Geology topics

R. D. Miller

Publications and source records attributed to R. D. Miller.

At least 37 records · Page 2Linked to original sources

USGS2007

Applications of the JARS method to study levee sites in southern Texas and southern New Mexico

We apply the joint analysis of refractions with surface waves (JARS) method to several sites and compare its results to traditional refraction-tomography methods in efforts of finding a more realistic solution to the inverse refraction-traveltime problem. The JARS method uses a reference model, derived from surface-wave shear-wave velocity estimates, as a constraint. In all of the cases JARS estimates appear more realistic than those from the conventional refraction-tomography methods. As a result, we consider, the JARS algorithm as the preferred method for finding solutions to the inverse refraction-tomography problems. ?? 2007 Society of Exploration Geophysicists.

Conference Paper↗

USGS2007

Generating an image of dispersive energy by frequency decomposition and slant stacking

We present a new algorithm for calculating an image of dispersive energy in the frequency-velocity (f-v) domain. The frequency decomposition is first applied to a shot gather in the offset-time domain to stretch impulsive data into pseudo-vibroseis data or frequency-swept data. Because there is a deterministic relationship between frequency and time in a sweep used in the frequency decomposition, the first step theoretically completes the transform from time to frequency. The slant stacking is then performed on the frequency-swept data to complete the transform from offset to velocity. This simple two-step algorithm generates an image of dispersive energy in the f-v domain. The straightforward transform only uses offset information of data so that this algorithm can be applied to data acquired with arbitrary geophone-acquisition geometry. Examples of synthetic and real-world data demonstrate that this algorithm generates accurate images of dispersive energy of the fundamental as well as higher modes. ?? Birkha??user Verlag, Basel, 2007.

Pure and Applied Geophysics↗

USGS2007

Feasibility of detecting near-surface feature with Rayleigh-wave diffraction

Detection of near-surfaces features such as voids and faults is challenging due to the complexity of near-surface materials and the limited resolution of geophysical methods. Although multichannel, high-frequency, surface-wave techniques can provide reliable shear (S)-wave velocities in different geological settings, they are not suitable for detecting voids directly based on anomalies of the S-wave velocity because of limitations on the resolution of S-wave velocity profiles inverted from surface-wave phase velocities. Therefore, we studied the feasibility of directly detecting near-surfaces features with surface-wave diffractions. Based on the properties of surface waves, we have derived a Rayleigh-wave diffraction traveltime equation. We also have solved the equation for the depth to the top of a void and an average velocity of Rayleigh waves. Using these equations, the depth to the top of a void/fault can be determined based on traveltime data from a diffraction curve. In practice, only two diffraction times are necessary to define the depth to the top of a void/fault and the average Rayleigh-wave velocity that generates the diffraction curve. We used four two-dimensional square voids to demonstrate the feasibility of detecting a void with Rayleigh-wave diffractions: a 2??m by 2??m with a depth to the top of the void of 2??m, 4??m by 4??m with a depth to the top of the void of 7??m, and 6??m by 6??m with depths to the top of the void 12??m and 17??m. We also modeled surface waves due to a vertical fault. Rayleigh-wave diffractions were recognizable for all these models after FK filtering was applied to the synthetic data. The Rayleigh-wave diffraction traveltime equation was verified by the modeled data. Modeling results suggested that FK filtering is critical to enhance diffracted surface waves. A real-world example is presented to show how to utilize the derived equation of surface-wave diffractions. ?? 2006 Elsevier B.V. All rights reserved.

Journal of Applied Geophysics↗

USGS2007

Multichannel analysis of surface waves (MASW) - Active and passive methods

The conventional seismic approaches for near-surface investigation have usually been either high-resolution reflection or refraction surveys that deal with a depth range of a few tens to hundreds meters. Seismic signals from these surveys consist of wavelets with frequencies higher than 50 Hz. The multichannel analysis of surface waves (MASW) method deals with surface waves in the lower frequencies (e.g., 1-30 Hz) and uses a much shallower depth range of investigation (e.g., a few to a few tens of meters). ?? 2007 Society of Exploration Geophysicists.

