ALBERT

Description: S"SUB g"-amplitudes and periods of 252 European seismic events recorded at GDR and Czechoslovak seismological stations have been measured and their dependence on distance (up to 650km) and azimuth has been analyzed. These will allow reliable local and regional magnitude determination.-after Authors

Description: An analysis of the steady-state heat conduction model for the Earth's crust and the upper mantle revealed that the main difficulties in the downward continuation of subsurface geothermal measurements q were connected with an estimation of the heat flow density q"SUB M" at the Moho boundary and of the source distribution f. Solving the steady-state heat conduction equation numerically by means of finite differences (finite elements), we can describe the relation between q, q"SUB M" and f by a linear algebraic system. To overcome the non-uniqueness and instability, a least squares approach is suggested to solve these systems. Bounds for the square-means of the unknown parameters q"SUB M" and f are introduced, whereby it is possible to find solutions with appropriate mean properties. A two-dimensional geothermal profile crossing Central Europe is used to demonstrate this method. The difficulties in estimating reasonable mantle heat flow density and optimal heat source models from geothermal measurements only are pointed out.-Authors

Description: In recent years the need for improved seismic risk evaluations in Sweden has led to accurate estimates of detection porbabilities with respect to weak Swedish earthquakes. Generally, these rather low-magnitude events (M"SUB l"4) are recorded only by means of the Swedish Seismograh Station Network (SSSN), currently consisting of 6 permanent stations. Only occasionally do neighbouring Finnish and/or Norwegian stations also contribute with arrival-time readings, hence, for weak regional events, we lack usual reference system of organisations like ISC, NEIS, or EMSC when estimating the detection performance of the SSSN-stations. The main objective of the present short communication is to indicate the ability of the SSSN to detect earthquakes in Sweden and the relative detection contributions from individual network stations. The data used comprise 121 earthquakes located within Sweden and adjacent waters (Wahlström 1978). The statistical model used and other theoretical aspects of the modified approach are discussed in an earlier paper.-Authors

Description: During the period of January 1977 to December 1979, 22 earthquakes were recorded and located in Sweden and/or adjacent waters by means of the Swedish Seismograph Station Network (SSSN). 8 were felt by residents in the repective areas and hence provide an opportunity for macroseismic investigations. Such investigations are extremely useful for estimating e.g. the depth of rupture and local ground accelerations, especially when teleseismic data and strong-motion records are not available. The long-term average gives approximately 3 earthquakes per year which are reported to be felt by people. In this respect, the seismic activity in Sweden during the years under review is well within the 'normal'. The main objective of the present study is to summarize and interpret available macroseismic observations collected at the Seismological Dept in Uppsala.-P.N.Chroston

Description: The unique solvability of the inverse gravimetric problem for systems of point masses arbitrarily distributed in a bounded region is proved. Using the equivalence of this statement to the linear independence of the corresponding Newtonian potentials for single point masses this proof can be given by means of a generalized momentum representation both in modern potential theory and in classical algebraical manner.-Authors

Description: Additional keywords: Maxwell body, standard linear solid, absorption band model, seismicity, earthquake migration, plate tectonics, seismic hazard, rupture planes, source parameters, Rheologie, Schichten, Dislokationen, Neigungen, numerische Modelle, Kolumbien, Tuerkei, Nordanatolische Verwerfung, Maxwell-Koerper, Zener, tektonische Spannungen, Seismizitaet, Platten-Tektonik, Erdbeben-Gefaehrdung, Erdbeben-Serie

Description: The evolution at the W margin of the E Antarctic platforms started with a Precambrian flyschoid formation which is overlain discordantly by Middle Cambrian limestones of an epicontinental environment and which leads to continental sedimentation conditions with acid, subsequent volcanic rocks of probably Cambrian age. A coarsely clastic red molasse without volcanic rocks of probably Upper Devonian age follows. The following evolution in Upper Paleozoic with continuation of the platform character is very incomplete. Tillites of probably Carboniferous age and Permian sandstone-siltstone interstratifications with coal intercalations are known. Structurally a historic, disharmonically superimposed stockwork structure can be detected. The processes of metamorphism which are connected with the Beardmore tectonogenesis at the turn of Precambrian/Cambrian took place in the range of the 'very low metamorphism'. With the younger, intraPaleozoic deformations no regional metamorphism is connected. Deformations which are connected with faults are of different character. Here the degree of biotite formation can be reached. -from Current Antarctic Literature

Description: Presents the time dependence of the statistical parameters alpha and beta describing seismic activity with a high time resolution. alpha stands for temporal event intensity and beta determines the distribution of magnitudes. It was studied whether these parameters are indicative as precursory phenomena predicting large aftershocks within the investigated earthquake sequences (Friuli region in 1976 and a section of the Montenegro sequence in 1979). No precursor effect could be found in the b-value of the quasi-linear Gutenberg-Richter model. b is decreasing abruptly exactly in that point when the computation window includes that large event which shall be found.-from Authors

