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13th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 20 Feb 2000 - 24 Feb 2000
- Location: Arlington, Virginia, USA
- Published: 20 February 2000
21 - 40 of 140 results
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Geophysics And Arms Control At The Defense Threat Reduction Agency
Authors Anton M. Dainty and Karl VeithOne of the missions of the Defense Threat Reduction Agency (DTRA) is arms control treaty
monitoring in accordance with the U.S. Department of Defense requirements. An example is the
Comprehensive Nuclear Test Ban Treaty (CTBT), which mandates hydroacoustic, infrasonic
(low frequency sound), radionuclide, and seismic monitoring to ensure compliance. An
International Monitoring System (IMS) of over 300 sensors distributed worldwide is currently
under construction; DTRA is responsible for the 38 stations and one laboratory that the United
States will contribute to the IMS. An International Data Centre (IDC) in Vienna, Austria will
process the data from the IMS. The United States has agreed to provide the initial software for
the IDC through DTRA contracts. This involves a large effort in the automatic processing of the
continuous data stream from the IMS using sound geophysical principles.
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Darpa Counter Underground Facilities Program: Interests In Selected Geophysical Technologies
By Dan CressDARPA is investing in the science and technologies applicable to characterizing
underground facilities (UGFs). Examples of characterization information include
orientation and depth of structure, operational tempo, locations of umbilicals and systems
(power, water, airflow-vents), and changes in activity levels. Geophysical exploration
techniques are among the areas of interest to DARPA, including both passive and actively
induced signals capable of extracting any portion of the characterization information.
Example geophysical observables of interest include seismic, acoustic, and
electromagnetic data. These observables have been evaluated for a number of
geophysical applications in the past.
The DARPA investment in this area is directed at defining the performance limits
for singular observables and evaluation of the information gain achievable by exploiting
the correlation among these observables. A number of questions need to be answered.
What are the maximum performance ranges? How can correlation among sensors be
used to enhance signal to noise ? What are the accuracy limits for source location? How
many sensors are required to achieve a given performance level in particular classes of
environments and backgrounds? Can reliable information be obtained for estimating
source depth? What are the source options for active seismic or active electromagnetic
techniques? How does grounding effect the electromagnetic response for operational
facilities?
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Changing Role Of Geophysics- U.S. Bureau Of Reclamation
By Jerry WrightIn response to decisions on dam safety issues being directed to a risk based process
requiring probability hazard assessments, geophysical applications strive for quantifiable results,
estimates of detection limits and accuracy. Many geophysical methods are employed for
evaluation of existing structures as well as soil and rock foundations, corrosion protection for
pipelines, environmental and stream restoration, seismic monitoring and seismic hazard
assessment. Methods include seismic refraction, high resolution reflection, multiple surface
resistivity and self potential methods, ground penetrating radar, gravity/magnetics, borehole
geophysical logging, cross hole and down hole shear wave velocity measurements, and cross
hole and surface to surface seismic tomography. Seismic monitoring for site ground motion is
used to determine site response characteristics, early warning and emergency action systems, and
deep brine injection monitoring. Utilizing existing oil and gas exploration data aids seismic
source characterization in blind thrust fault evaluation. Research activities include cooperative
efforts with the Canadian Electric Association on Internal Diagnostics for Embankment Dams,
focusing on quantification of seismic, self potential, temperature, and resistivity methods. Other
research includes development of seismo-electric measurements for seepage path identification
and seismic tomography for imaging internal quality of concrete and embankment dams. Public
safety and economic decisions are being based on geophysical results requiring well planned
surveys, sound interpretations, and clear presentations, incorporating engineering and geologic
properties.
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Laboratory Velocity Measurements Used For Recovering Soil Distributions From Field Seismic Data
Authors Patricia A. Berge and Hugo Bertete-AguirreRecent advances in field methods make it possible to obtain high quality compressional (P) and
shear (S) velocity data for the shallow subsurface. Environmental and engineering problems
require new methods for interpreting the velocity data in terms of sub-surface soil distribution.
Recent advances in laboratory measurement techniques have provided high quality velocity data
for soils at low pressures that can be used to improve interpretation of field data. We show how
laboratory data can be used to infer lithology from field data. We use laboratory ultrasonic
velocity measurements from artificial soils made by combining various amounts of sand and peat
moss.