Leading Edge (Tulsa, OK)↗

USGS2007

Numerical investigation of implementation of air-earth boundary by acoustic-elastic boundary approach

The need for incorporating the traction-free condition at the air-earth boundary for finite-difference modeling of seismic wave propagation has been discussed widely. A new implementation has been developed for simulating elastic wave propagation in which the free-surface condition is replaced by an explicit acoustic-elastic boundary. Detailed comparisons of seismograms with different implementations for the air-earth boundary were undertaken using the (2,2) (the finite-difference operators are second order in time and space) and the (2,6) (second order in time and sixth order in space) standard staggered-grid (SSG) schemes. Methods used in these comparisons to define the air-earth boundary included the stress image method (SIM), the heterogeneous approach, the scheme of modifying material properties based on transversely isotropic medium approach, the acoustic-elastic boundary approach, and an analytical approach. The method proposed achieves the same or higher accuracy of modeled body waves relative to the SIM. Rayleigh waves calculated using the explicit acoustic-elastic boundary approach differ slightly from those calculated using the SIM. Numerical results indicate that when using the (2,2) SSG scheme for SIM and our new method, a spatial step of 16 points per minimum wavelength is sufficient to achieve 90% accuracy; 32 points per minimum wavelength achieves 95% accuracy in modeled Rayleigh waves. When using the (2,6) SSG scheme for the two methods, a spatial step of eight points per minimum wavelength achieves 95% accuracy in modeled Rayleigh waves. Our proposed method is physically reasonable and, based on dispersive analysis of simulated seismographs from a layered half-space model, is highly accurate. As a bonus, our proposed method is easy to program and slightly faster than the SIM. ?? 2007 Society of Exploration Geophysicists.

Geophysics↗

USGS2007

Improving resolution and understanding controls on GPR response in carbonate strata: Implications for attribute analysis

For more than a decade, environmental, engineering, groundwater, and shallow stratigraphic studies have demonstrated and advanced the usefulness of ground-penetrating radar (GPR) in lithified and unconsolidated sedimentary deposits (e.g., see Neal, 2004 and references therein). Despite the advances, important questions still remain on factors that control the actual appearance and characteristics of GPR reflections and diffractions in any given setting. ?? 2007 Society of Exploration Geophysicists.

Leading Edge (Tulsa, OK)↗

USGS2006

Rayleigh-wave diffractions due to a void in the layered half space

Void detection is challenging due to the complexity of near-surface materials and the limited resolution of geophysical methods. Although multichannel, high-frequency, surface-wave techniques can provide reliable shear (S)-wave velocities in different geological settings, they are not suitable for detecting voids directly based on anomalies of the S-wave velocity because of limitations on the resolution of S-wave velocity profiles inverted from surface-wave phase velocities. Xia et al. (2006a) derived a Rayleigh-wave diffraction traveltime equation due to a void in the homogeneous half space. Encouraging results of directly detecting a void from Rayleigh-wave diffractions were presented (Xia et al., 2006a). In this paper we used four two-dimensional square voids in the layered half space to demonstrate the feasibility of detecting a void with Rayleigh-wave diffractions. Rayleigh-wave diffractions were recognizable for all these models after removing direct surface waves by F-K filtering. We evaluate the feasibility of applying the Rayleigh-wave diffraction traveltime equation to a void in the layered earth model. The phase velocity of diffracted Rayleigh waves is predominately determined by surrounding materials of a void. The modeling results demonstrate that the Rayleigh-wave diffraction traveltime equation due to a void in the homogeneous half space can be applied to the case of a void in the layered half space. In practice, only two diffraction times are necessary to define the depth to the top of a void and the average velocity of diffracted Rayleigh waves. ?? 2005 Society of Exploration Geophysicists.

SEG Technical Program Expanded Abstracts↗

USGS2006

High-resolution seismic-reflection imaging 25 years of change in I-70 sinkhole, Russell County, Kansas

Time-lapse seismic reflection imaging improved our understanding of the consistent, gradual surface subsidence ongoing at two sinkholes in the Gorham Oilfield discovered beneath a stretch of Interstate Highway 70 through Russell and Ellis Counties in Kansas in 1966. With subsidence occurring at a rate of around 10 cm per year since discovery, monitoring has been beneficial to ensure public safety and optimize maintenance. A miniSOSIE reflection survey conducted in 1980 delineated the affected subsurface and successfully predicted development of a third sinkhole at this site. In 2004 and 2005 a high-resolution vibroseis survey was completed to ascertain current conditions of the subsurface, rate and pattern of growth since 1980, and potential for continued growth. With time and improved understanding of the salt dissolution affected subsurface in this area it appears that these features represent little risk to the public from catastrophic failure. However, from an operational perspective the Kansas Department of Transportation should expect continued subsidence, with future increases in surface area likely at a slightly reduced vertical rate. Seismic characteristics appear empirically consistent with gradual earth material compaction/settling. ?? 2005 Society of Exploration Geophysicists.

SEG Technical Program Expanded Abstracts↗

USGS2006

Repeatability observations from a time-lapse seismic survey

Time-lapse seismic surveys have proven extremely valuable in recent years, having numerous economical and environmental applications. To fully utilize this monitoring technique, problems associated with recording repeatability must be minimized. Much work has been done to equalize data from one survey to the next via processing techniques (Huang et al., 1998). The purpose of this study is to investigate the potential for minimized processing, allowing study of extremely small changes in subsurface characteristics. The goal is to evaluate source and receiver terrain combination to optimize signal repeatability, and to improve deconvolution with the ground force to suppress different types of noise and increase repeatability. ?? 2005 Society of Exploration Geophysicists.

SEG Technical Program Expanded Abstracts↗

USGS2006

Time-lapse seismic study of levees in southern New Mexico

The primary objective of this work was to measure changes in compressional- (Vp) and shear-wave (Vs) velocities in an earthen levee during a ponding experiment designed to simulate flood conditions on the Rio Grande in south New Mexico. Although similar to such experiment, performed an year earlier on the Rio Grande in south Texas, the levee seismic response results are different. This work was similar to previous Preliminary testing at three levee sites, all within a 1 km radius and each with unique physical, EM, and core characteristics, was completed and a single low-conductivity, highly fractured site was selected for investigation. Several different types of seismic data were recorded. Seismic data analysis techniques appraised included P-refraction tomography and Rayleigh surface-wave analysis using multichannel analysis of surface waves (MASW). P-wave velocity change (decrease) was rapid and isolated to one section within the pool confines, which already had anomalously high velocity most likely related to burrowing animals modification of the levee structure. S-wave velocity change was gradual and could be observed along the whole width of the pond within and below the levee. The results within the levee sand core were consistent with the observations of sand S-wave velocity changed due to saturation. ?? 2005 Society of Exploration Geophysicists.

SEG Technical Program Expanded Abstracts↗

USGS2006

Estimation of elastic moduli in a compressible Gibson half-space by inverting Rayleigh-wave phase velocity

A Gibson half-space model (a non-layered Earth model) has the shear modulus varying linearly with depth in an inhomogeneous elastic half-space. In a half-space of sedimentary granular soil under a geostatic state of initial stress, the density and the Poisson's ratio do not vary considerably with depth. In such an Earth body, the dynamic shear modulus is the parameter that mainly affects the dispersion of propagating waves. We have estimated shear-wave velocities in the compressible Gibson half-space by inverting Rayleigh-wave phase velocities. An analytical dispersion law of Rayleigh-type waves in a compressible Gibson half-space is given in an algebraic form, which makes our inversion process extremely simple and fast. The convergence of the weighted damping solution is guaranteed through selection of the damping factor using the Levenberg-Marquardt method. Calculation efficiency is achieved by reconstructing a weighted damping solution using singular value decomposition techniques. The main advantage of this algorithm is that only three parameters define the compressible Gibson half-space model. Theoretically, to determine the model by the inversion, only three Rayleigh-wave phase velocities at different frequencies are required. This is useful in practice where Rayleigh-wave energy is only developed in a limited frequency range or at certain frequencies as data acquired at manmade structures such as dams and levees. Two real examples are presented and verified by borehole S-wave velocity measurements. The results of these real examples are also compared with the results of the layered-Earth model. ?? Springer 2006.

Surveys in Geophysics↗

USGS2006

Quantitative estimation of minimum offset for multichannel surface-wave survey with actively exciting source

Multichannel analysis of surface waves is a developing method widely used in shallow subsurface investigations. The field procedures and related parameters are very important for successful applications. Among these parameters, the source-receiver offset range is seldom discussed in theory and normally determined by empirical or semi-quantitative methods in current practice. This paper discusses the problem from a theoretical perspective. A formula for quantitatively evaluating a layered homogenous elastic model was developed. The analytical results based on simple models and experimental data demonstrate that the formula is correct for surface wave surveys for near-surface applications. ?? 2005 Elsevier B.V. All rights reserved.

