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18th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 03 Apr 2005 - 07 Apr 2005
- Location: Atlanta, Georgia, USA
- Published: 03 April 2005
101 - 146 of 146 results
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Use of Electromagnetic, Geoelectric and Seismic Tomography Refraction Geophysical Methods To Estimate The Water Content In The Subsoil
More LessThe interpretation of combined geophysical methods [Ground Penetrating Radar (GPR),
Electrical Resistivity Tomography (ERT) and Seismic Refraction Tomography (SRT)] are
proposed to assess the physical properties characterizing the near surface porous formations, and in
particular way the volumetric water content. The search was carried out in semi-controlled
situations. Were considered the variations of several geophysical parameters, (the electromagnetic
(EM) wave velocity, the seismic wave velocity, and the electrical resistivity) in the subsoil to
esteem the fluctuations of the volumetric water content in the same subsoil. Is, in fact, known that
the values of the geophysical parameters, that can be obtained from measures in surface, are
influenced by the presence of water in the pore and in the fractures of the materials in the subsoil.
The esteem of the variations of these parameters can be makes by measures repeated in the time
(i.e. measures realized before and after water's immission in the subsoil). This type of monitoring
can allow the individualization of the principal paths of outflow of the water in the subsoil.
The study conducted in this paper point out as the use of combined geophysical methods providing
models of water outflow from the surface down to some meter deep.
[Key words: Ground penetrating radar, seismic refraction tomography and electrical resistivity
tomography methods, water content, monitoring]
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Geophysical Characterization of Seawater Intrusion In Antigua, West Indies
The Inter-American Agency for Cooperation and Development is currently funding a project
focused on groundwater management in coastal karst environments in the Caribbean. The islands of
Jamaica, Antigua, and Barbados are currently the primary regional participants in this project.
Geophysical characterization of pilot sites on each of these islands is being used to provide input into
conceptual groundwater flow models, which in turn will be used to support the development of
sustainable groundwater management strategies for these coastal aquifers.
Geophysical fieldwork at a pilot site located in the northeast portion of the island of Antigua took
place in April 2004. Data from the survey support mapping the geology and hydrology of the region
and locating the freshwater-seawater interface. Geophysical methods used in the fieldwork included
time-domain electromagnetic (TEM) central-loop soundings, Schlumberger-array resistivity soundings,
EM-31 terrain conductivity profiling, and multi-electrode resistivity profiling. In-field analysis of data
collected at a regional scale led to a conceptual understanding of seawater intrusion into the study area.
This conceptual understanding led to concentrated data collection efforts in specific areas.
The first area surveyed in-depth to confirm our conceptual understanding of seawater intrusion at
the site was Mercers Creek channel that runs from west of the Collins and Potworks reservoirs to
Mercers Creek Bay located along the north coast of the island. TEM soundings, assembled into an eastwest
profile across the channel, reveal a conductive region, thought to represent seawater migrating
inland in response to the reduced freshwater head caused by pumping at the Collins well field. The
second area surveyed in-depth was the Ayres Creek channel that runs by the Collins and Bristol well
fields before draining into the extensive tidal flat at Nonsuch Bay located along the northeast coast of
the island. This channel contains a secondary dam that captures outflow from the Potworks and Collins
dams during periods of high rainfall and flooding, but is otherwise dry. This area was studied in detail
using a high-density geophysical data collection strategy. Subsequent data interpretation led to the
identification of a conductive zone that appears to be the result of seawater intrusion. The extent of the
intrusion in the vicinity of the channel is controlled by the groundwater pumping at the Collins and
Bristol well fields and storm surge/tidal fluctuations. This conceptual model has groundwater
management implications that are being evaluated using groundwater flow models.
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An Archaeological Investigation of The San Marcos Pueblo, New Mexico, Usa
Authors Jacob Hodges, John Ferguson and Louise PellerinAs part of the Summer of Applied Geophysical Experience (SAGE), a field-based educational program in applied geophysical methods, several geophysical surveys were performed at the San Marcos Pueblo for archaeological purposes. The San Marcos Pueblo was a large and significant Tano pueblo in the Galisteo Basin south of Santa Fe, NM. It is a sixty-acre preserve, currently owned by the Archaeological Conservancy, containing the remains of thirty-eight room blocks, up to 5,000 rooms, two springs, and the foundations of a seventeenth-century Franciscan Mission complex. Over two days in June 2004 SAGE students acquired ground penetrating radar (GPR), loop-loop electromagnetic (EM), magnetic, and shallow refraction seismic data to investigate the buried secrets. The seismic GPR, EM and magnetic data proved to be complementary in delineating room block walls and a possible kiva, a chamber used by men for ceremonies and council meetings. The seismic data were definitive in terms of the dimensions of the kiva.
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Geophysical Investigation of The Groundwater Regimes In The Lower Okavango Delta, Northwestern Botswana
Authors Elisha M. Shemang, Loago N. Molwalefhe, Harish Kumar, Tej Bakaya and Joel NtsatsiThe Okavango Delta in the northwestern part of Botswana is unique and it is the largest inland
delta in the world. Instead of flowing into the sea, the annual flood of fresh water from the
highlands flows inland, spreading over 15 000km² of the arid Kalahari environment and forming
several islands and channels that emerge from its waterways. Parts of the Lower Okavango
Delta that have been receiving large and frequent flood events have developed extensive fresh
water aquifers, while other parts that have been receiving intermittently small floods have limited
fresh water aquifers. The present study used aeromagnetic, airborne Electromagnetic
(AEM), ground transient electromagnetic (TEM) soundings, drilling and down-hole geophysical
logging data to map the distribution and geometry of these fresh water aquifer systems. The
results of this study showed that the occurrence of freshwater aquifers in the lower delta are associated
with active drainage channels and are bounded below and on their edges by brackish/
saline groundwater. The geometry of these aquifers provides an insight into the long term
flooding history of the delta. This can be seen from the Gomoti River, which has had only intermittent
flow in recent times, but is one of the largest fresh water aquifers in the lower delta.
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Temenos Estates, Anguilla, Bwi Hydrogeologic Investigation, Geophysical Mapping and Water Supply Development
More LessN. S. Nettles & Associates, Inc. (NSN) was contracted by Flagg Luxury Properties to perform a
hydrogeologic investigation of its Temenos property, the former Sonesta Resort, on the island of
Anguilla, Rendezvous Bay, BWI (Figure 1). Temenos Estates is a $300 million dollar development
comprised of a St. Regis Resort Hotel, Greg Norman Golf Course, private beach estate homes, and
private villas (Figure 2). The project site incorporates nearly one mile of beachfront property with
fringing reefs. Land elevations rise from the beach to elevations of 80 feet above sea level (Figure 3).
The island is of volcanic origin but has in excess of 300 feet of limestone overlying the igneous rocks.