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The Use Of Continuous Surface Wave Method To Determine In-Situ Stiffness Profiles Within A Natural Terrain Setting In Hong Kong
Authors Lung S. Chan and Julie D. BellA continuous surface wave survey was conducted in conjunction with geotechnical investigation
in a characterisation study of a hillslope in Hong Kong. Rayleigh waves with frequencies that
modulated incrementally from 2 to 100 Hz were used to reconstruct in-situ stiffness profiles
along designated traverses. The phase velocity and the stiffness modulus were computed based
on phase angles recorded for the different frequencies by geophones. The stiffness profiles were
then used to delineate the interface between the overlying colluvium and the weathered bedrock
at the site. The colluvium generally has a relatively low but highly varying shear modulus while
the shear modulus of the underlying weathered bedrock increases linearly with depth, The
colluvium isopachs reconstructed based on the CSW results were consistent with results from
drillhole and trial pit records. Variations in the penetration range and the shape of the stiffness
profiles at different locations are probably caused by the varying boulder-matrix ratio in the
colluvium. The study shows that the CSW method can be an important supplementary method
for engineering geology ground investigation.
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Borehole Techniques To Subsurface Water Flow Characterization
More LessThe Department of Applied Geophysics, Charles University, Prague, has contributed to the
solution of hydrogeologic tasks since the 1960s. At present, research on well log analysis
techniques is focused on providing a basis for protection and optimization of withdrawals
from both surface and ground waters. Well-logging methods applied to hydrogeologic
formation evaluation provide information on the reservoir properties of the penetrated rocks,
groundwater quality and groundwater flow. This manuscript presents a discussion of some
geophysical techniques used for logging fluid-movement. In addition, application and
verification of the methods under various geologic and hydrogeologic conditions are provided
to demonstrate the effectiveness of logging for hydrogeological investigations.
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Constraining Hydrogeologic Models Using Geophysical Techniques: Case Study Fortymile Wash And Amargosa Desert, Southern Nevada
Authors David A. Farrell, Peter La Femina, Amit Armstrong, Stewart Sandberg and Noel RogersFortymile Wash and the Amargosa Desert are located along the groundwater flow path from
Yucca Mountain, Nevada, site of a proposed high-level nuclear waste repository. Groundwater
flow models developed for .these regions are poorly constrained due to limited spatial information
on hydraulic head, hydraulic conductivity, and hydrostratigraphy. To overcome some of these
limitations, an integrated geophysical survey utilizing the time-domain electromagnetic method,
the induced polarization method, the Schlumberger resistivity method, and the magnetic method,
was used to map the spatial continuity of the hydrostratigraphy and watertable elevation between
point measurement locations in the region. Simultaneous inversion of the data from these surveys
identified several discontinuities that showed good correlation to stratigraphic units and
waterlevels identified at point measurement locations. In addition, several areas were identified
where units either thickened, terminated, or shallowed. The information obtained from these
surveys is currently being used to better constrain groundwater models for the region.
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Geophysical And Hydrogeological Studies In A Coastal Plain Affected By Salt Water Intrusion
Gravity, electrical and reflection seismic surveys, along with classical hydrogeological
investigations, were carried out in a coastal plain affected by salt water intrusion, within
the framework of a project aimed at constructing a structural and hydrogeological model
of the area. Hydrogeological investigations provide data necessary for characterizing the
aquifers at a depth of a few tens meters and show the zone of high contamination.
Gravity surveying allowed the depth to the basement to be estimated and hence the
thickness of sediments and alluvium. Electrical and seismic reflection surveys proved
to be effective tools for recognizing deep aquifer characteristics and the complex
stratigraphic structure of the plain.
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Geophysical Signature Of Moisture Distributions In The Vadose Zone
Authors Paula Hahesy, Graham Heinson, Anthony L. Endres and John L. HutsonGeophysicists commonly have a simplistic view of the watertable as a sharp interface
between the vadose zone (i.e., unsaturated region) and the phreatic zone (i.e., saturated
region). In reality, this boundary is a transition zone where moisture content continuously
varies with depth. Since geophysical methods respond to the depth variation in water
content, the use of this simplistic model could lead to significant errors in the interpretation
of geophysical data. An improved model for the moisture content profile that incorporates
different soil structures and types would allow better interpretation of near-surface
geophysical surveys. In addition, this model would permit the extraction of important near
surface hydrological information from geophysical data.
