Engineering topics

Frey, H.

Publications and source records attributed to Frey, H..

At least 37 records · Page 2

NASA NTRS1985

GRM crustal magnetic anomalies: Separating the Lord Howe Rise and Norfolk Ridge submarine structures

Multiple source bodies often lie within the resolution element of the MAGSAT and POGO data. Small weak sources lying near larger stronger sources will tend to be missed, although they do contribute to the total observed anomaly. Lower elevation magnetic anomaly surveys such as GRM alleviate this problem through the combined effects of significantly greater resolution and stronger signal amplitude. This permits the detection of smaller source bodies, and analysis of their structure and nature. The improvement a GRM will provide is demonstrated in the Lord Howe Rise/Norfolk Ridge area east of Australia, between the Tasman Sea and south Fiji Basin. The submarine features origin have important plate tectonic implications. The Lord Howe Rise (LHR) is a continental fragment broken off from Australia by the opening of the Tasman Sea. It is a wide, shallow structure lying between 160 and 165 deg longitude at 23 to 37 deg S latitude. Seismic refraction data show the LHR crust extending to depths in excess of 20 km.

Frey, H.↗

NASA NTRS1985

Space-age geodesy - The NASA Crustal Dynamics Project

The NASA Crustal Dynamics Project (CDP) has deployed satellite laser ranging (SLR) systems and VLBI techniques for measurements of global and regional crustal motions and earth rotation parameters. The measurement programs for the years 1984 and 1983 are described, and some preliminary results are presented. A complete list of the fixed receiving stations in the CDP network is given.

Coates, R. J.↗

NASA NTRS1985

Mapping Structures Characteristic of the Highland Boundary Scarp on Mars

In an effort to shed some light on the processes which have produced the highlands/lowlands boundary scrap on Mars, the global distributions of knobby terrain, detached and separated blocks and mesas, and craters larger than 10 km diameter were mapped. These data were represented as fractional areal percentages of the sample box, which is 2.5 deg high (latitude) along north-south profiles every 5 deg in longitude. The fractional area of crater interiors provides a way of quantitatively characterizing the boundary between cratered highlands and relatively uncratered plains. In the vicinity of the nomimal scarp there is generally good agreement between the dropoff in fractional area of craters and a drop-off in topography. Contoured versions of the fractional area of crater interiors, even at the low resolution imposed by the sample box, show good agreement with the geologic mapping. The most northerly occurrence of detached plateaus and knobby terrain were located in order to test the plausibility of the hypothesis that much of the present day highland boundary scrap is due to southward migration of a former boundary.

Frey, H.↗

NASA NTRS1985

Distribution and Properties of Large Symmetric Knobs on Mars

Knobby terrain on Mars exists in a variety of forms from small closely spaced hills to widely separated large massifs. Fractional areal distributions of knobby terrain range from over 49% of the sampled area in regions of chaotic terrain to less than 5% along the cratered highland boundary in Amenthes and Aeolis. All symmetric knobs with long dimensions greater than or equal to 10 km were identified, mapped, and classified by shape. The spatial and dimensional distributions and shape characteristics of these features are discussed. The most common shape is elliptical: 79% of the knobs fall into this category, 11% were circular or round, 6% were triangular or wedge-shaped and the remaining 4% other shapes. All types show a roughly similar trend of rapidly decreasing number with increasing size, such that overall less than 10% of the knobs are larger than 20 km in long dimension. Circular knobs show the steepest fall-off in numbers with increasing diameter. Triangular knobs have a broader maximum with more than 65% falling in the 10 to 14 km range.

Frey, H.↗

NASA NTRS1985

Magsat and POGO magnetic anomalies over the Lord Howe Rise Evidence against a simple continental crustal structure

Magsat average scalar and POGO reduced-to-pole magnetic anomaly data both show prominent positive signatures over the Lord Howe Rise. Although generally assumed to be continental in nature, the Lord Howe Rise cannot simply be submerged ordinary continental crust, which would produce a negative anomaly contrast with respect to the surrounding higher susceptibility oceanic crust. Three-dimensional modeling of the plateau, using the known crustal structure and assuming an induced origin for the satellite elevation anomaly, leads to a model in which the lowest crustal layer in an otherwise 'continental' crustal structure has an unusually high susceptibility in the range cgs 0.008-0.010 (SI 0.10-0.13). Replacement or alteration of the lowest layer by a high-susceptibility rock type may be related to the subsidence of the plateau.

