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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1985

Studies of the marine crustal magnetization at intermediate wavelengths

The data can be filtered at intermediate wavelengths to provde a data set which complements the satellite fields of MAGSAT, TSS and GRM. The filtered marine data set provides a high resolution data set which is closer to the source bodies than satellite survey data. However, the GRM and TSS could provide the necessary resolution to match the filtered sea surface field. The added resolution determines the nature of crustal magnetizations which give rise to the intermediate wavelength field. It is found that remanent magnetization is an important component over the oceans. Crustal deformation and plate motions result in magnetization vectors which differ significantly from the present day field directions. Induced magnetization or GRM are important components over the oceanic plateaus and spreading centers.

Labrecque, J. L.↗
NASA NTRS1985

Constraints on the rheological structure of the mantle

Rheological models of the mantle are at present limited to radial symmetry, usually with homogeneous linearly viscous or viscoelastic incompressible layers. While such models are probably overly simple, they readily allow calculation of geophysical effects, such as post glacial rebound and related changes in the Earth's shape. They are also directly applicable to problems of global mantle flow and plate motions.

Oconnell, R. J.↗
NASA NTRS1985

Evidence from satellite altimetry for small-scale convection in the mantle

Small scale convection can be defined as that part of the mantle circulation in which upwellings and downwellings can occur beneath the lithosphere within the interiors of plates, in contrast to the large scale flow associated with plate motions where upwellings and downwellings occur at ridges and trenches. The two scales of convection will interact so that the form of the small scale convection will depend on how it arises within the large scale flow. Observations based on GEOS-3 and SEASAT altimetry suggest that small scale convection occurs in at least two different ways.

Parsons, B.↗
NASA NTRS1986

An approach to modeling present-day deformation in southern California

This paper presents an approach to modeling the complete, time-dependent deformation in southern California. A variety of techniques are used to include the far-field plate motion, stress relaxation in the asthenosphere, aseismic fault slip within the elastic lithosphere, and the complex, three-dimensional nature of the faults within the southern California region. Among the conclusions of the work here are the following: (1) the data exibit a marginal preference for a relatively thin lithosphere in southern California: (2) the most sensitive determinant for lithospheric thickness and viscosity of the asthenosphere is the rotation rate of the motion vectors toward or away from major faults; (3) the major faults in southern California are slipping at depth, at or near their average Holocene rates; (4) a shallow, active decollement beneath the Transverse Ranges is apparently needed to realistically model the strain changes observed there; and (5) this modeling technique offers the best approach for understanding the complex deformation field in southern California.

Rundle, J. B.↗
NASA NTRS1986

Convection beneath young oceanic lithosphere - Implications for thermal structure and gravity

Small-scale convection under the oceanic lithosphere which begins in the first 5 m.y. of cooling can produce a gravity signal with the amplitude and wavelength observed for large areas of the central Pacific and southern Indian oceans using Seasat altimeter data. The trend of the observed anomalies is parallel to the direction of plate motion as might be expected if they were produced by small-scale convection. Models predict that the wavelengths of gravity anomalies increase more rapidly with age than is observed. The persistence of short relatively uniform wavelength anomalies (less than 200 km) to crustal ages of 50 Ma may indicate that they were produced when the lithosphere was very young and thin and were 'frozen in' as cooling thickened the elastic lithosphere. Small-scale convection which begins under very young lithosphere does not violate other geophysical data such as the rate of seafloor subsidence and variations of geoid height with age. After convection has begun, the subsidence due to thermal contraction within the lithosphere varies linearly with age, in the absence of mantle heat sources, although the rate of change of these quantities is affected by convection. Much of the variation of the geoid height across fracture zones can be fit by a model which includes small-scale convection.

Buck, W. R.↗
NASA NTRS1986

The Geoscience Laser Altimetry/Ranging System (GLARS)

The Geoscience Laser Altimetry Ranging System (GLARS) is a highly precise distance measurement system to be used for making extremely accurate geodetic observations from a space platform. It combines the attributes of a pointable laser ranging system making observations to cube corner retroreflectors placed on the ground with those of a nadir looking laser altimeter making height observations to ground, ice sheet, and oceanic surfaces. In the ranging mode, centimeter-level precise baseline and station coordinate determinations will be made on grids consisting of 100 to 200 targets separated by distances from a few tens of kilometers to about 1000 km. These measurements will be used for studies of seismic zone crustal deformations and tectonic plate motions. Ranging measurements will also be made to a coarser, but globally distributed array of retroreflectors for both precise geodetic and orbit determination applications. In the altimetric mode, relative height determinations will be obtained with approximately decimeter vertical precision and 70 to 100 meter horizontal resolution. The height data will be used to study surface topography and roughness, ice sheet and lava flow thickness, and ocean dynamics. Waveform digitization will provide a measure of the vertical extent of topography within each footprint. The planned Earth Observing System is an attractive candidate platform for GLARS since the GLAR data can be used both for direct analyses and for highly precise orbit determination needed in the reduction of data from other sensors on the multi-instrument platform. (1064, 532, and 355 nm)Nd:YAG laser meets the performance specifications for the system.