In this study, a systematic analysis of the relationship between moisture content profile and
the response of commonly used near surface geophysical methods (i.e., resistivity sounding,
ground penetrating radar, electromagnetic induction and refraction seismics) has been
performed. Using a computational model that considers the water and chemical regime in the
vadose zone, the water content profiles for various soil types (synthetic and field) were
generated. The corresponding geophysical profiles were constructed using petrophysical
relationships for electrical conductivity, dielectric permittivity and acoustic velocity. The
resulting surface geophysical responses were computed for these geophysical profiles.
Inversion of this data attempted to recover input soil profiles.
The results of the theoretical work have been compared with geophysical data from the North
Adelaide Plains, South Australia. The geophysical surveys were conducted in regions of soil
corresponding to established profiles. This field data has been analysed, establishing
common characteristics between models and observed data and providing insight into
inadequacies in the prediction models and near surface geophysical theory.
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Integrated Geophysical Study Of Near-Surface Faults In The Wilcox Group, Texas, With Application To Lignite Mining
Authors Sara A. Satti, Mark E. Everett and Richard L. Gibsonthe form of lignite, a soft coal found close to the surface. Since Texas gas reserves could
become exhausted by 2040, lignite mining will continue to play a major role in meeting
state energy requirements. Lignite can be mined only in opencast operations which
represents a serious incursion into the landscape. To open up or expand a mine costs tens
of millions of dollars. It is therefore important both economically and environmentally to
investigate subsurface geological structures before expanding mine operations.
This paper describes the results of near-surface geophysical studies conducted at the
Calvert Lignite Mine near Bremond, Texas. The research involved the coordinated use
of several geophysical methods to map near-surface faults within the host Wilcox Group
sedimentary formation. Several geophysical tools were used: magnetics, frequency and
time domain electromagnetic induction, and ground penetrating radar. We discuss how
these methods contribute to near-surface characterization, especially qualitative, rapid
mapping of faults.
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Integrating Geophysical And Geological Methods To Delineate Buried Paleochannels In The New Madrid Seismic Zone Of Southeastern Missouri
Authors Issa El-Hussain, John Holbrook and Clayton SneedBuried Mississippi River (MR) paleochannels within the New Madrid seismic zone
(NMSZ) were delineated using topographic, geological, satellite imagery, and electrical
conductivity data. Initially the abandoned paleochannels were delineated by using
topographic maps and satellite imagery to find associated ridges and swales. Boreholes were
used to collect sediment data to determine facies relationships and confirm the paleochannel
positions. The electromagnetic (EM) method was used to constrain the channel boundary,
confirm borehole data, and confirm topographic estimates of MR paleochannels. The Geonics
Em-3 1 was used to collect EM data and the Sting Rl was used to collect resistivity data at lofoot
intervals along protiles to measure the electrical conductivity of clay plugs filling two
abandoned paleochannels within the NMSZ near Portageville, Missouri. Conductivity
readings along the profiles were relatively high while resistivity readings were low above the
clay filled channel plugs. The conductivity values rapidly decline to relatively low values
when exiting the channel boundary while resistivity show opposite effect as expected. These
sharp declines in conductivities and increase in resistivities are indicative of the edge of the
channel plugs where they meet the paleobank. The EM/resistivity data, when compared to
topographic maps of the study area, shows a similarity of terrain to conductivityiresistivity
values. The data indicates that the clay plugs end well before the natural levee topographical
peak. When compared to a modern stream, the edge of clay fill channel indeed ends well
before the natural levee topographical peak. Comparison of this data to borehole data shows
that the scenario for the natural levee’s and the paleochannel are reasonable and conclusive.
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Gpr Attribute Analysis
Authors Seth R. Lemke and Leonard C. MankowskiInstantaneous amplitude, instantaneous phase, and instantaneous frequency were calculated
from a GPR data set acquired on St. Croix, U.S. Virgin Islands. The data was cross plotted to
search for any anomalous data clusters. These clusters were separated to determine their cause
and determine the implications of the clustering. This is the first step in an attempt to analyze
GPR data in terms of instantaneous amplitude, instantaneous frequency, and instantaneous phase
in order to more accurately determine the electrical properties of the subsurface.
