Engineering topics

Solomon, S. C.

Publications and source records attributed to Solomon, S. C..

At least 55 records · Page 3

NASA NTRS1985

Mars - Thickness of the lithosphere from the tectonic response to volcanic loads

The response to loading of the elastic lithosphere of Mars by seven large volcanic features is estimated based on the hypothesis of a flexural origin for a definable set of load-concentric graben. From the locations of such graben, or from their absence, the lithospheric thickness and flexural rigidity are inferred. For the Tharsis montes, Alba Patera, and Elysium Mons, elastic lithospheric thicknesses at the time of loading range from 20 to 50 km, assuming a Young's modulus of a trillion dyn/sq cm. The thickness exceeded 120 km beneath Olympus Mons and Isidis Planitia. The corresponding ranges in flexural rigidity are approximately 10 to the 30th to 31st dyn cm and greater than 10 to the 32nd dyn cm, respectively. These results indicate a local thinning of the lithosphere beneath portions of the central regions of the Tharsis and Elysium volcanic provinces at the time of loading-induced fracturing.

Comer, R. P.↗

NASA NTRS1985

Rift systems on Venus: An assessment of mechanical and thermal models

The formation and distribution of major tectonic features on Venus are closely linked to the dominant mechanism of lithospheric heat loss. Among the most spectacular and extensive of the major tectonic features on Venus are the Chasmata, deep linear valleys generally interpreted to be the products of lithospheric extension and rifting. Systems of chasmata and related features can be traced along several tectonic zones up to 20,000 km in linear extent. Mechanical and thermal models for terrestrial continental-rifting are applied to the rift systems of Venus. The models are tested against known topographic and tectonic characteristics of Venus chasmata as well as independent information on the physical properties of the Venus crust and lithosphere.

Solomon, S. C.↗

NASA NTRS1984

Source mechanisms of earthquakes near mid-ocean ridges from body waveform inversion - Implications for the early evolution of oceanic lithosphere

An evaluation is presented of the tectonics of the near-ridge environment based on the source mechanisms of earthquakes in young oceanic lithosphere. A catalog of near-ridge earthquakes is presented, and source parameters are determined from body waveform inversions. Source parameter-age relations are examined, and the near-ridge seismicity of the Indian Ocean is discussed. Deep normal faulting in young oceanic lithosphere is addressed, as is the relationship between thermoelastic stress and near-ridge earthquakes. The possibility of secondary convection beneath young oceanic lithosphere is considered. Finally, the broader tectonic implications of these results for the evolution of young oceanic lithosphere are discussed.

Bergman, E. A.↗

NASA NTRS1984

Tomographic inversion of satellite photometry

An inversion algorithm capable of reconstructing the volume emission rate of thermospheric airglow features from satellite photometry has been developed. The accuracy and resolution of this technique are investigated using simulated data, and the inversions of several sets of observations taken by the Visible Airglow Experiment are presented.

Solomon, S. C.↗

NASA NTRS1984

Venus banded terrain - Tectonic models for band formation and their relationship to lithospheric thermal structure

Two classes of tectonic models for the formation of band structure on Venus mountain ranges are quantitatively evaluated: folding models and extensional models. The characteristics of banded terrain on Ishtar Terra are reviewed, particularly the evidence for a tectonic origin and such important details of band geometry as the spacing between adjacent bands. The tectonic models are tested against these observed features, and it it shown that both classes of models are possible explanations of banded terrain as long as the outer elastic-brittle layer of the Venus crust is at most a few kilometers thick. A general assessment is given of hypotheses for the origin of banded terrain and of the relationship between mechanical models for band formation and the thermal structure of the Venus lithosphere.

Solomon, S. C.↗

NASA NTRS1984

The OI 989-A tropical nightglow

Attention is given to the morphology and origin of the OI 989 A emission in the tropical nightglow. Dielectronic recombination of O(+) is suggested as the mechanism responsible for populating the 3s' 3D0 state of this 2p4 3P 3s' 3D0 emission. The spectrometer used is that aboard the STP 78-1 satellite, which is in sun-synchronous orbit. The emission morphology is characterized by tropical arcs on each side of the dip equator.

Abreu, V. J.↗

NASA NTRS1984

An extensive region of off-ridge normal-faulting earthquakes in the southern Indian Ocean

A verified prediction of the theory of plate tectonics is that the focal mechanisms of earthquakes on the mid-ocean ridge system indicate either normal faulting on ridge segments or strike-slip faulting on transform faults. A broad region in the southern Indian Ocean which differs from typical ridge and intraplate regimes has been identified. In this region a number of large off-ridge earthquakes have occurred in the last 20 years. The mechanisms for these events, where known, all involve normal faulting. Nine of these earthquakes have been studied in detail using a formal inversion technique based on matching synthetic body waves to observed seismograms.

Bergman, E. A.↗

NASA NTRS1984

Venus banded terrain: Evaluation of tectonic models for the origin of banding

A tectonic orgin for Venus banded terrain is consistent with band spacing. Both compressional (folding) and extensional models for band formation can fit present observations. Band spacing cannot distinguish among scenarios for global heat loss and for the origin of highland terrain. Tectonic models for band formation indicate that the surface brittle layer in the venus highlands is no more than a few kilometers thick.

Solomon, S. C.↗

NASA NTRS1984

Elysium Region, Mars: Characterization of tectonic features

In this paper the tectonic features of the Elysium region are identified and characterized. Identification of features was made using USGS controlled photomosaics (Elysium quadrangle, and portions of Amenthes and Cebrenia quadrangles); Viking Orbiter photographic data were used in individual cases to assist in identification. The positions and orientations of tectonic features can then be used, in conjunction with estimates of the mass of the volcanic load obtained from gravity modelling, to constrain the thickness of the elastic lithosphere in the region.

Hall, J. L.↗

NASA NTRS1983

The dissociative recombination of O2(+) - The quantum yield of O(1S) and O(1D)

Data from the visible airglow experiment on the Atmosphere Explorer-E satellite have been used to determine the quantum yield of O(1S) and O(1D) from the dissociative recombination of O2(+). A range of values between 0.09 and 0.23 has been obtained for the quantum yield of O(1S). It is shown that the quantum yield of O(1S) depends on the ratio of electron density to atomic oxygen density. This suggests that the quantum yield of O(1S) may depend on the degree of vibrational excitation of the recombining O2(+). The quantum yield of O(1D) has been measured to be 1.23 + or - 0.42, with no dependence on the electron-oxygen ratio.

Abreu, V. J.↗

NASA NTRS1982

Evolution of the Tharsis province of Mars - The importance of heterogeneous lithospheric thickness and volcanic construction

A new model for the origin and evolution of the Tharsis province that emphasizes that the topography of Tharsis may be produced largely by construction, rather than uplift, is proposed. Underlying the model is the premise that the elastic lithosphere of Mars was laterally heterogeneous early in Martian history; such heterogeneity is discernible later in Martian history from the variable tectonic response of the lithosphere to local surface loads. It is contended that the mechanism for the evolution of Tharsis described here led to permanent topographic and gravity highs and a greatly thickened crust in the Tharsis region. An important advantage of the model is that no anomalous dynamical or chemical properties need be sustained in the Martian mantle beneath Tharsis for billions of years. The mantle beneath Tharsis is thus seen as playing a passive rather than an active role in the regional volcanic and tectonic activity, much like the role of the mantle beneath major midocean ridges on earth.

Solomon, S. C.↗

NASA NTRS1982

Mechanisms for lithospheric heat transport on Venus Implications for tectonic style and volcanism

The mechanisms of plate recycling, lithospheric conduction, and hot spot volcanism are each evaluated to determine which is the dominant mode of lithospheric heat transfer on Venus, with attention given to the implications of each mechanism for the interpretation of Venus surface features. It is thought that plate recycling on Venus cannot be excluded on the basis of either theoretical arguments or present observations on topography and radar backscatter. Landforms caused by plate convergence and divergence on Venus, it is noted, would differ substantially from those on the earth owing to the high surface temperature and the absence of oceans on Venus, the lack of free or hydrated water in subducted material, the possibility that subduction would more commonly be accompanied by lithospheric delamination, and the rapid spreading rates that would be required if plate recycling removed a significant fraction of the internal heat. The possibility that the dominant mechanism early in the history of the planet was different from the one at work now is thought to merit consideration.

Solomon, S. C.↗

NASA NTRS1982

On Venus impact basins - Viscous relaxation of topographic relief

The viscous relaxation with time of the topographic relief of impact basins on Venus is calculated under the assumption that the surface temperature of the planet has been at or near its presently high value since the time of basin formation. The effects of a decrease in effective viscosity with depth and of the partial to complete isostatic compensation of initial topography are included in the model. An impact basin several hundred kilometers or greater in diameter and three billion years old or older should have negligible topographic relief at present. On this basis, the hypothesis that quasi-circular features of low radar backscatter but little topographic relief may be relaxed remnants of ancient impact basins cannot be excluded. However, large quasi-circular depressions on Venus, such as Atlanta Planitia, are unlikely to be remnants of impact basins, because of their current relief, and so some other process should be found to account for them.