Two large hydric geomorphic features are present on the property that will be modified as part of NSN’s
scope of work. One feature is a 12 acre salt barren (a sea level plain with hyper-salinities) referred to as
the savanna, that was formed by a large sinkhole many thousands of years ago. The second is the 13-
acre Merrywing Salt Pond that was originally used to mine salt and was later used as the disposal site for
the Sonesta Resort septic system. This salt pond is also hyper-saline and very high in nutrients. The
investigation was designed as a three-phase program to define the hydrogeology of the site, construct
water supply wells, drainage wells and flushing channels.
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Geoelectrical Exploration for Groundwater Around The New Communities, East Nile Delta
Authors Abd El Hamid A. Taha, Ahmed S. El Mahmoudi and Islam M. El-HaddadWithin the last couple of decades, the groundwater development in Egypt has become more and
more important. New communities and land reclamation projects have been recently established in the
area to the east of the Nile Delta to overcome the growing population problem in Egypt. Groundwater is
the second source of water in Egypt.
The present paper deals with the hydrogeological investigation using geoelectrical vertical
electrical sounding technique around the new communities, East Nile Delta. A number of 53 vertical
electrical soundings using Schlumberger electrode configuration with maximum current electrode
spacing “AB” = 1400m have been carried out by the authors. Raw data of 92 VES from (Ezz El Din,
1993 and Abd El-Gawad, 1997) are reinterpreted. Records of the water wells drilled in the study area
and chemical analysis for the water samples are been guided.
The interpreted VES data in the form of layer thickness and resistivities presented on the crosssections
are found not to be easily a sequence of continuous sedimentary lithologic layers due to of the
lateral changes in layer resistivities. Therefore, the geoelectrical resistivity layers lumped into three
Litho- resistivity zones with different hydrogeological conditions. Litho-resistivity zone (A) represents
the detrital surface cover. Litho-resistivity zone (B) represents the dry zone. Litho-resistivity zone (C)
represents the saturation zone in the study area.
Geoelectric cross-sections have been constructed. The different aquifers have been recognized
with main structural elements controlling these aquifers.
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A Ground-Bas Ed Squid Magnetometer
Authors W.E. Doll, T.J. Gamey, L.P. Beard and J.R. SheehanOver the past five years, our group has focused on development of airborne magnetic and electromagnetic systems for mapping and detection of unexploded ordnance (UXO). Among these projects is one involving testing and development of a high temperature airborne Superconducting Quantum Interference Device (SQUID) tensor magnetometer. In association with the airborne SQUID development, we are conducting tests of the SQUID as a ground-based instrument for UXO mapping and detection. The ground-based SQUID is mounted on a man-portable litter with ancillary instrumentation mounted on a cart and connected by an umbilical. High-temperature SQUIDs use liquid nitrogen as the cryogen, which is more convenient than the helium-cooled lowtemperature devices. Preliminary data from the ground-SQUID prototype show good agreement with cesium vapor total magnetic field data along a test line. Noise frequencies and levels appear manageable and we anticipate that specialized processing should make it possible to extract more details about UXO items from their tensor magnetic properties.
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Comparison of Laboratory-Based Multi-Frequency Systems for Measuring Magnetic Susceptibility
Authors Ryan E. North, Eric W. Smith and Gary L. CavanoughMagnetic soils can have significant influence on instruments that are used for detecting
unexploded ordnance (UXO) as well as landmines. Magnetic susceptibility is a measure of the degree to
which a material can be magnetized. Magnetic viscosity is the frequency dependence of the magnetic
susceptibility and is normally characterized as the percentage difference of the magnetic susceptibility at
two frequencies separated by one decade (e.g. 465 Hz and 4.65 kHz). This may be too simplified of an
approach. Queensland Magnetic Research has built a prototype magnetic-susceptibility-measurement
system (MAGNASAT) that can measure the magnetic susceptibility of a small soil sample at multiple
frequencies ranging between 10 Hz and100 kHz. The comparison between the Queensland Magnetic
Research MAGNASAT and the Bartington MS2 is the focus of this presentation. Six different chemical
salts with known magnetic susceptibility values were measured multiple times with each system. The
results will demonstrate the accuracy and precision of each instrument. Characterization of a
measurement system is an important first step for collecting quality data.
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Mineralogy of Magnetic Soils at A Uxo Remediation Site In Kaho'Olawe Hawaii
Magnetic characteristics of soils can have a profound influence on electromagnetic sensors for
the detection of unexploded ordnance (UXO) and may cause false alarms in the case of spatially variable
concentrations. In particular, the performance of several electromagnetic sensors is hampered by viscous
remanent magnetism, which is caused by the presence of ferrimagnetic iron oxide minerals of different
sizes and shapes. Tropical soils formed on basaltic substrates commonly have large concentrations of
iron oxide minerals. To improve detection and discrimination of UXO in these soils it is crucial to have
a better understanding of the types of minerals responsible for the magnetic behavior, as well as their
distribution in space. In this paper we present the results of recent field and laboratory studies of soil
magnetic properties and soil mineralogy at the former Naval training range on Kaho’olawe Island,
Hawaii. We discuss the role of environmental controls such as parent material, age and precipitation on
the magnetic properties.
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Examples of The Effect of Magnetic Soil Environments On Time Domain Electromagnetic Data
During September 2004 a field study was carried out on the Hawaiian Island of Kaho’olawe to explore
various aspects of the effect of magnetic soils on time domain electromagnetic (TEM) measurements.
This field work was in support of two Strategic Environmental Research and Development Program funded
research projects (UX1355 and UX1414) whose goals are to investigate the source and spatial variability
of magnetic soil anomalies, to create a methodology for modelling the response of magnetic soils, and
to develop TEM data collection techniques that can better discriminate between the response of magnetic
soils and unexploded ordnance (UXO). Detailed electromagnetic surveys were carried out at a test site on
the island. The data from the surveys verify the commonly held belief that magnetic variations in the soil
can complicate the identification of UXO. However, the data also show that short wavelength variations in
the TEM response due to micro-topographic variations and coil orientation effects can generate responses
that could mask a UXO and/or result in a false positive. An overview of the surveys, a discussion of
preliminary results and some practical recommendations for surveying in magnetic soil environments will
be presented.
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Evaluating The Effectiveness of Varying Transmitterwaveforms for Uxo Detection In Magnetic Soil Environments
More LessMagnetic soils are a major source of false positives when searching for landmines or unexploded ordnance
(UXO) with electromagnetic induction sensors. In adverse areas up to 30% of identified electromagnetic (EM)
anomalies are attributed to geology. The EM phenomena that give rise to the response of magnetically viscous
soil and metal are fundamentally different. The viscosity effects of magnetic soil can be accurately modelled by
assuming a ferrite relaxation with a log-uniform distribution of time constants. The EM response of a metallic target
is due to eddy currents induced in the target and is a function of the target’s size, shape, conductivity and magnetic
susceptibility. In this presentation, we compare the range and variation of time decays of metallic targets (UXO
and scrap metal) with the time domain electromagnetic response of magnetically viscous ground. Electromagnetic
sensor measurements and modelling are used to assess the feasibility of multiple pulse widths to differentiate the
ground response from metallic targets. We present ground and metal responses measured by Geonics EM61-MK2
sensors with differing transmitter waveform characteristics.