Frey, H.↗

NASA NTRS1985

Satellite magnetic anomalies over subduction zones - The Aleutian Arc anomaly

Positive magnetic anomalies seen in MAGSAT average scalar anomaly data overlying some subduction zones can be explained in terms of the magnetization contrast between the cold subducted oceanic slab and the surrounding hotter, nonmagnetic mantle. Three-dimensional modeling studies show that peak anomaly amplitude and location depend on slab length and dip. A model for the Aleutian Arc anomaly matches the general trend of the observed MAGSAT anomaly if a slab thickness of 7 km and a relatively high (induced plus viscous) magnetization contrast of 4 A/m are used. A second source body along the present day continental margin is required to match the observed anomaly in detail, and may be modeled as a relic slab from subduction prior to 60 m.y. ago.

Clark, S. C.↗

NASA NTRS1984

Distribution and properties of small volcanoes in Acidalia Planitia

Eastern Acidalia Planitia contains a wide variety of terrain types on which are thousands of subkilometer volcanoes. Apparent morphometric variations were previously reported as a function of terrain type for the cones in the Cydonia area and extended to the rest of Acidalia for which high resolution Viking imagery exist. Crater counts are included for the six types of plains identified, density distributions of subkilometer cones found on each type of terrain, and orphometric data by morphological subclass as a function of terrain for more than 1400 cones.

Frey, H.↗

NASA NTRS1983

Crustal dynamics project observations: 1982 results and plans for 1983

The 1982 Crustal Dynamics Project observations by fixed and mobile SLR and VLBI systems are reviewed. Plate motion measurements between North America and Europe were conducted by both techniques and SLR measurements were also made between North America, the Pacific, Australia and South American plates. Regional deformation measurements by VLBI and SLR systems were restricted to the western United States in 1982, including a number of important intercomparison baseline measured by both techniques. In 1983 the observing program grows significantly, with new SLR systems in Mexico, Easter Island, the Pacific and Italy. New VLBI systems will include a dedicated VLBI site at Weltzell, in Germany. Two highly mobile SLR and two highly mobile VLBI systems will greatly increase the regional deformation measurements in California and through the Basin and Range, where more than 25 sites will be occupied in 1983.

Frey, H.↗

NASA NTRS1982

Subkilometer Martian volcanoes - Properties and possible terrestrial analogs

Kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of Mars. Based on examination of more than 12,000 high resolution Viking Orbiter images, most of these very small cones are located in parts of Eastern Acidalia and Utopia-Isidis-Elysium Planitia. Measurements of base and pit diameter for some 2000 well-resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater/cone diameter ratios. This suggests that the small cones had a similar origin with only minor variations in local conditions. The Acidalia cones are generally larger, more widely distributed, and occur on a greater variety of terrains than those in Utopia-Isidis-Elysium. Based on morphology, distribution, and the crater/cone ratio histograms, the smallest Martian cones may be similar to Icelandic pseudocraters. Somewhat larger, steeper cones with smaller crater/cone ratios which also occur in Eastern Acidalia may be analogs of terrestrial cinder cones.

Frey, H.↗

NASA NTRS1982

Magsat scalar anomaly distribution - The global perspective

It is established that geographic coincidences exist between high-altitude Magsat scalar anomalies and major geologic and tectonic structures, with oceanic abyssal plains overlain by negative anomalies agreeing well in spatial extent and position and submarine platforms lying beneath positive scalar anomalies. In addition, geographic coincidence is found in the continents between many high-latitude positive anomalies and shields and cratons in North America, Eurasia and Australia. While these correlations are qualitative, they serve to identify regions for detailed study. The global distribution of anomalies provides a basis for comparative study which will be enhanced when reduced-to-pole versions of the Magsat data become available.

Frey, H.↗

NASA NTRS1982

Magsat scalar anomalies and major tectonic boundaries in Asia

The distribution of Magsat scalar anomalies is compared with locations of major tectonic boundaries in Asia. Foldbelts separate large-scale positive and negative anomalies inside and outside the Siberian Platform, and sediment-filled aulacogens within the Platform separate the anomalies into two parts which overlie the Anabar and Aldan Shields. Tectonic boundaries appear to exercise some control over the extent and distribution of the satellite-observed crustal anomalies.