Journal of Applied Geophysics↗

USGS2006

Catastrophic sinkhole formation in Kansas: A case study

Sinkholes represent a hazard to property and human safety in a wide variety of geologic settings across the globe. In most cases, the subsidence rate of a sinkhole represents the most significant potential impact and risk to public safety. Since 1979, the Kansas Geological Survey has studied numerous sinkholes using high-resolution seismic reflection in an attempt to better understand the mechanisms that control their formation. Most sinkholes in central Kansas form as a result of dissolution of the Permian Hutchinson salt (Figure 1). The fluid source and associated pathway responsible for leaching these bedded evaporites have been natural, anthropogenic, and a combination of both. Sinkholes have been a part of the landscape in the North American midcontinent long before modern oil, gas, and mineral exploration, but clearly the activities of man have played a significant role in both increasing the number of sinkholes and affecting their subsidence rates.

Leading Edge (Tulsa, OK)↗

USGS2006

Delineating a shallow fault zone and dipping bed rock strata using multichannal analysis of surface waves with a land streamer

The multichannel analysis of surface waves (MASW) seismic method was used to delineate a fault zone and gently dipping sedimentary bedrock at a site overlain by several meters of regolith. Seismic data were collected rapidly and inexpensively using a towed 30-channel land streamer and a rubberband-accelerated weight-drop seismic source. Data processed using the MASW method imaged the subsurface to a depth of about 20 m "> 20 m 20m and allowed detection of the overburden, gross bedding features, and fault zone. The fault zone was characterized by a lower shear-wave velocity ( V s ) "> ( V s ) (Vs) than the competent bedrock, consistent with a large-scale fault, secondary fractures, and in-situ weathering. The MASW 2D V s "> V s Vs section was further interpreted to identify dipping beds consistent with local geologic mapping. Mapping of shallow-fault zones and dipping sedimentary rock substantially extends the applications of the MASW method.

New Jersey↗

USGS2006

Joint analysis of refractions with surface waves: An inverse solution to the refraction-traveltime problem

We describe a possible solution to the inverse refraction-traveltime problem (IRTP) that reduces the range of possible solutions (nonuniqueness). This approach uses a reference model, derived from surface-wave shear-wave velocity estimates, as a constraint. The application of the joint analysis of refractions with surface waves (JARS) method provided a more realistic solution than the conventional refraction/tomography methods, which did not benefit from a reference model derived from real data. This confirmed our conclusion that the proposed method is an advancement in the IRTP analysis. The unique basic principles of the JARS method might be applicable to other inverse geophysical problems. ?? 2006 Society of Exploration Geophysicists.

Geophysics↗

USGS2005

The inverse problem of refraction travel times, part I: Types of Geophysical Nonuniqueness through Minimization

In a set of two papers we study the inverse problem of refraction travel times. The purpose of this work is to use the study as a basis for development of more sophisticated methods for finding more reliable solutions to the inverse problem of refraction travel times, which is known to be nonunique. The first paper, "Types of Geophysical Nonuniqueness through Minimization," emphasizes the existence of different forms of nonuniqueness in the realm of inverse geophysical problems. Each type of nonuniqueness requires a different type and amount of a priori information to acquire a reliable solution. Based on such coupling, a nonuniqueness classification is designed. Therefore, since most inverse geophysical problems are nonunique, each inverse problem must be studied to define what type of nonuniqueness it belongs to and thus determine what type of a priori information is necessary to find a realistic solution. The second paper, "Quantifying Refraction Nonuniqueness Using a Three-layer Model," serves as an example of such an approach. However, its main purpose is to provide a better understanding of the inverse refraction problem by studying the type of nonuniqueness it possesses. An approach for obtaining a realistic solution to the inverse refraction problem is planned to be offered in a third paper that is in preparation. The main goal of this paper is to redefine the existing generalized notion of nonuniqueness and a priori information by offering a classified, discriminate structure. Nonuniqueness is often encountered when trying to solve inverse problems. However, possible nonuniqueness diversity is typically neglected and nonuniqueness is regarded as a whole, as an unpleasant "black box" and is approached in the same manner by applying smoothing constraints, damping constraints with respect to the solution increment and, rarely, damping constraints with respect to some sparse reference information about the true parameters. In practice, when solving geophysical problems different types of nonuniqueness exist, and thus there are different ways to solve the problems. Nonuniqueness is usually regarded as due to data error, assuming the true geology is acceptably approximated by simple mathematical models. Compounding the nonlinear problems, geophysical applications routinely exhibit exact-data nonuniqueness even for models with very few parameters adding to the nonuniqueness due to data error. While nonuniqueness variations have been defined earlier, they have not been linked to specific use of a priori information necessary to resolve each case. Four types of nonuniqueness, typical for minimization problems are defined with the corresponding methods for inclusion of a priori information to find a realistic solution without resorting to a non-discriminative approach. The above-developed stand-alone classification is expected to be helpful when solving any geophysical inverse problems. ?? Birkha??user Verlag, Basel, 2005.