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Progress in The Geophysical Delimitation of Fort St. Joseph, Niles, Mi
Authors Laura Smart, William Sauck and Daniel LynchFort St. Joseph was a French trading post built in 1691, later conquered by the English, and used until 1781. The exact location of the Fort was unknown for over a century, until archaeological investigations in 1998 recovered 18th Century artifacts along the southeast bank of the St. Joseph River. The site is located between a mid-20th Century landfill and a reservoir on the Saint Joseph River. Strata overlying the remains include a 0.3m organic surface layer and a 19th century silty gray plow zone approximately 0.25m thick. Cesium-vapor magnetometer/gradiometer, GPR, electrical resistivity, and EM induction surveys were employed in 2002 to guide archaeological excavations. All but one of the excavations oriented by the geophysical surveys yielded evidence of the Fort, as reported in SAGEEP 2003. Deposits associated with the geophysical anomalies include burnt pit features, building stones, and a charcoal layer derived from a burnt structure. The magnetometer survey was greatly expanded over the last two years, and additional excavations were made in 2004. At this time, only the boundary of the Fort facing the river has been defined. The surveys can be expanded in the up-river direction, but the landfill likely covers a significant area of the Fort.
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A Shallow Water Uxo Survey System
Authors Jim R. McDonald, Chester F. Bassani and David J. WrightWith support of the Environmental Security Technology Certification Program (ESTCP), AETC
is developing a UXO survey system for use in shallow water (up to 15 feet deep). The sensor platform
incorporates both an array of Cs-vapor magnetometers and a time domain EMI sensor array. A
performance modeling study defined the platform operational and deployment concepts. An
engineering design study established the performance characteristics of the new time-domain EMI
sensor, which incorporates an extended transmitter, coupled with an array of four receive coils. The
system incorporates a pilot guidance survey navigation aid, a dual GPS sensor system to provide
positioning and attitude information, and the Data Acquisition (DAQ) and Data Analysis Systems
(DAS) adapted from the Airborne Multi-sensor Towed Array Detection System (MTADS), which
incorporate 3-dimensional sensor position information into a 3-dimensional, physics-based target fitting
GUI. Additional marine components include an autopilot system to control the depth and attitude of the
sensor platform, digital magnetic compasses, a high-frequency digital imaging sonar, an inertial attitude
measurement sensor, depth sensors, and echo sounders. The tow vessel is a pontoon boat. The first full
scale demonstration at a former UXO target range will take place in 2005.
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Detection of Uxo In Marine Environments With Towed Array Ip Measurements
Authors D.D. “Skip” Snyder, Scott C. MacInnes, Douglas LaBrecque and Roger SharpeDuring World War II, scientists at the Naval Ordnance Laboratory (NOL) based the development
of the RX-1 Beach Mine Locator on “Induced Electrical Potential” (IEP), the phenomenon we now call
IP. Although deployed briefly in Okinawa just before the end of the war, there is no record of any
further development of the IP method for locating metal objects in the marine environment.
In this paper, we describe a research project undertaken jointly by Zonge Engineering and Multi-
Phase Technologies, LLC with the objective of demonstrating that IP is a practical method for detecting
metallic objects such as sea mines and UXO. The Strategic Environmental Research and Development
Program (SERDP) funded the project. During the project, we performed IP measurements in the
laboratory using a small metal target immersed in both fresh water and in salt water (30,000ppm NaCl).
These experiments provided us with an indication of the amplitude of the IP response that we can expect
from a target and the dependence of response amplitude on salinity of host medium. We used the
laboratory measurements to calibrate numerical models used to study electrode arrays for deployment in
full-scale experiments. Using results from our modeling, we assembled an electrode array and we
conducted experiments at the Mare Island Naval Shipyard in San Francisco Bay.
Our results confirm the presence of measurable IP responses associated with metallic targets.
The responses are 3-5 times larger in salt water than they are in fresh water. We estimate the intrinsic
response of metallic object in salt water is 100-200 ms (Newmont IP units). Detection range is
intimately tied both to the characteristic size of an object and to the size of the electric dipole used to
measure it. We conclude that measurement dipoles should have a length that is on the order of a
characteristic dimension of the object to be detected. Detection range is on the order of 3-5 dipole
lengths. Detection range is still an issue that can only be resolved with further research. Practical
exploitation of IP for UXO detection will require a submerged electrode platform with measurement
dipoles scaled to detect both small and large targets.
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Design and Testing An Airborne Squid Magnetometer for Uxo Detection
Authors T.J. Gamey, W.E. Doll, L.P. Beard and J.R. SheehanOak Ridge National Laboratory is conducting a project under SERDP to design, test and
field an airborne full-tensor magnetic gradiometer using a Superconducting Quantum Interference
Device (SQUID). This is the second year of a multi-year project. In this paper we discuss the
basic electronic design, the shielded operations, unshielded operations and orientation noise.
UXO signatures and results of ground-based walk over surveys are covered in the associated
paper by Doll et al. (this volume).
The electronics were designed to optimize the resolution of the digital data given
the limitations of 24-bit analog-digital converters (A/DC). This will be achieved to a
certain extent through variable gain settings and by halting operations during aircraft
turns. The greatest gains in resolution result from forcing the instrument to reset back to
zero each time it reaches a saturation threshold. This function requires reconstruction of
the original signal from a “saw-tooth” output.
Measurements during shielded operations were conducted to determine the
absolute minimum noise level in near-ideal laboratory conditions. In the bandwidth of
interest, these were found to be quite variable depending on the test facilities. Noise
levels at Tristan’s facilities were measured as 14.1pT/√Hz at 1Hz as compared to the
manufacturer’s measurements of 0.10pT/√Hz at 1Hz. The difference was attributed to
the high noise environment and potentially poorer shielding facilities. While in the
shield, a vertical dipole (85 μAm2) was synthesized and mapped using a calibrated loop
of wire dragged through the access port in the shield. The results were comparable in
character to synthetic models, indicating that the system was performing properly.
Unshielded static tests demonstrated an average background noise level of 46.5pT
(rms). They also revealed a requirement for additional RF-shielding to remove periodic
and random steps in the data. Three levels of shields have been designed and built.
Orientation tests measured a maximum instrument slew rate of approximately
42,000nT/s. This corresponds to motion equivalent to ±5° at 1Hz, which is within the
normal operating parameters of the helicopter while on line.
These tests also revealed several areas that require additional investigation. More
detailed measurements are required to calibrate the instrument for gain, orthogonality and
linearity. These additional tests are being planned for 2005 in cooperation with the
USGS-Denver, using their shielded facilities and calibration algorithms developed with
SERDP funding for their fluxgate tensor system.
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Combining Em and Lidar To Map Coastal Wetlands: An Example From Mustang Island, Texas
More LessWe combined airborne lidar and ground-based EM induction measurements with vegetation surveys along
two transects across Mustang Island, a barrier island on the Texas coast, to examine whether these methods can
be used to map coastal wetlands and associated geomorphic environments.
Conductivity varied inversely with elevation along both transects. Elevation and conductivity profiles correlated
reasonably well with habitat mapped in the largely imagery-based 1992 National Wetland Inventory (NWI),
but they possessed greater detail and identified misclassified habitat. Detail achievable with elevation and conductivity
data was similar to that achieved in on-the-ground vegetation surveys. Lowest elevations and highest conductivities
were measured in saline environments (marine and estuarine units, forebeach, salt marsh, and wind-tidal
flats). Highest elevations and lowest conductivities were measured in nonsaline environments (upland and palustrine
units, dunes, vegetated-barrier flats, and fresh marsh).
Elevation and conductivity data allow better discrimination among coastal wetland and geomorphic environments
than can be achieved from image interpretation alone. Future work should include evaluating the effect of
vegetation density on lidar-beam penetration, quantifying seasonal change in ground conductivity in fresh and saline
coastal environments, examining the geographic variability of elevation and conductivity statistics, and evaluating
the use of airborne EM sensors to measure ground conductivity at multiple exploration depths.
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Unconventional Deep-Water GPR Investigation of Drilling Obstructions
Authors Jutta Hager, Mario Carnevale and Brian R. JonesGPR was used at a dam rehabilitation drill site to assess the extent of a metal
obstruction within limestone bedrock beneath almost 100 feet of water. The obstruction,
thought to be pipe casing, was encountered during the emplacement of a concrete pile
cutoff wall. The metal had been removed by excavation to a depth of 20 feet and the
excavation filled with concrete, but further drilling encountered additional metal. The
problem was to determine if the metal persisted at depth. The lake bottom survey was
made more challenging by the constraints that the survey location was situated 5 feet
behind the dam and 5 to 15 feet from metal sheet piles of unknown depth. Other
constraints included spill-way releases during high water levels and power generating
schedules.
The survey was designed for an underwater investigation on the lake bottom using
the Tubewave-100 borehole radar antenna. Work was performed from a mini-tug, with
the antenna dragged along the lake bottom. Additional investigations were conducted in
the same manner to locate rebar in concrete structures.
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Uncommon Applications of Computer Assisted Radar Tomography
Authors Kate McKinley and E. Jorgen BergstromComputer Assisted Radar Tomography (CART) is typically best fit for projects where the
density of subsurface targets is high. It has proved to be invaluable in subsurface utility engineering
(SUE) projects and for cemetery mapping projects. In addition to such projects, we have found that
CART is very useful when high positioning accuracy is required, when a large amount of unimportant
targets exist in the subsurface, and when the project requirements include determining accurate target
sizes and shapes. Due to the ease of data acquisition and breakthroughs in data processing, these
surveys can still be performed cost-effectively. Over the past few years, we have encountered many
interesting applications for this technology. This paper will highlight some of these applications:
archaeology, depth profiling projects, and biological preservation.
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Senegal –Irrigation and Water Quality Project
More LessThe Colorado School of Mines has initiated a minor program in Humanitarian Engineering made
possible through a grant from the Paul and Flora Hewlett Foundation. A “Humanitarian Engineer” tries
to balance technical excellence, economic feasibility, ethical maturity, and cultural sensitivity to
significantly improve the lives of others. Clean groundwater is an important commodity needed
throughout the world. Through “Engineers Without Borders”, CSM has partnered with a community in
Senegal. In the village of Rao, Senegal, irrigation of onion fields is primitive and often is plagued by
problems of saltwater encroachment. Resistivity surveying will help to map both the depth to the water
table as well the salt/fresh water interface. The survey results will aid in the location of wells for
irrigation. At present, bucket watering of crops is the primary method for irrigation. We will replace
this slow and inefficient process with a drip irrigation system. A simple resistivity monitoring system
will be designed that can be used by the villagers and will provide a signal when the fresh well water has
been drawn down so much that saltwater has invaded.
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Archaeological Reconnaissance at Tel Yavne, Israel: 2-D Electrical Imaging and Low Altitude Aerial Photography
Authors Paul C. Bauman, Dan Parker, Avner Goren, Richard Freund and Phillip ReederTel Yavne in Israel is the site of the ancient city of Yavne. Located about 20 kilometers south of Tel Aviv, and about 8 km inland from the ancient seaport of Yavne Yam (meaning Yavne by the Sea), it is believed that underneath the tel (an archaeological mound) are the remains of more than 3,000 years of continuous occupation. The tel, at 4 hectares in area and approximately 30 m in elevation, is relatively large in comparison to other ancient sites in Israel. To date, no excavations have been carried out at the site. In preparation for excavation work at a later date, electrical resistivity tomography (ERT) surveys, ground penetrating radar surveys, and low altitude photography from kites and balloons were carried out at the site. This paper will discuss the ERT and photographic surveys. The objectives of these two surveys were to delineate the plan view and vertical extent of accumulated cultural debris, and to identify particular areas for initial test pitting by archaeologists. Eight ERT cross-sections were imaged, ranging in length from 80 to 140 m. Approximately 500 low altitude photographs were shot. Specific features possibly identified include a 9th century B.C.E. (before the common era) water system, the Philistine city wall dating from 790 B.C.E., the ruins of a 12th century C.E. Crusader castle, and numerous architectural features from the Mameluke, Ottoman, and Palestinian periods of habitation. This is the first time that non-destructive techniques have been used in the first phase of an
archaeological exploration program in Israel at such an important, well recognised ancient site.
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Using Time-Domain Electromagnetics To Map The Transition of An Aquifer To An Aquitard
Authors David J. Hart and Curtis L. ThomasThe Eau Claire Formation laterally transitions from a sandstone aquifer to a shale aquitard in
southern Wisconsin. We used a geophysical method, time-domain electromagnetics (TEM), to map that
transition along two 15-mile transects. Available geologic well logs located on the transects show no
shale to the west, a shale thickness of more than 100 feet at the transects’ centers, and thin shale to the
east. Using well logs alone, we could not precisely locate the edge of the shale aquitard or the determine
nature of the transition between the sandstone aquifer to the shale aquitard.
Our TEM surveys agreed with the well logs, provided a better location of the edge of the shale
aquitard, and showed a gradual thickening and deepening of the shale at the center of both transects. To
reduce equivalence common in electrical methods we used formation resistivities taken from normal
resistivity measurements in the geologic formations encountered in the TEM surveys. These TEM
results can be used to develop better geologic models of the Eau Claire Formation; incorporating the
transitional nature of this formation from sandstone to shale will help to provide more realistic
groundwater flow simulations for this region.
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Characterization of A Fractured Aquifer Using Multicomponent Seismic Data
Authors Nedra D. Bonal and Clark R. WilsonNine-component seismic equipment from the Network for Earthquake Engineering Simulation
(NEES) at the University of Texas is used to determine relationships between seismic and hydrogeologic
properties in a near-surface aquifer. The study area is a fractured limestone in the recharge portion of the
Edwards aquifer in Hays County south of Austin, Texas. Experiments are developed to measure
fracture-related seismic anisotropy and its relationship with the hydrogeologic characteristics of the
aquifer. One of the NEES seismic sources is a small vibrator capable of generating waves up to 500 Hz.
Three-component data from a traditional hammer source are also recorded.
The goal of this study is to estimate in situ fracture parameters of orientation, density, and filling
material from seismic data. Estimation of these parameters should be useful for determining
groundwater flow and storage, evaluating recharge enhancement, and understanding environmental
remediation of fluid contaminants.
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Seismic Reflection Imaging of Suspected “Windows” In The Upper Confining Unit of The Memphis (Tennessee) Aquifer
Authors Angela B. Pell, James B. Harris and Brian A. WaldronUntil recently, the Memphis (Tennessee) aquifer was believed to be well protected from
downward vertical seepage of urban surface waters and groundwater in the surficial (shallow) aquifers
by clay-rich layers of the upper Claiborne confining unit. However, recent studies of the Memphis
aquifer and upper Claiborne confining unit show evidence of “windows” through the confining layer in
the Memphis area. To investigate the size and structure of these confining layer breaches, S (shear) -
wave seismic reflection profiles were acquired at two locations in the Memphis area. The reflection data
were collected in SH mode (sensitive to horizontally polarized shear waves) and the seismic energy was
generated by horizontal sledgehammer impacts on a steel I-beam oriented perpendicular to the spread.
Data quality is moderate with variable amplitude, coherent reflection energy on all of the profiles.
However, parts of the profiles are dominated by diffracted energy, indicating complex stratigraphy
and/or structure. The most significant features imaged on the seismic data are near-surface
paleochannels (~ 140 to 350 m wide) cut into and through the confining layer, that may provide a
hydrologic connection between the surficial (paleochannel fill) and Memphis aquifers.
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Using Cpt To Estimate An Aquifers Heterogeneity
Authors Axel Tillmann, Zsuzsanna Nyari, Andreas Englert, Imre Fejes, Jan Vanderborght and Harry VereeckenThe intensive growth of industrial and agricultural activity causes an increase of polluted
areas. In order to predict the spreading of near-surface contamination it is essential to be familiar
with the hydrogeological parameters of the investigated earth. The cone penetration technology
is capable to resolve the structure of the subsurface in detail and logs various physical parameters
during soil penetration. Cone penetration tests (CPT) were performed at the test site Krauthausen
to investigate the aquifer's heterogeneity in detail.
We present the results of the CPT survey at the test site and the estimated three dimensional
heterogeneous distribution of physical soil properties. We estimated the hydraulic conductivity from
those data using regression analysis. Therefore the CPT method is capable to gain a spatial, highly
resolved data set of the hydraulic conductivity distribution. Furthermore we used this data set
to estimate the spatial heterogeneity of hydraulic conductivity, i.e. the correlation length and
anisotropy within the aquifer.
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Possible Extent and Depth of Salt Contamination In Ground Water Using Geophysical Techniques, Red River Aluminum Site, Stamps, Arkansas
Authors Gregory P. Stanton and Wade KressA surface-geophysical investigation of the Red River Aluminum site at Stamps, Arkansas, was
conducted in cooperation with the Arkansas Department of Environmental Quality to determine the
possible extent and depth of saltwater contamination. The two-dimensional, direct-current resistivity
method identified resistivities less than 5 ohm-meters which indicated possible areas of salt
contamination occurring in near-surface or deep subsurface ground water along four resistivity lines
within the site. One line located east of the site yielded data that demonstrated no effect of salt
contamination. Sections from two of the five data sets were modeled. The input model grids were
created on the basis of the known geology and the results and interpretations of borehole geophysical
data. Data from the resistivity lines indicate both near-surface and subsurface saltwater contamination.
The near-surface contamination appears as low resistivity (less than 5 ohm-meters) on four of the five
resistivity lines, extending up to 775 meters (2,542.8 feet) horizontally in a line that traverses the entire
site south to north. Model resistivity data indicate that the total depth of saltwater contamination is about
18 meters (59 feet) below land surface.
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A Comprehensive Geophysical Case Study at A former Radioactive Waste Disposal Site In The Columbia River Valley, Southeastern Washington
More LessAs part of a site investigation, sponsored by the United States Department of Energy, at the
Hanford superfund site in southeastern Washington, a magnetics, electromagnetics (EM), and resistivity
survey was completed. A dense coverage of geo-referenced EM and magnetics data was simultaneously
obtained over the 50-acre site to delineate the location of buried waste disposal trenches in the Hanford
alluvial formation. Radioactive contaminants of concern in the trenches consisted of Uranium,
Plutonium, Cesium, Strontium, and Technetium. The EM and magnetics results confirmed suspected
trench locations and the location of pipelines used to transport the liquid waste to the trenches.
High resolution resistivity (HRR), conducted in a pole-pole array, was used to image the vertical
and lateral distribution of the electrical resistivity beneath a single trench. Five parallel lines of lengths
200m to 300m and spaced approximately 8m apart indicated that the plume has migrated downward
from the trench to 30m below ground surface. A hydraulically resistive layer of fine silt has
significantly impeded the plume from reaching the water table. An additional line, which bisected
several trenches, suggested that the plume is extensive and the contributions from each trench combine
to form a single contiguous plume. Remediation strategies are currently being considered.
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The Use of Geophysics To Map Low Level Radioactive Waste Disposal Sites at former Air force Weapons Storage Areas
Authors Richard P. Allen and Ronald A. CrowsonAnecdotal reports of the burial of wipes, personal protective clothing, and other items used in the
maintenance of early weapons systems prompted the Air Force to initiate a series of investigations to
characterize the weapons storage areas (WSAs) at several former Strategic Air Command (SAC) bases.
These investigations are being conducted at five former SAC bases that were closed and are being
redeveloped, so it is important to ensure the public is protected against potential exposure to low levels
of radiation.
As specific information about weapons maintenance activities is 45 to 50 years old, and since
these activities took place during the height of the Cold War, when secrecy and “need to know” were
paramount to maintaining our national security, the record is disappointingly sparse.
Investigations consisted of radiological measurements in open areas and inside buildings, and a
dual-disciplined geophysical study, with primary reliance on multifrequency electromagnetic profiling
(EM) to characterize areas of interest. Traverse separation was 5 feet, a parameter dictated by the
anticipated size of the target. EM anomalies were further characterized with ground penetrating radar
(GPR). A test-pitting program at one of the bases confirmed the interpretation of several geophysical
anomalies, none of which represented targets of interest.
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Computer Simulation of Hydrocarbon Flow and Wave Field for Interpretation GPR Measurements In Contaminated Sites
Authors Henryk Marcak and Tomislaw GolebiowskiLocation of hydrocarbon contamination in the ground using a GPR system should be preceded
by a choose of the interpretative model. Four models i.e. Plume, Layer, String and Stochastical have
been described in the paper. Each model is dependent on the elapsed time since the initial discharge of
contaminants and the GPR surveys. The GPR measurements carried out in contaminated areas, after a
long time from discharge, showed the importance of Stochastical Model in interpretation of GPR data.
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High Resolution Ground Penetrating Radar Investigations In The Archeological Site of Cavallino (Lecce, Italy)
Authors Giovanni Leucci and Sergio NegriA Ground Penetrating Radar (GPR) survey was been carried out in the archaeological site of
Cavallino (Lecce, Apulia, Italy) in collaboration with the Dipartimento di Beni Culturali of the
University of Lecce. The archaeological site of Cavallino, located only 6 kilometres south-east of
Lecce, corresponds to an enormous settlement, about 70 hectares large, of notable historical
importance.
Keeping in mind the vastness of the site, the archaeologists selected an area, of about 4000m2, for a
systematic archaeological excavation. Contemporarily, GPR investigations using high-resolution
acquisition techniques (parallel profiles at 0.25 m spaced) were performed in a test-zone located
inside the same area. The objective of this preliminary geophysical investigation was to verify the
effectiveness of the technique for a spatial definition of the archaeological structures with nondestructive
methods, in view of their application in the rest of the site, that, for obvious reasons,
could not be entirely excavated in brief times.
The GPR data, previously processed, were used for 3D representations, in order to visualise in a
more effective manner the three-dimensional position of the anomalies evidenced in the single radar
sections. The results obtained in the survey underline the presence of structures of regular shape
related to the presence of walls confirmed by the excavations that are still in progress.
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3D Imaging Archaeological Tomb By Vertical Electric Soundings
Authors Keisuke Ushijima, Hideki Mizunaga, Toshiaki Tanaka and Kazuo MiyamotoApplication of geophysical methods has increased to investigate near-surface horizons of
interests in related to environmental and engineering geophysics because geophysical methods are
cost-effective and large areas can be quickly surveyed at relatively low cost without borings and trench
excavations. The most productive geophysical methods are Ground Penetrating Radar and Electrical
Resistivity methods for which the target exhibits the greatest physical contrast with respect to the
surrounding formations. However, the geoelectrical geophysics is very difficult to predict the
sub-surface using conventional techniques because of the shortage of the resolution. These geophysical
techniques have required upgrading of data acquisition accuracy of the methods using a multichannel
resistivity tool such as Handy Archaeological Resistivity Meter developed by the joint research of
Kyushu University and OYO Corporation in Japan. Geoelectrical methods have the economic
advantages to solve various archaeological problems. However, there was no successful 3D computer
program required for interpreting observed apparent resistivity data. In the present paper, a robust 3D
computer program was developed and applied to archaeological prospection. Results of 3D inversion of
VES data are compared with the results of GPR method and evaluated with archaeologists of
Archaeological Society of Japan.
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Cavity Detection By Dc Resistivity Imaging In Khalifa City B, Emirate of Abu Dhabi, Uae
Authors Baoshu Li, Ali Taleb and Hassan Al JafriUnderground cavities associated with the dissolution of gypsum and now filled with saline
ground water were encountered during the construction of infrastructure in Khalifa City B, Emirate of
Abu Dhabi. Heavy ground water flow through the cavities delayed the works for months. Moreover the
cavities are considered hazardous to the future civil works. DC resistivity imaging technique was
employed to detect the cavities, which are characterized by resistivity lows due to the infilling of saline
ground water. Quality analysis of field resistivity data was set as the first step of data interpretation
because poor quality data, mainly resulting from the dry fill materials at the surface result in false
resistivity anomalies not relevant to cavities. The pole-pole array was found the most suitable method to
provide cost-effective and accurate field data and reliable results. Cavity detection included the
identification of cavities and estimation of their vertical thickness, lateral extension and depth of cavities
below the existing ground surface. The cavity-related resistivity anomalies disturb the surrounding geoelectric
layers and form low resistivity window zones and shadow zones on both apparent and inverted
resistivity sections. The ability of DC resistivity imaging technique to define detailed features of cavity
depends significantly on calibration boreholes and careful interpretation of the data.
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Lessons From Northern Alabama: Multi-Technique Geophysical Investigation Characterizing The Bedrock and Fracture Network
Authors John M. Bartos Jr., Robert K. Davis, Dr. Bradley J. Carr and Colin MellorGolder Associates Inc. (Golder) and Geophex, Ltd (Geophex) performed a geophysical
investigation at a closed manufacturing plant in Alabama. This investigation used multiple geophysical
techniques (surface and borehole) to characterize the unconsolidated and limestone-shale bedrock at the
facility. Seismic refraction and direct-current resistivity distinguished areas of high permeability zones
(lineaments) across the site and offsite. Induced polarization was used to locate areas of NAPL in both
the residuum and bedrock. Borehole geophysical logging characterized the lithology, water-bearing
fractures, and distinguished the different fracture networks present on the site.
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Facilitating The Incorporation of Geophysics Into Geotechnical Practice
Authors F. Alex Rutledge, Dr. Matthew Mauldon and C.J. SmithAlthough geophysical methods have long been a mainstay of oil and gas exploration, they are not
yet routinely used in geotechnical practice. Recent advances in computing technology and reduced cost
of geophysical equipment have led to many advances in high-resolution geophysics that can be applied
to site investigation of engineering projects. Advances in these techniques and their applications,
however, have not been sufficiently communicated to practicing engineers. A Primer on Geophysics for
Geotechnical Practice has been prepared to help communicate basic understanding, advances,
applications, and limitations of the most commonly used geophysical techniques to practicing engineers.
The project engineer is often the one who determines the extent and type of subsurface investigation
needed, and, therefore, the dissemination of this information to the engineering community is critical for
the advancement of near-surface geophysics. A better understanding of the applications and limitations
of geophysical techniques within the engineering community will lead to more efficient site
investigation, and reduced costs associated with encountering unexpected subsurface conditions.
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Slope Stability Analysis of The Iliamna Volcano, Alaska, Using Aster Tir, Srtm Dem, and Aeromagnetic Data
More LessI use thermal IR and digital elevation models to create a hazard index that characterizes slope
stability on active volcanoes using Iliamna, Alaska as a case study. ASTER and SRTM data were
processed and scaled, then a script was run to plot the hazard index based on hydrothermal emissions
and topographic slope. The plots display areas at risk for slope failure, which correlate well to the
geologic field studies. These scripts can be run quickly and easily to improve field safety for geologists,
geophysicists, and other field crews.
