Open Access. Powered by Scholars. Published by Universities.®
- Keyword
-
- Seismology (3)
- Damping (2)
- Ground penetrating radar (2)
- Groundwater (2)
- Comparative studies (1)
-
- Compressibility (1)
- Contamination (1)
- Data acquisition (1)
- Earth crust (1)
- Faulting (1)
- Geophysical signal processing (1)
- Image processing (1)
- Permittivity (1)
- Radar theory (1)
- Rocks (1)
- Saturated soils (1)
- Seismic waves (1)
- Soil compression (1)
- Soil permeability (1)
- Stratigraphy (1)
- Unsaturated soils (1)
- Wave propagation (1)
- Well logging (1)
Articles 1 - 8 of 8
Full-Text Articles in Entire DC Network
Imaging Complex Structure In Shallow Seismic-Reflection Data Using Prestack Depth Migration, John H. Bradford, Lee M. Liberty, Mitchell W. Lyle, William P. Clement, Scott Hess
Imaging Complex Structure In Shallow Seismic-Reflection Data Using Prestack Depth Migration, John H. Bradford, Lee M. Liberty, Mitchell W. Lyle, William P. Clement, Scott Hess
CGISS Publications and Presentations
Prestack depth migration (PSDM) analysis has the potential to significantly improve the accuracy of both shallow seismic reflection images and the measured velocity distributions. In a study designed to image faults in the Alvord Basin, Oregon, at depths from 25–1000 m, PSDM produced a detailed reflection image over the full target depth range. In contrast, poststack time migration produced significant migration artifacts in the upper 100 m that obscured reflection events and limited the structural interpretation in the shallow section. Additionally, an abrupt increase from ~2500 to >3000 m/s in the PSDM velocity model constrained the interpretation of the transition …
Ground-Penetrating Radar Theory And Application Of Thin-Bed Offset-Dependent Reflectivity, John H. Bradford, Jacob C. Deeds
Ground-Penetrating Radar Theory And Application Of Thin-Bed Offset-Dependent Reflectivity, John H. Bradford, Jacob C. Deeds
CGISS Publications and Presentations
Offset-dependent reflectivity or amplitude-variationwith- offset (AVO) analysis of ground-penetrating radar (GPR) data may improve the resolution of subsurface dielectric permittivity estimates. A horizontally stratified medium has a limiting layer thickness below which thin-bed AVO analysis is necessary. For a typical GPR signal, this limit is approximately 0.75 of the characteristic wavelength of the signal. Our approach to modeling the GPR thin-bed response is a broadband, frequency-dependent computation that utilizes an analytical solution to the three-interface reflectivity and is easy to implement for either transverse electric (TE) or transverse magnetic (TM) polarizations. The AVO curves for TE and TM modes differ …
Investigating The Stratigraphy Of An Alluvial Aquifer Using Crosswell Seismic Traveltime Tomography, Geoff J.M. Moret, Michael D. Knoll, Warren Barrash, William P. Clement
Investigating The Stratigraphy Of An Alluvial Aquifer Using Crosswell Seismic Traveltime Tomography, Geoff J.M. Moret, Michael D. Knoll, Warren Barrash, William P. Clement
CGISS Publications and Presentations
In this study, we investigate the use of crosswell P-wave seismic tomography to obtain spatially extensive information about subsurface sedimentary architecture and heterogeneity in alluvial aquifers. Our field site was a research wellfield in an unconfined aquifer near Boise, Idaho. The aquifer consists of a ~ 20-m-thick sequence of alluvial cobble- and-sand deposits, which have been subdivided into five stratigraphic units based on neutron porosity logs, grainsize analysis, and radar reflection data. We collected crosswell and borehole-to-surface seismic data in wells 17.1 m apart. We carefully considered the impact of well deviation, data quality control, and the choice of inversion …
Applying Reflection Tomography In The Postmigration Domain To Multifold Ground-Penetrating Radar Data, John H. Bradford
Applying Reflection Tomography In The Postmigration Domain To Multifold Ground-Penetrating Radar Data, John H. Bradford
CGISS Publications and Presentations
