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Orcutt, John A.

Overview
Works: 27 works in 30 publications in 1 language and 31 library holdings
Genres: Observations 
Publication Timeline
Key
Publications about John A Orcutt
Publications by John A Orcutt
Most widely held works by John A Orcutt
Proceedings of the Ocean Drilling Program. B : Scientific results ( Book )
in English and held by 2 libraries worldwide
Migration of Backscatter Data from the Mid-Atlantic Ridge ( file )
2 editions published between 1996 and 1997 in English and held by 2 libraries worldwide
In studies of low-frequency reverberation within the marine environment, a central concern is the relationship between reverberation events and morphological features of the seafloor. A time-domain migration algorithm for the reverberation intensity field is developed that produces scattering coefficient maps coregistered with a bathymetry database. The algorithm is tailored to broadband transient sources with good range resolution, and was developed to analyze an extensive set of reverberation records from a 200-255 Hz source collected on the flanks of the Mid-Atlantic Ridge. The precise, sample-by-sample, tracking of wavefronts across elements 9f the bathymetry database that forms the foundation of the algorithms implementation, results in reverberation maps that show a clear and detailed correlation between scattering and morphology, with narrow scarp slopes consistently high- lighted. Environmentally induced asymmetries in transmission loss and incidence angle are exploited to break the inherent left-right ambiguity of the receiver array. Iterative migration, assuming a dominant dependence of backscatter on grazing angle, produces images, even from individual records, that show good ambiguity resolution. Results from multiple records corroborate the effectiveness of the ambiguity resolution and demonstrate the stability of the scattering coefficient estimates and the acoustic system
Regional Seismic Event Identification and Improved Locations With Small Arrays ( file )
2 editions published between 1994 and 1995 in English and held by 2 libraries worldwide
This final report contains a summary of our work on the use of seismic networks and arrays to improve locations and identify small seismic event. The research can be divided into three main areas. We have developed techniques to migrate 3-component array records of local, regional and teleseismic wavetrains to directly image buried two- and three-dimensional heterogeneities (e.g. layer irregularities, volumetric heterogeneities) in the vicinity of the array. The initial intent of this research effort was to identify noise sources excited by incident signals and isolate their contributions to seismic coda. This technique has been applied to small-aperture array data collected in southern California. We have developed a technique to empirically characterize local and regional seismic code by binning and stacking network recordings of dense aftershock sequences. The principle motivation for this work was to look for robust coda phases dependent on source depth. We've used these empirical results, obtained by examining ANZA network recordings of Lande and Superstition Hills aftershocks, and have developed a technique to constrain sour depth. We have extended our ripple-fired event discriminant (based on the time-independence of coda produced by ripple firing) by looking for an independence of the coda from the recording direction (also indicative of ripple-firing). (MM)
Scattering and Q within the Anza array : final technical report by John A Orcutt( Book )
1 edition published in 1987 in English and held by 2 libraries worldwide
Analysis of MSS (Marine Seismic System) and OBS (Ocean Bottom Seismograph) Data Collected during the NGENDEI Seismic Experiment ( Book )
2 editions published between 1985 and 1986 in English and held by 2 libraries worldwide
The results of the first year's data analysis employing data collected during the NGENDEI seismic experiment in the southwest Pacific are presented. This experiment tested the DARPA Marine Seismic System and verified the improved signal-to-noise ratio achieved by burying the instrument within the oceanic crust. The experiment, which took place on the Deep Sea Drilling Project Leg 91, was designed to test the Marine Seismic System (MSS) in a realistic environment near an active trench environment. An earlier test of the system in the northwest Pacific had been unsuccessful because of difficulties in drilling an acceptable borehole in the seafloor. The MSS was recorded aboard the D/V Glomar Challenger for several days of earthquake, refraction and environmental noise experiments. The subsequent deployment of an autonomous recording package on the seafloor was successful
LFASE Report: Crustal Study ( file )
1 edition published in 1993 in English and held by 1 library worldwide
The data set described in this report was collected on 150-154 Ma oceanic crust during the DARPA/Navy Low Frequency Acoustic Seismic Experiment (LFASE). This is some of the oldest lithosphere remaining in the modern oceans. The experiment used an array of airguns as a source and ocean bottom seismographs (OBS) and a borehole array as receivers. our final model of the seismic structure of oceanic crust at the LFASE Site was obtained using travel times along with general characteristics of amplitudes and waveforms of the crustal P-wave arrivals. In this paper we discuss the results of the LFASE seismic data interpretation and compare our results to those of Purdy (1983) for 140 Ma lithosphere ... Airgun refraction profiles, North Atlantic, Oldest oceanic lithosphere, Oceanic crust, WKBJ Synthetic seismograms
Regional Small-Event Identification Using Seismic Networks and Arrays ( Book )
1 edition published in 1995 in English and held by 1 library worldwide
In view of the importance of small seismic events to a monitored CTBT we have begun a survey of globally distributed regional seismic recordings of eatthquakes, quarry blasts and explosions with m sub b is approximately 2.5. The first goal of this project is to test the effectiveness of our automated time-frequency discriminant (ATFD) at distinguishing quarry blasts from single explosions and earthquakes using regional array and network recordings. We intend to use these data to develop and test enhancements of the technique and develop complementary discriminants for use when the ATFD proves to be ineffective. As part of this program we intend to determine if a low frequency spectral signature (perhaps caused by source finiteness) might be used for discrimination at far-regional distances. We will analyze these waveforms using the standard multi-taper estimation technique and a new wavelet based technique that will allow us to process 3-component data and analyze the evolution of spectral amplitude and polarization with time and frequency. The ATFD uses a binary sonogram which is derived from the original, spectral, sonogram by the application of filters which replace local spectral information with a binary code which simply reflects local spectral highs and lows. The ATFD calculates a two-dimensional Fourier transform of the binary sonogram which reveals the dependence of the binary pattern on frequency and time. In view of its resemblance to the cepstrum (which identifies periodicities in single spectra), and the fact that it is derived from onset and coda phases we refer to it as the coda cepstrum. We are currently working on an adaptive coda cepstrum which iteratively solves for filters that are optimal for extracting any time-independent pattern that exists in the sonogram of an individual event
Hydroacoustic Arrays for Seismic Detection, Location and Discrimination: A Comparison With Land-based Seismic Arrays and Networks ( file )
1 edition published in 1998 in English and held by 1 library worldwide
U.S. Navy hydrophone arrays (SOSUS) record signals in a range of frequencies that includes earthquake and explosive sources as well as those relevant to submarine detection, for which they were designed. In the Norwegian Sea we compared recordings of acoustic arrivals on SOSUS with seismic recordings at the arrays on land in Norway. We also studied seismic activity along the spreading centers between Iceland and Svalbard in an attempt to discern any difference in levels of seismicity associated with different sections of the ridge system
Seismoacoustic Studies of the Norwegian Sea ( Book )
1 edition published in 1995 in English and held by 1 library worldwide
The U.S. Navy hydrophone arrays (SOSUS) record seismoacoustic events in a range of frequencies which includes earthquake and explosive sources as well as those relevant to submarine detection, for which they were designed. In the Norwegian Sea we compare detection of seismoacoustic events on SOSUS with seismic detection by the arrays on land in Norway. We also study seismic activity along the spreading centers between Iceland and Svalbard in an attempt to discern any difference in levels of seismicity associated with different sections of the ridge system. Currently, we have assigned archive channels to focus on activity along the Mohns ridge. During March 1995 we recorded many T-phases whose sources have been located along the Mohns ridge using beam steering. Analysis of beamformed data for this continuous one-month period revealed several dozen acoustic events emanating from the southern Mohns ridge and about one third that number from the northern Mohns ridge. Part of this difference is probably due to the choice of beams for the archived data, which emphasizes the southern Mohns ridge, but some of the difference likely reflects the current level of magmatic/tectonic activity. About 10% of the recorded T-phases for this period are preceded by an arrival with greater low frequency content, most likely the P-phase. Approximately two dozen acoustic events were recorded by all channels during the March 95 period suggesting a more distant or larger source, possibly a regional or even teleseismic earthquake. Two of these events correspond to regional events listed in the Center for Monitoring Research (CMR) bulletin, both for which P- and T-phases are observed
Application of Physics-Based Underwater Acoustic Signal and Array-Processing Techniques to Infrasound-Source Localization ( file )
1 edition published in 2001 in English and held by 1 library worldwide