Cohen, S. C.↗
NASA NTRS1987

The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian Plate and surrounding regions in the Middle East

The long term objective of this project is to interpret NASA's Crustal Dynamics measurements (SLR) in the Eastern Mediterranean region in terms of relative plate motions and intraplate deformation. The approach is to combine realistic modeling studies with an analysis of available geophysical and geological observations to provide a framework for interpreting NASA's measurements. This semi-annual report concentrates on recent results regarding the tectonics of Anatolia and surrounding regions from ground based observations. Also briefly reported on is progress made in using GPS measurements to densify SLR observations in the Eastern Mediterranean.

Toksoz, M. Nafi↗
NASA NTRS1987

Aseismic crustal deformation in the Transverse Ranges of southern California

Using geodetic data at a plate boundary, the subsurface displacements that accompany plate motion were modeled as the sum of rigid block motion and the elastic effects of frictional drag between blocks in a model consisting of 12 blocks and 27 rectangular fault patches. The block motion inferred from the geodetic data has the same order of magnitude as the geologic estimates, and for many faults the agreement was excellent. The model implies about 20 mm/y of crustal shortening normal to the trend of the San Andreas fault.

Cheng, Abe↗
NASA NTRS1990

Smaller solar system bodies and orbits; Proceedings of Symposium 3, Workshops II, III, and XXVI, and Topical Meetings of the 27th COSPAR Plenary Meeting, Espoo, Finland, July 18-29, 1988

Topics discussed in this volume include the reappraisal of the moon and Mars/Phobos/Deimos; the origin and evolution of planetary and satellite systems; asteroids, comets, and dust (a post-IRAS perspective); satellite dynamics; future planetary missions; and orbital debris. Papers are presented on a comparison of the chemistry of moon and Mars, the use of a mobile surface radar to study the atmosphere and ionosphere, and laser-ionization studies with the technical models of the LIMA-D/Phobos. Attention is given to planetogonic scenarios and the evolution of relatively mass-rich preplanetary disks, the kinetic behavior of planetesimals revolving around the sun, the planetary evolution of Mars, and pre- and post-IRAS asteroid taxonomies. Consideration is also given to ocean tides and tectonic plate motions in high-precision orbit determination, the satellite altimeter calibration techniques, a theory of the motion of an artificial satellite in the earth atmosphere, ESA plans for planetary exploration, and the detection of earth orbiting objects by IRAS.

Runcorn, S. K.↗
NASA NTRS1991

Solid earth science in the 1990s. Volume 1: Program plan

This is volume one of a three volume series. A plan for solid earth science research for the next decade is outlined. The following topics are addressed: scientific requirements; status of current research; major new emphasis in the 1990's; interagency and international participation; and the program implementation plan. The following fields are represented: plate motion and deformation; lithospheric structure and evolution; volcanology; land surface (processes of change); earth structure and dynamics; earth rotation and reference frames; and geopotential fields. Other topics of discussion include remote sensing, space missions, and space techniques.

Source record↗
NASA NTRS1991

Solid earth science in the 1990s. Volume 2: Panel reports

This is the second volume of a three-volume report. Volume 2, Panel Reports, outlines a plan for solid Earth science research for the next decade. The science panels addressed the following fields: plate motion and deformation, lithospheric structure and evolution, volcanology, Earth structure and dynamics, Earth rotation and reference frames, and geopotential fields.

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NASA NTRS1991

Transonic shock-induced dynamics of a flexible wing with a thick circular-arc airfoil

Transonic shock boundary layer oscillations occur on rigid models over a small range of Mach numbers on thick circular-arc airfoils. Extensive tests and analyses of this phenomena have been made in the past but essentially all of them were for rigid models. A simple flexible wing model with an 18 pct. circular arc airfoil was constructed and tested in the Langley Transonic Dynamics Tunnel to study the dynamic characteristics that a wing might have under these circumstances. In the region of shock boundary layer oscillations, buffeting of the first bending mode was obtained. This mode was well separated in frequency from the shock boundary layer oscillations. A limit cycle oscillation was also measured in a third bending like mode, involving wind vertical bending and splitter plate motion, which was in the frequency range of the shock boundary layer oscillations. Several model configurations were tested, and a few potential fixes were investigated.

Bennett, Robert M.↗
NASA NTRS1991

Late Cenozoic tectonic evolution of southwestern California

Geologic and geophysical data from southern California and adjoining areas are used to reconstruct the tectonic evolution of the southern Coast Ranges, western Transverse Ranges, and borderland regions since 30 Myr ago. Premises include specified relative plate motions for times prior to 10.5 Myr ago and after 3 Myr ago, a mid-Tertiary bight in the continental margin, midcrustal detachment faults, rotation of the western Transverse Ranges about an eastern pivot, and specified fault displacement histories. Prior to 18 Myr ago, about 90 percent of the tangential component of Pacific-North America relative motion was accommodated on an offshore dextral fault system near the toe of the continental slope. From 18 to 5.5 Myr ago, dextral slip was accommodated predominantly on the offshore system but also on a second, inboard system that included the San Andreas fault.

Sedlock, Richard L.↗
NASA NTRS1991

First epoch geodetic measurements with the Global Positioning System across the northern Caribbean plate boundary zone

The first geodetic survey across the northern Caribbean plate boundary zone with GPS was conducted in June 1986. Baseline vectors defined by the six-station regional GPS network ranged from 170 to 1260 km in length. Repeatability of independent daily baseline estimates was better than 8 mm plus 1.3 parts in 10 to the 8th of baseline length for horizontal components. The wet tropospheric path delay during the experiment was both high, sometimes exceeding 30 cm at zenith, and variable, sometimes exceeding 5 cm variation over several hours. Successful carrier phase cycle ambiguity resolution (bias fixing) could not be achieved prior to construction of a regional troposphere model. With optimum troposphere treatment and single-day orbital arcs, most biases on baselines were resolved up to about 550 km in length. With multiday orbital arcs most biases in the network were resolved regardless of baseline length. The results suggest that constraints on plate-boundary zone deformation in the Greater Antilles, and on the North America-Caribbean relative plate motion vector, can be obtained with a series of GPS experiments spanning less than 10 and 15 years, respectively.

Dixon, T. H.↗
NASA NTRS1991

Transonic shock-induced dynamics of a flexible wing with a thick circular-arc airfoil

A simple flexible wing model with an 18-percent circular arc airfoil was constructed and tested in the Langley Transonic Dynamics Tunnel to investigate the dynamic characteristics that a wing might have under these conditions. In the region of shock-boundary layer oscillations, buffeting of the first bending mode was obtained. This mode was well separated in frequency from the shock boundary layer oscillations. A limit cycle oscillation was also measured in a 'third bending-like' mode, involving wing vertical bending and splitter plate motion, which was in the frequency range of the shock-boundary layer oscillations. Several model configurations were tested, and a few potential fixes were investigated.

Bennett, Robert M.↗
NASA NTRS1991

An introduction to the global positioning system and some geological applications

The fundamental principles of the global positioning system (GPS) are reviewed, with consideration given to geological and geophysical applications and related accuracy requirements. Recent improvements are emphasized which relate to areas such as equipment cost, limitations in the GPS satellite constellation, data analysis, uncertainties in satellite orbits and propagation delays, and problems in resolving carrier phase cycle ambiguities. Earthquake processes and near-fault crustal deformation monitoring have been facilitated by advances in GPS data acquisition and analysis. Horizontal positioning capability has been improved by new satellite constellation, better models, and global tracking networks. New classes of tectonic problems may now be studied through GPS, such as kinematic descriptions of crustal deformation and the measurement of relative plate motion at convergent boundaries. Continued improvements in the GPS are foreseen.

Dixon, T. H.↗
NASA NTRS1992

Precision GPS ephemerides and baselines

The required knowledge of the Global Positioning System (GPS) satellite position accuracy can vary depending on a particular application. Application to relative positioning of receiver locations on the ground to infer Earth's tectonic plate motion requires the most accurate knowledge of the GPS satellite orbits. Research directed towards improving and evaluating the accuracy of GPS satellite orbits was conducted at the University of Texas Center for Space Research (CSR). Understanding and modeling the forces acting on the satellites was a major focus of the research. Other aspects of orbit determination, such as the reference frame, time system, measurement modeling, and parameterization, were also investigated. Gravitational forces were modeled by truncated versions of extant gravity fields such as, Goddard Earth Model (GEM-L2), GEM-T1, TEG-2, and third body perturbations due to the Sun and Moon. Nongravitational forces considered were the solar radiation pressure, and perturbations due to thermal venting and thermal imbalance. At the GPS satellite orbit accuracy level required for crustal dynamic applications, models for the nongravitational perturbation play a critical role, since the gravitational forces are well understood and are modeled adequately for GPS satellite orbits.

Source record↗
NASA NTRS1991

Models of recurrent strike-slip earthquake cycles and the state of crustal stress

Numerical models of the strike-slip earthquake cycle, assuming a viscoelastic asthenosphere coupling model, are examined. The time-dependent simulations incorporate a stress-driven fault, which leads to tectonic stress fields and earthquake recurrence histories that are mutually consistent. Single-fault simulations with constant far-field plate motion lead to a nearly periodic earthquake cycle and a distinctive spatial distribution of crustal shear stress. The predicted stress distribution includes a local minimum in stress at depths less than typical seismogenic depths. The width of this stress 'trough' depends on the magnitude of crustal stress relative to asthenospheric drag stresses. The models further predict a local near-fault stress maximum at greater depths, sustained by the cyclic transfer of strain from the elastic crust to the ductile asthenosphere. Models incorporating both low-stress and high-stress fault strength assumptions are examined, under Newtonian and non-Newtonian rheology assumptions. Model results suggest a preference for low-stress (a shear stress level of about 10 MPa) fault models, in agreement with previous estimates based on heat flow measurements and other stress indicators.

Lyzenga, Gregory A.↗