Download or read book The Seismic Attenuation Structure of the East Pacific Rise written by William Sam Douglas Wilcock and published by . This book was released on 1992 with total page 356 pages. Available in PDF, EPUB and Kindle. Book excerpt: Studies of seismic propagation through oceanic crust have contributed enormously to our understanding of the generation and evolution of oceanic crust However, such work has largely been confined to the seismic velocity structure. In this thesis we present results from a study of seismic attenuation using a data set collected for three-dimensional tomographic imaging of a fast-spreading ridge. The experiment location at 9°30'N on the East Pacific Rise is the site of a strong mid-crustal seismic reflector which has been inferred to be the roof of a small axial magma chamber at about 1.6 km depth. A spectral method is used to estimate t*, a measure of the integrated attenuation along a wave path. Such a method asswnes that the dominant frequency-dependent component of propagation is intrinsic attenuation. A logarithmic parameterization is then used to invert t* measurements for Q-1 structure asswning that the velocity structure is given from earlier studies. To evaluate the method of Q tomography a full-waveform finitedifference technique which does not include attenuation is used to calculate solutions for seismic propagation through a two-dimensional velocity model. The results show a complex pattern of seismic propagation in the vicinity of the axial magma chamber. The first arrival always passes above the magma chamber. However, for paths of significant length that cross the rise axis the amplitude of this arrival is very small, and the first phase with significant amplitude is a diffraction below the magma chamber. High-amplitude Moho turning and PP arrivals may also be important secondary arrivals. Synthetic inversions show the importance of selecting time windows for power spectral estimation which are dominated by a single phase and of using wave paths which closely corresponds to that of the selected phase. A comparison of the finite difference solutions and the predictions of the a twodimensional, exact ray-tracing algorithm with record sections obtained during the tomography experiment significantly improves our understanding of seismic propagation across the East Pacific Rise. The results enable an objective choice of the position and length of the time window fort* estimation. Moreover, additional constraints are incorporated into an approximate three-dimensional ray-tracing algorithm used in the inversion so that the wave paths more closely correspond to those of the desired phase. The full data set to be inverted comprises about 3500 t* estimates and includes crustal paths which do not cross the rise axis, diffractions above and below the axial magma chamber, and Moho-turning phases. Wave paths for the Moho-turning phases cross the rise axis at a wide range of lower crustal depths. The Q-1 models resulting from two-dimensional and three-dimensional tomographic inversions show that the attenuation of seismic waves on the East Pacific Rise is dominated by two regions of low Q; one in the upper 1 km of crust, and one at depths greater than about 2 km below the rise axis. While the data do not resolve the details of vertical variations in near-surface Q-1, the results show a substantial variation in shallow attenuation within 0.05 My of the rise axis. On-axis, Q values averaged over the upper 1 km are about 100, while off-axis the average value rapidly decreases to about 30. Measurements of the seismic velocity suggest that the thickness of the surficial highporosity extrusive layer increases substantially off-axis. If such thickening is entirely responsible for the observed change in near-surface attenuation then Q within the extrusive layer must be much less than 20. Alternatively, in situ changes in porosity may also contribute to the observed increase in attenuation. Since significant tectonic activity is apparently restricted to locations well off-axis we suggest that such variations in porosity may result from hydrothermal activity. Regions of hydrothermal downwelling located off-axis will be subject to cooling and thermally-induced cracking while upwelling regions on-axis may be accompanied by rapid infilling of existing pores by hydrothermal deposits. Estimates of t* for all phases propagating below the magma chamber are markedly higher than those for other phases, resulting in Q-1 models which include a region of low Q extending from 2 to 7 km depth below the rise axis. The lowest Q values resolved are about 25-30 both immediately below the magma chamber and within the lower crust. While there is some evidence for a small decrease in attenuation with depth in the lower crust, axial Q values at depths ranging from less than 2.5 to 6 km are relatively constant, always lying below 50. Laboratory measurements at seismic frequencies suggest that Q values of 25-50 require only very small fractions of partial melt. The attenuation observations thus place constraints on the dimensions of the axial magma chamber and strongly suggest that the thickness of the region containing more than a few percent of partial melt is no more than 1 km.
