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14th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 04 Mar 2001 - 07 Mar 2001
- Location: Denver, Colorado, USA
- Published: 04 March 2001
21 - 40 of 129 results
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Integrated Use Of Geophysics, Gis And Archeological Records To Locate Seneca Village
Authors Roelof Versteeg, Nan Rothschild, Diana Wall, Cynthia Copeland, Herbert Seignoret and Koray ErgunSeneca Village was an African American - Irish village located in what is now New York City's
Central Park. As part of the construction of Central Park the village was razed in the 1850s and no
surficial remnants remain. Increasing interest in the history of Seneca Village led to an effort to use a
combination of geophysics, archeology and GIS to locate possible remnants of the village. This effort is
complicated due to possible intense (but unknown) site modification during the construction of the park
and post park infrastructure construction. Using a range of geophysical tools (GPR, resistivity and
EM31) a suite of layers of geophysical data was collected. These were integrated in a GIS with a high
quality basemap (which contains the current park layout), the subsurface infrastructure layout and
orthorectified and digitized historical maps. By interpreting these results jointly a number of more and
less promising areas were identified which possibly can contain undisturbed remnants of Seneca Village.
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Numerical Inversion Of Borehole Flow Logs
More LessBorehole flow logs are most effectively interpreted in conjunction with other borehole data.
Other geophysical logs are needed to help identify the hydraulically active zones within the scatter of
flow measurement data produced by borehole conditions. Ambient hydraulic-head conditions also need
to be taken into account in flow-log analysis. Hydraulic-head differences between zones intersecting the
borehole can be eliminated from the interpretation by subtracting a flow profile obtained under ambient
conditions from another flow profile obtained under stressed (pumping or injection) conditions. Fitting
of hydraulic flow model predictions to the flowmeter data set insures that flow interpretations are
physically possible and yields quantitative estimates of both zone transmissivity and zone hydraulic
head. Applications of flowmeter log interpretation methods are illustrated using data obtained in
fractured sedimentary and crystalline bedrock aquifers in Arizona, Wisconsin, Kentucky, and New York.
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Borehole-Surface And Cross-Borehole Mise-Á-La-Masse Delineation Of A Radial Injection Tracer Experiment In Partially Saturated Fractured Basalt
Authors Robin E. Nimmer, James L. Osiensky and Kenneth F. SprenkeBorehole-surface and cross-borehole mise-à-la-masse (MALM) measurements were taken over
time during an eight-well, radial injection, tracer experiment in partially saturated, fractured, Columbia
River basalt. In this experiment, an enhanced conductivity tracer stream was energized directly through
a current electrode placed in the bottom of the injection well. A constant concentration tracer solution of
potassium chloride was injected continuously above a perched water table at an average rate of 10
liters/day under a constant hydraulic head for 34 days. An asymmetrical ground water mound developed
over time during which borehole-surface and cross-borehole MALM measurements were taken to
delineate migration of the tracer. A 15 x 15 array of porous pot electrodes (copper sulfate), located
symmetrically about the centrally located injection well, was used for the borehole-surface MALM. The
cross-borehole MALM utilized 66 downhole electrodes in the eight wells combined with seven transect
arrays each comprised of six land surface, porous pot electrodes. Changes in the electrical potential
distributions over time were contoured to delineate anomalies caused by the presence of tracer solution
in the fractured basalt. Borehole-surface measurements delineated the lateral migration of tracer over
time. The cross-borehole measurements helped delineate the depth of a possible preferential pathway in
the fractured basalt.
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A High-Resolution, Short-Range, Directional Borehole Radar
Authors David L. Wright, Jared D. Abraham, David VonG. Smith and S. Raymond HuttonThe U.S. Geological Survey (USGS) has recently developed a prototype directional
borehole radar system designed to complement a commercial system that the USGS has used for
several years for fracture mapping in crystalline rock. The new prototype is designed for higher
resolution, shorter range operation. We have numerically modeled several types of antennas
using finite difference time domain (FDTD) code. Based on the FDTD numerical modeling, we
designed, fabricated, and physically tested a pair of cavity-backed monopole antennas. The
antennas were then incorporated into a pulsed time-domain radar system. Tests of the system in
a laboratory sand pack and an outdoor pit have demonstrated antenna directionality, good
detection of small metal and dielectric targets, and radial resolution of a few centimeters. Such a
radar system, with some modifications, might find use in utility and other obstacle avoidance in
horizontal drilling operations.