Description: A recent series of Swedish earthquakes at a focal depth not exceeding 2-3km, the largest with I"SUB O" = V+ (MSK scale) and M"SUB L" = 3.2 shows that relatively strong seismic activity can occur in the uppermost part of the Baltic Shield. During the last 15 years several near-surface earthquakes have occurred in this region, as indicated by recorded Rg-waves and/or macroseismic data. Many events are located along the coast of central Sweden, suggesting a seismic belt of minor, near-surface activity, which should be considered in connection with the radioactive waste storage in the Swedish bedrock. The appearance of Rg, common in seismic records of explosions and rockbursts, is not a sufficient discriminator between artificial events and earthquakes. -Author

Description: Station corrections have been introduced into the M"SUB L"-scale hitherto used for Baltic Shield earthquakes. The new formula is valid for Benioff and Grenet seismograph stations in Finland and Sweden. An extension of the magnitude scale to distances as small as 30 km is made by adding the constant 0.31 to the equation. Correlating the instrumental magnitude with macroseismic parameters, a relationship between the radius of areas of perceptibility (km) and maximum intensity has been obtained which is especially useful in quantification of historical earthquakes. For stations of the Finnish Seismic Array (FINSA) equipped with Geotech S13 seismographs, formulae has been obtained from which magnitudes may now be assigned to weak shocks, which were not possible to quantify previously. -from Authors

Description: Using data from explosions recorded by the Swedish Seismograph Station Network (SSSN), an average model of two horizontal layers was deduced for the Swedish crust: Layer thicknesses (km): top layer = 10, whole crust = 37; wave velocities (km s"SUP -1"): Pn = 7.87, P"SUP *" = 6.69, Pgl = 6.27, Sn = 4.55, S"SUP *" = 3.69, Sg1 = 3.54, Sg2 = 3.40, Rg = 2.81. A computer program was developed to determine locations of regional seismic events. Assuming a horizontal two-layered crust, arrival times of identified crustal and Moho-refracted waves are given as input. The location accuracy of seismic events using three-dimensional geophone networks was investigated for real and fictitious networks and events. The effects of arrival time and velocity model accuracies, computational method, network geometry and relative location of hypocentre to geophones are quantitatively demonstrated in various examples. - from Author

Description: On February 13, 1981, a relatively strong earthquake occurred in the Lake Vanern region in south-central Sweden. The shock had a magnitude of M"SUB L" = 3.3 and was followed within three weeks by three aftershocks, with magnitudes 0.5 = or 〈 M"SUB L" = or 〈 1.0. The focal mechanism solution of the main shock indicates reverse faulting with a strike in the N-S or NE-SW direction and a nearly horizontal compressional stress. The aftershocks were too small to yield data for a full mechanism solution, but first motions of P-waves, recorded at two stations, are consistent for the aftershocks. Dynamic source parameters, derived from Pg- and Sg- wave spectra, show similar stress drops for the main shock (2 bar) and the aftershocks (1 bar), while the differences in seismic moment (1.5X10"SUP 20" resp. 4X10"SUP 18" dyne cm), fault length (0.7 resp. 0.2 km) and relative displacement (0.15 resp. 0.03 cm) are significant.-Authors

Description: To detect and to locate the frequently occurring rockbursts within the mining area at Grangesberg, Sweden, the mining company has installed a local network of geophones. Mathematical technique is presented for hypocentre determination assuming a constant velocity model and a three-dimensional network of geophones with high-speed recording. Two sets of input data are feasible: 1) relative P arrival times; 2) S minus P arrival times. The former set requires readings from at least five geophones; for the latter readings from four geophones are sufficient. Factors influencing the resulting location accuracy are studied in various examples. General conclusions and recommendations are given.-Author

Description: The results of the collection and revision of the seismicity data are presented for the territory of the GDR depicted in epicentral maps. A new map of maximum observed intensities was compiled on the basis of the reinterpretation of the strongest seismic event since 1500, the earthquake of March 6, 1982. -Authors

Description: In the years 1963-79, altogether 176 Swedish earthquakes have been detected and located. The earthquakes have occurred within a belt from the SW to the NE part of the country and in N Lapland. Corresponding local magnitudes are not greater than 4. b-values of the magnitude-frequency relation are 0.7 and 1.5 for magnitude intervals 2.2-3.0 and 3.0-3.9, respectively. The strain energy release has been rather regular during most of the time. The apparent increase of small-size shocks in recent years is due to improved instrumental facilities and not to a real increase of seismicity. The presented data can be used as a base for seismotectonic and seismodynamic studies of the Swedish bedrock.-from Author

