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The 16 August 1997 Novaya Zemlya seismic event as viewed from GSN stations KEV and KBS

Description: Using current and historic seismic records from Global Seismic Network stations KEV and KBS, the authors find that S minus P arrival time comparisons between nuclear explosions and the 16 August 1997 seismic event (m{sub b} {approx} 3.6) from near Novaya Zemlya clearly indicate that (relative to KEV) the 16 August event occurred at least 80 km east of the Russian test site. Including S minus P arrival times from KBS constrains the location to beneath the Kara Sea and in good agreement with previously reported locations, over 100 km southeast of the test site. From an analysis of P{sub n}/S{sub n} waveform ratios at frequencies above 4 Hz, they find that the 16 August event falls within the population of regional earthquakes and is distinctly separated from Novaya Zemlya and other northern Eurasian nuclear explosion populations. Thus, given its location and waveform characteristics, they conclude the 16 August event was an earthquake. The 16 August event was not detected at teleseismic distances, and thus, this event provides a good example of the regional detection, location, and identification efforts that will be required to monitor the Comprehensive Test Ban Treaty below m{sub b} {approx} 4.
Date: November 1, 1997
Creator: Hartse, H.E.
Partner: UNT Libraries Government Documents Department

24-CHANNEL GEOPHONE ARRAY FOR HORIZONTAL OR VERTICAL BOREHOLES

Description: This report describes the technical progress on a project to design and construct a multi-channel geophone array that improves tomographic imaging capabilities in both surface and underground mines. Especially important in the design of the array is sensor placement. One issue related to sensor placement is addressed in this report: the development of simple, robust, MSHA-acceptable clamping unit. Improved imaging capabilities will produce energy, environmental, and economic benefits by increasing exploration accuracy and reducing operating costs.
Date: July 1, 2002
Creator: Westman, Erik C.
Partner: UNT Libraries Government Documents Department

24-CHANNEL GEOPHONE ARRAY FOR HORIZONTAL OR VERTICAL BOREHOLES

Description: This report describes the technical progress on a project to design and construct a multi-channel geophone array that improves tomographic imaging capabilities in both surface and underground mines. Especially important in the design of the array is sensor placement. One issue related to sensor placement is addressed in this report: the method for clamping the sensor once it is emplaced in the borehole. If the sensors (geophones) are not adequately coupled to the surrounding rock mass, the resulting data will be of very poor quality. Improved imaging capabilities will produce energy, environmental, and economic benefits by increasing exploration accuracy and reducing operating costs.
Date: July 1, 2002
Creator: Westman, Erik C.
Partner: UNT Libraries Government Documents Department

24-CHANNEL GEOPHONE ARRAY FOR HORIZONTAL OR VERTICAL BOREHOLES

Description: This report describes the technical progress on a project to design and construct a multi-channel geophone array that improves tomographic imaging capabilities in both surface and underground mines. Especially important in the design of the array is sensor placement. One issue related to sensor placement is addressed in this report: the method for orienting the sensor once it is emplaced in the borehole. If the sensors (geophones) do not have the same orientation, the data will be essentially worthless. Improved imaging capabilities will produce energy, environmental, and economic benefits by increasing exploration accuracy and reducing operating costs.
Date: July 1, 2002
Creator: Westman, Erik C.
Partner: UNT Libraries Government Documents Department

24-CHANNEL GEOPHONE ARRAY FOR HORIZONTAL OR VERTICAL BOREHOLES

Description: This report describes the technical progress on a project to design and construct a multi-channel geophone array that improves tomographic imaging capabilities in both surface and underground mines. Especially important in the design of the array is sensor placement. One issue related to sensor placement is addressed in this report: the method for clamping the sensor once it is emplaced in the borehole. If the sensors (geophones) are not adequately coupled to the surrounding rock mass, the resulting data will be of very poor quality. Improved imaging capabilities will produce energy, environmental, and economic benefits by increasing exploration accuracy and reducing operating costs.
Date: August 1, 2002
Creator: Westman, Erik C.
Partner: UNT Libraries Government Documents Department

