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10th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 23 Mar 1997 - 26 Mar 1997
- Location: Reno, Nevada, USA
- Published: 23 March 1997
21 - 40 of 106 results
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Deconvolution Of High Density Electrical Well Logs
Authors Flemming Effersø and Bo Holm JacobsenDetailed information on vertical resistivity variations is relevant as an indicator of change in
lithology, porefluid chemistry, porosity and permeability. Traditionally the formation resistivity
is estimated solely on curves of the observed data, which are plotted as apparent resistivity data.
Apparent resistivity data may be a poor approximation to the local formation resistivity, and it
can be impossible to determine the resistivity levels and the location of the layer-interfaces. Jn
this paper we will present results of deconvolution of normal log apparent resistivity data.
Deconvolution of data using dual electrode offsets gives a significantly enhanced resolution of
the formation resistivity when moderate resistivity contrasts are considered.
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Advances In Instrumentation And Data Processing For Multi-Spaced Resistmty Measurements: Hydrogeologic P Arameters And Lithostratigraphic Delineation
By Charles OdenRecent advances in portable borehole geophysical instrumentation and processing
software allow hydrogeologic characterization of sandstone aquifers. Lithostratigraphic
delineation is also performed. A slimline logging probe allows logging of 4 normal
resistivity measurements (8, 16, 32, and 64 inch), as well as single point resistance,
spontaneous potential, natural gamma, fluid temperature and fluid resistivity. The data
can be quickly and easily processed on site to provide derived parameters and properties.
Hydrogeologic information can be easily calculated using processing software. Water
resistivity is indicated using shallow and deep resistivity measurements along with the
resistivity of the mud filtrate. Total dissolved solids can be found fi-om the water
resistivity. Porosity can be determined from Archie’s Law if a fresh water correction is
used. Hydraulic conductivity is indicated using depth of mud filtrate invasion. Examples
illustrate that calculated parameters agree with measured or otherwise indicated values.
Lithostratigraphic units can be delineated by synthesizing an approximated Laterolog7 log.
The synthesized focusing currents provide good a indication of bed boundaries. The
models generated from data sets obtained with the new multi-spaced normal resistivity
probe provides better vertical resolution due to the 8 inch normal resistivity measurement.
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Neural Network Interpretation Of Em39 Well Log Data
Authors Lin Zhang and Mary M. PoultonWe used a Modular Neural Network(MNN) to invert well logging curves from a Geonics EM39
induction logger In the interpretation scheme, there are several subsets of networks that depend on the
relative resistivities of adjacent layers, e.g. Rl>R2, RlR3, etc. The well logging curves are
subdivided into several pieces and run through each sub-network. The results are estimates of resistivity
and thickness of every layer. Using synthetic data, several training sets were made. The networks were
also tested on field data. The networks were examined for their ability to compute the right output patterns
for the corresponding input patterns of the training set and the ability to interpret the new patterns that are
not present in the training sets.
The results show that neural networks do facilitate interpretation of well logging data. When tested on
data from shallow wells 4-5m deep representing uniform material, the trained networks had an overall
accuracy of about 90% for both resistivity and thickness. When tested on a multi-layer case, the networks
gave reasonable estimates for each layer’s thickness and resistivity, although a shift in depth was
observed for some layers. Recently, we generated more training patterns for thinner layers and
incorporated a new way to pick data points for the input patterns. We found the results more satisfactory.
For two complicated multi-layer field cases, the networks had an overall accuracy of 92.1% for the
resistivity and thicknesses of the layers.
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The Interest Of Geophysical Methods For Locating Hydromorphic Horizons In Acid Pedological Systems
Authors V. Chaplot, P. Curmi, A. Hollier-Larousse, J. Pellerin and C. WalterThe aim of this study is to determine the interest of some geophysical methods, in particular Radio&IT in
locating hydromorphic horizons for acid pedological systems. Two areas were studied, one under forest, another in
an intensive agricultural site. A direct relationship between apparent resistivity and horizon type distribution was
established on the first site with a relative uniform soil depth. On the second site, soil depth and topsoil water
content explained most of the variations of the apparent resistivity, the influence of which was modelized by
multiple regression. Deviations from the regression model were then interpreted by taking into account the
succession of soil horizons. Results of Ground Penetrating Radar and Electrostatic Quadripole confirmed the
position of some of the limits between soils suspected by Radio-MT data. Finally, the prediction of hydromorphic
soil systems with the help of geophysical techniques is discussed.
