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We have assembled a large suite of T-phase observations recorded on hydrophones located at Point Sur and Wake Island, in an attempt to understand how acoustic energy from underwater earthquakes is coupled to the sound channel and bow the sound propagates from source to receiver. The events cover a wide range of locations in the North Pacific. We find that T-phases observable at Point Sur are generated only in a limited number of geographical regions, the Aleutian Islands and Kodiak Island regions, south of Japan, and the southern portion of the Kuril Islands region. Too few records have been assembled to date for Wake Island to discern any pattern in the locations of observable T-phases. A signal to noise (SNR) measure was determined for each event. We found that there was no clear pattern in the SNR vs. magnitude when all the events were examined together. We narrowed the region of study to a small cluster of events in the Andreof Island region of the Aleutian Island chain in order to eliminate variables such as source mechanism, transmission path, and event depth. For this limited data set, we found that the SNR as observed at Pt. Sur was more strongly dependent upon event magnitude, however, there was still a considerable degree of scatter. This scatter is probably due to near source effects, such as the slope of the seafloor in the region of the events.
In September 1996, the United Nations General Assembly adopted the Comprehensive Nuclear-Test-Ban Treaty (CTBT), prohibiting nuclear explosions worldwide, in all environments. The treaty calls for a global verification system, including a network of 321 monitoring stations distributed around the globe, a data communications network, an international data centre (IDC), and on-site inspections, to verify compliance. A global hydroacoustic monitoring system is being planned and implemented for verification of the CTBT. Much of the research conducted over the past several decades on acoustic surveillance of the oceans, formerly driven by the need to detect and track submarines, is now being applied to the development of effective monitoring methods to verify compliance with the CTBT. The aim of this volume on Hydroacoustic Monitoring of the CTBT is to summarize the research being conducted in this field and to provide basic references for future research. Much of the new research emphasizes major advances in understanding the coupling of ocean acoustic waves with elastic waves in the solid Earth. Topics covered include source excitation, detection and classification of events generating hydroacoustic signals, discrimination between underwater explosions and naturally occurring events, as well as topics in coupling of acoustic to seismic wavefields.
Many coastal areas of the United States are at risk for tsunamis. After the catastrophic 2004 tsunami in the Indian Ocean, legislation was passed to expand U.S. tsunami warning capabilities. Since then, the nation has made progress in several related areas on both the federal and state levels. At the federal level, NOAA has improved the ability to detect and forecast tsunamis by expanding the sensor network. Other federal and state activities to increase tsunami safety include: improvements to tsunami hazard and evacuation maps for many coastal communities; vulnerability assessments of some coastal populations in several states; and new efforts to increase public awareness of the hazard and how to respond. Tsunami Warning and Preparedness explores the advances made in tsunami detection and preparedness, and identifies the challenges that still remain. The book describes areas of research and development that would improve tsunami education, preparation, and detection, especially with tsunamis that arrive less than an hour after the triggering event. It asserts that seamless coordination between the two Tsunami Warning Centers and clear communications to local officials and the public could create a timely and effective response to coastal communities facing a pending tsuanami. According to Tsunami Warning and Preparedness, minimizing future losses to the nation from tsunamis requires persistent progress across the broad spectrum of efforts including: risk assessment, public education, government coordination, detection and forecasting, and warning-center operations. The book also suggests designing effective interagency exercises, using professional emergency-management standards to prepare communities, and prioritizing funding based on tsunami risk.
Almost half the U.S. population lives along the coast. In another 20 years this population is expected to more than double in size. The unique weather and climate of the coastal zone, circulating pollutants, altering storms, changing temperature, and moving coastal currents affect air pollution and disaster preparedness, ocean pollution, and safeguarding near-shore ecosystems. Activities in commerce, industry, transportation, freshwater supply, safety, recreation, and national defense also are affected. The research community engaged in studies of coastal meteorology in recent years has made significant advancements in describing and predicting atmospheric properties along coasts. Coastal Meteorology reviews this progress and recommends research that would increase the value and application of what is known today.
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.
Edwin Hutchins combines his background as an anthropologist and an open ocean racing sailor and navigator in this account of how anthropological methods can be combined with cognitive theory to produce a new reading of cognitive science. His theoretical insights are grounded in an extended analysis of ship navigation—its computational basis, its historical roots, its social organization, and the details of its implementation in actual practice aboard large ships. The result is an unusual interdisciplinary approach to cognition in culturally constituted activities outside the laboratory—"in the wild." Hutchins examines a set of phenomena that have fallen in the cracks between the established disciplines of psychology and anthropology, bringing to light a new set of relationships between culture and cognition. The standard view is that culture affects the cognition of individuals. Hutchins argues instead that cultural activity systems have cognitive properties of their own that are different from the cognitive properties of the individuals who participate in them. Each action for bringing a large naval vessel into port, for example, is informed by culture: the navigation team can be seen as a cognitive and computational system. Introducing Navy life and work on the bridge, Hutchins makes a clear distinction between the cognitive properties of an individual and the cognitive properties of a system. In striking contrast to the usual laboratory tasks of research in cognitive science, he applies the principal metaphor of cognitive science—cognition as computation (adopting David Marr's paradigm)—to the navigation task. After comparing modern Western navigation with the method practiced in Micronesia, Hutchins explores the computational and cognitive properties of systems that are larger than an individual. He then turns to an analysis of learning or change in the organization of cognitive systems at several scales. Hutchins's conclusion illustrates the costs of ignoring the cultural nature of cognition, pointing to the ways in which contemporary cognitive science can be transformed by new meanings and interpretations. A Bradford Book