Description: A procedure for assessing the seismic hazard based on the algorithm proposed by Cornell (1968) and the respective computing programme by McGuire (1976), was applied to the territory of the GDR in view of the influence of 10 earthquake source regions. The delineated regions are described by the cumulative frequency of earthquakes as a function of their intensities and the expected maximum intensities I"SUB max". The intensity attenuation with distance was determined by generalizing the observed macroseismic observations. Hazard maps displaying the expected macroseismic intensities for mean return periods of 100, 500, 5000 and 10 000 years are presented and discussed, explicitly comparing the results with the map of maximum observed intensities of the GDR. -Authors

Description: On December 23, 1979 an earthquake sequence occurred near Bergshamra-Roslagen, Sweden, about 50km northeast of Stockholm. The main shock has been assigned a magnitude M"SUB L" = 3.2. A six- week field survey in the epicentral area revealed a number of small aftershocks located close to the main shock. Pg and Pn-readings suggest for the main shock reverse faulting with a strike of N36"SUP o"E and a dip of 55"SUP o" to the SE. Spectral analysis applied to available seismograms from Finnish, Norwegian and Swedish stations gave for the dynamic source parameters a fault length of 0.8km, a seismic moment estimate of 6.6 x 10"SUP 20" dyne cm and a stress drop of 6 bars. The Bergshamra sequence took place in a zone of very low seismicity in eastern central Sweden and for Swedish earthquakes at unusual shallow depth. The observed earthquake sequence suggests that the known fault system in this area represents a seismically active region. -Authors

Description: Station corrections have been introduced into the M"SUB L"-scale hitherto used for Baltic Shield earthquakes. This increases the consistency of the scale. The new formula has the design: M"SUB L"(UPP) = log a + log V(T) + 1.61 log DELTA - 3.22 + C"SUB I" + C"SUB s", where a = ground amplitude (mu m), V(T) = Wood-Anderson short-period seismometer magnification at period T, DELTA = epicentral distance (km), C"SUB I" = instrument type constant and C"SUB s" = station correction. The formula is valid for Benioff and Grenet seismograph stations in Finland and Sweden. An extension of the magnitude scale to distances as small as 30km has been made.-from Authors

Description: Near the E edge of Leipzig (GDR) an earthquake occurred on February 20, 1982, with an epicentral intensity of 5o. The last comparable earthquakes in this area were observed in 1905 and 1914. These events and the seismic activity of the focal region 'Northwest Saxonia' are presented. The source parameters of the 1982 earthquake determined from the polarities and the spectra of different wave types are given.-from Authors

Description: Highly industrialized and densely populated territories such as the GDR necessitate to consider very small probabilities of the occurrence of potentially damaging earthquakes. A concept was developed for the assessment of the seismic regime in the GDR. This concept as well as some first results are presented. Especially a possible connection between the seismicity level of a seismotectonic unit and its maximum earthquake will be discussed. -Author

Description: Using Sg-amplitudes measured at GDR and Czechoslovak stations from earthquakes in Central Europe and the surrounding area, and magnitudes given by various stations and agencies for the same events, calibration functions modelled to contain separated components of geometrical spreading (r"SUP -n") and anelastic attenuation (e"SUP -br/T") have been derived. Obtained b-values show significant variation for different spreading types, but surprisingly small scatter, for any given spreading type, for different geographical regions (sectors). Derives a magnitude formula applicable to short-period vertical-component seismograph readings at stations BRG, CLL, MOX, KHC and PRU. Epicentral distances should be greater than 100 km. The attenuation of Sg- waves in the Central European crust can be described by a mean value of Q = 230. -after Authors

Description: The discovery of concentrations of meteorites in Antarctica by Japanese field parties in 1969, and subsequently by joint U.S.-Japanese and U.S. field parties since 1976 has provided a significant new resource for understanding the origin and evolution of the solar system. The number of meteorites as well as the variety of meteorites has increased dramatically, and substantial amounts of data derived from their study has begun to appear in the scientific literature. The U.S. program of investigation has drawn on curatorial experience derived from the lunar program to: (1) develop specific collection and preliminary examination protocols; (2) provide documented samples for scientific investigations in response to specific requests; and (3) coordinate research by scientific consortia. The productivity of scientific research is significantly enhanced by these management approaches. Some of the results of the curatorial program for Antarctic meteorites carried out over the past three years are described.

Description: Opinions conflict over the role of surface gravity in shaping impact craters on Mercury. One view holds that the effects of g are evident in measurable aspects of crater form; other investigators find little or no evidence for g's geomorphic importance. Ambiguity in the role of g and other variables in cratering on Mercury stems largely from uncertainty in identifying major geomorphic contrasts and the crater sizes at which they occur. One of these, depth/diameter (d/D), undergoes a major change at the transition from simple (bowl shaped) to complex (peaks and terraces) crater interiors. Four least-squares d/D fits for fresh craters on Mercury were attemped. The results are inconsistent. The d/D data that should resolve previous shortcomings is presented. The revised d/D distributions for simple and complex craters, which intersect at a diameter of about 5 km, support the initial thesis that g substantially influences the form of Mercury's craters.