An important part of the development of the directional radar is data processing and
visualization. We can process our data in a number of ways, including average waveform
removal, filtering, and range-gain compensation. After processing, radar data can be displayed
in three dimensions using a graphical user interface (GUI). Received waveforms are mapped
into a cylindrical volume, where each waveform fills a cylindrical wedge. The angle subtended
by each wedge depends on the total number of waveforms acquired azimuthally in the borehole
at each depth. The length of the image cylinder is a function of the number of stations occupied
by the radar in the borehole. The GUI allows the operator to visualize the data using a variety of
tools, including: rotate, zoom, annulus view, slicing, and control of the color table into which
data values are mapped.
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Airborne And Ground Geophysical Surveys For Locating And Mapping Underground Storage Tanks At Bellows Air Force Station, Hawaii: An Integrated Approach
Authors Sandra A. Takata, Jeffery B. Hackworth and Doug McConnellAirborne and ground based geophysical surveys were conducted at Bellows Air Force
Station (BAFS), Oahu, Hawaii to locate buried metal potentially representing underground
storage tanks (USTs) and other buried debris of environmental concern. The airborne survey
was used for reconnaissance to screen approximately 3,000 acres of land and shallow offshore
areas at BAFS for buried debris. Once the airborne anomalies were evaluated for their potential
to have a UST source, focussed ground surveys were conducted to confirm the location and to
more accurately characterize anomaly source objects.
BAFS was established in 1917 as the Waimanalo Military Reservation and was
deactivated in 1970. Throughout BAFS’ history, USTs along with their associated pipelines
were installed to maintain base activities. Over the years, structures associated with the USTs
have been demolished resulting in the uncertainty of the UST locations.
Over 650 geophysical anomalies were identified in the airborne survey (both
electromagnetic and magnetic data). Following review of the flight path videos and further
scrutinizing of the data, most of the anomalies were attributed to surface cultural features or
geology and were eliminated from further investigation. The remaining 73 anomalies were
located on the ground and visual field reconnaissance at these locations eliminated some
anomalies from further investigation based on the terrain being unsuitable for construction and
surface metal hidden under thick canopy. Eighteen of the 73 anomalies were selected for
detailed ground surveys. The follow-up ground-based geophysical surveys were conducted
using frequency- and time-domain EM, magnetics and ground penetrating radar. Select
anomalies identified in the ground geophysical data were trenched and the sources excavated.
The technical approach of integrating site knowledge with airborne geophysical targets to
select ground geophysical survey locations proved to be efficient and successful in locating and
characterizing buried debris at Bellows Air Force Station.
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Sh-Wave Seismic Reflection Imaging Of Anomalous Foundation Conditions—Mississinewa Dam, Indiana
Authors Edward W. Woolery, Ron L. Street and Stephen T. HornbeckThe Mississinewa Dam in northern Indiana is a 2.4-km-long, 43-m-high, compacted earth-fill
embankment founded on approximately 25 m of glacio-alluvial sediment that overlies Mississippian
limestone bedrock. Differential settlement at the crest manifested in 1988; instrumentation indicates that
the increased rate of vertical deformation initiated in 1982, and has been approximately constant since
that time. As part of an effort to understand the cause for the irregular settlement, a noninvasive
seismic-reflection survey was performed in the general area of the crest deformation. The objectives
were to acquire a high-resolution image of the bedrock surface beneath the structure, and to identify
signal anomalies in the data that may be indicative of severely weathered rock or karst morphology. The
SH-wave reflection profile successfully imaged a coherent, relatively continuous signal consistent with
known points of top-of-rock elevation. Depth to bedrock along the profile varied from 20 m near the
right abutment, to 52 m near the outlet works at the western terminus. A sharp amplitude anomaly in the
bedrock reflector directly below the settlement area was imaged, and interpreted as a karst structure.
Subsequent geotechnical drilling of the anomaly found a 6.5 m discrepancy in the expected top-of-rock
elevation, as well as soft foundation fill, thus confirming the geophysical interpretation.