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Sonic Log To Estimate Engineering Characteristics of Deep Mixed Columns
Authors Ali Porbaha, Farid Ghaheri and Anand J. PuppalaThe results of a series of sonic log tests are presented to estimate engineering characteristics
of deep mixed soil cement columns of 900 mm in diameter treated up to a depth of 13 m using deep
mixing (DM) technology. Deep mixing is a ground modification technology that blends soil in situ
with a cementitious material, such as cement or lime, using specially designed equipment with
augers and paddles. Data obtained from the field are compared with those from core samples tested
using unconfined compression tests. The results show that porosity of the cement treated soil is in the
range of 40 and 44 percent, while the shear wave velocity varies between 595 and 1471 m/s. A linear
equation correlates porosity and shear wave velocity. In addition, the porosity of the soil generally
decreases with increase in soil’s compressive strength; and a linear equation represents the variations
in porosity with regard to the unconfined compressive strength. For the treated soil columns the
radioactivity ranges between 70 and 137 cps, while compression wave velocity changes between
1786 to 2500 m/s. The details of filed test, shear wave and compression wave velocities, shear and
Young’s moduli, porosity, and some correlations of field data with laboratory tests are presented.
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Evaluation of Linearity of First Mode of Vibration In Resonant Column Testing
Authors Zahid H. Khan, Giovanni Cascante and Hesham El NaggarThe shear strain along the height of a specimen in resonant column testing (ASTM D4015-92) is
assumed to vary linearly when evaluating its dynamic shear modulus and damping ratio. To examine
this assumption, specimens of dry sand, mine tailings, and cemented sand are tested at different
confinement and shear strain levels. The coupling between the cemented-sand specimen and the top and
bottom platens is enhanced using three different agents: gypsum cement, Portland cement, and epoxy
resin. The mode shapes are measured using a miniature accelerometer that is attached to the specimen at
predefined elevations and a reference accelerometer placed at the top of the specimen (driving plate).
The dynamic properties of the specimens are computed from the responses of both accelerometers. The
measured mode shapes for dry sands and mine tailings are linear but the cemented-sand specimen
displayed a nonlinear behavior in terms of the mode shape and change in dynamic properties with the
strain level. The accuracy of the measured mode shape and dynamic properties is improved as the
coupling between the specimen and the platens is enhanced. The epoxy resin produced best coupling,
followed by Portland and gypsum cements, with the latter two only effective at low confinement and
strain level.
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GPR and Archaeological Excavations at The West Point Foundry, New York
Authors Kimberly Finch and Charles T. YoungThe West Point Foundry in Cold Spring, New York, was a major producer of ordnance during the Civil War and manufactured sugar machinery, railway locomotives, and the nation's first locomotive. Now, it lies forested and disheveled with only wall foundations visible on the surface. Conventional archaeological methods provided information on site history and evolution, but the location of buried water channels remained unknown. The channels were used to supply for a giant water wheel which powered machinery. Ground penetrating radar was chosen to search for the channels because it was relatively rapid to deploy, and the data directly reveal the depth dimension. Small scale surveys were carried out at nine assessable areas within the site which were thought to contain the channels. Direct evidence of the subsurface was obtained by excavating at radar anomalies. All structures excavated were not water channels but will prove useful in interpreting the history of the site.
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A Simple and Effective CDI Analysis Software
Authors Garret A. Veloski and Ronald J. LynnA conductivity depth image (CDI) viewer program was developed for analysis of airborne EM
data inversions created in EM Flow and EM1DFM. The software was written in LabVIEW 7.0 for the
Windows platform and features an assortment of tools. The CDI intensity plots can be color-enhanced
programmatically according to image statistics. The cursor positions in CDI profiles are geographicallylinked
to an ActiveX imagery window with moving map capabilities and real world coordinates.
Apparent conductivity sounding profiles can be viewed simultaneously for any X-position along the
length of the geo-linked CDI image. The user can create custom map underlays in ECW compressed
image format using free software available on the Web. Features of interest can be selected/edited and
added to a list for export into a GIS or GPS compatible format. The CDI images can also be exported in
geo-referenced ER Mapper BIL format or HTML. The application can be bundled with 1D inversion
data and distributed with an installer to customers royalty-free.
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Quality Control/ Quality Assurance Software for Digital Geophysical Mapping
Authors Amy N. Walker and Lorraine GodwinThe Huntsville Center has been developing Quality Control/ Quality Assurance
(QC/QA) techniques and documentation to promote more consistent, higher quality
geophysical investigations. The Center partnered with Geosoft Inc. under ESTCP funding
to develop these techniques into a software package that runs under their Oasis montajTM
platform. The principal goals of the project include: standardization of QA/QC processes
within the UXO community, improved data quality, improved detection methods and to
provide a standard software platform for algorithm sharing. The software package has
been supported and applied in the field since April 2002, with continuing enhancements
and additions to evolve into a capable tool set. Utilizing the standardized software tools
and techniques developed under this project will help ensure acceptable quality standards.
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Landmine and Uxo Discrimination Using Beam forming Tomography
Authors David Tillson and Beiyuan LiangThis paper presents results of processing landmine and UXO data collected with a
3-D GPR system using beam forming tomography. We provide a brief summary of the
beam forming tomography concept for discriminating UXO based on processing data
provided by the EPFL\LAMI\DeTec project Lausanne. Using this technique the efficacy
of producing high-resolution 3-D images using synthetic GPR array processing was
demonstrated. We follow by a description of a new wide band linear array GPR system
that uses step-frequency continuous waveform (SFCW). This 3D-GPR system is capable
of operating in a stand-off mode; surveying a 2.4 meter swath at speeds up to 5 km/hr;
penetrating depths > 2 meters; and providing 5 cm object resolution. Results of
processing landmine and UXO data collected from a European training site with this
system are presented. A comparison of real time low-level data processing capabilities
provided with the 3D-GPR system and advanced beam forming tomographic imaging and
analysis capabilities using a separate software package is provided.
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Time-Lapse High Resolution Seismic Imaging of A Catastrophic Salt Dissolution Sinkhole In Central Kansas
Authors Jamie L. Lambrecht, Richard D. Miller and Steve DurrantTime-lapse 2-D high-resolution seismic reflection surveys successfully imaged and mapped
changes in structural features associated with a sinkhole that formed catastrophically after dissolution of
the Permian-age Hutchinson Salt in central Kansas (Figure 1). Symmetric steep sided cone structure
defined by reverse faults formed instantaneously continuing over time to gradually enlarge and elongate
along normal fault planes. Two orthogonal high-resolution seismic lines were acquired, in 1998 and
2004, to map the upper thousand feet and resolve structural features controlling development subsidence
rate preferential dissolution mechanism for fluid movement and to predict future growth. High
frequency vibrator and high-resolution seismic methods were used to acquire data from a 204 channel
fixed spread. Stations used in 1998 were as close as possible reoccupied on the 2004 survey. Common
mid-point stacked sections depict a very disturbed subsurface that has undergone multiple discrete
phases of loading, failure, and subsidence. Stress built up in roof rock overlying the salt void until its
strength is surpassed when failure, and subsidence occurs (Figure 2 (a), (b), and (c)). Strain associated
with layers bridging voids outside the tensional dome appears to be controlled by normal faults. Oilfield
disposal practices provided original fluids and pathway that initiated the dissolution process.