Download or read book Treatise on Geophysics written by and published by Elsevier. This book was released on 2015-04-17 with total page 5604 pages. Available in PDF, EPUB and Kindle. Book excerpt: Treatise on Geophysics, Second Edition, is a comprehensive and in-depth study of the physics of the Earth beyond what any geophysics text has provided previously. Thoroughly revised and updated, it provides fundamental and state-of-the-art discussion of all aspects of geophysics. A highlight of the second edition is a new volume on Near Surface Geophysics that discusses the role of geophysics in the exploitation and conservation of natural resources and the assessment of degradation of natural systems by pollution. Additional features include new material in the Planets and Moon, Mantle Dynamics, Core Dynamics, Crustal and Lithosphere Dynamics, Evolution of the Earth, and Geodesy volumes. New material is also presented on the uses of Earth gravity measurements. This title is essential for professionals, researchers, professors, and advanced undergraduate and graduate students in the fields of Geophysics and Earth system science. Comprehensive and detailed coverage of all aspects of geophysics Fundamental and state-of-the-art discussions of all research topics Integration of topics into a coherent whole
Download or read book Seismology and Structure of the Earth written by Barbara Romanowicz and published by Elsevier. This book was released on 2010-04-20 with total page 873 pages. Available in PDF, EPUB and Kindle. Book excerpt: Treatise on Geophysics: Seismology and Structure of the Earth, Volume 1, provides a comprehensive review of the state of knowledge on the Earths structure and earthquakes. It addresses various aspects of structural seismology and its applications to other fields of Earth sciences. The book is organized into four parts. The first part principally covers theoretical developments and seismic data analysis techniques from the end of the nineteenth century until the present, with the main emphasis on the development of instrumentation and its deployment. The second part reviews the status of knowledge on the structure of the Earths shallow layers, starting with a global review of the Earth's crustal structure. The third part focuses on the Earth's deep structure, divided into its main units: the upper mantle, the transition zone and upper-mantle discontinuities, the D region at the base of the mantle, and the Earth's core. The fourth part comprises two chapters which discuss constraints on Earth structure from fields other than seismology: mineral physics and geodynamics. - Self-contained volume starts with an overview of the subject then explores each topic with in depth detail - Extensive reference lists and cross references with other volumes to facilitate further research - Full-color figures and tables support the text and aid in understanding - Content suited for both the expert and non-expert
Download or read book Tectonics of the East Pacific Rise written by Sang-Mook Lee and published by . This book was released on 1995 with total page 530 pages. Available in PDF, EPUB and Kindle. Book excerpt: The global mid-ocean ridge system is one of the most striking geological features on the surface of the Earth. In this system, the East Pacific Rise (EPR) is the fastest spreading ridge and is thus considered as the most active magmatically among the plate boundaries. In January and February of 1988, an extensive survey by the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution was conducted along the EPR between 9°05' and 9°55'N to study the crustal structure of the axial region. This thesis, the result of that cruise, comprises four main topics: (1) characterization of normal faulting from Sea Beam bathymetric data, (2) application of mechanical models to explore the hypothesis that buoyancy arising from crustal magma chambers and gravitational spreading of the upper crust are the principal processes leading to the initiation and development of normal faults, (3) investigation of seafloor magnetization anomalies to constrain upper crustal structure, and (4) analysis of gravity anomalies to examine possible correlations between observed variations in seafloor manifestations of volcanism and deformation and underlying structure. Thus, each topic focuses on different levels of the mid-ocean ridge. Together with the results of seismic and other observations, the findings are woven into a better understanding of the tectonic processes and structure of fastspreading mid-ocean ridges.
Download or read book Geology and Geophysics Program Summary for FY written by and published by . This book was released on 1990 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Rock Quality Seismic Velocity Attenuation and Anisotropy written by Nick Barton and published by CRC Press. This book was released on 2006-11-03 with total page 756 pages. Available in PDF, EPUB and Kindle. Book excerpt: Seismic measurements take many forms, and appear to have a universal role in the Earth Sciences. They are the means for most easily and economically interpreting what lies beneath the visible surface. There are huge economic rewards and losses to be made when interpreting the shallow crust or subsurface more, or less accurately, as the case may be.
