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Regional Variations In Upper Mantle Structure Beneath North America
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Book Synopsis Regional variations in upper mantle structure beneath North America by : Bruce Rene Julian
Download or read book Regional variations in upper mantle structure beneath North America written by Bruce Rene Julian and published by . This book was released on 1970 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Regional Variations in Upper Mantle Structure Beneath North America by : Bruce Rene Julian
Download or read book Regional Variations in Upper Mantle Structure Beneath North America written by Bruce Rene Julian and published by . This book was released on 1979 with total page 456 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Earth's Crust and Upper Mantle by : Pembroke J. Hart
Download or read book The Earth's Crust and Upper Mantle written by Pembroke J. Hart and published by American Geophysical Union. This book was released on 1969 with total page 801 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Crustal and Uppermost Mantle Structure Beneath the Western United States from USArray Regional Phase Analysis by : Janine Sylvia Buehler
Download or read book Crustal and Uppermost Mantle Structure Beneath the Western United States from USArray Regional Phase Analysis written by Janine Sylvia Buehler and published by . This book was released on 2013 with total page 118 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this dissertation is to improve our understanding of the crust and uppermost mantle structure in the western United States, profiting from the wealth of regional phase data recorded at USArray stations. USArray, a transportable seismic array of ~400 seismometers, has greatly increased seismic data coverage across the United States in the past few years, and allows imaging of the lithosphere of the North American continent with better resolution and new methods. The regional phases are often challenging to analyze, especially in a tectonically-active region like the western United States, because of their sensitivities to the heterogeneities of the crust and uppermost mantle. However, knowledge of the seismic structure of the lithosphere is not only essential in order to accurately image the velocity structure at greater depths, but also for constraining geodynamic models that reconstruct the tectonic evolution of the continent, and hence the information that is carried by the regional phases is very valuable. The data set used in this study consists mostly of the regional seismic phases Pn and Sn, which propagate horizontally along the Moho in the mantle lid and constrain the seismic velocity structure at a confined depth. We applied traditional tomographic methods that profit from the improved ray coverage through USArray, but also employed array-based techniques that take advantage of the regular station spacing of the transportable array and don't depend on regularization. In addition, we used stacking methods to image the propagation efficiency of the Sn phase, which is often highly attenuated in tectonically active regions, on a regional scale. The results complement other seismic studies that average over greater depth intervals, such as surface- and body-wave tomographies and anisotropy analysis from shear-wave splitting, to provide information on temperature, composition, and tectonic processes at depth. Comparisons between Pn azimuthal anisotropy and fast polarization direction from shear wave splitting suggest significant vertical changes in anisotropy in several regions of the upper mantle beneath the western United States. Sn can in theory further constrain the nature of anisotropy in the mantle lid. However, we have so far been unable to resolve shear-wave splitting directly in the Sn waveforms as the phase is often attenuated and difficult to detect. Still, we obtained evidence for Sn propagation in several regions of the western United States such as the central Great Basin and the northeastern part of the Colorado Plateau. We found that there are enough quality Sn picks for joint Pn-Sn tomography and identified prominent Vp/Vs anomalies, such as large high Vp/Vs regions --- typically associated with partial melt --- below the Snake River Plain and the Colorado Plateau.
Book Synopsis Structure of the Uppermost Mantle Beneath North America by : Stéphanie Godey
Download or read book Structure of the Uppermost Mantle Beneath North America written by Stéphanie Godey and published by . This book was released on 2002 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Variations in Crust and Upper Mantle Structure Beneath Diverse Geologic Provinces in Asia by :
Download or read book Variations in Crust and Upper Mantle Structure Beneath Diverse Geologic Provinces in Asia written by and published by . This book was released on 1997 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report presents results of a two year effort to determine crust and mantle lithospheric structure beneath Eurasia and to explore the effects that structural variations have on regional wave propagation. First, variations in crust and lid structure on Pn and Lg propagation are investigated using regionalized velocity models previously determined under China. While explosion Pn/Lg ratios are higher than earthquake ratios for all of the regionalized Chinese velocity models, this difference is much smaller than the variations in Pn/Lg ratios caused by propagation differences. This emphasizes the importance of resolving crust and upper mantle structure for successful discrimination. The second part of this report describes detailed regional wave modeling studies to determine crustal and mantle lithospheric structure beneath Tibet. We find low average crustal P-wave velocities (5.9-6.1 km/s), thick crust (68-76 km) and fast lithospheric mantle (8.2-8.25 km/s) beneath the Lhasa Terrane in southern Tibet. Crustal and mantle lithospheric structure to the north in the Qiangtang Terrane differs dramatically with average crustal P and S-wave velocities 4% faster and 2% slower, respectively relative to the Lhasa Terrane. These differences are too large to be explained by temperature differences alone and require a partially molten uppermost mantle lithosphere in the Qiangtang Terrane.
Book Synopsis A Review of the Nature and Variability of the Anelastic Properties of the Upper Mantle Beneath North America and Eurasia by : Brian J. Mitchell
Download or read book A Review of the Nature and Variability of the Anelastic Properties of the Upper Mantle Beneath North America and Eurasia written by Brian J. Mitchell and published by . This book was released on 1977 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: All reasonable mechanisms for producing low-velocity zones in the upper mantle should also produce zones of low omega. The available studies of upper mantle omega and velocity for the same regions suggest that a coincidence of low velocity and low omega zones does indeed occur. Seismic body- and surface-wave data indicate a substantial low velocity, low omega zone in the upper mantle beneath western North America. The zone appears to be 150 km thick or more, the velocities for both P and S waves being lower than typical upper mantle velocities for stable regions. The available evidence for eastern North America indicates that a low velocity zone is either absent for that region or more poorly developed than it is in western North America. Most interpretations for P waves in eastern North America include no low velocity zone. Surface wave studies of the shear wave velocity structure beneath eastern North America indicate the possibility of a low velocity zone for S waves, at least in some regions. The available data for northern Europe and Asia indicate that it is a stable region with velocity and attenuative properties much like those of eastern North America.
