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8th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 23 Apr 1995 - 26 Apr 1995
- Location: Orlando, Florida, Canada
- Published: 23 April 1995
41 - 60 of 104 results
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3-D High-Resolution Seismic And Georadar Reflection Mapping Of Glacial, Glaciolacustrinel And Glaciofluvial Sediments In Switzerland
Authors A. Green, A. Pugin, M. Beres, E. Lanz, F. Bilker, P. Huggenberger, H. Horstmeyer, M. Grasmtick, R. De Iaco, K. Holliger and H.R. MaurerDuring the past decade significant progress has been made in the development of geophysical techniques designed
to resolve problems associated with the unconsolidated sedimentary layers of the shallow subsurface. Two of these
techniques, the high-resolution seismic reflection and the ground-penetrating radar (georadar) methods, have the
potential to define the character, size, and geometry of surficial sedimentary units. In an attempt to determine
optimum recording and processing strategies, seismic and gwradar reflection profiles have been recorded across
a variety of glacial, glaciolacustrine, and glaciofluvial deposits in Switzerland. At one test location we have also
conducted a pilot 3-D high-resolution seismic reflection survey and at another we have collected an experimental
3-D gwradar data set. Results of the 3-D surveys are striking images of the shallow subsurface that provide many
more details and much more reliable information on the 3-D heterogeneities of the shallow subsurface than are
afforded by conventional 2-D data sets; at both 3-D test sites critical geological features would have been misinterpreted
had only limited profile information been available.
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3-D Gpr Imaging Of Complex Stratigraphy Within The Ferron Sandstone, Castle Valley, Utah
Authors Chris Thompson, George McMechan, Robert Szerbiak and Neil GaynorTwo detailed 3-D Ground Penetrating Radar surveys were recorded on outcrops of the Ferron Sandstone in Castle
Valley, Utah in an effort to image internal sedimentary structures. The Ferron Sandstone is a fluvial to proximal
marine sandstone which is considered to be a good analogue for some Gulf Coast oil and gas reservoirs. Because of
its excellent exposure in Castle Valley, the stratigraphy of the Ferron has been, and continues to be very extensively
studied to determine the relationships of bedforms to the distribution of reservoir properties. Our goal in imaging
these outcrops with 3-D GPR is to interpret reservoir heterogeneities at interwell scales. Correlation of these
heterogeneities to known porosity and permeability distributions from outcrop studies will be used to establish three
dimensional scales of reservoir flow behaviour. These data will subsequently be used to improve flow simulations
of analogous oil and gas reservoirs. Results of this study indicate that 3D GPR is indeed suitable for this application.
The first 3-D survey was recorded on a 15m by 15m grid with traces recorded every 25cm in both directions.
Adjacent outcrop showed the near-surface sandstones to be of a tidally reworked deltaic lithofacies, overlying lower
coastal plain carbonaceous siltstones. More than 4m of penetration and finer than 25cm resolution were achieved
using a PulseEKKO IV GPR system with 200 MHz antennae.
The second 3-D survey was recorded about 250m away from the first, over a stacked distributary channel to
nearshore sandstone lithofacies. 100 MHz antennae were used over a 25m by 25m grid, with 5Ocm spacing in both
directions. More than 8m of penetration and finer than 50cm resolution were observed.
A 2-D line with 50 MHz antennae and 1 .Om trace spacing was recorded to connect the two 3-D surveys and to
provide a more regional picture of stratigraphy. Reflections were recovered from as deep as 20m.
The data were processed both at Chevron, using the Promax seismic processing system, and at UT Dallas, using
in-house software. Data were flattened on the air arrival, gained, spatially smoothed and then migrated using a
fixed-offset prestack migration. Results were visualized with VoxelGeo, a software package which allows the user
to selectively render the volume with transparency to see the interior of the data cube in 3-D perspective.
Connectivity analysis within the cubes highlights discrete reflectors, and by implication, the main flow units of the
facies. Work is underway to correlate the vertical and horizontal scales of heterogeneity from the GPR data, with
the facies’ permeability distribution from outcrop studies.
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Location And Identification Of Compact Metallic Objects By Magnetics And Electromagnetic Induction
Authors John E. McFee and Yogadhish DasThis paper discusses methods of location and identification of compact metallic and ferrous objects
using magnetometers and electromagnetic pulse induction. To date, no commercially available systems
exist which can explicitly and accurately estimate the location of a compact ferrous or metallic object and
identify it reliably. Self-contained systems which could do so in real-time would represent a significant
advance in the state-of-the-art.
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Detection Of Buried Contaminant Containers Using Gpr
Authors Leon Peters, Jonathan D. Young, Chi-Chih Chen and Jeffrey J. DanielsThe detection of buried containers is dependent on several factors including the GPR antenna properties,
the size, shape, material construction of the container, its contents and the physical and electrical properties
of the soil in which it is buried. These features will be discussed as will some target identification techniques.
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An Integrated Approach For Measuring And Processing Geophysical Data For The Detection Of Unexploded Ordnance
Authors Jerzy Pawlowski, Dr. Richard Lewis, Tim Dobush and Nicholas ValleauLand and water borne electromagnetic and magnetic surveys were performed near
the old Lake Erie Ordnance depot in Ohio. The purpose of the study was to
determine the presence and subsurface density of unexploded ordnance (UXO).
Measurements were carried out within selected onshore and offshore areas using
instruments adapted for underwater investigations. A test site with known buried
ordnance was prepared in order to establish a base reference for conducting
detailed land surveys and transects for the underwater investigation.
The interpretation of magnetic field data for man-made metallic ordnance is often
difficult because of distortions to the observed field caused by permanent
magnetization. The interpretation of the electromagnetic data is dependent on the
condition of the metallic content of the object which will have an effect on the
electromagnetic field. Advanced data processing and presentation software
techniques were employed to determine the criteria for the plan and depth locations
of the buried ordnance.
The goal of the tests is to help to establish a baseline against which to evaluate
future changes in the rate of on-shore deposition of new ordnance. As the magnetic
results were limited for the Lake Erie site (low sampling density), magnetic data
from a Naval Research Laboratory (NRL) demonstration site at Fort Devens, MA
was utilized as a further example for this paper. The purpose was to examine the
relationship of higher sampling densities to the accuracy of the plan location and
depth calculations of magnetic data.
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Army Research Laboratory Ultra-Wideband Crane Sar: System Overview And Results Of Early Ground Penetrating Radar Studies
Authors Keith A. Sturgess, Lam Nguyen, Marc Ressler, Tuan Ton and T.O. GroschArmy Research Laboratory (ARL) and Massachusetts Institute of Technology/Lincoln Laboratory (MIT/LL)
have been working in the field of ultra-wideband (UWB) synthetic aperture imaging radar (SAR) for foliage
penetration for a number of years. In 1993, ARL was appointed executing agent for a Defense Intelligence Agency
program to investigate ground penetrating radars on airborne platforms. In the summer of 1993 an experiment was
conducted at Yuma Proving Ground, Arizona involving many existing airborne radar sensors to assess GPR
potential. Data collected by Stanford Research Institute International on a minefield emplaced at Yuma is presented,
along with statistics of the targets and clutter as a function of frequency and depression angle, to show the current
capability and potential of improved sensors. An automatic group target detection algorithm designed to find
distributed targets is discussed and results of applying it to the minefield data are shown. Based on analysis of data
collected at Yuma and other research conducted, a new crane-based UWB SAR collection asset has been designed
and built at ARL that is fully polarimetric and covers a frequency range of 60 MHz to 1 GHz. This highly capable
radar system is described, and future data collection plans are discussed.
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An Innovative And Cost Effective Approach For Uxo Detection Using Gis Is Setting A New Standard
Authors Charles Heaton, Robert Menke and Matthew GiffordFort Monroe is a 584-acre U.S. Army facility approximately ten miles north of Norfolk,
VA, near Hampton Roads, VA. Conventional OEW, some dating back to the 186Os, has been
found at many areas of Fort Monroe, and it is expected that much more remains. The ordnance
may represent a serious OEW safety hazard and a significant cost to remediate the site. The
1993 Base Realignment and Closure Commission Report recommended a comprehensive
investigation of UXO contamination at Fort Monroe.
