Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “crustal”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Investigation of lunar crustal structure and isostasy

The lunar mascon basins have strongly free air gravity anomalies, generally exceeding 100 milligals at an elevation of 100 km. The source of the anomalies is a combination of mantle uplift beneath the impact basins and subsequent infilling by high-density mare basalts. The relative contribution of these two components is still somewhat uncertain, although it is generally accepted that the amount of mantle uplift greatly exceeds the thickness of the basalts. Extensive studies have been carried out of the crustal structure of mare basins, based on gravity data, and their tectonic evolution, based on compressive and extensional tectonic features. The present study endeavored to develop a unified, self-consistent model of the lunar crust and lithosphere incorporating both gravity and tectonic constraints.

Thurber, Clifford H.↗
NASA NTRS1986

Mechanisms of crustal deformation in the western US

The deformation processes in the western United States were studied, considering both deterministic models and random or statistical models. The role of the intracrustal delamination and mechanisms of crustal thinning were also examined. The application of fractal techniques to understand how the crust is deforming was studied in complex regions. Work continued on the development of a fractal based model for deformation in the western United States. Fractal studies were also extended to the study of topography and the geoid.

Turcotte, Donald L.↗
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 NTRS1986

The global tracking networks for crustal dynamics

Highly accurate Satellite Laser Ranging (SLR) and Very-Long-Baseline Interferometry (VLBI) have been implemented by the NASA Crustal Dynamics Project and many cooperating groups in many countries to form global SLR and VLBI networks for geodetic measurements of global plate motion, plate deformation, regional deformations in areas of high earthquake activity, and accurate measurements of the earth's polar motion and changes in rotation rate. These systems are measuring vector baselines between stations to an accuracy of 2-5 cm. New improvements being implemented will improve the accuracy to about 1 cm.

Coates, R. J.↗
NASA NTRS1986

Mobile very long baseline interferometry and Global Positioning System measurement of vertical crustal motion

Mobile Very Long Base Interferometry (VLBI) and Global Positioning System (GPS) geodetic measurements have many error sources in common. Calibration of the effects of water vapor on signal transmission through the atmosphere, however, remains the primary limitation to the accuracy of vertical crustal motion measurements made by either technique. The two primary methods of water vapor calibration currently in use for mobile VLBI baseline measurements were evaluated: radiometric measurements of the sky brightness near the 22 GHz emission line of free water molecules and surface meteorological measurements used as input to an atmospheric model. Based upon a limited set of 9 baselines, it is shown that calibrating VLBI data with water vapor radiometer measurements provides a significantly better fit to the theoretical decay model than calibrating the same data with surface meteorological measurements. The effect of estimating a systematic error in the surface meteorological calibration is shown to improve the consistency of the vertical baseline components obtained by the two calibration methods. A detailed error model for the vertical baseline components obtained indicates current mobile VLBI technology should allow accuracies of order 3 cm with WVR calibration and 10 cm when surface meteorological calibration is used.

Kroger, Peter M.↗
NASA NTRS1986

Dislocation model for aseismic crustal deformation at Hollister, California

A model of crustal deformation during the interseismic phase is developed and applied (using the improved Bayesian inversion algorithm described by Jackson and Matsu'ura, 1985) to trilateration data for the USGS Hollister (CA) network. In the model, rigid blocks in motion relative to each other experience friction only in a brittle upper zone, while their ductile lower zones slide freely; the Hollister model comprises five blocks and nine rectangular fault patches. The data and results are presented in tables, graphs, and maps and characterized in detail. The model predicts steady block motion on time scales between 10 yr and 1 Myr, with net motion across the San Andreas/Calaveras fault system 38 + or - 3 mm/yr and brittle/ductile transition depths ranging from 0.4 to 11 km. Two San Andreas segments with higher probabilities of moderate-to-large earthquakes are identified.

Matsuura, Mitsuhiro↗
NASA NTRS1987

Horizontal gravity gradient - An aid to the definition of crustal structure in North America

A map of the magnitude of the horizontal Bouguer gravity gradient over the North American continent is used to delineate lateral discontinuities in upper crustal density and/or thickness associated with such processes as suturing and rifting. The usefulness of gradient trends in mapping major structural boundaries, which are sometimes poorly exposed or completely buried, is demonstrated by examples such as the buried southward extension of the Grenville Front and buried boundaries of the Superior Province. Gradient trends also draw attention to poorly known structures, which may have major tectonic significance, and to a continent-wide structural fabric, which may provide a record of the tectonic growth of the North American continent.

