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Event identification from seismic/magnetic feature vectors: a comparative study

Description: The event identification problem plays a large role in the application of unattended ground sensors to the monitoring of borders and checkpoints. The choice of features and methods for classifying features affects how accurately these classifications are made. Finding features which reliably distinguish events of interest may require measurements based on separate physical phenomena. Classification methods include neural net versus fuzzy logic approaches, and within the neural category, different architectures and transfer functions for reaching decisions. This study examines ways of optimizing feature sets and surveys common techniques for classifying feature vectors corresponding to physical events. We apply each technique to samples of existing data, and compare discrimination attributes. Specifically, we calculate the confusion matrices for each technique applied to each sample dataset, and reduce them statistically to scalar scores. In addition, we gauge how the accuracy of each method is degraded by reducing the feature vector length by one element. Finally, we gather rough estimates of the relative cpu performance of the forward prediction algorithms.
Date: April 1, 1997
Creator: Wolford, J. K.
Partner: UNT Libraries Government Documents Department

Utilization of near-source video and ground motion in the assessment of seismic source functions from mining explosions

Description: Constraint of the operative physical processes in the source region of mining explosions and the linkage to the generation of seismic waveforms provides the opportunity for controlling ground motion. Development of these physical models can also be used in conjunction with the ground motion data as diagnostics of blasting efficiency. In order to properly address the multi-dimensional aspect of data sets designed to constrain these sources, we are investigating a number of modem visualization tools that have only recently become available with new, high-speed graphical computers that can utilize relatively large data sets. The data sets that are combined in the study of mining explosion sources include near-source ground motion acceleration and velocity records, velocity of detonation measurements in each explosive hole, high speed film, video and shot design information.
Date: April 1, 1995
Creator: Stump, B.W. & Anderson, D.P.
Partner: UNT Libraries Government Documents Department

Poroelastic measurement schemes resulting in complete data sets for granular and other anisotropic porous media

Description: Poroelastic analysis usually progresses from assumed knowledge of dry or drained porous media to the predicted behavior of fluid-saturated and undrained porous media. Unfortunately, the experimental situation is often incompatible with these assumptions, especially when field data (from hydrological or oil/gas reservoirs) are involved. The present work considers several different experimental scenarios typified by one in which a set of undrained poroelastic (stiffness) constants has been measured using either ultrasound or seismic wave analysis, while some or all of the dry or drained constants are normally unknown. Drained constants for such a poroelastic system can be deduced for isotropic systems from available data if a complete set of undrained compliance data for the principal stresses are available - together with a few other commonly measured quantities such as porosity, fluid bulk modulus, and grain bulk modulus. Similar results are also developed here for anisotropic systems having up to orthotropic symmetry if the system is granular (i.e., composed of solid grains assembled into a solid matrix, either by a cementation process or by applied stress) and the grains are known to be elastically homogeneous. Finally, the analysis is also fully developed for anisotropic systems with nonhomogeneous (more than one mineral type), but still isotropic, grains - as well as for uniform collections of anisotropic grains as long as their axes of symmetry are either perfectly aligned or perfectly random.
Date: November 20, 2009
Creator: Berryman, J.G.
Partner: UNT Libraries Government Documents Department

Low-frequency asymptotic analysis of seismic reflection from afluid-saturated medium

Description: Reflection of a seismic wave from a plane interface betweentwo elastic media does not depend on the frequency. If one of the mediais poroelastic and fluid-saturated, then the reflection becomesfrequency-dependent. This paper presents a low-frequency asymptoticformula for the reflection of seismic plane p-wave from a fluid-saturatedporous medium. The obtained asymptotic scaling of the frequency-dependentcomponent of the reflection coefficient shows that it is asymptoticallyproportional to the square root of the product of the reservoir fluidmobility and the frequency of the signal. The dependence of this scalingon the dynamic Darcy's law relaxation time is investigated as well.Derivation of the main equations of the theory of poroelasticity from thedynamic filtration theory reveals that this relaxation time isproportional to Biot's tortuosity parameter.
Date: April 14, 2004
Creator: Silin, D.B.; Korneev, V.A.; Goloshubin, G.M. & Patzek, T.W.
Partner: UNT Libraries Government Documents Department

Preseismic Velocity Changes Observed from Active Source Monitoringat the Parkfield SAFOD Drill Site

Description: Measuring stress changes within seismically active fault zones has been a long-sought goal of seismology. Here we show that such stress changes are measurable by exploiting the stress dependence of seismic wave speed from an active source cross-well experiment conducted at the SAFOD drill site. Over a two-month period we observed an excellent anti-correlation between changes in the time required for an S wave to travel through the rock along a fixed pathway--a few microseconds--and variations in barometric pressure. We also observed two large excursions in the traveltime data that are coincident with two earthquakes that are among those predicted to produce the largest coseismic stress changes at SAFOD. Interestingly, the two excursions started approximately 10 and 2 hours before the events, respectively, suggesting that they may be related to pre-rupture stress induced changes in crack properties, as observed in early laboratory studies.
Date: June 10, 2008
Creator: Daley, Thomas; Niu, Fenglin; Silver, Paul G.; Daley, Thomas M.; Cheng, Xin & Majer, Ernest L.
Partner: UNT Libraries Government Documents Department

Pore-fluid effects on seismic waves in vertically fractured earth with orthotropic symmetry

Description: For elastically noninteracting vertical-fracture sets at arbitrary orientation angles to each other, a detailed model is presented in which the resulting anisotropic fractured medium generally has orthorhombic symmetry overall. Some of the analysis methods and ideas of Schoenberg are emphasized, together with their connections to other similarly motivated and conceptually related methods by Sayers and Kachanov, among others. Examples show how parallel vertical-fracture sets having HTI (horizontal transversely isotropic) symmetry transform into orthotropic fractured media if some subsets of the vertical fractures are misaligned with the others, and then the fractured system can have VTI (vertical transversely isotropic) symmetry if all of the fractures are aligned randomly or half parallel and half perpendicular to a given vertical plane. An orthotropic example having vertical fractures in an otherwise VTI earth system (studied previously by Schoenberg and Helbig) is compared with the other examples treated and it is finally shown how fluids in the fractures affect the orthotropic poroelastic system response to seismic waves. The key result is that fracture-influence parameters are multiplied by a factor of (1-B), where 0 {le} B < 1 is Skempton's second coefficient for poroelastic media. Skempton's B coefficient is itself a measurable characteristic of fluid-saturated porous rocks, depending on porosity, solid moduli, and the pore-fluid bulk modulus. For heterogeneous porous media, connections between the present work and earlier related results of Brown and Korringa are also established.
Date: May 15, 2010
Creator: Berryman, J.G.
Partner: UNT Libraries Government Documents Department

Aligned vertical fractures, HTI reservoir symmetry, and Thomsenseismic anisotropy parameters

Description: The Sayers and Kachanov (1991) crack-influence parametersare shown to be directly related to Thomsen (1986) weak-anisotropyseismic parameters for fractured reservoirs when the crack density issmall enough. These results are then applied to seismic wave propagationin reservoirs having HTI symmetry due to aligned vertical fractures. Theapproach suggests a method of inverting for fracture density from wavespeed data.
Date: June 27, 2007
Creator: Berryman, James G.
Partner: UNT Libraries Government Documents Department

Seismic Moment Tensor Report for the 06 Aug 2007, M3.9 Seismic Event in Central Utah

Description: We have performed a complete moment tensor analysis (Minson and Dreger, 2007) of the seismic event, which occurred on Monday August 6, 2007 at 08:48:40 UTC, 21 km from Mount Pleasant, Utah. The purpose of this report is to present our scientific results, making them available to other researchers working on seismic source determination problems, and source type identification. In our analysis we used complete, three-component seismic records recorded by stations operated by the USGS, the University of Utah and EarthScope. The results of our analysis show that most of the seismic wave energy is consistent with an underground collapse, however the cause of the mine collapse is still unknown.
Date: August 15, 2007
Creator: Ford, S R; Dreger, D S; Walter, W R; Hellweg, M & Urhammer, R
Partner: UNT Libraries Government Documents Department