24 CHANNEL GEOPHONE ARRAY FOR HORIZONTAL OR VERTICAL BOREHOLES

Description: This report describes the technical progress on a project to design and construct a multi-channel geophone array that improves tomographic imaging capabilities in both surface and underground mines. Especially important in the design of the array is sensor placement. One issue related to sensor placement is addressed in this report: the method of emplacing the array in a long, horizontal borehole. Improved imaging capabilities will produce energy, environmental, and economic benefits by increasing exploration accuracy and reducing operating costs.
Date: July 1, 2002
Creator: Westman, Erik C.
Partner: UNT Libraries Government Documents Department

24-CHANNEL GEOPHONE ARRAY FOR HORIZONTAL OR VERTICAL BOREHOLES

Description: This report describes the technical progress on a project to design and construct a multi-channel geophone array that improves tomographic imaging capabilities in both surface and underground mines. Especially important in the design of the array is sensor placement. One issue related to sensor placement is addressed in this report: the method for clamping the sensor once it is emplaced in the borehole. If the sensors (geophones) are not adequately coupled to the surrounding rock mass, the resulting data will be of very poor quality. Improved imaging capabilities will produce energy, environmental, and economic benefits by increasing exploration accuracy and reducing operating costs.
Date: August 1, 2002
Creator: Westman, Erik C.
Partner: UNT Libraries Government Documents Department

2D Depth migration in transversely isotropic media using explicit operators

Description: Stable, explicit depth-extrapolation filters can be used to propagate plane waves corresponding to the qP and qSV (quasi-P and quasi-SV propagation) modes for transversely isotropic (TI) media. The author discusses and compare results of two different methods for obtaining the filters for TI media with a vertical axis of symmetry (VTI). The first, a modified Taylor series method, is used to calculate the N-coefficients of a finite-length filter such that the Taylor expansion around vertical propagation matches the spatial Fourier transform of the downward-continuation operator for VTI media. Second, a least-squares method is used to calculate the filter coefficients such that the amplitude and phase departures from the ideal response of the downward-continuation operator for VTI media are minimized over a range of frequencies and propagation angles. In both methods, the amplitude response of the filter is forced to be less than unity in the evanescent region in order to achieve stability. In general, as exemplified in all the cases studied here, the constrained least-squares method produced filters with accurate wavefield extrapolation for a wider range of propagation angles than that obtained for the modified Taylor series method. In both methods, the maximum angle that can be accurately propagated depends on the ratio of frequency to vertical phase velocity (f/V{sub v}), and on the length of the filter. However, for a fixed filter length and for a given ratio f/V{sub v}, the maximum angle propagated with accuracy depends on the elastic constants of the medium. The accuracy of the filters degrades as the degree of anisotropy becomes more extreme.
Date: April 1, 1994
Creator: Uzcategui, O.
Partner: UNT Libraries Government Documents Department

Adaptive and mobile ground sensor array.

Description: The goal of this LDRD was to demonstrate the use of robotic vehicles for deploying and autonomously reconfiguring seismic and acoustic sensor arrays with high (centimeter) accuracy to obtain enhancement of our capability to locate and characterize remote targets. The capability to accurately place sensors and then retrieve and reconfigure them allows sensors to be placed in phased arrays in an initial monitoring configuration and then to be reconfigured in an array tuned to the specific frequencies and directions of the selected target. This report reviews the findings and accomplishments achieved during this three-year project. This project successfully demonstrated autonomous deployment and retrieval of a payload package with an accuracy of a few centimeters using differential global positioning system (GPS) signals. It developed an autonomous, multisensor, temporally aligned, radio-frequency communication and signal processing capability, and an array optimization algorithm, which was implemented on a digital signal processor (DSP). Additionally, the project converted the existing single-threaded, monolithic robotic vehicle control code into a multi-threaded, modular control architecture that enhances the reuse of control code in future projects.
Date: December 1, 2003
Creator: Holzrichter, Michael Warren; O'Rourke, William T.; Zenner, Jennifer & Maish, Alexander B.
Partner: UNT Libraries Government Documents Department