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Development And Testing Of A Tensor Magnetic Gradiometer
Authors D.D. Snyder and Robert BrackenMagnetic gradient measurementsp ossesss everal advantages compared with other magnetic field measurementsin
shallow-site investigations, hazardous-waste site characterization, and other investigations to locate buried ferromagnetic
objects. These advantages include (1) immunity from time-varying geomagnetic noise, (2) improved spatial resolution
because of the more rapid spatial attenuation of the gradient components compared with magnetic field components, and
(3) generally low-background gradient values from geological effects. For this reason, conventional magnetic surveys for
site investigations and for object detection routinely acquire the vertical gradient of the total magnetic field with a pair of
identical proton or alkali vapor (e.g., Cesium) magnetometers with spatial separations of a few feet.
Quantitative interpretation of magnetic gradient data requires the knowledge of several components of the gradient (Hood
1965; Reid et. al 1990). Theoretically, these gradients can be calculated from a properly sampled map of one of the
components of magnetic field (Nabighian 1984), but the advantage to their direct measurement is that interpretation can
be performed with data acquired at a few data points along a profile. Consequently, interpretation in near real time either
during acquisition or immediately after it is therefore quite feasible.
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Time-Term Method With Tomographic Determination Of Refractor Velocities
Authors Masaya Yamauchi and Hideki SaitoThe authors applied time-term method in a seismic refraction survey to determine the variation of the
thickness of a gravel layer overlaying a weathered granite basement in a 100 x 400m area. The reason why we used
time-term method in this survey was that the ground surface at the site was covered with boulders as large as 1
meter in diameter, it was difficult to apply conventional refraction survey in which sources and receivers have to be
in a line. Before doing field measurements, it seemed that the velocity structure of the site satisfied all
requirements for the applicability of time-term method. However, when analyzing observed seismic refraction data,
we found that the structure was not satisfied one of the requirements that the basement had no lateral variation in
velocity. To determine the variation of basement velocities as well as the distribution of the thickness of gravel
layer, we incorporated a tomographic technique into a conventional method and successfully applied it to the survey
data.
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Tomography Between Wells, A Transient Dielectric Logging Tool, And The Very Early Time Electromagnetic (Vetem) System
This paper reviews progress on three site characterization technologies we are developing
at the U.S. Geological Survey (USGS).
We produced hole-to-hole electromagnetic and seismic tomograms of fractured crystalline
rock at the Mirror Lake, New Hampshire, hydrology research site. Both electromagnetic
and seismic tomograms between well pairs correlate with zones of high hydraulic
conductivity. We processed the electromagnetic full wave recordings in a variety of ways
to produce velocity tomograms, attenuation tomograms, and dispersion tomograms. Since
tomograms image not only fracture zones, but lithology as well, it is important to examine
all additional available geological, hydrological, and geophysical information in order to
achieve the most accurate interpretation of the tomograms.
Dielectric single-hole tools should be useful for direct detection of non-aqueous phase
liquids. Borehole dielectric logging tools were developed by the petroleum industry for
measuring oil saturation in cases where electrical resistivity is too high for resistivity tools
to be effective. However, for many shallow environmental applications existing commercial
borehole tools are physically too large to be practical. Previous experience with single-hole
borehole radar suggested to us that a time-domain dielectric logging tool might be feasible.
An experiment in a laboratory sandpack confirmed that supposition. A further experiment
is in progress to assess resolution of such a tool and to measure the effects on the calculated
values of dielectric permittivity of borehole diameter and tool location in a borehole.
The very early time electromagnetic (VETEM) system is a time-domain, surface-deployed
system that has potential applications to direct detection of non-aqueous phase liquids as
well as to the detection of buried objects. It is designed to operate in environments that are
too conductive for ground penetrating radar to be effective, and too.shallow for standard
electromagnetic systems. The VETEM system provides a faster profiling alternative to the
frequency-domain high frequency sounder (HFS) we been built and successfully applied in
a number of field experiments. The VETEM system construction is essentially complete.
Laboratory system evaluation tests are in progress, and field tests will soon follow.
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Imaging And Inversion Of Transient Electromagnetic Soundings
More LessThe success of geophysical investigations associated with environmental problems is to a large
extent determined by the density of the measurements and the quality of the interpretations. Many case
studies of mapping of raw materials and hydrogeological investigations have confirmed that dense
measurements with traditional methods of geoelectrical and transient (TEM) soundings as well as novel
methods of continuous electrical profiling (CEP) and El-logging enhance the data reliability and the
possibilities of finding a trustworthy interpretation of the complexities of the geological settings
(Christensen and Sorensen 1994).