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Use Of Seismic Reflection Amplitude Versus Offset (Avo) Techniques To Image Dense Nonaqueous Phase Liquids (Dnapl)
Authors Michael G. Waddell, William J. Domoracki and Tom J. TemplesField experiments were conducted to determine the location and distribution of subsurface DNAPL
contamination at two DOE sites by use of two-dimensional, high-resolution seismic reflection surveys and
borehole geophysical data. These studies make use of seismic reflection amplitude versus offset (AVO)
technology to directly detect the presence of subsurface free-phase DNAPL.
The research was conducted at Savannah River Site, SC and Hanford Site, WA. At each of these sites
research consisted of site evaluation, seismic model studies, seismic acquisition, processing, and interpretation.
The seismic model studies were undertaken prior to field acquisition to determine the likelihood of an AVO
response from the DNAPL. The full Zoeppritz equations were used to create the model responses.
At M-Area, Savannah River Site the model data show that at the base of the DNAPL plume the
seismic amplitude should flip polarity on the far offsets (Class 2 AVO). The 2D seismic reflection field data
processed into near and far offset stacks indicate such anomalies occur at the depth where the known DNAPL
occurs. At the 200 West Area, Hanford Site the DNAPL is suspected to pool at two different stratigraphic
intervals. The model data show that at the upper interval, the Hanford Fine/Plio-Pleistocene boundary,
amplitude should decrease along the boundary if DNAPL is present (Class 1 AVO anomaly dim-out). At the
lower boundary the models show that, if DNAPL is present, the seismic amplitude should become very negative
(Class 3 AVO bright spot). A series of 2D seismic lines were acquired and processed. In the areas where
DNAPL was suspected to occur (high concentrations measured in wells) seismic amplitude was found to
decrease dramatically along the Hanford Fine/Plio-Pleistocene contact and along the Plio-Pleistocene/caliche
contact the seismic amplitudes became even more negative consistent with the model study.
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Investigation Of Seepage Through An Earthen Dam Using Ground Penetrating Radar
Authors Mark J. Howell and Scott J. LudlowA GPR survey was conducted during a seepage investigation of an earth dam. The survey
successfully imaged areas where perched water breached a geotextile drain fabric, delineated mounded
groundwater, and revealed structural features within the dam. This information, in conjunction with an
array of detailed geotechnical data assimilated by others, was used to evaluate seepage conditions and
develop remedial procedures. This paper presents images of selected features within the dam and
documents the methodologies used to for data acquisition and processing.
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A Gpr Mapping Survey On Jacui River
Authors Jandyr. M. Travassos and Adekunle. A. AdepelumiA combined marine and land GPR survey was conducted on the Jacui river, southern Brazil,
where it flows close to an abrupt end of the Serra Geral Cretaceous magmatic cover. The extruded basalt
overlays sandstone of the Triassic/Jurassic period. The survey covered an area on the river and on its
bank opposite to the basalt. The land survey was conducted on medium to coarser sand with occurrences
of gravel. About half of the area was forested displaying variable topography. The field configuration
allowed depths of penetration in excess of 15 m on land. Most lines averaged 200 m in length covering a
total area of 90,000 m2. Landlines successfully mapped the top of the sandstone unit below the soil
cover. A previously unknown landfill was also mapped. River lines revealed a rocky bottom with strong
and chaotic reflections reaching the end of the data window.
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Integrating Geophysical Methods In A Hydrogeological Pilot Study In The Northern Coastal Plain Of Rio De Janeiro State - Brazil
Authors Abel Carrasquilla, Luiz Geraldo Loures and Sergio L. FontesON/MCT and LENEP/UENF undertook a geophysical pilot study in the Northern
Coastal Plain of Rio de Janeiro State, near Rio das Ostras Town, 200 km NE from Rio de Janeiro
City. This region is characterized by both scarcity of drinking water for human consumption
and existence of saline intrusions, this last caused mainly by the presence of a complex
quaternary geology and excessive exploitation of aquifers. The research was performed by
employing magnetic and electromagnetic methods (time (TEM) and frequency (FEM) domains),
in order to evaluate the effectiveness of these methods in this particular geological
condition to allow the formulation of a more comprehensive hydrogeological research in the
region in near future. FEM profiles and one-dimensional interpretation of TEM data were capable
of depicting different geological formations, to locate the main aquifer and to reveal the
fresh-saline water contact. On the other hand, the magnetic method showed the presence of
a NE-SW direction geological fault, which is located just in the geological contact between
sand and clay, coincidentally with the fresh-saline water contact. Our results evince a promising
future for using electromagnetic geophysical methods in this region in small scale surveys,
as well as it confirmed that a precursory regional survey, chiefly using the magnetic method,
is essential in the indication of most suitable places to locate productive fresh-water wells.