Advanced array techniques for unattended ground sensor applications

Description: Sensor arrays offer opportunities to beam form, and time-frequency analyses offer additional insights to the wavefield data. Data collected while monitoring three different sources with unattended ground sensors in a 16-element, small-aperture (approximately 5 meters) geophone array are used as examples of model-based seismic signal processing on actual geophone array data. The three sources monitored were: (Source 01). A frequency-modulated chirp of an electromechanical shaker mounted on the floor of an underground bunker. Three 60-second time-windows corresponding to (a) 50 Hz to 55 Hz sweep, (b) 60 Hz to 70 Hz sweep, and (c) 80 Hz to 90 Hz sweep. (Source 02). A single transient impact of a hammer striking the floor of the bunker. Twenty seconds of data (with the transient event approximately mid-point in the time window.(Source 11)). The transient event of a diesel generator turning on, including a few seconds before the turn-on time and a few seconds after the generator reaches steady-state conditions. The high-frequency seismic array was positioned at the surface of the ground at a distance of 150 meters (North) of the underground bunker. Four Y-shaped subarrays (each with 2-meter apertures) in a Y-shaped pattern (with a 6-meter aperture) using a total of 16 3-component, high-frequency geophones were deployed. These 48 channels of seismic data were recorded at 6000 and 12000 samples per second on 16-bit data loggers. Representative examples of the data and analyses illustrate the results of this experiment.
Date: May 6, 1997
Creator: Followill, F.E.; Wolford, J.K. & Candy, J.V.
Partner: UNT Libraries Government Documents Department

Los Alamos National Laboratory Northern New Mexico Seismic Network and seismicity

Description: The Northern New Mexico Seismic Network (NNMSN) is described and the research conducted there briefly discussed. Its purpose is to: (1) monitor seismic activity that can pose a risk to the Los Alamos National Laboratory; (2) monitor induced seismicity that might result from the Laboratory's experimental activities, such as the Hot Dry Rock project; (3) provide data for research in test ban verification; and (4) provide data for fundamental research in seismology, tectonics, and geologic structure of the Rio Grande Rift and the Jemez Mountains. (ACR)
Date: January 1, 1981
Creator: Cash, D.J.
Partner: UNT Libraries Government Documents Department

An Analysis of the Mt. Meron Seismic Array

Description: We have performed a quick analysis of the Mt. Meron seismic array to monitor regional seismic events in the Middle East. The Meron array is the only current array in the Levant and Arabian Peninsula and, as such, might be useful in contributing to event location, identification, and other analysis. Here, we provide a brief description of the array and a review of the travel time and array analysis done to assess its performance.
Date: January 10, 2008
Creator: Pasyanos, M E & Ryall, F
Partner: UNT Libraries Government Documents Department

Analysis of the time-reversal operator for planar dipole arrays

Description: The problem of imaging of targets in random media or cluttered environments is found in a wide variety of different applications, including ocean acoustics, medical ultrasound, geophysics, and radar. The solution often requires separating targets of interest from other scatterers, and compensating for wave speed variations in the medium. The problem is not usually the lack of data, but too much data, specifically the lack of a useful organizing principle for the data. The difficult part is separating the meaningful data from the remainder. It would therefore be most helpful if there were some means for skipping over those parts of the data that we do not really want to image very much, and looking at those parts (targets) that do interest us. This sounds challenging (maybe even impossible), but recent developments in acoustics make it clear that certain very limited imaging goals are achievable with much smaller data sets than are traditionally needed in, for example, seismic array processing. Early versions of this new method have been given the names of ''time-reversal acoustics'' or ''time-reversal mirrors,'' and have been developed most extensively by the French ultrasonics group led by Fink.
Date: January 16, 2004
Creator: Chambers, D H & Berryman, J G
Partner: UNT Libraries Government Documents Department