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Monitoring Infiltration Within The Vadose Zone Using Cross Borehole Ground Penetrating Radar
Authors David Alumbaugh, Lee Paprocki, James Brainard and Christopher RautmanCross-borehole ground-penetrating radar (XBGPR) imaging has been employed to
monitor changes in moisture content within the vadose zone during an infiltration
experiment at a test site in Socorro, New Mexico. XBGPR data are being collected
between five wells located along a 1 l-m profile. The wells span a 3-by-3-m infiltrometer
which is producing a constant flux of 2.5 cm of water per day. This flux rate yields
unsaturated flow conditions within the sediments at the site. The XBCPR data are first
converted to velocity images via a non-linear travel time inversion scheme, next to
apparent dielectric constant, and finally to images of moisture content using an empirical
relationship derived from laboratory time domain reflectometry (TDR) measurements
made on samples collected at the site. This empirical relationship was employed rather
than Topp’s equation due to the presence of magnetic minerals in the soils. The results
indicate that the XBGPR images map the progress of the infiltration as it occurs. In
addition, although some lateral smearing is apparent in the images, the XBGPR derived
moisture contents compare well with calibrated borehole neutron-log data. XBGPR data
acquisition and imaging will continue until the hydrologic system is verified to have
reached steady state.
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Controlled Imaging Of Fluid Flow And A Saline Tracer Using Time Lapse Gpr And Electrical Resistivity Tomography
Authors Roelof Versteeg, Ralf Birken, Stewart Sandberg and Lee SlaterA controlled imaging facility was used to setup and execute a number of lD, 2D and 3D
time lapse experiments in which geophysical and direct measurements were used to
image fluid flow and a saline tracer. The resulting data definitely proves that geophysical
data can map 4D fluid flow, however it is imperative to have extremely high spatial and
temporal sampling in order to be able to see the processes.
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Determlning And Mapplng Dnapl Saturation Values From Nonlnvasive Gpr Measurements
Authors Kristen W. Sneddon, Gary R. Olhoeft and Michael H. PowersWith the possible application to fluid-flow modeling, saturation values of dense nonaqueous phase liquids
(DNAPLs) may be determined and mapped through the use of measurements acquited by noninvasive ground
penetrating radar (GPR). In 1991, a controlled injection of perchloroethylene @CE), a common DNAPL, was
performed by the University of Waterloo into an isolated, water-saturated, sandy aquifer at Canadian Forces Base
Borden. One of the geophysical techniques employed by the U. S. Geological Survey to monitor the location and
migration of the subsequent plume was 5OOMHz surface GPR acquited on a one meter grid spacing across the
nine meter by nine meter cell over a period of 340 hours. This paper describes how full-waveform GPR modeling
of these data for relative dielectric permittivity versus depth may be used to calculate and map spatial distributions of
DNAPL saturation over time using recursive solutions of the Bmggeman-Hark-Sen (BHS) mixing formula.
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A Physical Model Experiment Of The Gpr Response Over Gasoline
Authors Changryol Kim, Jeffrey J. Daniels, Jennifer J. Holt and Erich D. GuyAn experiment was conducted at the Ohio State University using a sand and gravel-filled tank
model, to investigate the influence on the GPR response of vadose zone gasoline vapor phase effects
and residual gasoline distributed by a fluctuating water table. After background GPR measurements
were made with only water in the tank, gasoline was injected into the bottom of the model to simulate
a subsurface discharge from a leaking pipe or tank. GPR measurements were made on a 3-D grid on
the surface of the tank for an extended period of time after the injection to monitor changes in a
vadose zone with no residual gasoline. Water was then introduced beneath this gasoline and the
water table was raised and lowered in stages with GPR measurements made at each liquid level.
Results from this experiment show the sensitivity of GPR to moisture content and it’s
effectiveness for monitoring changes in the water table. After the injection of gasoline into the tank
and prior to water table fluctuations, a decrease in reflection amplitudes within the vadose zone
occurred as a function of time. One interpretation of these results is that increasing hydrocarbon
vapor pressure displaced redistributed interstitial moisture in the vadose zone, which led to this
observed change in the GPR response. Additionally, data show that the GPR response can be
enhanced when residual gasoline is present in a water saturated system due to less attenuation through
the medium.
