Download or read book Analysis of Multichannel Seismic Reflection Data from Mesozoic Oceanic Crust in the Western North Atlantic written by Gillian Catherine Barrett and published by . This book was released on 2001 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Multichannel Seismic Investigation of Variations in Crustal Structure in the Western North Atlantic written by John C. Mutter and published by . This book was released on 1991 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study's goal was to provide a seismic characterization of the Mesozoic-aged oceanic crust in a region of the western North Atlantic adjacent to the Blake Spur Fracture zone, using single and two-ship reflection methods, and two-ship wide-angle refraction methods. The observation of dipping reflectors on a previous seismic reflection line through the area led us to propose the current work. This same line also showed an apparent thinning of the crust as it obliquely crosses the Blake Spur Fracture Zone.
Download or read book The Role of Multichannel Seismology in U S Marine Geological and Geophysical Research written by National Oceanic Reflection Profiling Organization and published by . This book was released on 1986 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Publications of the Geological Survey written by Geological Survey (U.S.) and published by . This book was released on 1989 with total page 836 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Search for Layering in the Oceanic Crust written by John Anthony Collins and published by . This book was released on 1988 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt: The results of numerous seismic refraction and reflection experiments have shown that the seismic structure of the oceanic crust can be usefully parameterized by a small number of locally horizontal layers within which the rates of change of velocity and impedance as a function of depth are approximately constant. Layer boundaries are defined by changes in velocity and/or impedance gradient. This dissertation discusses the structure of seismic layer boundaries within the oceanic crust, and investigates the relationships between the seismic characteristics of these boundaries and the geological structure of the crust. The seismic signature of the crust/mantle boundary (Moho) is a prominent event on multichannel seismic (MCS) reflection data. In the Western North Atlantic, the character of the Moho reflection event varies from a single well-defined phase to a more complex event consisting of two or more overlapping phases of up to 1.0 s total duration. In Chapter 1 of this dissertation, the geological structures generating Moho reflections are investigated by calculating synthetic reflection profiles for three laterally varying velocity models totaling 64 km in length. These velocity models were derived from the observed distribution of lithologies that comprise the inferred fossil crust/mantle transition found in the Bay of Islands Ophiolite. Along the synthetic profiles, the Moho reflection is characterized by both single-phase and multi-phase events, the geometry and durations of the latter being similar to those observed on MCS data from the Western North Atlantic. In addition, the lateral variation in Moho travel time, up to 0.25 s over distances of less than 10 km, is similar to that observed on MCS data. The similarities between the observed and synthetic data suggest that the complicated interlayered sequences of mafic and ultramafic rocks that comprise the inferred crust/mantle transition in ophiolites might also be characteristic of the oceanic crust. Although ophiolites provide a useful model of the lithological structure of the oceanic crust, the unambiguous correlation of geologic and seismic structures can only be achieved by conducting seismic experiments in the vicinity of deep crustal drillholes. Chapters 2 and 3 of this dissertation present analyses of the velocity and reflectivity structure of the crust in the immediate vicinity of Deep Sea Drilling Project Hole 504B in the Panama Basin, currently the deepest drillhole (1.288 km) into oceanic igneous crust. Reflectivity synthetic seismogram modeling of amplitude features common to four sonobuoy profiles collected in the immediate vicinity of Site 504B shows that crustal thickness at the drillsite is only 5 km. A critical constraint on this interpretation is the observation, on four MCS profiles passing through the drillsite, of a near-normal-incidence reflection event with a crustal travel time of 1.4-1.5 s. This event is assumed to correlate with a wide-angle reflection/refraction event observed at ranges of 16-28 km on the sonobuoy profiles. Seismic modeling demonstrates that both of these events are generated at the Moho. The crustal velocity-depth profile at Site 504B is unusual in comparison to typical oceanic profiles in having high velocity gradients (up to 0.6 km s- 1 km- 1) in the middle crust and a 1.8 km thick low-velocity zone (Vp=7.1-6.7 km s- 1) immediately above Moho. A simple explanation for this unusual profile is that the velocity of the middle crust has been increased by the addition of a high-velocity mineral component such as olivine. The olivine concentration of the middle crust need be no greater than 34-37%. Hole 504B is the only site where the volcanics/sheeted-dike boundary, predicted by the ophiolite model to Qe a fundamental feature of oceanic crust, has been drilled. The downward change in rock type coincides with changes in a variety of logged physical properties. The normal-incidence travel time to this boundary is similar to the travel times of shallow reflection events observed in other areas. Accordingly, Site 504B is an ideal location to test the hypothesis that shallow reflection events correlate with the extrusives/dike boundary. Despite extensive processing, MCS data collected 'in the immediate vicinity of Hole 504B show no conclusive evidence for a laterally coherent reflection event generated within the upper crust. The lack of a detectable reflection event from the upper crust is consistent with the results of synthetic seismogram modeling of velocity-depth profiles constructed from the logged downhole variation in physical properties. On these normal-incidence synthetic seismograms, low-amplitude reflections from the volcanic/dike contact are obscured by the high-amplitude basement reflection and by sediment-column multiples. In contrast to the synthetic reflection data, the seismic signature of the volcanics/dike boundary is readily recognizable on a synthetic wide-angle reflection/refraction profile. The change in velocity across this boundary causes focusing of refracted arrivals in the range window 6-7 km. High-amplitude arrivals are observed at similar ranges on the sonobuoy profiles collected near the drillsite, suggesting that at Site 504B, variations in depth to this layer boundary are more easily mapped with the wide-angle reflection/refraction method.
Download or read book A Study of the Seismic Structure of Upper Oceanic Crust Using Wide angle Reflections written by Kristin Marie Michener Rohr and published by . This book was released on 1983 with total page 1010 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Multichannel Seismic Reflection Study of the Ocean Crust in the Eastern Central Atlantic written by César Rodríguez Ranero and published by . This book was released on 1993 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Modern Ocean Floor Processes and the Geological Record written by Rachel A. Mills and published by Geological Society of London. This book was released on 1998 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1991 with total page 602 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Centennial Articles written by Robert D. Hatcher and published by Geological Society of America. This book was released on 1990-01-01 with total page 473 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Crustal Structure of Western North America Using Surface Waves and Marine Multichannel Seismic Reflection Data written by Triparna Das and published by . This book was released on 1997 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Publications of the U S Geological Survey written by Geological Survey (U.S.) and published by . This book was released on 1990 with total page 380 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Exploring the Earth s Crust written by C. Prodehl and published by Geological Society of America. This book was released on 2012 with total page 784 pages. Available in PDF, EPUB and Kindle. Book excerpt: "This volume contains a comprehensive, worldwide history of seismological studies of the Earth's crust using controlled sources from 1850 to 2005. Essentially all major seismic projects on land and the most important oceanic projects are covered. The time period 1850 to 1939 is presented as a general synthesis, and from 1940 onward the history and results are presented in separate chapters for each decade, with the material organized by geographical region. Each chapter highlights the major advances achieved during that decade in terms of data acquisition, processing technology, and interpretation methods. For all major seismic projects, the authors provide specific details on field observations, interpreted crustal cross sections, and key references. They conclude with global and continental-scale maps of all field measurements and interpreted Moho contours. An accompanying DVD contains important out-of-print publications and an extensive collection of controlled-source data, location maps, and crustal cross sections."--Publisher's description.
Download or read book Grants and Awards for the Fiscal Year Ended written by National Science Foundation (U.S.) and published by . This book was released on 1977 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Nature of the Lower Continental Crust written by John Barry Dawson and published by Blackwell Scientific Publications Limited. This book was released on 1986 with total page 412 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Highlights in Marine Research written by and published by . This book was released on 1984 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: The reports and abstracts in this volume illustrates the breadth and depth of U.S. Geological Survey (USGS) research in marine geology.
Download or read book U S Geological Survey Circular written by and published by . This book was released on 1984 with total page 614 pages. Available in PDF, EPUB and Kindle. Book excerpt:
