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The Twin-Otter aircraft performing surveys over the Charles River west of Boston, Massachusetts, during applications testing of the Aerial Profiling of Terrain System.

cobalt ratio (trend 1). New data on tholeiitic dikes and flows in Triassic-Jurassic basins in the eastern United States show a contrasting trend of decreasing copper with a decreasing nickelcobalt ratio (trend 2). Copper content in the trend 2 group is as much as one-half to one-third lower than it is in rocks of virtually identical major and stable traceelement composition. Geochemical features of trend 2 rocks are attributed to the strong partitioning of copper and nickel into an immiscible sulfide melt that separated from the magmas during ascent. Most tholeiitic basalts showing the largest copper depletion are in North and South Carolina. These contrasting trends

of nickel-cobalt versus copper can be used to identify mafic rocks in which fractionation of nickel- and copper-bearing sulfide liquids took place and thus can be a guide in the exploration for magmatic nickel-copper deposits.

AERIAL PROFILING OF TERRAIN SYSTEM

• The U.S. Geological Survey has developed an airborne surveying system that is capable of surveying the terrain with very high accuracy from a low-flying aircraft using a laser profiler and inertial guidance technology. The Aerial Profiling of Terrain System (APT) consists of an inertial measuring unit, a laser

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profiler, a laser tracker, a

computer, a video imaging system and supporting electronics, all mounted in a Twin-Otter aircraft. The inertial measuring unit provides an accurate reference frame to the local datum. The laser profiler measures the distance from the aircraft to the ground. Periodic positional updates are provided by the laser tracker, which measures range and angle from the inertial measuring unit to previously placed retroreflectors on the ground. The computer serves as a system controller, data collector, and processor, while continuously navigating the aircraft during data collection activities. The video system records the ground image below the aircraft. In addition to measuring accurate terrain profiles for flood-plain mapping, however, the unique capability of the system to provide rapidly survey data of centimeter accuracy with a minimal requirement for ground control offers numerous other possible uses, such as monitoring subsidence, testing of old maps for reliability, establishing control for new mapping, measuring volcanic swelling, and serving as an airborne gravity mapping instrument. The new system represents a revolutionary combination of advanced inertial guidance and laser technologies, by providing an airborne remote sensing platform that is unprecedented not only in precision but in mobility and speed of data acquisition as well. Operational testing of the system now is complete, and further efforts will focus on applications testing to demonstrate various uses in earth science data-collection activities.

SCREENING OF GEOHYDROLOGIC ENVIRONMENTS IN THE BASIN AND RANGE PROVINCE FOR HIGH-LEVEL RADIOACTIVE WASTE DISPOSAL

Deeply buried repositories in specially constructed mines offer several properties suitable for

disposal of high-level radioactive waste. Principal among these properties are adequate shielding, isolation from the environment, absorption and dispersion of heat generated by the radioactive waste, and protection from intrusion by man. The potential for migration of high-level radioactive wastes from the repository demands that attention be given not only to the selection of a suitable host material for the waste but also to the selection of the geohydrologic environment of the repository. The U.S. Geological Survey's program for identifying potential environments suitable for locating acceptable repositories in the Basin and Range province was an outgrowth of a plan developed jointly with the U.S. Department of Energy, which has the responsibility for selecting, building, and operating the repositories. Although this is a Geological Survey study, earth scientists from the particular States involved are participating actively.

OFFSHORE GEOLOGIC SURVEYS

• Seafloor sonar imaging of the Pacific conterminous Exclusive Economic Zone (EEZ) produced a spectacular mosaic revealing new underwater volcanos, faults, meandering river channels, and previously unknown aspects of spreading centers, deep sea fans, and major fracture zones. This activity, conducted in cooperation with the Institute of Oceanographic Sciences of England and using their Geologic Long Range Inclined Asdic (GLORIA) system, is the first such investigation to be completed under the U.S. Geological Survey's program that is being implemented in response to the President's proclamation of the EEZ. The results, to date, along the west coast have already had a profound effect on geologic theory regarding the evolution of the area, its energyand mineral-resource potential, and potential geologic hazards. "Operation Deep Sweep" took the Research Vessel Samuel P. Lee from pole to pole across the Pacific

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In 1975, the Geological Survey had identified the Lost River fault as potentially active; in 1982, Geological Survey scientists had calculated that the area including the Lost River fault could generate an earthquake of magnitude 7.

• A remarkable set of strong-ground motion recordings was obtained for the Morgan Hill, California, earthquake of April 24, 1984. The moderate-sized (magnitude 6.1) earthquake occurred on the Calaveras fault east of San Jose, within a dense network of U.S. Geological Survey earthquake-monitoring instruments that had been deployed earlier along the fault. The 1.3-gravity acceleration registered at a station near Morgan Hill was one of the largest horizontal accelerations ever recorded.

• Evidence of at least two, and possibly three, large prehistoric earthquakes has been discovered in the Charleston, South Carolina, area.

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Reduced version of the image from Landsat 4 Thematic Mapper data used to prepare the Washington, D.C., and Vicinity image map at 1:100,000 scale. It is printed here at approximately 1:550,000 scale.

SATELLITE IMAGE MAPPING

• The U.S. Geological Survey has long recognized the need for image maps as tools for resource analysis and as map supplements, as well as a means to provide coverage of unmapped areas. After Landsat 1 was launched in 1972, the Geological Survey began to produce multicolor maps from the multispectral scanner imagery, and earth scientists quickly recognized the global application of small-scale, image-base maps for compiling and analyzing land use, geologic, and hydrologic data over large regions. The Survey continued to develop optimum techniques for producing color-image maps at 1:250,000 scale from multispectral scanner imagery. Imagery from the higher resolution Landsat 4 Thematic

Mapper recently has made possible the production of color-image maps at 1:100,000 scale. Advances in image-mapping science at the Geological Survey include the development of innovative techniques for geodetic control extension, computer processing for enhancement of digital image data, photographic and digital mosaicking, and calibrated lithographic printing. Current research includes (1) refining computer technqiues for digital mosaicking of Landsat image data over areas as large as 6° in latitude and longitude and extracting individual quadrangles for more efficient image-map production, (2) developing methods for preparing map separates directly from computer tapes, (3) improving digital techniques for geometric correction and image enhancement, and (4)

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