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An Empirical Approach To Interpretation Of A Challenging Helicopter Electromagnetic Dataset
Authors Louise Pellerin, Victor F. Labson and Victor F. LabsonA helicopter electromagnetic survey acquired at the U.S. Deptartment of Energy Idaho National
Engineering and Environmental Laboratory used a traditional mining airborne method flown at low
levels for detailed characterization of shallow waste sites. The low sensor height, used to increase
resolution, invalidates most assumptions traditionally used in processing HEM data. Although the survey
design strategy was sound, interpretation techniques routinely used in industry, proved ineffective.
Apparent resistivity maps were severely distorted, and hence unusable, due to low flight height effects,
high magnetic permeability of the basalt host, and the conductive, highly three-dimensional nature of the
waste site targets.
To accommodate these interpretational challenges we modified a one-dimensional inversion
routine to include a linear term in the objective function to allow for the magnetic and three-dimensional
responses in the in-phase data. Although somewhat of an ad hoc approach the use of this term in the
inverse routine, referred to as the shift factor, was successful in defining the waste sites and reducing
problems due to the low flight height and magnetic characteristics of the host rock. Data from three areas
processed with this scheme highlight different interpretational aspects of the survey. Wastes sites were
delineated with the shift terms in two of the areas, allowing for separation of the anthropomorphic
targets from the natural one-dimensional host. In the other area, the estimated resistivity and the shift
factor were used for geological mapping. This was particularly interesting in that the disturbance of the
soil in the near surface was mapped with the shift term, because of the high magnetic content of the
native soil.
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Monitoring Of An In-Situ Air Sparging Experiment Using Electrical Resistivity Tomography
Electrical resistivity tomography (ERT) was successfully used for monitoring the air distribution
in an in-situ air sparging (IAS) experiment at the Oregon Graduate Institute of Science and Technology.
The experiment evaluated the removal of residual gasoline from the source zone of a simulated gasoline
spill in a tank filled with water-saturated sands The percent difference in resistivity provided a
quantitative view of air saturation in the sand tank. The initial background resistivity image suggests the
tank filled with water-saturated sands is geoelectrically non-homogenous though the sands in tank are
homogeneous in the sense of grain sizes. The background resistivity images also showed the evidence of
trapped residual gasoline around the water table.
The in-situ air sparging (IAS) in three different modes was carried out. The IAS at a flow rate of
20 cubic feet per minute (cfm) resulted in a larger radius of influence than the IAS at 5 cfm. At the same
air flow rate, the IAS in the pulse mode created a larger affected zone than the IAS in the continuous
mode. Two weeks was not long enough for the trapped air to escape from the tank. Unlike the
continuous IAS operation, the pulse operation produced a more complex air distribution in the tank.
Skewed airflow at both 5 cfm and 20 cfm flow rates indicated that there are preferential pathways in the
tank.
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Conductivity And Susceptibility Mapping Using Broadband Electromagnetic Sensors
Authors Haoping Huang and I.J. WonThe apparent conductivity and apparent magnetic permeability are derived from broadband
electromagnetic data using a conductive and magnetic half-space model. The apparent permeability is
first estimated from the inphase and quadrature (or amplitude and phase) data at a low frequency. This is
followed by the computation of the apparent conductivity at each frequency, using the pre-computed
apparent permeability. The apparent conductivity may be computed from broadband data using five
different algorithms. In general, three of the five methods yield a unique solution; the three yielding a
unique solution are the apparent conductivity defined from inphase, phase, or phase-amplitude.