Acquisition and processing of multifold ground-penetrating radar (GPR) data enable detailed measurements of lateral velocity variability. The velocities constrain interpretation of subsurface materials and lead to significant improvement in image accuracy when coupled with prestack depth migration (PSDM). Reflection tomography in the postmigration domain was introduced in the early 1990s for velocity estimation in seismic reflection. This robust, accurate method is directly applicable in multifold GPR imaging. At a contaminated waste facility within the U.S. Department of Energy’s Hanford site in Washington, the method is used to identify significant lateral and vertical velocity heterogeneity associated with infilled waste pits. Using …
Relating Damping To Soil Permeability, Paul Michaels
Relating Damping To Soil Permeability, Paul Michaels
CGISS Publications and Presentations
Published comparisons of complex moduli in dry and saturated soils have shown that viscous behavior is only evident when a sufficiently massive viscous fluid (like water) is present. That is, the loss tangent is frequency dependent for water saturated specimens, but nearly frequency independent for dry samples. While the Kelvin-Voigt (KV) representation of a soil captures the general viscous behavior using a dashpot, it fails to account for the possibly separate motions of the fluid and frame (there is only a single mass element). An alternative representation which separates the two masses, water and frame, is presented here. This Kelvin-Voigt-Maxwell-Biot …
Comparison Of Viscous Damping In Unsaturated Soils, Compression And Shear, Paul Michaels
Comparison Of Viscous Damping In Unsaturated Soils, Compression And Shear, Paul Michaels
CGISS Publications and Presentations
Geophysical down-hole surveys can be used to measure the small strain dynamic properties of soils by the effects these properties have on wave propagation. The relevant effects include amplitude decay (corrected for beam divergence) and velocity dispersion. In this paper, down-hole data collected during the GeoInstitute's Denver 2000 field day are presented and analyzed as a Kelvin-Voigt solid. Findings for these unsaturated soils include viscous damping and stiffness which differ significantly for shear and compressional waves. A strong viscous damping is observed in compression, but weak damping is presented in shear. Lumped parameter constitutive models are discussed which mathematically represent …
Seeing Through The Noise: Seismic Reflection Profiling In Urban Areas, Lee M. Liberty, Thomas L. Pratt, Scott S. Hess
Seeing Through The Noise: Seismic Reflection Profiling In Urban Areas, Lee M. Liberty, Thomas L. Pratt, Scott S. Hess
CGISS Publications and Presentations
Studies for urban hazard or resource assessment often take place in densely populated areas characterized by considerable cultural noise. These site conditions can severely compromise seismic reflection data quality. We have collected vibroseis and hammer (weight drop) seismic reflection data in a range of geologic conditions to image stratigraphy and structures in the upper one km along regional highways, city streets,and power line access roads. In addition to the challenges of safety and outreach, acquisition efforts along busy streets and highways often encounter poor receiver coupling and large-amplitude coherent noise from traffic and power lines. Although higher quality seismic reflection …
Crosshole Radar Tomography In An Alluvial Aquifer Nearboise, Idaho, William P. Clement, Warren Barrash
Crosshole Radar Tomography In An Alluvial Aquifer Nearboise, Idaho, William P. Clement, Warren Barrash
CGISS Publications and Presentations
To determine the distribution of heterogeneities in an unconfined aquifer in Boise, ID, we compute radar tomograms for three adjacent well pairs. The fluvial deposits consist of unconsolidated cobbles and sands. We used a curved‐ray, finite‐difference approximation to the eikonal equation to generate the forward model. The inversion uses a linearized, iterative scheme to determine the slowness distribution from the first arrival traveltimes. The tomograms consist of a sequence of layers representing the saturated aquifer. The velocities in this saturated zone range between 0.06 to 0.10 m/ns. We use a variety of methods to assess the reliability of our velocity …