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Gpr Attenuation Tomography For Detecting Dnapls
Authors Lanbo Liu and Youli QuanUsing the ground penetrating radar (GPR) to detect organic contaminants in the geological
formations is a relatively new technique for environmental site characterization. We present here an
attenuation tomography method that could be used to image subsurface organic contaminants like
DNAPLs. This method is based on centroid frequency shift when the electromagnetic (EM) waves
propagate in subsurface media. In most natural materials, EM wave attenuation increases with
frequency. As a result, the centroid of the signal’s spectrum experiences a downshift during
propagation. This downshift is proportional to a path integral through the attenuation distribution
and can be applied to the GPR data to tomographically reconstruct the attenuation distribution. The
frequency shift method is applicable to any data when the signal bandwidth is broad enough and
the attenuation is high enough to cause noticeable losses of high frequencies during propagation. In
comparison to some other methods of estimating attenuation, the frequency shift method is
relatively insensitive to geometric spreading, reflection effect, source and receiver coupling,
radiation patterns, and instrument responses. High attenuation has been regarded as the major
hurdle for using GPR in areas with high electric conductivity, this method provides an alternative
view to the attenuation.
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An Evaluation Of Geophysical Techniques To Measure Sub-Surface Hydrocarbon Contamination At A Disused Fuel Distribution Depot
Authors V.T. Nguyen, M.J. Quick, A.S. Eriksen, S. Booth, D. van der Roest, A. Wagebert, W. Al-Nuamy, M. Nakhkash, D. Zhang and Y. HuangAs part of a continuing programme to evaluate the potentials of non-invasive methods for rapid site assessment,
measurements have been made at a disused fuel distribution depot using geophysics techniques with particular
emphasis on the detection of sub-surface contamination. These include GPR, EM conductivity and 2D resistivity
imaging. The data have been analysed by a number of approaches and the results are compared with traditionally
acquired and chemically analysed soil samples.
The analysis of the data highlights the need for more work to be directed to the understanding of the physical processes
that give rise to the observed features, but encouragingly the comparison between the interpreted geophysics results
and the soil analysis has indicated that the non-invasive methods have potential to be developed into useful cost
effective screening tools. The direction for future work is discussed.
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Case Studies Of 2D Resistivity Surveying For Soils, Waste Management, Geotechnical, And Groundwater Contaminant Investigations
Authors Paul D. Bauman, Mike Lockhard, Anil Sharma and Richard KellettThe direct-current (DC) resistivity method has seen wide use in mining, groundwater, contaminant, and
geotechnical applications since its first use in the early 1920’s. More recently, however, fixed frequency and
transient electromagnetic (EM) methods have supplanted many applications traditionally addressed by resistivity
techniques. In particular, the application of resistivity profiling and sounding has suffered from the time intensive
nature of these surveys as compared to using EM equipment.
The advent of the automation of 2D resistivity surveys (Dahlin. 1993) and the ability to quickly invert relatively
large 2D data sets (Loke and Barker, 1996) promises to re-introduce the DC resistivity method into a wide variety
of applications in the geosciences. This paper presents four case studies where 2D resistivity surveying was
applied. The technique was used in various geological terrains, extremes of weather, studies requiring varying
depths of investigation, and with varying degrees of cultural interference. The accuracy of the method is evaluated.
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Electromagnetic Terrain Conductivity Surveys Used To Screen Swine Confinement Facilities For Groundwater Contamination
Authors T.H. Larson, I.G. Krapac, W.S. Dey and C.J. SuchomskiElectromagnetic terrain conductivity (EM) surveys were conducted at two swine confinement
facilities in Illinois to assess the presence and extent of groundwater contamination and to guide
the installation of monitoring wells. At Site A, the waste lagoon was on a glacial outwash terrace
near an alluvial valley. At Site C, the waste lagoon was on glacial till overlying shale bedrock.