Book Synopsis Shear Velocity Structure of the Mantle Beneath the North American Plate by : Stephen Pierre Grand
Download or read book Shear Velocity Structure of the Mantle Beneath the North American Plate written by Stephen Pierre Grand and published by . This book was released on 1986 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Proterozoic Crustal Evolution by : K.C. Condie
Download or read book Proterozoic Crustal Evolution written by K.C. Condie and published by Elsevier. This book was released on 1993-02-03 with total page 553 pages. Available in PDF, EPUB and Kindle. Book excerpt: As a final product of the International Geological Correlation Program (IGCP) Project 217, this volume brings together significant advances in the understanding of Proterozoic crustal evolution. This IGCP Project focussed on nine research objectives: 1) Comparison of Archean and Proterozoic supracrustal assemblages to more fully understand differences between Archean and post-Archean tectonic regimes; 2) To more fully understand the geochemical differences between Archean and post-Archean sediments and to evaluate the various factors that control sediment composition; 3) From combined U/Pb zircon and whole-rock Sm/Nd studies, to see if the apparent 2.4-2.0 continental crust "generation gap" is real; 4) To employ new techniques in the dating of individual zircons to more fully understand Proterozoic tectonic history and the role of crustal reworking; 5) From trace element ratios and Nd isotopic data from basalts, to better understand Proterozoic mantle evolution; 6) To encourage more detailed studies of the anorogenic granite-anorthosite association to better understand its origin and significance in terms of crustal evolution; 7) From combined Nd, Pb, and Sr isotopic data, to more precisely estimate the amount of new continental crust formed during the Proterozoic; 8) To encourage joint P-T and geochronological studies of Proterozoic and high-grade terranes to better understand Proterozoic orogenesis: and 9) To try and understand why hydrothermal precious metal deposits are relatively rare in the Proterozoic compared to both the Archean and the Phanerozoic. The book should be of interest to professionals in the geosciences (especially geochemists, petrologists and structural geologists) and graduate students in the same fields.
Download or read book Geological Survey Bulletin written by and published by . This book was released on 1973 with total page 1324 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis NUREG/CR. by : U.S. Nuclear Regulatory Commission
Download or read book NUREG/CR. written by U.S. Nuclear Regulatory Commission and published by . This book was released on 1961 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Abstracts of North American Geology by : Geological Survey (U.S.)
Download or read book Abstracts of North American Geology written by Geological Survey (U.S.) and published by . This book was released on 1971-07 with total page 1178 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Upper Mantle Structure Under the Stable Regions by : Ahmed Ali Fouda
Download or read book The Upper Mantle Structure Under the Stable Regions written by Ahmed Ali Fouda and published by . This book was released on 1973 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis U.S. Geological Survey Professional Paper by :
Download or read book U.S. Geological Survey Professional Paper written by and published by . This book was released on 1981 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Geophysical Framework of the Continental United States by : Louis Charles Pakiser
Download or read book Geophysical Framework of the Continental United States written by Louis Charles Pakiser and published by Geological Society of America. This book was released on 1989 with total page 843 pages. Available in PDF, EPUB and Kindle. Book excerpt: A review and evaluation of our knowledge of the structure of the crust and upper mantle of the continental United States, exclusive of Alaska, as determined from geophysical observations. Covers geophysical methods of studying the crust and upper mantle; a region-by-region review of crustal and upper-mantle structure; continental overviews based on the different geophysical methods; and geologic and petrologic syntheses based largely on the geophysical results.
Download or read book Geophysical Abstracts written by and published by . This book was released on 1970 with total page 962 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Mapping Crust and Upper Mantle Structure Beneath Southern Eurasia by :
Download or read book Mapping Crust and Upper Mantle Structure Beneath Southern Eurasia written by and published by . This book was released on 1995 with total page 70 pages. Available in PDF, EPUB and Kindle. Book excerpt: Travel-time tomography was used to obtain the lateral variations in P(n) velocities and P(n) velocity azimuthal anisotropy beneath the Basin and Range Province. We used 1226 P(n) arrivals from 184 earthquakes recorded by 113 stations. The tomographic image shows the lateral variation in P(n) velocity from 7.9 km/s in the northern Province to 7.6 km/s in the southern Province. Azimuthal variations in P(n) velocities are less than one percent as determined from the travel time residuals after taking out the contribution of the lateral velocity variations of the P(n) tomography. Although the standard errors of the azimuthal variations are about two percent, there is no reason to believe the existence of the P(n) azimuthal anisotropy in the uppermost mantle beneath the Basin and Range Province. Beghoul and Barazangi's (1990) suggestion of more than three percent azimuthal anisotropy is the result of the lateral heterogeneity and mantle velocity gradient Before tomographic inversion, we refined the P(n) travel times by considering the lateral variations in the crustal thickness and velocities in the region based on the numerical experiment and theoretical development given in this paper. These refinements are crucial in obtaining an accurate velocity image. (MM).