Description: Craters within the Ganymede Jg-7 quadrangle were divided into seven mappable units. The units represent: (1) irregular or elongate craters, (2) craters with dark ejecta, (3) palimpsests, (4) secondary craters, (5) and craters of young, mature, and old age. Symbols used for crater floors include: (1) flat floors, (2) floors with pits, (3) floora with a central dome or peak, (4) and floors with a central dome and pit. Grooved terrains were divided into five mappable units. Three units of light grooved material represent small, medium, and large grooves, which are arbitrarily divided. The other two units of grooved terrain represent dark grooved materials, and reticulate grooves. Two units of ungrooved dark terrain and two units of ungrooved light terrain were defined. In Galileo Regio, two units were defined repesenting large furrowed grooves, and smaller grooves which are orthogonal to the furrowed grooves.

Description: The relative time of emplacement of some major rock units on Mars was recognized to some degree from geologic mapping using Mariner Images. Correlation charts showing the map units and their position in sequence, however, displayed little discrimination in their vertical range of occurrence. A more detailed time-stratigraphy is currently being developed as Viking geologic mapping of the planet progresses.

Description: Although many radar profiles and images of the area within 20 deg of Mercury's equator had been obtained from 1971 to 1981, at both Goldstone and Arecibo radar facilities, surprisingly little geological analysis had been done with these data until recently. Topographic profiles and radar roughness reflectivity images which can be derived from these data will be crucial in completing the geological mapping of Mercury now underway at the U.S. Geological Survey. Processing of available radar data must be completed to establish any systematic relationship between radar reflectivities and roughness, density, dielectric constant, and other related geological parameters. Specific tasks accomplished for these purposes include the following. Documentation was located and searched to establish the type and quantity of Goldstone 12.5 cm radar observations which were available for Mercury. Data has been collected during approximately 50 observation periods from 1971 to 1981. About half of the data, collected during 1972 and 1973, have been processed, but without adequate documentation. A standardized, well-documented procedure for processing and analysis for all Goldstone Earth-based observations of Mercury was established.

Description: The origin of Mars surface units and the extent of subsequent cratering play key roles in determining surface texture. At scale sizes of 0.1-10 meters, however, there is a growing body of evidence that wind is the dominant force. The direct and indirect evidence which implies that meter-scale surface texture on Mars is controlled by the wind is presented. Since radar is uniquely sensitive to structure on these scales, radio wave scattering data can provide insight on aeolian activity available from no other source.

Description: Two old volcano-tectonic collapse structures are exposed north and northeast of the huge shield volcano, Olympus Mons. They are semicircular and were probably low shield volcanoes similar to Alba Patera, but whose central portions have subsided or collapsed. They form the basement upon which younger volcanic materials of Alba Patera Olympus Mons have been emplaced. The oldest structure, Acheron Fossae is over 700 km across and is north of Olympus Mons. It has a surface of considerable relief broken by graben and extensive en echelon and parallel fractures and faults with varied displacements. Acheron Fossae is the most densely cratered in the Olympus Mons region. The structure must have formed very early in martian time. The second is Halex Fossae, northeast of Olympus Mons. Where exposed, it is cut by a series of arcuate grabens that become closer spaced toward its center. The radii of the fractures indicate that the structure may be at least 250 km across and centered beneath the Olympus Plains. Lava flows appear to have issued from some of the arcuate fractures and to have flowed radially away from the center of Halex Fossae. North of Halex Fossae, material of the same age as Halex Fossae overlaps Acheron Fossae.

Description: High spatial resolution data from the Viking infrared thermal mapper (IRTM) are used to examine the Tharsis volcanoes which are situated within a vast area of low thermal inertia material very fine particle size or very high porosity, with the volcanoes having the lowest thermal inertias. Thermal infrared images of the 1823 flow on Kilauea's southwest rift zone show lower thermal inertias near the vent area where shelly pahoehoe is common while individual channelized aa flows with abundant broken pahoehoe slabs are higher thermal inertia. The increase in aa flows to the southeast leads to a general trend of increasing thermal inertias from near vent to distal areas. Martian shield volcanoes have thermal inertias equal to or higher than their surrounding plans when atmospheric effects are removed from the data. The general increase in thermal inertias away from the summit calderas is consistent with the trend of the Hawaiian 1823 flow and may be related to changing lava properties away from the summit.

Description: A photometrically and geometrically reduced data base is being produced for the Galilean Satellites using Voyager Imaging data. The basic data set used is essentially all the useful satellite images returned by Voyager. Each frame was radiometrically calibrated and many are projected into cartographic formats. Mosaics of low, medium and high resolution frames being made for each satellite consist of registered digital images with intensity values scaled through a traceable calibration procedure to normal albedo values. Many of the mosaics are being made in two versions. One version is an albedo version and the second is a maximum discrimination version in which large variations in brightness across the picture are suppressed.