TEM soundings have proven very valuable in delineating the geometry of aquifers in
hydrogeological investigations in the Quaternary deposits in Denmark, and they are now routinely used
for the purpose of mapping the dept,h to a good conductor, which may be well conducting heavy clays or
salt water horizons, both being the effective bottom of an aquifer. A hydrogeological investigation may
contain 100-500 TEM soundings, often along profile lines, and it is of importance that the interpreter as
well as the field crew get an overview of the results as quickly as possible to adjust the strategy of data
aquisition.
An ordinary 1D least squares iterative inversion of TEM sounding data require that the
interpreter supply an initial model, and the computation time is usually between 10 and 30 minutes on a
PC. With a daily production of more than 15 soundings this procedure is slow. and there is need for fast
approximate ways of interpretation. The newly developed pulled array transient electromagnetic method
(PA-TEM) (Sorensen 1995), where a transient equipment is towed behind a small vehicle while
measuring, produces huge amounts of data to be interpreted. It would be an impossible task to interpret
the resulting number of TEM soundings with ordinary least squares inversion procedures.
An algorithm for imaging of TEICl soundings based on the Frechet kernel is presented, where the
computation time is appr. 0.5s/sounding / Mflop. The imaging produces models with 20-40 layers, which
fit the original data typically within 510%. No initial model is required, and the algorithm is therefore
well suited for automatic inversion. The algorithm makes it possible to see the results of a days work in a
matter of minutes and to implement on-line inversion simultaneous with the measurements.
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Geological/Geophysical Modeling Of Seismic/Gpr Tomographic Imaging For Environmental Applications
Authors Douglas Baumgardt, Zoltan Der, Jeanne Carney, Michael Maxson and Alan BeAn interactive graphics system, called GeoSim/GeoEyes, has been developed to model acoustic and electromagnetic
wave propagation in realistic geological media and to assess tomographic imaging scenarios on simulated data for
shallow subsurface exploration applications using seismic and ground-penetrating radar (GPR) data. The GeoSim/
GeoEyes simulation environment has been developed on a UNIX workstation using X Windows/Motif interactive
graphics. The system consists of four main sets of subprocesses controlled from the top-level main function: (1) geological
model and parameters scenario generation, (2) signal simulation, (3) tomographic image preview and generation,
(4) and image display and analysis. Although GeoSim/GeoEyes has been primarily developed to assess tomographic
imaging schemes using simulated signals prior to actual data collection, the system has also been developed to process
actual seismic and electromagnetic data collected in the field. Thus, comparison of simulated imaging scenarios with
those generated from actual data will allow the evaluation of the validity of the models and to improve the accuracy of
the model parameters.
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Assessment Of Potential Karst Conditions For A New Bridge In The Florida Keys
Authors Richard C. Benson, Lynn Yuhr and Paul PasseWhile the probability of locating a foundation over critical karst, and the probability of a collapse is usually
relatively low, problems have and do continue to occur. When a karst problem does occur, it usually has a
significant impact upon structures and or groundwater.
The purpose of this investigation was to evaluate the possible presence of significant karst (old sinkholes or
cavities) within the area of a proposed 7,500-foot bridge to be built over Lake Surprise and Jewfish Creek, just
north of Key Largo, Florida. Five independent sets of data indicate anomalous geologic conditions between Lake
Surprise and Jewfish Creek, and include:
. A large microgravity anomaly of 100 microGals;
. Three boreholes near the center of the gravity anomaly contain 45% of the total fluid loss noted among 34
boreholes;
. Subbottom profiling (seismic reflection) data indicates possible dissolution-enlarged joints;
. A major photo-lineament indicates the possible presence of joints and fractures; and
. Extensive road maintenance within the immediate area of concern.
In addition, the presence of a large 2,000 foot diameter paleocollapse sinkhole, located in the area by USGS,
indicates that larger deeper cave systems and sinkholes can and do exist in the Florida Keys.
The subbottom data, lineaments, borehole fluid loss, and the DOT maintenance records each by themselves could
be dismissed as irrelevant. However, the coincidence of these independent sets of data with a large gravity
anomaly clearly focus attention on the area as an area of unusual geologic conditions, with a strong possibility of
significant karst. This case-history outlines the approach and the resulting data used to identi& karst conditions
and assess its impact upon the proposed bridge design.