Measurements were made with a GEONICS EM-34 terrain conductivity meter on 10-m grids
surrounding the waste lagoons. Wells were installed in areas where EM surveys suggested that
contamination may and may not be occurring. Two shallow wells at Site A and one well at Site
C yielded water samples with electrical conductivity values 6 times higher than background,
suggesting contamination. Each of these wells was in areas of high EM conductivity. None of the
deep wells in areas of high EM conductivity or shallow wells in areas of low EM conductivity at
Site A or Site C yielded water samples with electrical conductivity values much higher than
background. It appeared that a terrain conductivity survey is a useful tool for for delineating
areas of groundwater contamination.
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High Resolution Seismic Reflection Survey To Map Bedrock And Glacial/Fluvial Layers In Fridley, Minnesota
Authors Richard D. Miller and Jianghai XiaShallow seismic reflection in conjunction with uphole velocity profiles and local borehole
data allowed delineation of discrete laying within the alluvial materials and glacial drift overlying
the St. Peters Sandstone and/or the Prairie du Chien dolomites at an average depth of around 120 ft
along the western perimeter of the Naval Industrial Reserve Ordnance Plant (NIROP) in Fridley,
Minnesota. The primary goals of this study were to determine the feasibility and limitations of the
technique and develop a continuous subsurface image of as many geologic/hydrologic contrasts as
possible that can be characterized by changes in acoustic impedance. Establishing feasibility includes
determining the horizontal and vertical resolution potential, optimum acquisition geometries
and parameters, best suited equipment for surface and subsurface conditions, level of effort necessary
to delineate the geologic/hydrologic features of interest, and to establish a reasonable set of
expectations for the technique at various unique near-surface settings across the entire facility.
Shallow seismic reflection profiles allowed delineation of potentially discontinuous confining units
within the glacial drift at this site. Incorporation of a high confidence reflection profile with existing
hydrologic models should greatly improve the understanding and therefore prediction of contaminant
transport and fate models in areas with significant lateral variability. The glacial drift that
covers the entire site consists of till, outwash, valley train, and lake deposits.
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Seismic Reflection Processing For Characterization Of A Hazardous Waste Site
Authors Zhi-Ming Liu and William E. DollSeismic reflection data have been acquired by the Kansas Geological Survey near the Oak Ridge
K-25 Plant on the Oak Ridge Reservation, Tennessee, to assist in the selection of ground water
monitoring well locations. The data were recorded in uncorrelated format to allow flexibility in
enhancement of stacked images.
During the summer of 1996, five of the thirteen seismic reflection lines acquired were
processed. An unconventional correlation procedure, “Vibroseis Whitening” (VSW) (Coruh and
Costain, 1983) has been applied to produce improved seismic sections. Refraction statics
corrections, which remove the detrimental effect of an irregular weathered layer, have also been
utilized to improve the seismic sections. The seismic data were stacked using the velocities
obtained from a standard semblance velocity analysis tool. Locations and orientations of faults
or fault zones can be interpreted from these stacked sections, and they are in agreement with the
interpretations of the surface mapping in the area.
This paper concludes that VSW and refraction statics can be important to near-surface
swept source seismic data processing.
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Dynamic Properties Of Municipal Solid Waste Landfills From Surface Wave Tests
Authors Christopher D. Haker, Glenn J. Rix and Carlo G. LaiThe seismic stability of municipal solid waste (MSW) landfills is often a significant consideration in landfill
design. However, until recently, the dynamic properties of the waste material itself, which govern the seismic
response of MSW landfills, have often been approximated or assumed. Tests to determine the dynamic properties
of the material directly have been limited. Measurements of seismic surface waves were used to determine the
dynamic properties of MSW, which are the initial tangent shear modulus and low-strain hysteretic damping ratio.