Description: One unique feature on Mars is the presence of ring furrows which are apparently produced by inversion of topography at the rims of partially buried craters. Ring furrows are flat-floored trenches, circular in plan view, forming rings 7 to 50 km in diameter. The moat is on the order of 0.5 km deep and 2 to 10 km wide, and it surrounds a flat topped circular mesa or plateau that is 5 to 40 km across. The central plateau is at the same elevation or lower than the surrounding plain outside the ring. The circular nature and size range of ring furrows tend to suggest that these features are related to craters partially buried by younger lava flows. The rings have been formed by preferential removal of the exposed crater rims. Ground ice decay, sapping, or fluvial erosion removed the less resistant, porous material of crater rims while leaving the more resistant volcanic flow material. Differential erosion has thus led to a reversal of topography in which the original positive relief of the rim is reduced to a negative relief feature.

Description: The morphology of channels, valleys, chaotic and fretted terrains and many smaller features on Mars is consistent with the hypothesis that localized deterioration of thick layers of ice-rich permafrost was a dominant geologic process on the Martian surface. Such ground ice deterioration gave rise to large-scale mass movement, including sliding, slumping and sediment gravity flowage, perhaps also catastropic floods. In contrast to Earth, such mass movement processes on Mars lack effective competition from erosion by surface runoff. Therefore, Martian features due to mass movement grew to reach immense size without being greatly modified by secondary erosional processes. The Viking Mission to Mars in 1976 provided adequate measurements of the relevant physical parameters to constrain models for Martian permafrost.

Description: High-resolution pictures of talus slopes on Mars show small, dark streaks that characteristically widen downward. These streaks are different from the thin and even streaks of various albedos that stream from cliffs on talus slopes, but gradations between the two streak types occur and not all streaks can be classified with confidence. In order to study the nature and origin of the small, widening, dark streaks, all Viking pictures with a resolution of less than 100 m/pixel were surveyed. To date several hundred streaks were located, but only few are of high enough resolution to be confidently identified as widening downwards. The approximate dimensions of the streaks were measured and their shapes, numbers, position, and spacing on slopes were noted. They were plotted on a topographic map, and their relation to topography, geologic units, and regions of distinct thermal inertia and albedo were studied. Also noted was the season at which images containing streaks were acquired and the direction of illumination. Albedo measurements are in progress. Several streaks can be seen stereoscopically, but none are observed on color images. The observation of small dark streaks on talus slopes on Mars is compatible with an interpretation of their origin as eruptions of small masses of wet debris in places where steep walls intersect aquifers or where seasonal equatorial warming permits the local melting of ground ice.

Description: The valley networks of Mars are widely believed to have formed at a time when climatic conditions on the planet were significantly different from those that currently prevail. This view arises from the following observations: (1) the valleys form integrated branching networks which suggests fluid drainage, and water is the most plausible fluid, (2) the present atmosphere contains only minute amounts of water, (3) the networks appear to be more akin to terrestrial valleys that are eroded by streams of modest discharges than features that form by catastrophic floods, and (4) small streams of water will rapidly freeze under present climatic conditions. Climatic conditions at the time of formation of the valleys are studied based on the assumption that they were cut by running water.

Description: Images of the surface of Venus obtained by the Soviet Venera 9, 10, 13 and 14 landers are analyzed to provide a basis for understanding the nature of geologic processes operating there. Bedrock is exposed at the Venera 10, 13 and 14 sites and is characterized by semi-continuous, flat polygonal to subrounded patches up to several meters in width. The bedrock surface is often dominated by sub horizontal to horizontal layered plates with thicknesses of several cm and abundant linear and polygonal vertical fractures. Soils (particles 1 cm) are abundant at the Venera 9, 10 and 13 sites, but are uncommon at Venera 14. Features indicative of a strong aeolian influence (moats, dunes, wind tails) are not observed. Several hypotheses are considered for the origin of the bedrock surfaces, and it is concluded that bedrock originated from surface lava flows. The relative freshness of features observed by the Veneras suggests that erosion rates are very low or that some bedrock surfaces are geologically young.

Description: 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.

Description: A study to determine the feasibility of conducting experiments to simulate the aeolian environment on Venus as related to wind abrasion was completed. Ideally, such experiments should involve complete investigation of weathering, in which mechanical, thermal, and chemical parameters are taken into account. This is particularly important for Venus, where atmospheric temperatures and pressures at the surface produce an environment which is equivalent to low or medium grade metamorphic conditions on Earth. Details that describe the Venus Aeolian Abrasion Device (VAAD) are included. The VAAD device would enable experiments to be conducted with the same chemistry, temperature, pressure, and other physical properties of the Venus atmosphere near the surface. The proposed device enables the important aeolian parameters to be controlled and monitored, including particle size, velocity, impact-angle and flux, atmospheric pressure, temperature, and gas composition.