Array analysis of regional Pn and Pg wavefields from the Nevada Test Site

Description: Small-aperture high-frequency seismic arrays with dimensions of a few kilometers or less, can improve our ability to seismically monitor compliance with a low-yield Threshold Test Ban Treaty. This work studies the characteristics and effectiveness of array processing of the regional Pn and Pg wavefields generated by underground nuclear explosions at the Nevada Test Site. Waveform data from the explosion HARDIN (m{sub b} = 5.5) is recorded at a temporary 12-element, 3-component, 1.5 km-aperture array sited in an area of northern Nevada. The explosions VILLE (m{sub b} = 4.4) and SALUT (m{sub b} = 5.5) are recorded at two arrays sited in the Mojave desert, one a 96-element vertical-component 7 km-aperture array and the other a 155-element vertical-component 4 km-aperture array. Among the mean spectra for the m{sub b} = 5.5 events there are significant differences in low-frequency spectral amplitudes between array sites. The spectra become nearly identical beyond about 6 Hz. Spectral ratios are used to examine seismic source properties and the partitioning of energy between Pn and Pg. Frequency-wavenumber analysis at the 12-element array is used to obtain estimates of signal gain, phase velocity, and source azimuth. This analysis reveals frequency-dependent biases in velocity and azimuth of the coherent Pn and Pg arrivals. Signal correlation, the principal factor governing array performance, is examined in terms of spatial coherence estimates. The coherence is found to vary between the three sites. In all cases the coherence of Pn is greater than that for Pg. 81 refs., 92 figs., 5 tabs.
Date: June 1, 1991
Creator: Leonard, M.A. (California Univ., Berkeley, CA (United States). Dept. of Geology and Geophysics Lawrence Berkeley Lab., CA (United States))
Partner: UNT Libraries Government Documents Department

Assessment and interpretation of cross- and down-hole seismograms at the Paducah Gaseous Diffusion Plant

Description: This paper is an assessment and interpretation of cross-and down-hole seismograms recorded at four sites in the vicinity of the Paducah Gaseous Diffusion Plant (PGDP). Arrival times of shear (S-) and compressional (P-) waves are recorded on these seismograms in milliseconds. Together with known distances between energy sources and seismometers lowered into boreholes, these arrival times are used to calculate S- and P-wave velocities in unconsolidated soils and sediments that overlie bedrock approximately 320 ft beneath PGDP. The soil columns are modified after an earlier draft by ERC Environmental and Energy Services Company (ERCE), 1990. In addition to S- and P- wave velocity estimates from this paper, the soil columns contain ERCE's lithologic and other geotechnical data for unconsolidated soils and sediments from the surface to bedrock. Soil columns for Sites 1 through 4 and a site location map are in Plates 1 through 5 of Appendix 6. The velocities in the four columns are input parameters for the SHAKE computer program, a nationally recognized computer model that simulates ground response of unconsolidated materials to earthquake generated seismic waves. The results of the SHAKE simulation are combined with predicted ground responses on rock foundations (caused by a given design earthquake) to predict ground responses of facilities with foundations placed on unconsolidated materials. 3 refs.
Date: September 1, 1991
Creator: Staub, W.P.; Wang, J.C. (Oak Ridge National Lab., TN (United States)) & Selfridge, R.J. (Automated Sciences Group, (United States))
Partner: UNT Libraries Government Documents Department

Automated Data Processing (ADP) research and development

Description: Monitoring a comprehensive test ban treaty (CTBT) will require screening tens of thousands of seismic events each year. Reliable automated data analysis will be essential in keeping up with the continuous stream of events that a global monitoring network will detect. We are developing automated event location and identification algorithms by looking at the gaps and weaknesses in conventional ADP systems and by taking advantage of modem computational paradigms. Our research focus is on three areas: developing robust algorithms for signal feature extraction, integrating the analysis of critical measurements, and exploiting joint estimation techniques such as using data from acoustic, hydroacoustic, and seismic sensors. We identify several important problems for research and development; e.g., event location with approximate velocity models and event identification in the presence of outliers. We are employing both linear and nonlinear methods and advanced signal transform techniques to solve these event monitoring problems. Our goal is to increase event-interpretation throughput by employing the power and efficiency of modem computational techniques, and to improve the reliability of automated analysis by reducing the rates of false alarms and missed detections.
Date: July 1, 1995
Creator: Dowla, F.U.; Kohlhepp, V.N. & Leach, R.R. Jr.
Partner: UNT Libraries Government Documents Department

Berkeley Seismological Laboratory Seismic Moment Tensor Report for the August 6, 2007 M3.9 Seismic event in central Utah