Pure and Applied Geophysics↗

USGS2005

The inverse problem of refraction travel times, part II: Quantifying refraction nonuniqueness using a three-layer model

This paper is the second of a set of two papers in which we study the inverse refraction problem. The first paper, "Types of Geophysical Nonuniqueness through Minimization," studies and classifies the types of nonuniqueness that exist when solving inverse problems depending on the participation of a priori information required to obtain reliable solutions of inverse geophysical problems. In view of the classification developed, in this paper we study the type of nonuniqueness associated with the inverse refraction problem. An approach for obtaining a realistic solution to the inverse refraction problem is offered in a third paper that is in preparation. The nonuniqueness of the inverse refraction problem is examined by using a simple three-layer model. Like many other inverse geophysical problems, the inverse refraction problem does not have a unique solution. Conventionally, nonuniqueness is considered to be a result of insufficient data and/or error in the data, for any fixed number of model parameters. This study illustrates that even for overdetermined and error free data, nonlinear inverse refraction problems exhibit exact-data nonuniqueness, which further complicates the problem of nonuniqueness. By evaluating the nonuniqueness of the inverse refraction problem, this paper targets the improvement of refraction inversion algorithms, and as a result, the achievement of more realistic solutions. The nonuniqueness of the inverse refraction problem is examined initially by using a simple three-layer model. The observations and conclusions of the three-layer model nonuniqueness study are used to evaluate the nonuniqueness of more complicated n-layer models and multi-parameter cell models such as in refraction tomography. For any fixed number of model parameters, the inverse refraction problem exhibits continuous ranges of exact-data nonuniqueness. Such an unfavorable type of nonuniqueness can be uniquely solved only by providing abundant a priori information. Insufficient a priori information during the inversion is the reason why refraction methods often may not produce desired results or even fail. This work also demonstrates that the application of the smoothing constraints, typical when solving ill-posed inverse problems, has a dual and contradictory role when applied to the ill-posed inverse problem of refraction travel times. This observation indicates that smoothing constraints may play such a two-fold role when applied to other inverse problems. Other factors that contribute to inverse-refraction-problem nonuniqueness are also considered, including indeterminacy, statistical data-error distribution, numerical error and instability, finite data, and model parameters. ?? Birkha??user Verlag, Basel, 2005.

Pure and Applied Geophysics↗

USGS2005

A moving hum filter to suppress rotor noise in high-resolution airborne magnetic data

A unique filtering approach is developed to eliminate helicopter rotor noise. It is designed to suppress harmonic noise from a rotor that varies slightly in amplitude, phase, and frequency and that contaminates aero-magnetic data. The filter provides a powerful harmonic noise-suppression tool for data acquired with modern large-dynamic-range recording systems. This three-step approach - polynomial fitting, bandpass filtering, and rotor-noise synthesis - significantly reduces rotor noise without altering the spectra of signals of interest. Two steps before hum filtering - polynomial fitting and bandpass filtering - are critical to accurately model the weak rotor noise. During rotor-noise synthesis, amplitude, phase, and frequency are determined. Data are processed segment by segment so that there is no limit on the length of data. The segment length changes dynamically along a line based on modeling results. Modeling the rotor noise is stable and efficient. Real-world data examples demonstrate that this method can suppress rotor noise by more than 95% when implemented in an aeromagnetic data-processing flow. ?? 2005 Society of Exploration Geophysicists. All rights reserved.

Geophysics↗