Description: Why the lowlands of Mars are concentrated in the Northern Hemisphere and the highlands in the Southern Hemisphere is probably the most fundamental unsolved problem in martian geology. No explanation that accounts both for this asymmetric distribution and for the isostatic equilibrium across the scarp or sloping transition zone dividing the two provinces has been generally accepted; thinning of the lithosphere in the northern hemisphere by internal processes has been suggested. Because other lowland-highland distributions on Mars, Moon, and Mercury are controlled by impact basins, it is proposed that a giant basin formed early in Mars' history has caused the martian hemispheric dichotomy as well.

Description: A number of researchers have concluded that saturation equilibrium cratering exists nowhere in the solar system, and therefore that diameter distributions in even the most heavily cratered provinces reveal initial production functions related to impacting bodies. Based on this premise, different populations of impactors are identified in different epochs and regions of the solar system. These hypotheses are clearly crucial to interpreting planetary history and need further independent examination. The production function in the outer solar system may differ from that in the inner solar system, but it is also possible that viscous relaxation of ice craters or immediate flooding of craters that penetrate through an ice lithosphere into watery substrate may explain the greater deficiency of large craters on icy moons. This problem is controversial and needs more study.

Description: Properties of the planetary surface and subsurface can affect the morphology of impact craters. A mechanism was proposed to explain pedestal craters and domed floors within fresh craters on Ganymede. Voyager 1 and 2 images with resolutions = to or 3.2 km/lp were examined and 523 fresh craters were identified. For each crater, the rim and ejecta diameters were measured, and the crater was characterized by ejecta class(es), interior features, floor morphology and target terrain. Of the craters examined, 97 show moderate to prominent doming of the crater floor; 340 craters have continuous ejecta which terminates in a scarp pedestal craters, of which 86 (25%) have a high albedo diffuse deposit beyond the pedestal.

Description: A systematic survey of the entire Mariner 10 coverage of Mercury was performed to determine the number, distribution and dimensions of additional ancient basins on the planet. Ancient multi-ringed basins on Mercury can be recognized by the following criteria: (1) arcs of massif chains and isolated massifs that protrude through younger units, (2) arcuate segments of lobate ridges (rupes) that align with massifs in circular patterns, (3) arcuate scarps that are aligned with ridges and massif, and (4) isolated regions of anomalously high topography within the intercrater regions of heavily cratered terrain. All of the newly identified basins predate the mercurian intercrater plains, previously held to be the oldest geologic unit on the planet. Subsequent structural evolution of various regions was influenced by the presence of these basins. Smooth plains units appear to be more extensive than mapped by Mariner 10 and more than 90 percent of them appear to be basin contained or basin related. The concentration of extensive smooth plains material within and associated with basin structural and depositional environments suggests a volcanic origin for most of this unit, analogous to the lunar maria. Basins appear to provide the basic structural pattern of early terrestrial planetary crusts.

Description: An improved version of the Pionner-Venus orbital data was used for a statistical analysis of global radar roughness and (alpha(0)) (rho) reflectivity. Classification maps of the venusian surface are produced in a supervised manner on the basis of statistical and empirical studies of the individual data sets. The primary objective is to assess the degree of homogeneity of surface radar properties within topographic provinces in order to map possible geologic boundaries. Maps were produced by correlating two data sets at a time. Classification of specific regions, such as Ishtar, has demonstrated that distinct geological units can be identified.

Description: Interest on Venus has centered on three regions; (1) Aphrodite Terra, especially east of the main uplant portion, (2) Ishtar Terra, especially Lakshmi Planum and its bounding scarp and massifs, and (3) Beta Regio-Phoebe Regio. The last region is topographically similar to the East African rift system, and has been inferred to have a similar tectonic origin. The Aphrodite region is part of a 21,000 km long tectonic zone that seems best explained as due to extension, and that may represent hot spots clustered along an incipient divergent plate boundary. The most interesting and complex portion of this tectonic zone is that part of eastern Aphrodite between Thetis Regio and Atla Regio. In contrast, the Lakshmi Planum region has many topographic characteristics suggesting that it is a true continent, and thus indicative of convergence and a thick crust. Detailed topographic contour maps of eastern Aphrodite Terra and of Lakshmi Planum are included.

Description: The results of analyses of near infrared reflectance spectra are inconsistent with numerous previous interpretations of the Reiner Gamma Formation. These include: (1) nue ardente or volcanic ash deposits, (2) volcanically derived sublimates, (3) high albedo volcanic deposits, and (4) highlands debris emplaced as impact ejecta. These results, strongly suggest that the selective preservation of high albedo features (formed by secondaries) by a local magnetic field enhancement is not a viable hypothesis. The results are generally consistent with, but place constraints on, the cometary impact hypothesis of Schultz and co-workers. While the presence of a magnetized component was not detected in either the bright or dark portions of the Reiner Gamma Formation, this material may be present in amounts under the current detection limits.

Description: On the basis of the icy conglomerate model of cometary nuclei, various observations demonstrate the spotted nature of many or most nuclei, i.e., regions of unusual activity, either high or low. Rotation periods, spin axes and even precession of the axes are determined. The observational evidence for variations in activity over the surfaces of cometary nuclei are listed and discussed. On June 11 the comet IRAS-ARAKI-ALCOCK approached the Earth to a distance of 0.031 AU, the nearest since C/Lexell, 1770 I, providing a unique opportunity for near-nucleus observations. Preliminary analysis of these images establishes the spin axis of the nucleus, with an oblioquity to the orbit plane of approximately 50 deg, and a lag angle of sublimation approximately 35 deg from the solar meridian on the nucleus. Asymmetries of the inner coma suggests a crazy-quilt distribution of ices with differing volatility over the surface of the nucleus. The observations of Comet P/Homes 1892 III, exhibiting two 8-10 magnitude bursts, are carefully analyzed. The grazing encounter produced, besides the first great burst, an active area on the nucleus, which was rotating retrograde with a period of 16.3hr and inclination nearly 180 deg. After the first burst the total magnitude fell less than two magnitudes from November 7 to November 30 (barely naked eye) while the nuclear region remained diffuse or complex, rarely if ever showing a stellar appearance. The fading was much more rapid after the second burst. The grazing encounter distributed a volume of large chunks in the neighborhood of the nucleus, maintaining activity for weeks.

Description: Dione is one of the most geologically complex of the Saturnian satellites. Crater counts and surface morphology indicates the geologic units observed are of variable age and origin. In an attempt to understand the processes which have affected Dione, a geologic map was prepared. Several geologic units were identified; ancient heavily cratered terrain, two plains units: cratered plains and lightly cratered plains, lobate deposits, crater rim deposits and bright wispy materials.

Description: For large parts of the surfaces of the Galilean satellites there is no stereoscopic high resolution imagery, and so for shadow-free regions far from the terminator, the only method of obtaining topograpic information is photoclinometry, the technique of converting brightness variations into local surface tilts and hence into topographic profiles and contour maps. The conversion from brightness changes to slopes require knowledge of the angular photometric function for the type of planetary surface terrain being analyzed, i.e., the relationship describing the brightness of the surface as a function of the angles of incidence (I) and emergence (E) of light at a surface element. In order to investigate the effects of these changes on the shapes of topographic profiles deduced from the functions, an area of grooved terrain (lines 500-505, samples 550-650 on frame 20640.27 0060J2) using wide ranges of values of all the adjustable parameters in Hapke's new photometric function were analyzed.

Description: Exploratory work on the structure of the Ionian lithosphere is reported. The approach is to examine temperature profiles within the lithosphere that result from different distributions of sulfur and silicates and different conductive heat fluxes, then compare such profiles with observations in the expectation that only a limited set of the profiles are possible. In this preliminary work some rather simplistic assumptions were taken and the report should be viewed more as a demonstration of a method rather than a presentation of results.

Description: Improvements to the design of the Mariner spacecraft resulted in the Viking spacecraft. The Viking spacecraft would consist of two major systems - an orbiter and a lander, while the lander would provide the means for safely delivering the scientific instruments to the surface, house, and provide the necessary power source and communication links for those experiments, the orbiter would transport the lander to Mars, rovide a platform for the Viking imaging system so that proposed landing sites could be surveyed and certified, relay lander science information back to Earth, and conduct scientific observations in its own right.

Description: The Tharsis ridge system appears to form a great circle around the major volcanoes. The roughly circumferential orientation of these ridges could be interpreted as the formation of a ridge system in response to a single stress field with a center near Pavonis Mons. Wise, et al. (1979) plotted the perpendiculars to strikes of ridges on the eastern flanks of Tharsis as great circles on the upper hemisphere of an equal area net. In order to further test for circular symmetry and possible other influences on ridge orientations, normals to vector means of ridge orientations were calculated using over 1850 digitized ridge segments sampled in 10 degree boxes. Orientations of individual ridge segments were weighted by their lengths, and the magnitudes of normals to vectors means were weighted by cummulative length of the ridge segments. Normals to vector means with magnitudes less than 100 km are not shown. Assuming a single fold origin for ridges, the resulting plot shows compressive stress trajectories for the ridges in the Tharsis region. The averaged compressive stress orientation around Tharsis confirm the suggestion by Wise, et al. that the ridge system is not concentric to any single point.

Description: 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.

Description: Several 3.8 cm radar frames were calibrated empirically by histogram fitting, because no instrument background data is available. Then data were corrected for geometric distortion by: (1) redetermining position of individual frames using most accurate recent lunar ephemerides; (2) reprojecting frames into simple cylindrical map projection; (3) using most recent catalog of lunar craters to determine the exact positions of features identifiable on radar frames; and (4) correcting for apparent distortion (misplacement of features in frames) by resampling using a different bilinear interpolation derived for each of the parallelopideds of the set defined for each frame. A hardcopy set of corrected frames was produced. Attempts to produce a mosaic of such corrected frames continue. The resulting mosaic can be used to show the systematic relationship between photographic thermal IR and radar data at different wavelengths in a region dominated by both mare and highland terrain.