A suite of synthetic data based on two-layer models is presented and it is concluded that the
phase-amplitude approach is preferred method. The apparent permeability is virtually independent of the
conductivity contrast at low induction numbers. However, the permeability contrast affects the apparent
conductivity, especially when a resistive layer overlays a conductive basement. The field data examples
show the usefulness of the broadband electromagnetic data and the resultant frequency-dependent
conductivity-permeability maps for characterizing complex environmental sites.
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Transient Controlled-Source Electromagnetic Induction In A Uniaxial Half-Space
Authors Mansour A. Al-Garni and Mark E. EverettAnisotropy in Earth materials often leads to unexpected geophysical responses that can not be
anticipated from simple isotropic models. In this paper, we investigate the effects of lateral anisotropy on
the time-domain, controlled-source electromagnetic (CSEM) response of a uniaxial conducting half-space
excited by a horizontal loop. In the theoretical results, a “paradox of anisotropy” is observed in which the
response is more pronounced along the strike of relatively conductive fractures. This is opposite to what
one might expect based on the isotropic theory. The results presented here have applications to fracture
mapping in bedrock.
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Inversion Of Multifrequency Electromagnetic Data To A Conductive And Permeable Sphere
Authors Haoping Huang and I.J. WonWe have developed an algorithm for inverting broadband electromagnetic (EM) data to
determine its electrical conductivity, magnetic permeability, radius, and depth using a sphere model. The
algorithm is based on traditional non-linear inverse methods with singular value decomposition. Studies
using synthetic GEM-3 broadband EM data indicate that the technique is dependable and produces fastconverging
solutions.
The geometrical parameters obtained through this technique are very close to true values, and the
electric parameters for noise-free data are correct to within a few percent. When a 10 percent noise is
added to the data, the geometric parameters are still well determined, but the electric parameters are
poorly resolved, particularly for a sphere that is both conductive and permeable. We also present an
analysis of the relative importance and reliability of the model parameters based on their partial
derivatives with respect to EM response.
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Quantitative Geoelectric Mapping Of The Hydraulic Conductivity Field
More LessThis paper describes in a stochastic framework how geoelectrics can be used to quantitatively
map the hydraulic conductivity field. This is achieved by describing both a microscale and a macroscale
model of aquifer electrical and hydraulic flow. The microscale model reveals that electrical and
hydraulic conductivities are a function of two common microscopic parameters. They are connected
pore volumes and connected pore surface areas, both assumed to be spatial random variables. Assuming
either a predominating pore-volume or pore-surface electrical flow environment, the self-similar scaling
of pore sizes, resulting in skewed pore size distributions, produces power-law relationships between
electrical and hydraulic conductivities and porosity and specific surface area. In turn these power-law
relationships imply a log-log linear relationship between electrical and hydraulic conductivities. The
coefficients of this log-log linear relationship are a function of several unique aquifer properties.
However, they can be field calibrated by linearly regressing coincident and equal-scale field
measurements of electrical and hydraulic conductivity. This electrical-hydraulic conductivity
relationship offers the quantitative physical rationale for converting inexpensive field measurements of
electrical conductivity into hydraulic conductivity.
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Constrained Time-Lapse Resistivity Imaging Inversion
By M.H. LokeChanges in the subsurface resistivity with time are frequently measured by conducting 2D or 3D
resistivity imaging surveys over the same area at different times. Examples of such studies include
mapping the flow of water through the unsaturated zone, changes in the aquifer saturation due to water
extraction, subsurface flow of chemical pollutants and leakage from dams. One common technique to
interpret the data from such surveys is carry the inversion of each data set individually and then
determine the relative changes in the subsurface resistivity from the differences in the resulting models.
This approach can lead to artifacts in the sections showing the relative changes in the subsurface
resistivity. In order to reduce such artifacts, a joint inversion technique that uses the results from the
inversion of the first data set as a reference model to constrain the inversion of the later time data sets is
used. Several types of cross-model constrains are examined. They are the simple damped or Marquardt
constrain, the l2 norm least-squares smoothness constrain and the l1 norm or robust constrain. By using
the appropriate cross-model constrain, artifacts in the sections showing the relative changes in the
subsurface resistivity can be significantly reduced. Where the changes in the model resistivity values are
expected to vary spatially in a gradual manner, the l2 norm constrain is more appropriate. When the
changes have sharp boundaries, the l1 norm constrain gives better results. In cases where the relationship
between the resistivity of the subsurface material and water content follows Archie’s Law, the change in
the water saturation can be estimated from the change in the model resistivity.