Frey, H.↗

NASA NTRS1980

Crustal dynamics project observing plan for highly mobile systems 1981 - 1986

Measurement of crustal motion in the western United States and other tectonically active regions makes use of fixed, movable and highly mobile satellite laser ranging and very long baseline interferometry systems. Measurement of the rotational dynamics of the Earth as well as regional deformation and plate motion are discussed.

Frey, H.↗

NASA NTRS1979

Pseudocraters on Mars

In the Cydonia region of southern Acidalium Planitia are small, low-relief, apparently volcanic domelike structures, whose size, morphology, and general occurrence suggest they are martian analogs of terrestrial pseudocraters, a type of phreatic eruption. Average base diameters are about 800 m, which is somewhat larger than typical Icelandic examples. All the domes have summit pits; elongate domes generally have elongate summit pits or, in extreme cases, double pits. The greatest concentration of these domes is in a region of subdued fractured plains which may be old volcanic flows. Pseudocraters on the earth are produced when lava flows over water-logged ground. On Mars surface or subsurface ice was the likley medium that produced the steam eruptions resulting in cratered domelike structures on the lava surfaces.

Frey, H.↗

NASA NTRS1979

Pseudocraters on Mars

The morphology and origin of the Martian volcanic-dome like structures are compared to the terrestial pseudocraters.

Frey, H.↗

NASA NTRS1979

Large impact basins on Mercury and relative crater production rates

Mariner 10 revealed evidence for 40 impact basins having diameters greater than or equal to 200 km on the portion of Mercury imaged at sufficient resolution. A log (cumulative number/unit area) vs. log (diameter) plot for the mercurian basins has a least squares slope of -2. Mercury has (in cumulative number/unit area) only 37 percent as many basins as does the Moon over the entire range of diameters greater than or equal to 300 km. If both the Moon and Mercury have had similar preservation times for craters and if common populations of impactors are involved, then Mars crossers may have been a dominant contribution to the basin forming objects.

Frey, H.↗

NASA NTRS1979

Thaumasia - A fossilized early forming Tharsis uplift

The structure of the present-day Valles Marineris rift canyons and related features is a consequence of episodic crustal uplift, dominated by two major events. The first of these occurred near the present-day Thaumasia crustal dome and produced a structural pattern in old plains-forming units which is principally transverse to the main trend of the Valles Marineris canyons. This pattern has provided some structural control over later tectonic and volcanic events. The major crustal deformation in this region is associated with the younger Tharsis uplift, which is responsible for the major trends observed in the Valles Marineris. These two distinct structural patterns are best observed in the resistant, least eroded parts of the canyon walls; linear trends in such resistant points provide a closer approximation to the original bounding scarps of the Martian rifts than do the modern, highly eroded canyon walls. Crustal deformation was dominated by the Tharsis uplift but began much earlier in Martian history.

Frey, H.↗

NASA NTRS1979

Crustal evolution of the early earth: The role of major impacts

The role of major impact basins (such as those which formed on the moon before 4 billion years ago) is examined to determine the effects of such impacts on the early crustal evolution of the earth. Specifically addressed is the fundamental problem of what is the origin of the earth's fundamental crustal dichotomy of low density continental and high density oceanic crust and its relationship to the superficially similar highlands/maria crustal dichotomies of the moon, Mercury and Mars.

Frey, H.↗

NASA NTRS1979

Martian canyons and African rifts - Structural comparisons and implications

The resistant parts of the canyon walls of the Martian rift complex Valles Marineris have been used to infer an earlier, less eroded reconstruction of the major troughs. The individual canyons are compared with individual rifts of East Africa. When measured in units of planetary radius, Martian canyons show a distribution of lengths nearly identical to those in Africa, both for individual rifts and for compound rift systems. A common mechanism which scales with planetary radius is suggested. Martian canyons are significantly wider than African rifts. This is consistent with the longstanding idea that rift width is related to crustal thickness: most evidence favors a crust on Mars at least 50% thicker than that of Africa. The overall patterns of the rift systems of Africa and Mars are quite different in that the African systems are composed of numerous small faults with highly variable trend. On Mars the trends are less variable; individual scraps are straighter for longer than on earth. The basement and lithosphere of Mars are inferred to be simple, reflecting a relatively inactive tectonic history prior to the formation of the canyonlands.

Frey, H.↗