Description: We have performed a complete moment tensor analysis of the seismic event, which occurred on Monday August 6, 2007 at 08:48:40 UTC 21 km from Mt.Pleasant, Utah. In our analysis we utilized complete three-component seismic records recorded by the USArray, University of Utah, and EarthScope seismic arrays. The seismic waveform data was integrated to displacement and filtered between 0.02 to 0.10 Hz following instrument removal. We used the Song et al. (1996) velocity model to compute Green's functions used in the moment tensor inversion. A map of the stations we used and the location of the event is shown in Figure 1. In our moment tensor analysis we assumed a shallow source depth of 1 km consistent with the shallow depth reported for this event. As shown in Figure 2 the results point to a source mechanism with negligible double-couple radiation and is composed of dominant CLVD and implosive isotropic components. The total scalar seismic moment is 2.12e22 dyne cm corresponding to a moment magnitude (Mw) of 4.2. The long-period records are very well matched by the model (Figure 2) with a variance reduction of 73.4%. An all dilational (down) first motion radiation pattern is predicted by the moment tensor solution, and observations of first motions are in agreement.
Date: August 8, 2007
Creator: Ford, S.; Dreger, D. & Hellweg, P.
Partner: UNT Libraries Government Documents Department

Broadband Seismic Station Deployment at Hadabat Al-Marhi, Halban, Saudi Arabia

Description: A broadband three-component seismic station was deployed on the Arabian Shield near the town of Halban in central Saudi Arabia. This site is near the proposed site of a primary seismic array (PS38) of the International Monitoring System (IMS) of the Comprehensive Nuclear Test-Ban Treaty (CTBT). The purpose of this deployment was to collect calibration data for the primary array to be deployed in the future.
Date: February 11, 2002
Creator: Rodgers, A; Lewis, J P & Al-Amri, A
Partner: UNT Libraries Government Documents Department

Building on and spinning off: Sandia National Labs` creation of sensors for Vietnam

Description: This paper discusses Sandia National Laboratories` development of new technologies for use in the Vietnam War - specifically the seismic sensors deployed to detect troop and vehicle movement - first along the Ho Chi Minh Trail and later in perimeter defense for American military encampments in South Vietnam. Although the sensor story is a small one, it is interesting because it dovetails nicely with our understanding of the war in Vietnam and its frustrations; of the creation of new technologies for war and American enthusiasm for that technology; and of a technological military and the organizational research and a m am development structure created to support it. Within the defense establishment, the sensors were proposed within the context of a larger concept - that of a barrier to prevent the infiltration of troops and supplies from North Vietnam to the South. All of the discussion of the best way to fight in Vietnam is couched in the perception that this was a different kind of war than America was used to fighting. The emphasis was on countering the problems posed by guerrilla/revolutionary warfare and eventually by the apparent constraints of being involved in a military action, not an outright war. The American response was to find the right technology to do the job - to control the war by applying a technological tincture to its wounds and to make the war familiar and fightable on American terms. And, when doubts were raised about the effectiveness of applying existing technologies (namely, the bombing of North Vietnam and Laos), the doubters turned to new technologies. The sensors that were developed for use in Vietnam were a direct product of this sort of thinking - on the part of the engineers at Sandia who created the sensors, the civilian scientific advisors who recommended ...
Date: December 31, 1996
Creator: Ullrich, R.
Partner: UNT Libraries Government Documents Department

Calibration of the Sonseca array with large magnitude regional and teleseismic events

Description: In order to calibrate the Sonseca station, a 19-element short-period seismic array with a 9 km diameter circular aperture located in central Spain (39.68N, 3.96W), wavefield measurements made on observed seismic phases are compared with expected values. Thirty-five well-recorded regional and teleseismic events are used to study bearing and phase velocity estimation properties. Preliminary results indicate that in general the Sonseca array performs well for both regional and teleseismic events for frequencies less than 5 Hz using standard array signal processing techniques. Main findings of this study are: (1) A systematic bias is observed in bearing estimates; the bias is a function of the true bearing for events from the easterly directions of the array and can be mitigated with a simple bias correction. Using a least-squares quadratic polynomial fit, the bearing estimation error can be reduced to less than two or three degrees. (2) Measured signal and noise coherence functions and beamforming suggest that for regional events improved SNR is obtained by beamforming in the frequency band of 0.5 to 4 Hz with a resulting array gain as high as 10 dB. (3) Because the element spacing of Sonseca array corresponds to that of a sparse regional array, spatial aliasing can be observed in narrowband f-K analysis at the higher frequencies. We compare performance of narrowband and broadband frequency-wavenumber (f-k) analysis and suggest preliminary recipes for f-k and beamforming analysis.
Date: July 1, 1996
Creator: Dowla, F.U.
Partner: UNT Libraries Government Documents Department