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Use Of Electromagnetic Induction Tools In Salinity Assessment/Appraisals In Eastern Colorado
More LessElectromagnetic induction (EMI) is a relatively low-cost and rapid method for measuring,
assessing spatially soil salinity. The two studies were conducted to evaluate data obtained with a
single-frequency (EM38 meter) and multi-frequency (GEM300 sensor) EMI instruments and to relate
apparent conductivity measured by these instruments with the more conventional conductivity of the
saturated soil extract. These two studies were geo-referenced for soil correlation sampling, salinity
mapping and future monitoring of salinization and/or degradation. The one study area (54 hectares)
utilized a subset sample area for the comparison procedure; the other site (323 hectares) was conducted
solely with the EM38 instrument. Data was incorporated into modeling programs and further used into
mapping software to develop two-dimensional maps.
Correlation coefficients between the two instruments ranged from 0.8039 to 0.8617. Although
the GEM300 sensor predicted somewhat less accurately the conductivity of the soil samples collected
and also produced higher apparent conductivity measurements, spatial patterns of apparent and
electrical conductivity produced by the two instruments were similar, reasonable and practical for the
end user, the agricultural producer.
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A New Fast Method To Measure Azimuthal Resistivity Anisotropy
More LessApparent electric anisotropy can be estimated with an electrode configuration formed as the letter
X. One electrode is placed at the end of each branch of the X and one is placed at about 1/3 of the
distance from the center. Together with one electrode at the center, by the instrument, this makes a total
of nine electrodes. By combining different electrodes it is now possible to measure the potential
difference to current ratio in a large number of ways. Wenner arrays can e.g. be formed along the two
diagonals of the X and square array measurements can be made with the four outermost electrodes. It is
convenient to use multi-channel equipment since many electrode combinations can be measured quickly.
For single reading methods we usually normalize the data by calculating an apparent resistivity.
The X-configuration measurements are also normalized, but in this case we use a homogeneous
anisotropic half-space for the normalization. There is of course no explicit formula for this conversion.
The data are fitted to the model in a least-squares sense by Monte-Carlo inversion. The output of the
inversion is apparent resistivity, apparent anisotropy direction and apparent anisotropy coefficient. The
apparent resistivity is defined as the geometric mean of the horizontal resistivities and it is usually a
good estimate of the bulk resistivity of the investigated rock volume. The influence of any local
heterogeneity is small due to the large number of measurements with different geometry and the rather
large electrode separations.
Examples are shown where X-configuration measurements have been performed on Precambrian
rocks in Sweden. The apparent anisotropy direction correlates well with direction of bedding in folded
supracrustal rocks and with the direction of foliation in metamorphic rocks.
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Problem Of Inductive Interference Between Current And Measuring Lines At Electrical Sounding
Authors Abbas Mohammed Abbas, Alexey Bobachev, Alexandr Karinski and Vladimir ShevninVertical electrical sounding (VES) is rather simple and very popular geophysical method with
wide spectrum of application for the decision of shallow depth hydrogeological, engineering geological
and ecological problems. During the last few years VES method has been transformed to a very
powerful technology, called electrical imaging or electrical resistivity tomography (ERT). At the field
registration of electrical signals in measuring line, some problems can arise and produce distortions,
which sometimes can spoil the data obtained. For realization of great amount of measurements at ERT,
pulsed current with short impulses (0.5-2 sec) is used. Such current is very close to AC. An example of
field data, highly distorted at large distances was the main cause of this investigation. In this report the
origin of induction is considered. This inductive interference is more dangerous in the case of low
ground resistivity. Calculations for Schlumberger array and dipole axial array were made. Criteria for
checking inductive interference are formulated. Knowledge of this phenomenon can help in avoiding
distortions and receiving high quality field data. Some other sources of distortions are also discussed.
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