observed from 100 to 250 deg C, and high Q values were obtained at 450 deg C. The temperature and pressure dependences of Q suggest that high lunar seismic Q values imply a very dry crust to depths of at least 50 km. These results further indicate that elastic waves are damped in volatile-rich rock by an absorption mechanism which involves changes in the bonding, structure and coverage of the molecular, physisorbed and chemisorbed H2O at crack and grain boundaries.

Tittmann, B. R.↗
NASA NTRS1983

the P-wave upper mantle structure beneath an active spreading center: The Gulf of California

Detailed analysis of short period travel time, and waveform data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km. More than 1400 digital seismograms from earthquakes in Mexico and central America recorded at SCARLET yield 1753 travel times and 58 direct measurements of short period travel time as well as high quality, stable waveforms. The 29 events combine to form a continuous record section from 9 deg to 40 deg with an average station spacing of less than 5 km. First the travel times are inverted. Further constraints arise from the observed relative amplitudes of mantle phases, which are modeled by trial and error.

Walck, M. C.↗
NASA NTRS1983

The rupture process and asperity distribution of three great earthquakes from long-period diffracted P-waves

The variation of maximum earthquake size along the subduction zones has been interpreted as a variation in the seismic coupling ostensibly related to the mechanical conditions of the fault zone. Great differences are noted between the seismographs of the three great earthquakes whose rupture processes are presently considered: in the Kurile Islands (1963), The Rat Islands (1965) and Alaska (1964). On-scale long period P waves were recorded in all cases. Source time functions are deconvolved from the observed periods. It is concluded that maximum earthquake size is related to the asperity distribution on the fault. The subduction zones with the largest earthquakes have very large asperities, as in the Alaskan case, while the zones with the smaller great earthquakes, such as the Kurile Islands, have smaller scattered asperities.

Ruff, L.↗
NASA NTRS1984

The p-wave upper mantle structure beneath an active spreading centre - The Gulf of California

Over 1400 seismograms of earthquakes in Mexico are analyzed and data sets for the travel time, apparent phase velocity, and relative amplitude information are utilized to produce a tightly constrained, detailed model for depths to 900 km beneath an active oceanic ridge region, the Gulf of California. The data are combined by first inverting the travel times, perturbing that model to fit the p-delta data, and then performing trial and error synthetic seismogram modelling to fit the short-period waveforms. The final model satisfies all three data sets. The ridge model is similar to existing upper mantle models for shield, tectonic-continental, and arc-trench regimes below 400 km, but differs significantly in the upper 350 km. Ridge model velocities are very low in this depth range; the model 'catches up' with the others with a very large velocity gradient from 225 to 390 km.

Walck, M. C.↗
NASA NTRS1973

Velocity structure and evolution of the moon

Seismic data from the Apollo Passive Seismic Network stations are analyzed to determine the velocity structure and to infer the composition and physical properties of the lunar interior. Data from artificial impacts (SIBV booster and LM-ascent stage) cover a distance range of 9 to 1750 km. Travel times and amplitudes, as well as theoretical seismograms, are used to derive a velocity model for the outer 150 km of the moon. The P-wave velocity model confirms an earlier report of a lunar crust in the eastern part of Oceanus Procellarum. The crust is about 60 km thick and may consist of two layers in the mare regions. Possible values for the P-wave velocity in the uppermost mantle are between 7.6 and 9.0 km/sec. The 9 km/sec velocity represents either a localized heterogeneous unit, or a thin layer less than about 40 km in thickness. The elastic properties of the deep interior, as inferred from the seismograms of natural events (meteoroid impacts and moonquakes) occurring at great distances, indicate that there is an increase in attenuation and a possible decrease of velocity at depths below about 1000 km.

Toksoz, M. N.↗
NASA NTRS1974

Annihilation during positron-hydrogen collisions

Using the precision s- and p-wave elastic-scattering wave functions obtained previously, we have calculated the annihilation rate for positrons colliding with hydrogen atoms below the positronium-formation threshold. The s-wave results agree well with those of Humberston, while the p-wave results, which are new, contribute about 20% of the total at the higher energies.

Bhatia, A. K.↗
NASA NTRS1976

Seismic investigation of the lunar interior

The velocity and attenuation structure of the moon below the crust is examined using surface events. The moon is divided into an upper mantle and a lower mantle, the division at a depth of about 500 km being marked by a reflector identified on polarization filtered record sections. The upper mantle has a P-wave velocity of about 8 km/sec, a Poisson's ratio of about 0.25 and a Q for P waves of about 5000. This region contains no partial melt and is depleted in volatiles, notably water. The lower mantle has a lower S-wave velocity and probably a lower P-wave velocity than the upper mantle, with a Poisson's ratio of about 0.34. The lower mantle has a Q for P waves of approximately 1500, substantially lower than the upper mantle but probably still high enough to preclude partial melting. The velocity structure and the current value of the moment of inertia factor indicate an increase of density below about 500 km, perhaps due to an increase in iron content. We do not have any information directly pertaining to seismic velocities below 1000 km depth.