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Detectability Of Crude Oil In The Subsurface Near Bemid Ji, Minnesota, Using Ground Penetrating Radar
More LessNear Bemidji, Minnesota, where crude oil contaminates a glacial aquifer, ground
penetrating radar (GPR) data were collected to determine whether the subsurface distribution of
the crude oil could be detected using a geophysical technique. The crude oil, which is very
resistive (greater than lo7 Ohm-m), is in the fine-grained layers of the vadose zone and is pooled
near the water table. Geochemical analysis shows that biodegradation of the crude oil has
increased total dissolved solids in the ground water. Near the oil pools, the ground water
conductivity is three times higher than the background values. This increase in conductivity
causes attenuation of the radar signal, which is seen in both the cross-well borehole data and in
the surface data. However, the interpretation of the radar data is complicated by the fact that
signal attenuation also occurs in the saturated zone in uncontaminated areas.
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Gpr Jet Fuel Spill Investigation
Authors Mario Carnevale and Jutta HagerHager Geoscience, Inc. used ground penetrating radar as part of an integrated study to
investigate a jet fuel spill at Logan International Airport in Boston, Massachusetts. The
survey was performed at night on airport taxiways and runways. The primary objective was
to characterize soil stratigraphy and delineate trenches for utility conduits, areas of
excavation, and the boundary between granular till and the underlying native material that
could act as migration pathways for contaminants. Also considered was the response of GPR
signals to varying levels of sediment contamination.
In addition to GPR, several types of data were integrated to characterize the subsurface
conditions, including borehole and probe data regarding soil stratigraphy, water table
elevations, and measured VOC concentrations. Cross sections were constructed and used to
integrate all available data and characterize the effect of confined and unconfined
groundwater regimes on contaminant migration.
The cross sections and maps showing a series of horizontal slices of the subsurface were used
to decipher the spatial distribution of jet fuel at various depth intervals. The study showed
that an integrated geological and geophysical subsurface evaluation program is an effective
tool in deciphering contamination at complex sites.
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Seismic Mapping Of Subsurface Cavities
Authors Roland Gritto and Ernest L. MajerThe present numerical study investigates the possibility to invert seismic data
for the location and volume of a cavity. The data is generated using an exact solution
for the scattering of elastic waves by a sphere, whereas the inversion is based on the
low frequency Mie approximation to the exact solution. We use a correlation analysis
between these solutions to solve the inverse problem in two steps. First, the location
of the cavity is determined, before the volume is estimated in a second step. The
robustness of the results is tested by adding correlated and uncorrelated noise. We
find this method to be robust as long as the source receiver coverage is good enough
to reduce the noise level. The locations of the cavities are well determined while the
estimates of the radii are more susceptible to noise and the deviation between
approximation and exact solution.
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Geophysical Surveys To Map The Vertical Extension Of A Sinkhole: A Comparison Study
Authors M.G. El-Behiry and S.M. HanafySinkholes are important near-surface indicators of active karst features at depth,
such as cavities and solutionally enlarged fractures. Geophysical surveys were made at
an engineered site in the lSth-May City, south of Cairo, Egypt, where excavations show
two openings (about 0.5 m2 each) in the limestone bedrock. Subsurface extension of the
two holes could not be revealed by visual inspection. This study compare between
different geophysical methods to map the vertical extension of a sinkhole as a means of
inferring the possible existence of this deeper hydraulically active karst feature.
The performed GPR profiles, with 200 & 500 MHz antennas, showed that the
two holes are a part of main sinkhole that extend l-2m deep, 6m length and about 4.5m
wide. Numerous subsurface voids and fractures could also be delineated with no
evidence of deep cavities.
Dipole-dipole resistivity survey was carried across the two holes using electrode
separation “a” of 5 and 1 Om. The 2D-inversion of resistivity profile with a=5m revealed
very high resistivity anomaly (20,000 Ohmm) at the location of the two holes and
extend to a depth of 6m. The inversion of the other profile (a=lOm) gave the vertical
extension of the same anomaly outlined above to a depth of 16m. This anomaly was
interpreted as due to highly fractured zone rather than cavity.
Seismic refraction data acquired at the location of the two holes show delayed
first breaks and wave attenuation. Low seismic velocity of 570 m/s was obtained for the
surface layer containing the two holes. A bedrock refractor (3800 m/s) was identified at
3m deep and considered as the base of the holes.
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