A Model-Based Signal Processing Approach to Nuclear Explosion Monitoring

Description: This report describes research performed under Laboratory Research and Development Project 05-ERD-019, entitled ''A New Capability for Regional High-Frequency Seismic Wave Simulation in Realistic Three-Dimensional Earth Models to Improve Nuclear Explosion Monitoring''. A more appropriate title for this project is ''A Model-Based Signal Processing Approach to Nuclear Explosion Monitoring''. This project supported research for a radically new approach to nuclear explosion monitoring as well as allowed the development new capabilities in computational seismology that can contribute to NNSA/NA-22 Programs.
Date: March 14, 2007
Creator: Rodgers, A; Harris, D & Pasyanos, M
Partner: UNT Libraries Government Documents Department

New perspectives on the damage estimation for buried pipeline systems due to seismic wave propagation

Description: Over the past three decades, seismic fragility fonnulations for buried pipeline systems have been developed following two tendencies: the use of earthquake damage scenarios from several pipeline systems to create general pipeline fragility functions; and, the use of damage scenarios from one pipeline system to create specific-system fragility functions. In this paper, the advantages and disadvantages of both tendencies are analyzed and discussed; in addition, a summary of what can be considered the new challenges for developing better pipeline seismic fragility formulations is discussed. The most important conclusion of this paper states that more efforts are needed to improve the estimation of transient ground strain -the main cause of pipeline damage due to seismic wave propagation; with relevant advances in that research field, new and better fragility formulations could be developed.
Date: January 1, 2009
Creator: Pineda Porras, Omar Andrey
Partner: UNT Libraries Government Documents Department

Scale-up in Poroelastic System and Applications to Reservoirs

Description: A fundamental problem of heterogeneous systems is that the macroscale behavior is not necessarily well-described by equations familiar to us at the meso- or microscale. In relatively simple cases like electrical conduction and elasticity, it is hue that the equations describing macroscale behavior take the same form as those at the microscale. But in more complex systems, these simple results do not hold. Consider fluid flow in porous media where the microscale behavior is well-described by Navier-Stokes' equations for liquid in the pores while the macroscale behavior instead obeys Darcy's equation. Rigorous methods for establishing the form of such equations for macroscale behavior include multiscale homogenization methods and also the volume averaging method. In addition, it has been shown that Biot's equations of poroelasticity follow in a scale-up of the microscale equations of elasticity coupled to Navier-Stokes. Laboratory measurements have shown that Biot's equations indeed hold for simple systems but heterogeneous systems can have quite different behavior. So the question arises whether there is yet another level of scale-up needed to arrive at equations valid for the reservoir scale? And if so, do these equations take the form of Biot's equations or some other form? We will discuss these issues and show that the double-porosity equations play a special role in the scale-up to equations describing reservoir behavior, for fluid pumping, geomechanics, as well as seismic wave propagation.
Date: July 1, 2003
Creator: Berryman, J G
Partner: UNT Libraries Government Documents Department

Analysis of thomsen parameters for finely layered VTI media

Description: The range of Thomsen`s anisotropy parameters {epsilon} and {delta} for vertical transversely isotropic (VTI) media when the anisotropy is due to fine layering of isotropic elas-tic materials is considered. We show that {epsilon} lies in the range -3/8 {<=} {epsilon} {<=} {1/2}[<v{sub p}{sup 2}><v{sup p}{sup -2}>-1], for finely lay-ered media having constant density; smaller positive and all negative values of {epsilon} occur for media with large fluctuations in the Lam{acute e} parameter {lambda} We show that sign({delta}) = sign (<v{sub p}{sup -2}> - <v{sub s}{sup -2}><v{sub s}{sup 2}/v{sub p}{sup 2}>) for constant density media, so {delta} can be either positive or negative. Among all theoretically possible random media, posi-tive and negative {delta} are equally likely in finely layered media limited to two types of constituent layers. Lay-ered media having large fluctuations in Lam{acute e} {lambda} are the ones most likely to have positive {delta}. Since Gassmann`s results for fluid-saturated porous media show that the effects of fluids influence only the {lambda} Lam{acute e} constant, not the shear modulus {mu}, these results suggest that positive {delta} occurring together with positive but small {epsilon} may be indicative of changing fluid content in layered earth.
Date: April 1, 1997
Creator: Berryman, J.G. & Berge, P.A.
Partner: UNT Libraries Government Documents Department