Currently shallower groundwater fuels the dissolution process with little or no contribution from
oil-field brines. Growth appears to be controlled by geologic trends with failure occurring much more
plastically during the later years, which initially growth was characterized by rapid brittle
deformation.
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Observation of Shear-Wave Splitting In Quaternary Sediments of The New Madrid Seismic Zone: An Indicator of Insitu Stress Conditions?
More LessShear-wave splitting, induced by stress-aligned inclusions (pore spaces, fractures, faults), causes
shear waves to exhibit directional polarizations in response to propagation through azimuthally
anisotropic media. This phenomenon is manifested by differences in shear-wave velocity between
waves traveling parallel (S1 - fast shear wave) and perpendicular (S2 - slow shear wave) to the trend of
the inclusions. This investigation provides further evidence of shear-wave splitting in Quaternary
sediments of the Lake County uplift (New Madrid seismic zone; central United States). Preliminary
analysis of a multicomponent downhole data set from Ridgely, Tennessee, recorded using hammer and
mass sources, indicates azimuthally-controlled shear-wave splitting related to in-situ tensional stresses
developed across the crest of the Lake County uplift. Orientation of the split shear waves, determined
from particle motion plots of the three-component downhole records, shows alignment of the S1
polarization with the major axis of the topographic uplift, and analysis of travel-time delays between S1
and S2 suggests anisotropy values of 10 to 12% for the upper ~30 m of the subsurface.
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Near-Surface Cavity Detection By High-Resolution Seismic Reflection Methods Using Short-Spacing Type Land Streamer
Authors Tomio Inazaki, Shigeki Kawamura, Oshie Tazawa, Yoshihiro Yamanaka and Naomi KanoHigh-resolution seismic reflection surveying by means of short-spacing type Land Streamers was
conducted to detect near-surface cavities. The target cavities were inferred to have high potentiality of
collapsing because they had been excavated about 60 years ago as air-raid shelter tunnels or drifts of
lignite mines. Until now, several surface geophysical methods have been applied to the cavity detection,
however, they only provided blurry images for cavities due to the poorness of spatial resolution or
insufficiency in obtaining information at the target depths. In contrast, our short-spacing type Land
Streamer tools, which were originally developed by the first author, can provide high-resolution images
up to 30 m in depth.
We applied three types of Land Streamer tools to the cavity detection: a horizontal geophone
array at 30 cm spacing, the same array but 20 cm spacing, and an accelerometer array at 20 cm spacing.
Each array has 48 channel sensors mounted on a woven belt which is easy to tow by hand. The targets of
this study were abandoned drifts of lignite mine at Nagoya, central Japan, and air-raid shelter tunnels
excavated in pyroclastic flow deposits at Kanoya, southern Kyushu.
As a result, distinct diffraction anomalies were imaged in unmigrated stacked sections at the just
points where actual abandoned cavities were checked by sounding or drilling from the surface. Some
anomalies occurred at depths shallower than the inferred horizons of shelter tunnels or lignite mines,
which indicates roof falling and upward growing of cavities. It is concluded that our Land Streamer tools
have high capability of detecting cavities smaller than 2 m in diameter located 5 to 10 m in depth.
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A Land Streamer Aided, Three-Dimensional (3-D) Seismic Reflection Survey, Belt, Montana
More LessThe Three-Dimensional (3-D) seismic reflection method has not been extensively utilized for
shallow subsurface investigations because of the relatively high cost of performing 3-D surveys. We
have designed and constructed a system that makes 3-D seismic reflection an affordable option for
shallow subsurface exploration by significantly reducing time and manpower. In a fashion similar to
marine work, an All Terrain Vehicle (ATV) tows an array of four parallel seismic cables, or land
streamers. Each streamer consists of 24 gimbaled geophones. The ATV drags the array from station to
station and shots are taken while the array is stationary. We tested our system near Belt, Montana to
help locate abandoned subsurface coal mines. For this survey, our receiver, receiver line, source, and
source line spacings were all 1 m. In total, we covered a surface area of 100 m by 34 m and achieved a
nominal fold of 24. Typical combined advance and occupation times for each station were less than 30
seconds using a crew of three people. A brute stack shows horizontal layering of the local geology.
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High-Resolution Seismic Reflection Survey Using Land Streamer In A Large Urban Area
More LessHigh-resolution shallow seismic reflection surveying using SH-wave type Land Streamer was
conducted in the Tokyo Metropolitan area, where more than 25 million inhabitants concentrate in small
but highly developed region of 3,500 square km. While seismic reflection surveys have been frequently
conducted in the area to delineate relatively deep geologic structure, shallow reflection surveys have
been exceptional due to the difficulty in surveying at such a high land-use area as well as under high
noise level condition caused by heavy traffic and industrial activities. In contrast, the Land Streamer
makes it easy to set a survey line and acquire high-quality data even in urban area because it was
originally developed to be utilized on a paved area and to sense SH waves instead of P wave signals
which are prone to be affected with ground noises. We applied it in combination with borehole logging
and passive surface wave method to field surveys in the Tokyo Metropolitan area. The objectives of the
field survey were to clarify the detailed structure in Holocene soft sediments, and to characterize them
based on the S-wave velocity and other physical properties. As a result, the seismic reflection surveys
helped to interpret the sedimentary sequence of Holocene and to assess the geotechnical properties of the
surface sediments in the area.
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Detecting Cavities With Seismic Refraction Tomography: Can It Be Done?
Authors Jacob R. Sheehan, William E. Doll, David B. Watson and Wayne MandelConventional seismic refraction analyses (e.g. delay-time or generalized reciprocal method)
generally perform poorly for imaging many karst-related features because first-arriving seismic waves
can generally circumvent the low-velocity target of interest without a major impact on travel time,
particularly where the target is three-dimensional. We are using synthetic models and field data to
evaluate the performance of seismic refraction tomography codes for karst detection. Two-dimensional
karst models have been created and used to generate synthetic travel time data for tomography analysis.
The results of this analysis suggest that the presence of a feature can sometimes be determined, but the
velocity is not accurately represented. In no synthetic case that we have tested has the velocity of the
cavity been an accurate approximation to the true low velocity. In contrast to the inconclusive synthetic
results, we have refraction tomography data that clearly indicate karst features. A refraction tomography
data set collected on the Oak Ridge Reservation shows a well-defined low velocity feature that crosses
three parallel lines along an axis that extends more than 200 meters. The feature that was detected has
velocities of about 1500-2000 m/s in a matrix of 3000-4000 m/s, reasonable velocities for a mud filled
void in saprolite at these depths, rather than having a velocity slightly lower than the matrix velocity, as
would be expected from our synthetic study. This suggests that the synthetic models are incomplete or
inaccurate. In one case, matrix smoothing of the synthetic model before generation of synthetic
traveltimes generates synthetic results that better match field results.
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