The purpose of this project is to apply physics-based signal and array processing techniques, recently developed in the area of underwater acoustics, to atmospheric infrasound data and co-located seismic field data. The source of the infrasound data is the newly installed International Monitoring System (IMS) infrasound station at Pinon Flat (PFO). The seismic data are being collected by the Southern California ANZA seismic network. Installation of the eight sensors that comprise the infrasound station at PFO was completed by mid April of this year. The space filters of the array (18 m for the inner centered triangle elements and 70 m for the outer centered triangle elements) also are nearly all in place. Preliminary data collected by this array contain some signals with significant spatial coherence across the array aperture. In particular, a large event with high signal-to-noise ratio was recorded on 23 April. Analyses of the arrival structure of this signal are presented in this paper. In addition, the spatial and temporal properties of the background noise in relation to the local environmental conditions are discussed. A focused experiment involving the temporary installation of additional infrasound sensors to provide larger array aperture is being planned for this summer. A description of the planned experiment is presented below
Modern Seismic Travel Time Tables and Station Corrections for P and S waves ( file )
1 edition published in 1992 in English and held by 1 library worldwide
(1) We refine estimates of inner core structure by examining PKP travel times and find that anisotropy is a simpler explanation than heterogeneity for the observed residual patterns. Our preferred model of inner core anisotropy contains velocities that are 0.5% faster in a N-S direction than an E-W direction. (2) We study various mantle differential travel times including SS-S, ScS-S, PP-P, and PcP-P and compare these results to those obtained from handpicked waveform data. Large-scale coherent patterns of residuals are seen which indicate, mantle heterogeneity. (3) We examine PKP travel times to study the possibility of outer core heterogeneity models which are suggested by observations of anomalous splitting in normal modes. We find that the travel times limit the scale of possible outer core heterogeneity to models much smaller than those required to explain the mode splitting data. (4) We develop computer codes which return travel time and ray geometries for a given seismic phase, source-receiver pair, and arbitrary 3-d earth models specified by their spherical harmonic expansions. Seismic travel times, Earth models, Core structure
Very Low Frequency Seismo-Acoustic Scattering from a Rough Seafloor ( file )
1 edition published in 1990 in English and held by 1 library worldwide
Long Range Localization of Impulsive Sources in the Atmosphere and Ocean From Focus Regions in Single Element Spectrograms ( file )
1 edition published in 2000 in English and held by 1 library worldwide
Waveguide propagation often displays transitions from one type of propagation to another as the mode number (or the take-off angle from a ray theory point of view) increases. An example of such a transition occurs when the boundary of the waveguide changes from being formed by refraction to being formed by reflection. When these transitions occur, they can result in broadband focusing of energy. These focus regions are observable in time series and in single element spectrograms. By measuring the difference in arrival times between these focus regions and knowing the group velocities involved, the range to a longrange impulsive source can be estimated, in the same way that time-of-arrival differences between seismic phases in single station seismograms are used to estimate epicentral distances. Examples of such broadband focusing in low-frequency acoustic propagation in the ocean and infrasonic propagation in the atmosphere are presented in this paper
Regional Phases: Oceanic and Continental Propagation ( Book )
1 edition published in 1989 in English and held by 1 library worldwide
In this report we present the results of several investigations dealing with two diverse topics: We compare ambient noise levels on islands with those present at and beneath the seafloor to determine the value of permanent seafloor seismic stations. We compare signal power spectral levels expected from earthquakes with ambient noise levels at these locations to determine a lower magnitude limit of detectable events. We study the nature of propagation of seismic waves through the continental and oceanic crusts. We investigate the influence the regular repetition of features in seismograms, introduced at the source and/or during propagation by layer resonance, has on the spectrum of the recorded coda
Modern seismic travel time tables and station corrections for P and S waves by John A Orcutt( Book )
1 edition published in 1992 in English and held by 1 library worldwide
Modeling Hydroacoustic Propagation for Seismic Events ( Book )
1 edition published in 1995 in English and held by 1 library worldwide