Sharpton, V. L.↗
NASA NTRS1987

An algorithmic approach to crustal deformation analysis

In recent years the analysis of crustal deformation measurements has become important as a result of current improvements in geodetic methods and an increasing amount of theoretical and observational data provided by several earth sciences. A first-generation data analysis algorithm which combines a priori information with current geodetic measurements was proposed. Relevant methods which can be used in the algorithm were discussed. Prior information is the unifying feature of this algorithm. Some of the problems which may arise through the use of a priori information in the analysis were indicated and preventive measures were demonstrated. The first step in the algorithm is the optimal design of deformation networks. The second step in the algorithm identifies the descriptive model of the deformation field. The final step in the algorithm is the improved estimation of deformation parameters. Although deformation parameters are estimated in the process of model discrimination, they can further be improved by the use of a priori information about them. According to the proposed algorithm this information must first be tested against the estimates calculated using the sample data only. Null-hypothesis testing procedures were developed for this purpose. Six different estimators which employ a priori information were examined. Emphasis was put on the case when the prior information is wrong and analytical expressions for possible improvements under incompatible prior information were derived.

Iz, Huseyin Baki↗
NASA NTRS1987

Crustal dynamics project data analysis, 1987. Volume 1: Fixed station VLBI geodetic results, 1979-1986

The Goddard VLBI group reports the results of analyzing Mark III data sets from fixed observatories through the end of 1986 and available to the Crustal Dynamics Project. All full-day data from POLARIS/IRIS are included. The mobile VLBI sites at Platteville (Colorado), Penticton (British Columbia), and Yellowknife (Northwest Territories) are also included since these occupations bear on the study of plate stability. Two large solutions, GLB121 and GLB122, were used to obtain Earth rotation parameters and baseline evolutions, respectively. Radio source positions were estimated globally while nutation offsets were estimated from each data set. The results include 25 sites and 108 baselines.

Ryan, J. W.↗
NASA NTRS1987

Crustal dynamics project data analysis, 1987. Volume 2: Mobile VLBI geodetic results, 1982-1986

The Goddard VLBI group reports the results of analyzing 101 Mark III data sets acquired from mobile observing sites through the end of 1986 and available to the Crustal Dynamics Project. The fixed VLBI observations at Hat Creek, Ft. Davis, Mojave, and OVRO are included as they participate heavily in the mobile schedules. One large solution GLB171 was used to obtain baseline length and transverse evolutions. Radio source positions were estimated globally, while nutation offsets were estimated from each data set. The results include 28 mobile sites.

Ma, C.↗
NASA NTRS1987

The crustal dynamics intelligent user interface anthology

The National Space Science Data Center (NSSDC) has initiated an Intelligent Data Management (IDM) research effort which has, as one of its components, the development of an Intelligent User Interface (IUI). The intent of the IUI is to develop a friendly and intelligent user interface service based on expert systems and natural language processing technologies. The purpose of such a service is to support the large number of potential scientific and engineering users that have need of space and land-related research and technical data, but have little or no experience in query languages or understanding of the information content or architecture of the databases of interest. This document presents the design concepts, development approach and evaluation of the performance of a prototype IUI system for the Crustal Dynamics Project Database, which was developed using a microcomputer-based expert system tool (M. 1), the natural language query processor THEMIS, and the graphics software system GSS. The IUI design is based on a multiple view representation of a database from both the user and database perspective, with intelligent processes to translate between the views.

Short, Nicholas M., Jr.↗
NASA NTRS1988

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 movements and intraplate deformation. The approach is to combine realistic modeling studies with 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 reported on briefly is progress in the use of the Global Positioning System to densify SLR observations in the Eastern Mediterranean. Reference is made to the previous annual report for a discussion of modeling results.

Toksoz, M. Nafi↗
NASA NTRS1987

Morphologic contrasts between Nirgal and Auqakuh Valles, Mars: Evidence of different crustal properties

Photoclinometric measurements were made of sidewall slopes in Nirgal and Auqakuh Valles and these results were interpreted in terms of the geologic setting and a simple geomorphic model to provide insights into the physical properties of crustal materials in these areas. Nirgal was interpreted to be a runoff channel and Auqakuh to be a fretted channel. Geomorphologic arguments for the sapping origin of Nirgal and Auqakuh Valles were presented. The morphologies of the channels, however, differ greatly: the tributaries of Nirgal end abruptly in theater-headed canyons, whereas the heads of tributaries of Auqakuh shallow gradually. The plateau surface surrounding both channels appears to be covered by smooth materials, presumably lava flows; they are continuous and uneroded in the Nirgal area, but at Auqakuh they are largely eroded and several layers are exposed that total about 200 m in thickness. For Nirgal Valles, the measurements show that sidewalls in the ralatively shallow upper reaches of the channel have average slopes near 30 degrees and, in the lower reaches, sidewall slopes exceed 50 degrees. Auqakuh, on the other hand, has maximum sidewall slopes of 14 degrees and an approximate maximum depth of 1000 m. Faint, horizontal layering in portions of the lower reaches of Nirgal may indicate inhomogeneity in either composition or topography.

Mackinnon, David J.↗
NASA NTRS1988

Genesis of archean granitoids in the Pilbara block and implications for crustal growth

The origin of the Mount Edgar Batholith of the Pilbara Block in Western Australia is discussed, along with other Archean granitoids that show relatively primitive isotopic characteristics but more evolved bulk geochemistry. Geochemical evidence is presented in support of a multistage process of crustal ripening, involving partial melting of a thick basaltic crust to produce the tonalitic and dacitic sources of the more evolved granitoids. These events must produce stable continental crust in less than 200 Ma and are different geologically and geochemically from those which produced Phanerozoic granitoids in Andean margin settings.

Collins, W. J.↗
NASA NTRS1988

Pb isotope constaints on the extent of crustal recycling into a steady state mantle

Isotopic and geochemical evidence was discussed against recycling of continental crust into the mantle. Element ratios such as Sm/Nd, Th/Sc, and U/Pb in sedimentary masses have remained relatively constant throughout Earth history, and this can only be reconciled with steady state recycling models if new crustal materials added from the mantle have had similar ratios. Such recycling models would also require shorter processing times for U, Th, and Pb through the mantle than are geodynamically reasonable. Models favoring subduction of pelagic sediments as the only recycling mechanism fail to account for the Pb isotopic signature of the mantle. Recycling of bulk crust with Pb isotopic compositions similar to those expected for primitive mantle would be permissable with available data, but there appear to be no plausible tectonic mechanisms to carry this out.

Galer, S. J. G.↗
NASA NTRS1988

Crustal evolution and the eclogite to granulite phase transition in xenoliths from the West African Craton

A suite of eclogite and granulite facies xenoliths from kimberlite pipes in the Archean Man Shield of West Africa is described. The xenoliths include lithologies ranging in composition from komatiite to anorthosite and appear to be geochemically, petrologically, and geophysically related. The suite may represent fractionation of felsic material separated from ancient mantle and added to early Archean crust. The samples can be used to define a xenolith geotherm, which may represent an ancient episode of high heat flow. The samples also imply that the crust-mantle boundary is a gradational and possibly interlayered geochemical, mineralogical, and seismic transition. It is speculated that the depleted subcontinental mantle required by diamond bearing coalescence of smaller depletion cells formed by extraction of ancient crustal components. These depleted zones are surrounded by fertile asthenospheric mantle, which may have given rise to later flood basalts such as the Karroo and Parana Provinces.

Haggerty, S. E.↗
NASA NTRS1988

The early archaean crustal history of West Greenland as recorded by detrital zircons

The isotope systematics of some of the oldest samples on Earth from both Greenland and Australia was discussed. The antiquity was confirmed of the 4.1 to 4.2 Ga zircons from Western Australia; the model Lu-Hf age of these zircons, as measured with the ANU ion probe is 4.14 + or - 0.24 Ga, although the oldest preserved rock units there are anorthosites with a Lu-Hf model age of about 3.73 Ga. U-Pb ion probe ages of detrital zircons ranging between 2.87 and 3.89 Ga from an Akilia association quartzite was reported, whose age of deposition is probably around 3.8 Ga. It was argued that the younger age in this range are discordant because of late Pb-loss, probably associated with a high grade metamorphic event at about 3.6 Ga. It was also argued that the earliest crust in West Greenland and elsewhere is about 3.9 Ga, but in some places, such as Western Australia, crustal evolution took place much earlier, perhaps starting as far back as 4.3 Ga. This would account for the presence in that terrane of abundant K rich granitoid, the paucity of tonalitic and trondhjemitic materials, and the existence of Eu anomalies in early Archean sediments.

Kinny, P. D.↗
NASA NTRS1988

Reappraisal of the geology of Kangimut Sammisoq, Ameralik Fjord, Southern West Greenland: Crustal structure and interpretation of isotopic data

In Godthabsfjord, in the North Atlantic Archean Craton, early Archean Amitsoq gneisses are found in association with the mid to late Archean Nuk gneisses. The Amitsoq gneisses contain the Ameralik dykes, now subconcordant strips of amphibolite. The Nuk and Amitsoq gneisses have amphibolite facies polymetamorphic assemblages. To the southeast of Godthabsfjord, there is an extensive region affected by granulite facies metamorphism at 2800 Ma. Early models of crustal evolution for Godthabsfjord and the region to the SE are discussed. Recent detailed mapping combined with U-Pb zircon dating is examined.

Nutman, Allen P.↗