Surface wave tests were performed at three MSW landfills to determine their shear modulus and damping ratio
profiles. Surface wave tests are ideal for measuring the near-surface shear modulus and damping profiles of MSW
landflls because the tests are non-invasive, an advantage for testing environmentally sensitive waste material.
Factors which influence the dynamic properties of waste including density, confinement, age, and placement
techniques are used to interpret the measured shear modulus and damping ratio profiles.
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Evaluation Of Earth-Fill Embankments In Romania Using Electrical Methods And Ground Penetrating Radar
Authors Jean Christophe Gourry and Traian MoldoveanuDuring the 1970s embankments were constructed along several hundred kilometres of
rivers in Romania In recent years, several leaks have developed along the berms.
The aim of this study is to check whether GPR and electrical methods are efficient for
characterizing anomalies above the known leaks and, if so, to extrapolate the results into
unknown areas for systematic surveillance. GPR revealed variations of 5 to 10% in the
apparent water level, whereas piezometric measurements showed variations of less than
5%. Such large variations in the apparent water level may be due to variations in EMwave
velocity. CMP results confirmed a lower EM-wave velocity in the landslip area than
in the safe zone. The apparent water level drops in the area affected by the landslip.
Electrical soundings revealed that resistivity is higher in the anomalous crest areas than in
the secure parts of the embankment. One striking feature recorded in the anomalous zones
was that resistivity anomalies were positive along the crest, yet negative along the berm,
i.e. high resistivity along the crest but low along the berm for the landslip area. One
explanation is that the weak crest areas are made up of porous material, whereas those
along the berm consist of saturated material.
This study has demonstrated the correlation between known leakage areas and geophysical
anomalies. Furthermore, the coupling of GPR and electrical soundings proved efficient
for detecting most of the known anomalies. Due to its good spatial resolution and high
acquisition speed, GPR is perfectly adapted to this type of application.
2-D GPR tomography along the dams also provided detailed and interesting results.
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Seepage Investigation Using Geophysical Techniques At Coursier Lake Dam, B.C., Canada
By Phil SirlesSubsurface seepage flow at Coursier Lake Dam was identified by onshore
and offshore self-potential surveys, and electrical resistivity
profiles and soundings during a Deficiency Investigation by BChydro.
For typical seepage investigations baseline geophysical data are
collected at @llow-pool I1 level and the measurements are repeated when
high hydraulic gradient conditions exist. At Coursier Lake Dam a
rather unanticipated outcome of the low-no01 surveys was that
significant seepage beneath the structure'was detected. The low-pool
results were conclusive enough that, when combined with visual
inspection and observation of sinkholes on the embankment, an
immediate restriction was placed on the pool elevation. Thus, because
of the identified potential hazard, the remaining geophysical
investigations were conducted under a "minimum-pool" reservoir level
in order to complete the comparative study. Therefore, the dam was
studied under low- and minimum-pool reservoir conditions in the spring
and fall of 1993, respectively.
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Seepage Characterization During Dewatering Activities - Bradbury Dam, California
Authors Robert Furgerson, Robert Corwin and Jerry WrightA geophysical investigations program was performed at Bradbury Dam near Santa Ynez, California. The purpose of
the investigation was to 1) provide data on possible seepage paths into the dewatering area downstream of Bradbury
Dam, and 2) determine lithologies and stratigraphic correlation within the alluvium. The geophysical investigations
included surface self potential (SP) surveys along the centerline and offsets right and left of the newly constructed
cutoff wall, SP surveys within the dewatering area and stilling basin, borehole induction conductivity, borehole
temperature logs and other borehole geophysical logging.
Anomalies from the SP data were indicated along the downstream cutoff wall at several wall stations . SP data
collected within the dewatering area confirmed these anomalies No significant SP anomalies were noted in the
spillway stilling basin.
Correlation of borehole induction conductivity logs run in 34 observation wells and 8 geophysical shear wave holes
indicated the existence of two correlatable main units and four sub-units within the foundation alluvium. Lithologic
descriptions of these units are based on variations in electrical conductivity with supporting data Ii-om SPT samples,
core samples, grab samples, and corrected Becker blow counts. These lithologic units were used to aid in the
interpretation of the borehole temperature data, SPT and Becker results.