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Identification Of Dolines And Karst Recharge Points Using Geophysical Techniques, Oak Ridge, Tennessee
Authors Philip J. Carpenter, William E. Doll and Ronald D. KaufmannSurface water and contaminants often enter karst systems through a doline, or sinkhole.
In this study ground penetrating radar (GPR) and other geophysical methods were applied
to identify filled dolines on a colluvium-covered hillslope overlying cavernous limestone
at the Y-12 Plant, Oak Ridge Reservation, Tennessee. Although 25 and 50 MHz GPR
signals did not penetrate deep enough to reveal mud-filled cavities in the bedrock, dipping
radar reflections were obtained over the flanks of a known doline and another filled doline
may have been discovered near monitoring well GW734. A troughlike pattern of radar
diffractions at least 120 ft (37 m) across and 12 ft (3.7 m) deep was recorded at this
location by several GPR profiles. Electromagnetic, resistivity, seismic refraction and
gravity surveys suggest this doline structure is filled with relatively dense, resistive
residuum or colluvium, and floored by silt or clay. This structure also lies almost directly
above a large hydraulically active bedrock cavity (intercepted by monitoring well GW734)
for which it may be a recharge point. Further detailed investigation of this doline structure
should be undertaken, based on the results of the geophysical surveys and its proximity to
the cavity.
Note: The submitted manuscript has been authored by a contractor of the U.S.
Government under contract No. DE-ACW840R21400. Accordingly, the U.S.
Government retains a nonexclusive, royalty-free license to publish or reproduce the
published form of this contributioq or allows others to do so, for U.S. Government
purposes.
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Assessment Of Geological And Hydrological Features In A Basaltic Environment Using Borehole Geophysical Techniques
Authors Robert Crowder, William Pedler, Joseph Seracuse, Neil Myers, James Daniel and Laurie HainesA comprehensive borehole geophysical logging program was conducted in four newly drilled monitoring well boreholes
and one existing water-supply well located in the hydrageologically complex basaltic volcanics underlying Schofield
Army Barracks, Oahu, Hawaii. The purpose of this logging program was to cost effectively evaluate the complex geologic
and hydrologic conditions in this basaltic environment and the associated aquifer thereby minimizing the need for drilling
additional expensive monitoring wells. This logging program was successful in effectively characterizing the geologic and
hydrologic characteristics of the site including vadose zone moisture content.
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Practical Hydraulic Tomography In Heterogeneous Fractured Aquifers
More LessConventional geophysical tomography produces images of fractured
aquifers where the images are based on physical properties other than the
hydraulic parameters of interest, and where individual fractures usually
cannot be resolved. Hydraulic tomography can be used to define the hydraulic
connections in a volume of rock between boreholes, but requires prolonged
measurements and extensive use of straddle packer equipment. We propose a
practical form of hydraulic tomography where general patterns of hydraulic
connections are defined by conventional geophysics, and cross-borehole
flowmeter tests are used to define the hydraulic properties of this limited
number of possible flow paths. The technique is based on the analysis of
type curves for a family of nondimensionalized boundary value problems
analogous to those used in conventional aquifer test analysis. We show that
the method can delineate connections between fracture zones within rock
masses away from boreholes, and can be used to greatly reduce the time and
effort needed for conventional hydraulic testing.
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Improvement Of Shallow Seismic Reflection Section Using Migration: Two Case Studies
More LessMigration is seldom applied to shallow seismic reflection data because migration on microcomputer
is slow and final seismic sections are often only minimally improved. Black et.al. (1994) show that for
small values of velocity and traveltime, the horizontal and vertical displacements of a reflector point after
migration may not be large enough compared to the trace spacing and time sampling interval to make a
noticeable change on a migrated section. They do mention, however, that migration may be useful in
shallow seismic survey which requires high resolution.
