Download or read book Seismic Detection and Discrimination Using Ocean bottom Seismographs written by LeRoy M. Dorman and published by . This book was released on 1980 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research progress on seismic detection and discrimination using ocean-bottom seismographs (OBS's) is outlined. During this first year of DARPA contract work, our investigations have been focused primarily on using existing OBS data to address the problem of sea-floor seismic noise and to constrain models of the near-bottom seismic environment. We have completed noise studies at six of our previously occupied OBS sites. The noise levels of typical amplitude spectra roll off rapidly out to 2-4 Hz and much less rapidly beyond 4 Hz. At frequencies above 4 Hz, the noise levels are low, typically a few nanometers/Hz1/2 or less and comparable to good land-based stations. Several correlations between noise levels and other parameters, such as sediment thickness, distance from the continental margin and sea state, are discussed and used to constrain possible noise mechanisms. We hypothesize that the dominant mechanism of high-frequency (>2 Hz) noise generation at most of the sites examined thus far is of local oceanographic origin, exciting acoustic modes in the water column which couple to Stoneley modes at the sediment-water interface and waveguide modes within the sediment column. This hypothesis is supported by the analysis of noise data from two OBS arrays, which shows that the noise coherence is very low for pairs of sensors separated by as little as 200 m. We also outline some of the conclusions relevant to the seismic noise problem deduced by us from the data collected during the Lopez Island intercalibration experiment.
Download or read book Seismic Detection and Discrimination Using Ocean Bottom Seismographs written by and published by . This book was released on 1981 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: Around January 29, 1980 a mild storm occurred on the Southern California coast. During this time one of our ocean bottom seismographs (O.B.S.) was periodically recording noise samples at 31 deg N, 119 deg 48 min W, about 370 km offshore in 4 km of water. The noise energy in the 1-3 Hz frequency range correlates most strongly with the wave height on the nearby coast. The local and distant wind data were dissimilar in the durations of the disturbance and in the time of the peak amplitude. We conclude that sea floor noise near 1 Hz comes predominantly from the surf. The nonlinear mechanisms which transfer energy from gravity waves on the sea surface into the sea floor are so inefficient at these frequencies that the contribution from surf a few hundred km away dominates the energy from the sea surface a few km away. An array of 4 ocean-bottom seismometers (O.B.S.) was operated for one month during June-July, 1977 at 16.5 deg N, 100.5 deg W in the Middle America Trench near Acapulco. The purpose of the experiment was to investigate the seismicity of the accretionary prism and to study the propagation of seismic waves across the continental margin. The location of earthquakes occurring landward of the OBS array was controlled by a 7-station land-based array operated by a team of Mexican seismologists under the direction of Dr. Lautaro Ponce Mori.
Download or read book Structure and Development of the Greenland Scotland Ridge written by Martin H. P. Bott and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 675 pages. Available in PDF, EPUB and Kindle. Book excerpt: A group of geoscientists from a number of NATO countries met under NATO sponsorship in Copenhagen on February 27 and 28, 1978, and formulated a proposal entitled "EVOLUTION OF THE GREENLAND ICELAND-FAEROE-SCOTLAND RIDGE, A KEY AREA IN MARINE GEOSCIENCE". This part of the North Atlantic Ocean is of particular interest because of its anomalously shallow bathymetry which has profoundly influenced many aspects of the evolution of the North Atlantic. The proposed investigations therefore aim to study the deep crustal structure including relationship of continental and oceanic crust, history of subsidence of the ridge including its past role as a land bridge, age of the oceanic basement along it and its history of formation, and the influence of the ridge on Tertiary and Quaternary depositional palaeoenvironments. In furtherance of this proposal, it is intended to carry out a series of seismic and drilling operations on the Ridge during the coming years. These major marine investigations will be mainly funded from national sources. An important preliminary stage to the project is the collec tion and synthesis of available data. NATO has already approved a small budget for this purpose which has enabled a geoscientist to work partly at the Department of Geological Sciences of Durham University, UK, and partly at Lamont-Doherty Geological Observatory of Columbia University, Palisades, USA, for about six months to compile the data. The most important map showing magnetic anomalies and lineations in the area, is included in a pocket at the back of this volume.
Download or read book Technical Abstract Bulletin written by and published by . This book was released on with total page 992 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Ocean Bottom Seismometer Study of the Kuril Trench Area written by Junzo Kasahara and published by . This book was released on 1976 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: An ocean bottom seismograph was deployed on the seaward side of the Kuril Trench off Hokkaido, Japan, in 5460 m of water, in August 1975 during the joint Soviet-American Tsunami Expedition. During the seven-day record, S-P times were distributed in three groups: 19-24 sec, corresponding to aftershocks of the 10 June and 13 June 1975 earthquakes southeast of Nemuro, Japan and to earthquakes east of Sanriku, Japan; approximately 30 sec, from south of Erimo Peninsula, Hokkaido; and approximately 100 sec, from the Izu-Bonin Islands. Seven earthquakes, with hypocenters well determined by the land seismic net, are studied in detail. A shallow focus earthquake yields typical oceanic mantle velocities shallower than 50 km in the slab which dips under the Japanese archipelago. However, deeper focus earthquakes reveal anomalously high velocities averaged over the upper 230 km, in agreement with the models of Utsu and Oliver and Isacks. Two deep earthquakes, whose paths lie in the Pacific Ocean asthenosphere, suggest a velocity 3% lower than that predicted by Jeffreys-Bullen, in agreement with the above models. Spectral analysis of S arrivals suggests Q sub s values of 1000-1500 for nearby earthquakes and 4000-6000 for longer-distance earthquakes, implying an unusual attenuation mechanism for long travel paths, which enhances the high frequencies.
Download or read book International Underwater Systems Design written by and published by . This book was released on 1981 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Ocean Bottom Seismometer Measurements on the Gorda Ridge written by L. Dale Bibee and published by . This book was released on 1986 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Seismic Discrimination written by and published by . This book was released on 1976 with total page 608 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 1992 with total page 1572 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Oceanic Abstracts with Indexes written by and published by . This book was released on 1987 with total page 646 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Government Reports Announcements Index written by and published by . This book was released on 1976 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Government reports annual index written by and published by . This book was released on 199? with total page 966 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Government Reports Annual Index Keyword A L written by and published by . This book was released on 1985 with total page 976 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Government Reports Announcements Index written by and published by . This book was released on 1981 with total page 658 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Advances in ocean bottom seismology written by Francisco Javier Nuñez-Cornu and published by Frontiers Media SA. This book was released on 2023-03-27 with total page 199 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Earthquakes in the United States 1963 64 and an Evaluation of the Detection Capability of the United States Seismograph Stations written by Stepp, J.C. and published by . This book was released on 1965 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study is based on earthquakes reported on the Preliminary Determination of Epicenter (P.D.E.) cards of the Coast and Geodetic Survey. Four types of presentations are made: (1) a chronological list of earthquakes: (2) a magnitude map showing the geographical distribution of earthquakes whose magnitudes are greater than, or equal to, 3.0; (3) a presentation of frequency versus magnitude for the total United States for and individual regions of high seismicity; and (4) a 'seismicity' map giving a quantitative measure of relative seismic activity.
Download or read book Telemetering Seismographs for Ocean Bottom Observations written by D. E. Koelsch and published by . This book was released on 1962 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:
