M.S. - Geology and Geophysics
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Item Petrology, geochemistry, and ages of volcanic rocks from the Line Islands, Central Pacific Ocean(University of Hawaii at Manoa, 1986) Davis, Geoffrey Trevor; Geology and Geophysics (Volcanology, Petrology and Geochemistry)The Line Islands chain is a major linear volcanic feature on the Pacific plate which, when combined with the Tuamotu Archipelago and the Gambier Islands, extends for over 6000 km from the Mid-Pacific Mountains southeast to Pitcairn Island, a recently actiItem Hydrogeochemistry of a small limestone-island: Laura, Majuro Atoll, Marshall Islands(University of Hawaii at Manoa, 1987) Anthony, Stephen S.; Geology and GeophysicsThe isolated atoll of Majuro is an ideal location to apply a hydrogeochemical approach to the occurrence and movement of groundwater in an island aquifer system. Majuro is typical of many atolls throughout the Pacific. It exhibits calcareous atoll geologyItem Petrology of the phosphates on Tuvuca, Fiji(University of Hawaii at Manoa, 1982) Lee, Annabelle Inn Ngue; Geology and GeophysicsPhosphatic pelletal packstones and grainstones were collected from Tuvuca, Fiji, an island in the northern section of the Lau Islands. The deposits occur within cavities and fractures in the limestone, which is Futuna Limestone of middle Miocene to possibItem A magnetotelluric investigation of the electrical conductivity of the upper mantle beneath Midway Island(University of Hawaii at Manoa, 1981) Thomas, Tommie Lee; Geology and GeophysicsThe magnetotelluric response functions for one month of data from Midway Island have been modelled by one-dimensional structures of varying complexity after removal of the island effect. These models reveal an anomalous zone of conductivity between .8 andItem Crustal structure of the Mariana Trough from seismic refraction data(University of Hawaii at Manoa, 1980) Ambos, Elizabeth L.; Geology and GeophysicsThree seismic refraction profiles were shot in the Mariana Trough in the vicinity of the proposed axial rift spreading center. One long east-west trending line was shot across the axial high region, the elevated portion of the Trough associated with the rItem Crustal structure of the Mariana Island arc system and old Pacific plate from seismic refraction data(University of Hawaii at Manoa, 1978) LaTraille, Sharon L.; Geology and GeophysicsTwenty-six new explosion refraction profiles from the Mariana island arc system and old Pacific plate along a 750 km east-west line at about 18°N latitude are analyzed to determine crustal structure across the Mariana basin (old Pacific plate ), arc-trench gap, Mariana ridge and Mariana trough. The Pacific plate east of the Mariana trench has a crustal thickness of 6.8 km, similar to that of average Pacific ocean crust, but has thicker than average layers 2A and 2B. This is most likely due to lower velocity material introduced by local seamount volcanism. Large scale vertical faulting in the arc-trench gap is supported by the data in this study, while plate accretion is not. Thick sequences of low-velocity material are also found in the arc-trench gap, and no mantle velocities are found. Crustal structure on the Mariana ridge is roughly similar to that of the arc-trench gap. There is evidence here of arrivals from a relatively high velocity body under the ridge, possibly a volcanic plug or sill. In the Mariana trough, an average crustal thickness of S km is found, with evidence of crustal thinning toward the center of the trough. These data, together with depth-age and depth-heat flow relationships, indicate crustal formation in the Mariana marginal basin differs considerably from that at mid-ocean ridges. Crust which forms in the marginal basin is thinner, cools faster and sinks more quickly than oceanic crust.Item The accuracy of charted port positions in the Pacific as defined by satellite determined positions using multiple observations(University of Hawaii at Manoa, 1977) Hanna, Valerie M.; Geology and GeophysicsAs a by-product of the marine scientific program on the oceanographic cruises of the University of Hawaii's research vessels, positions for 34 dock or anchorage sites in and around the Pacific basin were determined using the Magnavox 702 CA (MX 702/hp) Satellite Navigator as a fixed point positioning device. While it is apparent that not all positions were determined to the same accuracy, a significant number represent improvements of 15 seconds or more in the charted positions of islands, ports and harbors in the Pacific basin. Thus this work may prove to be of considerable benefit by establishing a network of well known and well surveyed Doppler determined positions in the Pacific which may serve as geodetic position references. More fundamentally, this study will contribute to the safety of navigation in making land approaches by providing more modern and accurate positional information than can be obtained from charts.Item The structure of the Mariana arc as inferred from gravity and seismic data(University of Hawaii at Manoa, 1979) Sager, W. W.; Geology and GeophysicsA two dimensional gravity model of the lithosphere was constructed along a seismic refraction line, 800 km in length, across the Mariana arc near l8°N latitude. Included in the model are crustal layers constrained by seismic refraction results, an estimatItem A seismic study of the crustal structure of the Ontong Java Plateau and Nauru Basin(University of Hawaii at Manoa, 1978) Halada, Richard S.; Geology and GeophysicsIn May, 1976 seismic refraction measurements were made across the northern Ontong Java Plateau and Nauru Basin by the R/V KANA KEOKI. Forty sonobuoys were deployed and data were obtained along a 930 km line. The purpose of this study was to better defineItem Ita Mai Tai Guyot: a comparative geophysical study of western Pacific seamounts(University of Hawaii at Manoa, 1985) Wedgeworth, Bruce Steven; Geology and GeophysicsIta Mai Tai is a large, uncompensated seamount on the eastern edge of the East Mariana Basin. A large positive gravity anomaly of 254 mgal characterizes the summit and a low of -69 mgal, the surrounding moat. Using polygonal prisms to approximate the bath