Download or read book Statistical Adjustment of Data written by William Edwards Deming and published by . This book was released on 1964 with total page 298 pages. Available in PDF, EPUB and Kindle. Book excerpt: Introduction to basic concepts of statistics, curve fitting, least squares solution, conditions without parameter, conditions containing parameters. 26 exercises worked out.
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 Theoretical Global Seismology written by F. A. Dahlen and published by Princeton University Press. This book was released on 2020-08-04 with total page 1040 pages. Available in PDF, EPUB and Kindle. Book excerpt: After every major earthquake, the Earth rings like a bell for several days. These free oscillations of the Earth and the related propagating body and surface waves are routinely detected at broad-band seismographic stations around the world. In this book, F. A. Dahlen and Jeroen Tromp present an advanced theoretical treatment of global seismology, describing the normal-mode, body-wave, and surface-wave methods employed in the determination of the Earth's three-dimensional internal structure and the source mechanisms of earthquakes. The authors provide a survey of both the history of global seismological research and the major theoretical and observational advances made in the past decade. The book is divided into three parts. In the first, "Foundations," Dahlen and Tromp give an extensive introduction to continuum mechanics and discuss the representation of seismic sources and the free oscillations of a completely general Earth model. The resulting theory should provide the basis for future scientific discussions of the elastic-gravitational deformation of the Earth. The second part, "The Spherical Earth," is devoted to the free oscillations of a spherically symmetric Earth. In the third part, "The Aspherical Earth," the authors discuss methods of dealing with the Earth's three-dimensional heterogeneity. The book is concerned primarily with the forward problem of global seismology--detailing how synthetic seismograms and spectra may be calculated and interpreted. As a long-needed unification of theories in global seismology, the book will be important to graduate students and to professional seismologists, geodynamicists, and geomagnetists, as well as to astronomers who study the free oscillations of the Sun and other stars.
Download or read book An Introduction to Seismology Earthquakes and Earth Structure written by Seth Stein and published by John Wiley & Sons. This book was released on 2013-05-30 with total page 512 pages. Available in PDF, EPUB and Kindle. Book excerpt: An Introduction to Seismology, Earthquakes and Earth Structures is an introduction to seismology and its role in the earth sciences, and is written for advanced undergraduate and beginning graduate students. The fundamentals of seismic wave propagation are developed using a physical approach and then applied to show how refraction, reflection, and teleseismic techniques are used to study the structure and thus the composition and evolution of the earth. The book shows how seismic waves are used to study earthquakes and are integrated with other data to investigate the plate tectonic processes that cause earthquakes. Figures, examples, problems, and computer exercises teach students about seismology in a creative and intuitive manner. Necessary mathematical tools including vector and tensor analysis, matrix algebra, Fourier analysis, statistics of errors, signal processing, and data inversion are introduced with many relevant examples. The text also addresses the fundamentals of seismometry and applications of seismology to societal issues. Special attention is paid to help students visualize connections between different topics and view seismology as an integrated science. An Introduction to Seismology, Earthquakes, and Earth Structure gives an excellent overview for students of geophysics and tectonics, and provides a strong foundation for further studies in seismology. Multidisciplinary examples throughout the text - catering to students in varied disciplines (geology, mineralogy, petrology, physics, etc.). Most up to date book on the market - includes recent seismic events such as the 1999 Earthquakes in Turkey, Greece, and Taiwan). Chapter outlines - each chapter begins with an outline and a list of learning objectives to help students focus and study. Essential math review - an entire section reviews the essential math needed to understand seismology. This can be covered in class or left to students to review as needed. End of chapter problem sets - homework problems that cover the material presented in the chapter. Solutions to all odd numbered problem sets are listed in the back so that students can track their progress. Extensive References - classic references and more current references are listed at the end of each chapter. A set of instructor's resources containing downloadable versions of all the figures in the book, errata and answers to homework problems is available at: http://levee.wustl.edu/seismology/book/. Also available on this website are PowerPoint lecture slides corresponding to the first 5 chapters of the book.