Two cases showing significant improvement of a shallow seismic section after migration, due to
increased resolution or decreased noise, are presented here. The first case is a common-midpoint section
over buried sand channels. Before migration, the section showed two contiguous channels at a depth of
about 60 m in a sequence of horizontal beds . Improved lateral resolution after migration revealed a third
channel. This case illustrates the possiblevalue of migration even when the reflectors are horizontal. The
second case is a common-offset survey over a channel cut in Precambrian bedrock and overlain by glaciofluvial
sands and gravels. Migration, by collapsing the diffraction noise, resulted in a clearer picture of
the channel and revealed the presence of two terraces.
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Compressional Wave Character In Gassy, Near-Surface Sediments In Southern Louisiana Determined From Variable Frequency Cross-Well, Borehole Logging, And Surface Seismic Measurements
Authors M.D. Thompson, L.D. McGinnis, P.L. Wilkey and T. FasnachtVelocity and attenuation data were used to test theoretical equations describing
the frequency dependence of compressional wave velocity and attenuation through gas-rich
sediments in coastal Louisiana. The cross-well data (obtained from a variable-frequency,
cross-well seismic experiment using source frequencies of 1, 3, 5, and 7 kHz) were
augmented with velocities derived from a nearby seismic refraction station using a lowfrequency
(~20 Hz) source. Velocities obtained from the borehole-sonic tool (18 kHz)
were not used, because it is unclear at this time what signal phase was being detected.
Energy at 1 and 3 kHz was successfully transmitted over distances from 3.69 to 30 m; the
5- and 7-kHz data were obtained only at distances up to 20 m.
Velocity tomograms were constructed for one borehole pair and covered a depth
interval of lo-50 m. Results from the tomographic modeling indicate that gas-induced
low velocities are present to depths of greater than 40 m. Analysis of the velocity
dispersion suggests that gas-bubble resonance must be greater than 7 kHz, which is
above the range of frequencies used in the experiment. Washout of the boreholes at
depths above 15 m resulted in a degassed zone containing velocities higher than those
indicated in both nearby refraction and reflection surveys.
Velocity and attenuation information were obtained for a low-velocity zone
centered at a depth of approximately 18 m. Measured attenuations of 1.57, 2.95, and
3.24 dB/m for the 3-, 5-, and 7-kHz signals, respectively, were modeled along with the
velocity data using a silt-clay sediment type. Density and porosity data for the model
were obtained from the geophysical logs; the bulk and shear moduli were estimated from
published relationships. Modeling results indicate that gas bubbles measuring 1 mm in
diameter occupy at least 25% to 35% of the pore space.
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Comparison Of Lower-Frequency (<Lo00 Hz) Downhole Seismic Sources For Use At Environmental Sites
More LessIn conjunction with crosswell seismic surveying being done at the Hanford Site in south-central Washington,
four different downhole seismic sources have been tested between the same set of boreholes. The four sources
evaluated were the Bolt airgun, the OYO-Conoco orbital vibrator, and two Sandia-developed vertical vibrators,
one pneumatically-driven, and the other based on a magnetostrictive actuator. The sources generate seismic
energy in the lower frequency range of less than 1000 Hz and have different frequency characteristics, radiation
patterns, energy levels, and operational considerations. Collection of identical data sets with all four sources
allows the direct comparison of these characteristics and an evaluation of the suitability of each source for a
given site and target.
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Very Shallow Seismic Reflection Profiling Using Portable Vibrator
Authors Y. Kaida, M. Matsubara, R. Ghose and T. KanemoriA portable, high frequency vibrator system has been developed to effectively increase seismic resolution.
The vibrator is based on the principles of electrodynamics. A 65 kg magnet serves as the reaction mass, no external
hold down force is applied. Two persons can easily move the light-weight vibrator in the field. Amplitude and phase
of the vibrator sweep are controlled by a multipurpose data acquisition system.
Several experiments to test the performance of the vibrator as a seismic source have been carried out. This
paper describes results of two of these tests. The first experiment was conducted on an embankment that consists of
gravelly soil underlain by an alluvial silty clay and a diluvial clayey silt. Distinct reflecting interfaces of these layers
were clearly mapped to a depth of 50 m. The second experiment was conducted at an OYO test site where pieces of
styrcne foam hav.e been buried at known depths ( 0.5 m -2 m) below pavement. Using the portable vibrator system,
diffraction events from the styrene foam at depths of 1.5 m and 2.0 m were detected.
Results of these experiments indicate that the portable vibrator is a promising seismic source for high
resolution seismic reflection profiling.
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