The goal of our research is to understand how acoustic energy from underwater earthquakes is coupled to the sound channel and how the sound is propagated from the source to the hydrophone receivers. We intend to compare results from numerical modeling of long-range acoustic propagation to hydroacoustic data. A large suite of hydroacoustic data will be assembled, in order to obtain optimal azimuthal coverage from source to receiver, as well as a wide range of source depths and source parameters. The numerical modeling will involve integrating bathymetric and sound speed databases into the models since sound propagation in the oceans is strongly dependent upon these parameters. Our object is to be able to distinguish between source effects and propagation effects. We have conducted some simple numerical modeling experiments to compare hydroacoustic signatures for models with and without significant bathymetric interaction along the transmission path. The acoustic wavefield is computed using the parabolic equation method for a large number of frequencies within the band of interest; time domain arrivals are computed by Fourier synthesis of these calculations
Relationships between Ocean Bottom Noise and the Environment ( file )
1 edition published in 1995 in English and held by 1 library worldwide
Observations of ocean bottom low frequency noise and surface environmental data over a period of 27 days in the North Atlantic during the SAMSON and SWAE experiments reveal how closely related the noise is to meteorological conditions. Double frequency microseisms produced by nonlinear interactions of storm-induced surface gravity waves are especially evident in the frequency band O.16-0.3 Hz and show a high variability in both amplitude and peak frequencies. Bifurcated at times, the peak which characterizes the microseism band contains local and distant or teleseismic components which are generated at different locations. Weather and storm fetch appear to be the major contributors to the size and shape of microseism spectra. Storm development on the sea surface is associated with progressively lower microseism frequencies along with a concurrent increase in amplitude. The single frequency microseism peak is a continuous feature and is observed to portray the same time-dependent spectral characteristics as the portion of the double frequency peak associated with distant storms. Coherence studies confirm that both peaks (single and teleseismic double) originate at a distant source. These peaks are generated at roughly the same location with some storm component over the coastline. (AN)
Numerical, Theoretical and Experimental Studies of Seafloor and Subseafloor Reverberation ( file )
1 edition published in 2000 in English and held by 1 library worldwide
In studies of low-frequency reverberation within the marine environment, a central concern is the relationship between reverberation events and morphological features of the seafloor. A time-domain migration algorithm for the reverberation intensity field is developed that produces scattering coefficient maps coregistered with a bathymetry database. The algorithm is tailored to broadband transient sources with good range resolution, and was developed to analyze an extensive set of reverberation records from a 200-255 Hz source collected on the flanks of the Mid-Atlantic ridge. The precise, sample-by-sample, tracking of wavefronts across elements of the bathymetry database that forms the foundation of the algorithms implementation results in reverberation maps that show a clear and detailed correlation between scattering and morphology with narrow scarp slopes consistently highlighted. Environmentally induced asymmetries in transmission loss and incidence angle are exploited to break the inherent left-right ambiguity of the receiver array. Iterative migration, assuming a dominant dependence of backscatter on grazing angle, produces images, even from individual records, that show good ambiguity resolution. Results from multiple records corroborate the effectiveness of the ambiguity resolution and demonstrate the stability of the scattering coefficient estimates and the acoustic system
Detection of T-Phases at Island Seismic Stations: Dependence on Seafloor Slope, Seismic Velocity and Roughness ( file )
1 edition published in 2000 in English and held by 1 library worldwide
The hydroacoustic segment of the International Monitoring System (IMS) currently being installed for use in verifying compliance with the Comprehensive Nuclear Test Ban Treaty (CTBT), will consist of six hydrophone stations and five supplemental T-phase stations. The ability to detect acoustic signals at T-phase stations relies on an understanding of the acoustic to seismic coupling mechanisms. In this paper, we model upslope propagation of acoustic energy at a sloping wedge using an elastic parabolic equation (PE) modeling method. We synthesize both vertical and horizontal displacement waveforms for broadband sources, and show that the signal amplitudes are strongly dependent on the properties of the offshore slope. For all slope types, the signal amplitudes at onshore seismic stations decrease rapidly with increasing frequency. This decrease with frequency is most pronounced for sources with high mode number content at a shallow sloping wedge. Finally, we show that a significant amount of energy can be lost to surface shear waves at the sloping wedge. We investigate the dependence of surface shear wave excitation on seafloor roughness
Retrieval of earthquake source mechanisms using southern California arrays (CA) by John A Orcutt( Book )
1 edition published in 1979 in English and held by 1 library worldwide
 
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