Solomon, S. C.↗

NASA NTRS1982

The evolution of impact basins - Viscous relaxation of topographic relief

A topographic profile of the young large lunar basin, Orientale, is presented in order to examine the effects of viscous relaxation on basin topography. Analytical models for viscous flow are considered, showing a wavelength-dependence of time constants for viscous decay on the decrease in viscosity with depth and on the extent of the isostatic compensation of the initial topography. Lunar rheological models which are developed include a half-space model for uniform Newtonian viscosity, density, and gravitational acceleration, a layer over inviscid half space model with material inviscid over geological time scales, and a layer with isostatic compensation where a uniformly viscous layer overlies an inviscid half space of higher density. Greater roughness is concluded, and has been observed, on the moon's dark side due to continued lower temperatures since the time of heavy bombardment.

Solomon, S. C.↗

NASA NTRS1981

Topography of Venus and earth - A test for the presence of plate tectonics

Comparisons of earth and Venus topography by use of Pioneer/Venus radar altimetry are examined. Approximately 93% of the Venus surface has been mapped with a horizontal resolution of 200 km and a vertical resolution of 200 m. Tectonic troughs have been indicated in plains regions which cover 65% of Venus, and hypsometric comparisons between the two planets' elevation distributions revealed that while the earth has a bimodal height distribution, Venus displays a unimodal configuration, with 60% of the planet surface within 500 m of the modal planet radius. The effects of mapping the earth at the same resolution as the Venus observations were explored. Continents and oceans were apparent, and although folded mountains appeared as high spots, no indications of tectonic activity were discernible. A NASA Venus Orbiting Imaging radar is outlined, which is designed to detect volcanoes, folded mountain ranges, craters, and faults, and thereby allow definition of possible plate-tectonic activity on Venus.

Head, J. W.↗

NASA NTRS1981

Lunar floor-fractured craters - Evidence for viscous relaxation of crater topography

Viscous relaxation is evaluated quantitatively as a possible mechanism to account for the observed topographical modification of floor-fractured lunar craters. On the basis of a model of the moon as a viscous material of uniform Newtonian viscosity, the ultimate topographic profiles of fresh craters predicted taking into account viscous relaxation effects are compared with the observed profiles of floor-fractured craters of similar diameter. It is found that for a number of crater pairs, the agreement of the observations with the predictions of the simple viscous relaxation model is good, suggesting that isostatic adjustment of craters in areas of anomalously high temperatures at shallow depth may be a more important source of deformation than previously realized.

Hall, J. L.↗

NASA NTRS1981

Tectonic evolution of terrestrial planets

The tectonic style of each terrestrial planet, referring to the thickness and division of its lithosphere, can be inferred from surface features and compared to models of planetary thermal history. Factors governing planetary tectonic evolution are planet diameter, chemistry, and external and internal heat sources, all of which determine how a planet generates and rids itself of heat. The earth is distinguished by its distinct, mobile plates, which are recycled into the mantle and show large-scale lateral movements, whereas the moon, Mars, and Mercury are single spherical shells, showing no evidence of destruction and renewal of the lithospheric plates over the latter 80% of their history. Their smaller volume to surface area results in a more rapid cooling, formation, and thickening of the lithosphere. Vertical tectonics, due to lithospheric loading, is controlled by the local thickness and rheology of the lithosphere. Further studies of Venus, which displays both the craterlike surface features of the one-plate planets, and the rifts and plateaus of earth, may indicate which factors are most important in controlling the tectonic evolution of terrestrial planets.

Head, J. W.↗

NASA NTRS1980

Tectonic stress - Models and magnitudes

It is shown that global data on directions of principal stresses in plate interiors can serve as a test of possible plate tectonic force models. Such tests performed to date favor force models in which ridge pushing forces play a significant role. For such models the general magnitude of regional deviatoric stresses is comparable to the 200-300 bar compressive stress exerted by spreading ridges. An alternative approach to estimating magnitudes of regional deviatoric stresses from stress orientations is to seek regions of local stress either demonstrably smaller than or larger than the regional stresses. The regional stresses in oceanic intraplate regions are larger than the 100-bar compression exerted by the Ninetyeast Ridge and less than the bending stresses (not less than 1 kbar) beneath Hawaii.

Solomon, S. C.↗