Preliminary regional magnitude in the Middle East Region using narrowband Lg coda envelopes

Description: Because many regional seismic discriminants are functions of magnitude, it is important to obtain a stable measurement especially for smaller events that will likely have very limited station coverage. We have collected and analyzed regional broad band waveforms from stations in the middle east region for the purpose of calibrating a stable regional magnitude scale that can be applied to events that are too small to detect teleseismically. Our approach is to obtain frequency-dependent empirical Greens function coda envelopes for narrow frequency bands that can be used to correct for gross path effects. We make the assumption that the moment-rate spectra are generally flat below{approximately}2 Hz for these events smaller than Mw{approximately}3.5. In a least squares sense, we obtain frequency-dependent corrections to the Lg coda measurements to fit the scalar moment estimates. These frequency-dependent corrections remove the effects of the S-to-Lg coda transfer function, thus correcting back to the S-wave source spectra. Due to the averaging nature of Lg coda waves we are then able to obtain a stable single-station estimate of the source spectra.To avoid regional biases we tie our coda envelope amplitude measurements to seismic moments obtained from long period 1-D waveform modeling for moderate sized earthquakes (A4w-3.5.- 4.5). Most importantly, we can now apply the same corrections to significantly smaller events that cannot be observed teleseismically. Our empirical approach takes into account scattering,absorption, and waveguide losses as well as frequency-dependent site effects.Moreover, the use of the coda envelope mitigates the undesirable effects of source anisotropy, random site interference, path variability, and directivity that plague direct wave measurements. This approach was successfully applied to other regions where it was observed that the coda-derived Mw estimates showed significantly smaller dependence on lateral path variation and source radiation anisotropy than the more conventional approaches such as mb(Pg),mb(Lg),and teleseismic mb.
Date: July 1, 1997
Creator: Mayeda, K. & Walter, W.R.
Partner: UNT Libraries Government Documents Department

Identifying structures in clouds of induced microseismic events

Description: A method for finding improved relative locations of microearthquakes accompanying fluid production and injection is presented. The method is based on the assumption that the microearthquake locations are more clustered than found when events are located using conventional techniques. By allowing the rms misfit between measured arrival times and predicted arrival times to increase if events move closer together, the authors find that there is more structure in the pattern of seismic locations. The method is demonstrated using a dataset of microearthquakes induced by hydraulic fracturing. The authors find that structures found using relative arrival times of events having similar waveforms to find improved relative locations of events can also be recovered using the new inversion method but without the laborious repicking procedure. The method provides improved relative locations and hence, an improved image of the structure within the seismic zone that may allow for a better relation between microearthquake locations and zones of increased fluid permeability to be found.
Date: July 1, 1997
Creator: Fehler, M.; House, L. & Phillips, W.S.
Partner: UNT Libraries Government Documents Department

Anomalous wave propagation across the South Caspian Basin

Description: The Caspian basin blocks the propagation of the regional seismic phase Lg and this has importance consequences for seismic discrimination in the Middle East. Intermediate period surface waves propagating across the basin are also severely affected. In a separate study we have developed a crustal model of the south Caspian basin and the surrounding region. The crust of the basin consists of 15-25 km of low velocity, highly attenuating sediments lying on high velocity crystalline crust. The Moho beneath the basin is at a depth of about 30 km as compared to about 50 km in the surrounding region. In this study we used an idealized rendition of this crustal model to compute hybrid normal mode finite difference synthetic seismograms to identify the features of the Caspian basin which lead to the seismic blockage. Of the various features of the basin, the thickness and attenuation of the sediments appear to be the dominant blocking mechanism.
Date: October 1, 1997
Creator: Priestly, K.; Patton, H.J. & Schultz, C.
Partner: UNT Libraries Government Documents Department

Optimized filtering of regional and teleseismic seismograms: results of maximizing SNR measurements from the wavelet transform and filter banks

Description: Development of a worldwide network to monitor seismic activity requires deployment of seismic sensors in areas which have not been well studied or may have from available recordings. Development and testing of detection and discrimination algorithms requires a robust representative set of calibrated seismic events for a given region. Utilizing events with poor signal-to-noise (SNR) can add significant numbers to usable data sets, but these events must first be adequately filtered. Source and path effects can make this a difficult task as filtering demands are highly varied as a function of distance, event magnitude, bearing, depth etc. For a given region, conventional methods of filter selection can be quite subjective and may require intensive analysis of many events. In addition, filter parameters are often overly generalized or contain complicated switching. We have developed a method to provide an optimized filter for any regional or teleseismically recorded event. Recorded seismic signals contain arrival energy which is localized in frequency and time. Localized temporal signals whose frequency content is different from the frequency content of the pre-arrival record are identified using rms power measurements. The method is based on the decomposition of a time series into a set of time series signals or scales. Each scale represents a time-frequency band with a constant Q. SNR is calculated for a pre-event noise window and for a window estimated to contain the arrival. Scales with high SNR are used to indicate the band pass limits for the optimized filter.The results offer a significant improvement in SNR particularly for low SNR events. Our method provides a straightforward, optimized filter which can be immediately applied to unknown regions as knowledge of the geophysical characteristics is not required. The filtered signals can be used to map the seismic frequency response of a region and may provide improvements ...
Date: July 15, 1997
Creator: Leach, R.R.; Schultz, C. & Dowla, F.
Partner: UNT Libraries Government Documents Department

Quadratic negative evidence discrimination

Description: This paper develops regional discrimination methods which use information inherent in phase magnitudes that are unmeasurable due to small amplitudes and/or high noise levels. The methods are enhancements to teleseismic techniques proposed by, and are extended to regional discrimination. Events observed at teleseismic distances are effectively identified with the M{sub s} vs m{sub b} discriminant because relative to the pressure wave energy (m{sub b}) of an event, an earthquake generates more shear wave energy (M{sub s}) than does an explosion. For some teleseismic events, the M{sub s} magnitude is difficult to measure and is known only to be below a threshold . With M{sub s} unmeasurable, the M{sub s} vs m{sub b} discriminant cannot be formed. However, if the M{sub s} is sufficiently small relative to a measured m{sub b}, then the event is still likely to be an explosion. The methods presented in this report are developed for a single seismic station, and make use of empirical evidence in the regional L{sub g} vs p{sub g} discriminant. The L{sub g} vs p{sub g} discriminant is analogous to the teleseismic M{sub s} vs m{sub b} discriminant.
Date: May 1, 1997
Creator: Anderson, D.N.; Redgate, T.; Anderson, K.K.; Rohay, A.C. & Ryan, F.M.
Partner: UNT Libraries Government Documents Department

Comments on the geophysics paper -- Multiparameter l(1) norm waveform fitting: Interpretation of Gulf of Mexico reflection seismograms: by H. Djikpesse and A. Tarantola

Description: In their recent paper, Djikpesse and Tarantola (Geophysics 65 (4) pp. 1023-1035, hereinafter D and T) raise a central question about geophysical inversion: how accurately must the physics of seismic waves in the Earth be modeled in order that inversion succeed? Two general criteria for successful inversion appear in D and T's discussion: fit of predicted to observed data, and prediction of Earth structure. The hypothesis underlying inversion is that these criteria are unextricably linked, so that data fit should lead to accurate inference of subsurface features. The authors have also worked on the data discussed in D and T, using different modeling choices and inversion algorithms but also achieving quite successful inversions, in both senses. They feel that a brief comparison of methods and results might highlight the subtle relation between accuracy in modeling and success in inversion as well as raising questions about the appropriateness of D and T's modeling and inversion choices.
Date: January 3, 2000
Creator: Minkoff, S.E. & Symes, W.W.
Partner: UNT Libraries Government Documents Department