Dainty, A. M.↗
NASA NTRS1977

Internal structure and properties of Mars

Theoretical physical models of the Martian interior are presented in the light of recent and revised data and constraints. These models include thermal evolution, densities, and seismic-wave velocities. The interior of Mars appears to be earthlike in many respects. Although thermal models indicate that Mars has passed its peak of evolution, it may still have an asthenosphere and may be moderately active tectonically. Mars has an Fe-FeS core with a radius of 1500-2000 km. The mantle is enriched in FeO with an olivine composition of about Fo75. Theoretically determined seismic-wave velocities are relatively well constrained in the mantle, with upper-mantle P-wave velocities ranging from 7.64 to 7.80 km/sec. However, there are wide variations in P-wave velocity in the core, dependent on composition. The shadow zone due to the core is larger than earth's.

Johnston, D. H.↗
NASA NTRS1972

Time dependent Hartree-Fock treatment of elastic scattering of electrons by H and He/+/.

Time dependent Hartree-Fock theory, in its coupled and uncoupled forms, is used to calculate the elastic singlet p-wave phase shifts for the scattering of electrons by H and He/+/. On comparison with the best available results it is concluded that the coupled scheme, which contains correlation to at least first order, is superior. Levinson's theorem is confirmed.

Jamieson, M. J.↗
NASA NTRS1972

Generalized pseudopotential approach for electron-atom scattering.

A generalized many-electron pseudopotential approach is presented for electron-neutral-atom scattering problems. A calculation based on this formulation is carried out for the singlet s-wave and p-wave electron-hydrogen phase shifts with excellent results. We compare the method with other approaches as well as discuss its applications for inelastic and rearrangement collision problems.

Zarlingo, D. G.↗
NASA NTRS1972

Elastic properties of Apollo 14 and 15 rocks.

Ultrasonic P- and S-wave velocities of lunar samples 14310,72 and 15418,43 and P-wave velocities of sample 15015,18 were measured at room temperature to 5 kb confining pressure. The velocities of both igneous and breccia samples increased sharply over this pressure range. At low confining pressures, the shape of velocity-pressure curves of rocks is determined by the distribution function of crack aspect ratios. We suggest that analogue studies on terrestrial rocks having a wide assortment of crack parameters may be used to infer the nature of cracks in lunar rocks.

Todd, T.↗
NASA NTRS1973

Intermediate energy nucleon-deuteron scattering theory.

Sloan's conclusion (1969) that terms of the multiple-scattering series beyond single scattering contribute only to S- and P-wave amplitudes in an S-wave separable model is examined. A comparison of experiments with the calculation at 146 MeV shows that the conclusion is valid in nucleon-deuteron scattering applications.

Wilson, J. W.↗
NASA NTRS1975

Seismic effects from major basin formations on the moon and Mercury

Grooved and hilly terrains occur at the antipode of major basins on the moon (Imbrium, Orientale) and Mercury (Caloris). Such terrains may represent extensive landslides and surface disruption produced by impact-generated P-waves and antipodal convergence of surface waves. Order-of-magnitude calculations for an Imbrium-size impact on the moon indicate P-wave-induced surface displacements of 10 m at the basin antipode that would arrive prior to secondary ejecta. Comparable surface waves would arrive subsequent to secondary ejecta impacts beyond 1000 km and would increase in magnitude as they converge at the antipode. Other seismically induced surface features include: subdued, furrowed crater walls produced by landslides and concomitant secondary impacts; emplacement and leveling of light plains units owing to seismically induced 'fluidization' of slide material; and perhaps the production and enhancement of deep-seated fractures that led to the concentration of farside lunar maria in the Apollo-Ingenii region.

Schultz, P. H.↗
NASA NTRS1974

Implications of elastic wave velocities for Apollo 17 rock powders

Ultrasonic P- and S-wave velocities of lunar rock powders 172701, 172161, 170051, and 175081 were measured at room temperature and to 2.5 kb confining pressure. The results compare well with those of terrestrial volcanic ash and powdered basalt. P-wave velocity values up to pressures corresponding to a lunar depth of 1.4 km preclude cold compaction alone as an explanation for the observed seismic velocity structure at the Apollo 17 site. Application of small amounts of heat with simultaneous application of pressure causes rock powders to achieve equivalence of seismic velocities for competent rocks.

Talwani, P.↗
NASA NTRS1975

Photoionization of lithium

The photoionization of lithium from threshold to 50 eV above threshold is calculated using the method of polarized orbitals. The method is applied in as orthodox a manner as possible; this means that total wave functions are constructed as by Temkin and Lamkin (1961) using only the static dipole part of the perturbation of core electrons by the outer part of the external electron. According to other previously given prescriptions, both initial (bound) and final (continuum) wave functions are so polarized, only the length form of the matrix is calculated, and bilinear terms from the polarization contributions are retained (although their effect in this calculation is small). The results themselves are essentially identical to those of a recent diagrammatic calculation of Chang and Poe (1975) (in the region below 5 eV where thay have calculated), and as such they differ in certain significant components from exchange-adiabatic and extended-polarization results of Matese and LaBahn (1969) (although their overall result is similar). The s- and p-wave e-Li(+) phase shifts, which are derived as by-products of this calculation, are also presented and compared with other phase-shift calculations.

Bhatia, A. K.↗