Description: Studies of the stratigraphy of southwest Coprates have led to further constraints on both the geographic extent and the relative age of the major compressional ridge forming events in the Tharsis region of Mars. Southwestern Coprates is characterized by curvilinear ridges that are regularly spaced, suggestive of harmonic folding. The western edge of the ridged plains unit of Coprates is marked by volcanic flow fronts. In an enhanced Viking-Orbiter image, a ridge can be seen completely surrounded by a flow with only a small portion of the ridge crest still exposed. Comparison of partially buried ridges on the western edge of the ridged plains to those in central Coprates suggests that flooding of the inter-ridge plains does not exceed a few hundred meters. The morphological relationship between the flow units to the west and the ridged plains indicates that the deformational events in this region predates the emplacement of the younger units.

Description: Layered deposits within Valles Marineris and its associated system of canyons have been considered to consist of two different rock types: (1) thick, competent, cliff-forming, light and dark bedded material in canyon walls, and (2) relatively thin, alternating series of light and dark layered material, both horizontal and inclined, that form rounded hills and large flat-topped mesas rising above the canyon floors. The dissimilarity in appearance between canyon wall and floor materials, as well as their contrasting patterns of erosion, have been considered strong evidence that their modes of origin were different.

Description: The scarps along the margins of the Vales Marineris display a complex assemblage of forms that have been related to a variety of mass wasting and sapping processes. These scarp segments display variations in the degree of development of spur and gully topography, the number and density of apparent sapping features and the frequency of large scale landslides which reflect the age, geology and processes of slope development throughout the Valles Marineris. This regional analysis should provide more information on the geologic evolution of the Valles Marineris as well as new insight into the relative importance of different processes in the development of the scarp forms. In order to evaluate the regional variation in scarp form and the influence of time and structure on scarp development geomorphic mapping and morphometric analysis of geologically distinct regions of Valles Marineris is being undertaken.

Description: Parallel studies of Martian geomorphic features and their analogs on Earth continue to be fruitful in deciphering the geologic history of Mars. In the context of rock weathering, the Earth-analog approach is admirably served by the study of meteorites recovered from ice sheets in Antarctica. The weathering environment of Victoria Land possesses several Mars-like attributes. Four of the five Antarctic meteorites being studied contain rust and EETA79005 further possesses a conspicuous, dark, weathering rind on one side. Secondary minerals (rust and salts) occur both on the surfaces and interiors of some of the samples and textural evidence indicates that such secondary mineralization contributed to physical weathering (by salt riving) of the rocks. Several different rust morphologies occur and emphasis is being placed on identifying the phase compositions of the various rust occurrances. A thorough understanding of terrestrial weathering features of the meteorites is a prerequisite for identifying possible Martian weathering features (if such features exist) that might be postulated to occur in some meteorites.

Description: Photometric studies of crater related bright and dark streaks have strongly supported the hypothesis that the bright streaks are excess dust deposits and dark streaks are erosional windows in a partial dust cover. Red-blue (and red-violet) plots show that bright streaks are consistent with mosaics of bright red dust and background material. Here the plains are also consistent with a partial dust cover; the dark streak is the least covered area. Bright and dark streaks both reverse contrast relative to surrounding plains at phase angles over 100 deg in violet filter images. The similar phase behavior of both bright and dark streaks supports the idea that they are both changes in the amount of dust cover. Red-violet plots of bright streaks are most easily explained by mosaics of optically thick dust and plains material. Lengths of bright streaks are independent of their contrasts. This suggests the streak deposition, if in the mosaic patterns indicated above, is a function of available sites of deposition, rather than atmospheric dust loading. Contrasts of dark streaks with plains indicate the plains have fractional dust covers nealy as great as the maximum additional cover in bright streaks. The bright streaks thus store little of the global supply of dust.

Description: Viking Lander 1 observations on Mars were punctuated by a strong local dust storm after two martian years of mild wind conditions. Tens of micrometers of dust settled to the surface during global dust storms of the first two falls and winters; some of this dust was locally removed during the second year. A late winter local dust storm of the first year caused little or no erosion of the surface materials despite wind speeds of 25 to 30 m/s. The strong local dust storm occurred during late winter of the third martian year. Winds of this storm altered and demolished small conical piles of surface materials constructed at the onset the first winter, removed 4 to 5 mm size fragments, displaced centimeter size fragments, destroyed clouds in areas disrupted by the sampler and footpad, eroded impact pits, and darkened the sky. Movement of erosional products and tiny wind tails indicate easterly to northeasterly winds. If the 4 to 5 mm size fragments were entrained and removd by the wind, threshold friction speeds near 3 to 5 m/s would have been required for the atmospheric temperatures and pressures that prevailed during the late winter of the third year.