Characterizing source regions with signal subspace methods: Theory and computational methods

Description: A mathematical approach is developed for empirically characterizing a given source region using waveforms from a collection of calibration events. A region is considered to be adequately characterized if the waveforms from any event in the source region can be represented as a linear combination of calibration event waveforms. The purpose of such characterizations is to build waveform recognizers'' for specific regions for precision location applications, and to provide a means of separating superimposed waveforms from multiple events in different source regions. The particular form of characterization used is insensitive to variations in the source time function and to anything but changes from the normal range of source mechanisms encountered in the source region. The standard waveform correlation coefficient used to estimate event clustering is generalized to estimate separation between single events and event clusters, and between two clusters of events. The generalized correlation coefficient is insensitive to variations in source time function and, to some extent, mechanism. The statistics of waveform correlation coefficients are developed, and show that conventional estimates made from single station data are often developed for network or array data removes the ambiguity. 23 refs., 4 figs.
Date: December 1, 1989
Creator: Harris, D.B.
Partner: UNT Libraries Government Documents Department

Compensated intruder-detection systems

Description: The invention is an improvement to an intruder-detection system of the kind where intruder-induced signals are transmitted through a medium whose conductance varies with certain climatic conditions. The improved system includes means coupled to the medium for converting the intruder-induced signals received therefrom to a first electrical signal. Means also are provided for generating a reference signal proportional to the climate-induced changes in the signal-conductance of the medium. Means are provided for generating, from the first electrical signal and the reference signal, an electrical output signal which is unaffected by the changes in signal-conductance. Means are provided to give warning when the output signal exceeds a selected value. In another aspect, the invention is a method for operating an intruder-detection system of the kind wherein an intrusion-generated signal transmitted through a detection medium is converted to a first electrical signal. The first electrical signal contains variations resulting from climate-induced changes in the medium. The method of the invention comprises generating an electrical reference signal proportional to the climate-induced changes in the medium; conditioning the first signal with the reference signal to produce an electrical output signal which is unaffected by the climate-induced changes in the medium; and impressing the resulting output signal across an alarm circuit to actuate the same when the output signal exceeds a selected value.
Date: January 20, 1982
Creator: McNeilly, D.R. & Miller, W.R.
Partner: UNT Libraries Government Documents Department

Comprehensive study of the seismotectonics of the eastern Aleutian ARC and associated volcanic systems. Annual progress report, March 1, 1981-February 28, 1982

Description: Assessment of the seismic potential for occurrence of great earthquakes in three seismic gaps (Shumagin Islands, Unalaska Island, and Yakataga-Kayak regions) has been completed. In the best-instrumented seismic gap in the Shumagin Islands region, the likelihood for a great earthquake within the next two decades is high. Analysis of earthquake data collected from a telemetered network operated in the Shumagin seismic gap shows near-quiescence in the shallow portion of the main thrust zone. Installation of digital recording equipment at the central station of the Shumagin network, combined with interactive computer analysis at Lamont-Doherty of either digitally recorded or digitized analog seismic data has provided new research possibilities for studying seismic source properties, wave propagation in a laterally heterogeneous velocity structure of the subduction zone, and for seismically screening the root-zone and volcanic pile of Pavlof volcano. High time-resolution data (0.01 sec), and wider frequency band-pass data (0.5 to 30 Hz) are now being collected. Seismic data for two eruptive sequences of Pavlof-volcano have been obtained.
Date: January 1, 1981
Creator: Jacob, K. H.; Hauksson, E. & Sykes, L. R.
Partner: UNT Libraries Government Documents Department