Download or read book Magmatic Systems written by Michael P. Ryan and published by Academic Press. This book was released on 1994-08-26 with total page 427 pages. Available in PDF, EPUB and Kindle. Book excerpt: With its integrated and cohesive coverage of the current research, Magmatic Systems skillfully explores the physical processes, mechanics, and dynamics of volcanism. The text utilizes a synthesized perspective--theoretical, experimental, and observational--to address the powerful regulatory mechanisms controlling the movement of melts and cooling, with emphasis on mantle plumes, mid-ocean ridges, and intraplate magmatism. Further coverage of subduction zone magmatism includes:Fluid mechanics of mixed magma migrationInternal structure of active systemsGrain-scale melt flowRheology of partial meltsNumerical simulation of porous media melt migrationNonlinear (chaotic and fractal) processes in magma transportIn all, Magmatic Systems will prove invaluable reading to those in search of an interdisciplinary perspective on this active topic.Key Features* Fluid mechanics of magma migration from surface region to eruption site* Internal structure of active magmatic systems* Grain-scale melt flow in mantle plumes and beneath mid-ocean ridges* Physics of magmatic systems and magma dynamics
Download or read book Ecosystem Dynamics in a Polar Desert written by and published by American Geophysical Union. This book was released on 1998 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presents information from the primary abiotic forces defining the system, and from the present hydrology, biogeochemistry and physics of major sites of organic carbon production of the McMurdo Dry Valleys. Additionally, research on the physical, chemical, and biological properties of the dry valley soils is included. The role of environmental management in long-term ecological studies is also addressed. The accompanying CDROM provides details and scale to visualize the McMurdo Dry Valleys from an ecosystem perspective.
Download or read book Hydrogeology of the Oceanic Lithosphere with CD ROM written by Earl E. Davis and published by Cambridge University Press. This book was released on 2004-12-09 with total page 736 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book, first published in 2004, reviews the subject of the nature, causes, and consequences of fluid flow in oceanic crust.
Download or read book Seismic Tomography written by H.M. Iyer and published by Springer Science & Business Media. This book was released on 1993-05-31 with total page 890 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a systematic review of tomographic applications in seismology and the future directions. Theories and case histories are discussed by the international authors, drawing on their own practical experiences with global and local case histories.
Download or read book Government wide Index to Federal Research Development Reports written by and published by . This book was released on 1967 with total page 1062 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Lithosphere written by Irina Mikhaĭlovna Artemʹeva and published by Cambridge University Press. This book was released on 2011-07-28 with total page 795 pages. Available in PDF, EPUB and Kindle. Book excerpt: Multidisciplinary overview of lithospheric structure and evolution, based on a full set of geophysical methods, for researchers and advanced students.
Download or read book Q of the Earth Global Regional and Laboratory Studies written by Barbara Romanowicz and published by Birkhäuser. This book was released on 2012-12-06 with total page 490 pages. Available in PDF, EPUB and Kindle. Book excerpt: Variations in seismic Q are sensitive to a much greater extent than are seismic velocity variations on factors such as temperature, fluid content, and the movement of solid state defects in the earth. For that reason an understanding of Q and its variation with position in the earth and with time should provide information in earth's tectonic evolution, as well as on aspects of its internal structure. Progress in understanding Q has suffered from difficulty in obtaining reliable amplitude data at global and temporary stations. Moreover, laboratory determinations of Q, until recently, were most often made at frequencies much higher than those measured by seismologists for waves propagating through the earth. Recent advances in seismic station distribution and quality, as well as in methodology at both high and low fequencies, have greatly improved the quality of observational data available to seismologists from global stations. Concurrent advances have been made in measuring Q using laboratory samples at frequencies that pertain to the earth and in theoretical understanding of seismic wave attenuation. Papers of this volume present new information on Q in the earth from several perspectives: methodology, results from global and regional observations of both body and surface waves, laboratory measurements, and theoretical understanding. The editors believe that we have reached a new threshold in Q studies and that advances in data quality and methodology will spur increased interest in this difficult, but interesting field.
