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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Project Pyralp: Tectonics relationships between Pyrenees and Alps (Southern France)

The author has identified the following significant results. In the Eastern Aquitaine Basin in southern France, investigations using SL 3 photographs from an S190A camera reveal a slight line joining a Paleozoic trend of the Montagne Noire massif to a more recent Pyrenean fault zone of Cretaceous to Tertiary age. According to the interpretation of this line as the superficial geomorphological trace of a deep-seated fault zone, Hercynian weakness lines appear to have played a more important part than previously thought in the building of the Pyrenean range. The Lezat line is a trend of small morphological features obvious only in the photographs having the highest resolution.

Guillemot, J.↗
NASA NTRS1974

Lunar seismicity, structure, and tectonics

Natural seismic events have been detected by the long-period seismometers at Apollo stations 16, 14, 15, and 12 at annual rates of 3300, 1700, 800, and 700, respectively, with peak activity at 13- to 14-day intervals. The data are used to describe magnitudes, source characteristics, and periodic features of lunar seismicity. In a present model, the rigid lithosphere overlies an asthenosphere of reduced rigidity in which present-day partial melting is probable. Tidal deformation presumably leads to critical stress concentrations at the base of the lithosphere, where moonquakes are found to occur. The striking tidal periodicities in the pattern of moonquake occurrence and energy release suggest that tidal energy is the dominant source of energy released as moonquakes. Thus, tidal energy is dissipated by moonquakes in the lithosphere and probably by inelastic processes in the asthenosphere.

Lammlein, D. R.↗
NASA NTRS1974

Numerical modelling of instantaneous plate tectonics

Assuming lithospheric plates to be rigid, 68 spreading rates, 62 fracture zones trends, and 106 earthquake slip vectors are systematically inverted to obtain a self-consistent model of instantaneous relative motions for eleven major plates. The inverse problem is linearized and solved iteratively by a maximum-likelihood procedure. Because the uncertainties in the data are small, Gaussian statistics are shown to be adequate. The use of a linear theory permits (1) the calculation of the uncertainties in the various angular velocity vectors caused by uncertainties in the data, and (2) quantitative examination of the distribution of information within the data set. The existence of a self-consistent model satisfying all the data is strong justification of the rigid plate assumption. Slow movement between North and South America is shown to be resolvable.

Minster, J. B.↗
NASA NTRS1974

Tectonism and volcanism of the Tharsis region of Mars

The Tharsis region of Mars, where the planet's largest shield volcanoes are located, is at the center of a fracture system that extends over almost half the surface of the planet. The fractures are tensional and aligned roughly radial to Tharsis and form two opposing fanlike arrangements that converge on the line of the Tharsis volcanoes. The fractures are attributed to a broad asymmetric updoming of the Martian crust centered to the southeast of the volcano line. Formation of the dome took place before the formation of the shield volcanoes. The location of the shields was controlled by the fractures, and volcano formation may have reactivated some of the fractures. The updoming, thought to result from mantle convection, separates eras of different volcanism and appears to have been a discrete and unique event in the history of Mars.

Carr, M. H.↗
NASA NTRS1974

Fault tectonics and earthquake hazards in the Peninsular Ranges, Southern California

The author has identified the following significant results. ERTS and Skylab images reveal a number of prominent lineaments in the basement terrane of the Peninsular Ranges, Southern California. The major, well-known, active, northwest trending, right-slip faults are well displayed, but northeast and west to west-northwest trending lineaments are also present. Study of large-scale airphotos followed by field investigations have shown that several of these lineaments represent previously unmapped faults. Pitches of striations on shear surfaces of the northeast and west trending faults indicate oblique-slip movement; data are insufficient to determine the net-slip. These faults are restricted to the pre-Tertiary basement terrane and are truncated by the major northwest trending faults; therefore, they may have formed in response to an earlier stress system. Future work should be directed toward determining whether the northeast and west trending faults are related to the presently active stress system or to an older inactive system, because this question relates to the earthquake risk in the vicinity of these faults.

Merifield, P. M.↗
NASA NTRS1974

Identification and interpretation of tectonic features from Skylab imagery

The author has identified the following significant results. S190-B imagery confirmed previous conclusions from S190-A that the Garlock fault does not extend eastward beyond its known termination near the southern end of Death Valley. In the Avawatz Mountains, California, two faults related to the Garlock fault zone (Mule Spring fault and Leach Spring fault) show evidence of recent activity. There is evidence that faulting related to Death Valley fault zone extends southeastward across the Old Dad Mountains. There, the Old Dad fault shows evidence of recent activity. A significant fault lineament has been identified from McCullough Range, California southeastward to Eagle Tail Mountains in southwestern Arizona. The lineament appears to control tertiary and possible cretaceous intrusives. Considerable right lateral shear is suspected to have taken place along parts of this lineament.

Abdel-Gawad, M.↗
NASA NTRS1974

Identification and interpretation of tectonic features from Skylab imagery

The author has identified the following significant results. A remarkable system of northwest and west-northwest trending faults was found to continue from eastern California into southwestern Arizona. The most significant is a fault belt which extends from west of Marble Mountains (southeastern California) across the Colorado River at Parker Valley towards Silver Bell Mountains, southern Arizona.

Abdel-Gawad, M.↗
NASA NTRS1975

Identification and interpretation of tectonic features from Skylab imagery

The author has identified the following significant results. Two alternate models for the extension of the Texas zone through the Mojave Desert block have been developed: (1) along the Pisgah Line, and (2) along the eastern Transverse Ranges; this model suggests a counterclockwise rotation of the Mojave block. Analysis of S190B photographs of the western Mojave Desert provides strong evidence for the feasibility of identifying recent fault breaks.

Abdel-Gawad, M.↗