Borehole temperature logging was conducted on four separate dates in the observation wells. Temperatures in the
spillway stilling basin were also measured. Average temperatures in each borehole were calculated at the water
table, the base of the alluvium, and within bedrock where available. In addition the maximum variation of
temperature within the alluvium was also calculated.
A geologic model was constructed from correlation of induction conductivity logs , Becker blows, and analysis of
grab samples obtained during excavation of the downstream cutoff wall. SP and temperature data provided seepage
and hydrologic information within the dewatering area.
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Seismic Refraction And Downhole Velocity Surveys For Investigation Of The Tinemaha Dam Inyo County, California
Authors Mark Olson, Yogesh Prashar and Sinan InelSeismic refraction and downhole velocity surveys were conducted as part of a
geotechnical investigation of the Tinemaha Dam. Thirteen P and S-wave velocity surveys
were conducted concurrently with cone penetration testing along the crest and
downstream toe of this dam. One additional velocity survey was conducted from a
borehole on the crest of the dam using a downhole geophone array. The shear wave
velocities estimated for the dam and its underlying alluvium ranged from 345 to 2008
ft/sec. A depth profile of these velocities indicates areas within the dam and its
foundation where the shear wave velocities are less than 600 ft/sec. These velocity
estimates were used with other geotechnical data, to calculate the dynamic elastic moduli
for the dam and its foundation, to evaluate the stability of the dam in the event of a local
earthquake on the Owens Valley fault. To further investigate the location of this active
strike-slip fault, seismic refraction surveys were conducted at two locations. The first
refraction survey was positioned south of the dam across the expected trend of the Owens
Valley fault. A velocity analysis of the upper refracting horizon was conducted using the
generalized reciprocal method. This revealed changes in lateral velocity that were
interpreted as due to a fault-transition from saturated alluvium to volcanic bedrock. The
second survey was positioned along the dam’s crest at the west abutment to help locate a
possible fault beneath this area. The interpreted depth section from this survey locates a
point where the deeper bedrock unit appears to be truncated by faulting. This information
will help locate additional boreholes to evaluate lithologic conditions.
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Multi-Frequency Gpr Surveys
Authors Jeffrey E. Lucius and Michael H. PowersGround penetrating radar (GPR) antenna selection must be based on specific survey objectives. The choice of
antenna is primarily a compromise between resolution and depth of penetration. This paper briefly presents three
case histories of multi-frequency GPR surveys that explain and illustrate how the antenna and the electromagnetic
(EM) properties of the ground affect wavelength, loss mechanisms, far-field radiation, and the near-field. Changes in
these parameters are important because they affect vertical and horizontal resolution, and depth of penetration. In
general, when the depth of penetration is limited by conductive losses instead of scattering losses, changing to a
lower-frequency antenna will not help in detecting shallow features, and may not help in detecting deeper features.
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Locating Salinity Sources In West Texas With Airborne And Ground-Based Geophysical Methods And Gis
Authors Jeffrey G. Paine, Erika M. Boghici, Alan R. Dutton and Steven W. TweedySalinization of soil, surface water, and ground water is a chronic environmental and
agricultural concern in the southwestern U.S. In this study of a 91 km2 area near Ballinger in
Runnels County, Texas, we used a geographic information system (GIS) to integrate results from
airborne and ground-based geophysical surveys, water and soil sampling, and chemical analyses
to locate areas of brine concentration and determine their origin. Potential salinity sources in this
area are (a) subsurface brine moving upward along natural conduits (faults, fractures, joints, and
permeable stratigraphic units), (b) brine migrating downward from surface disposal pits,
(c) leaking oil and gas wells, and (d) evaporating shallow ground water as a result of agricultural
landscaping. A prime goal of the study was to determine the effectiveness of the method in
distinguishing potentially leaking wells from other salinity sources.
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Mapping Bedrock Topography With Seismic Refraction At An Oil And Gas Field: A Comparison Of Engineering And Petroleum Exploration Methods At A Site In The Wind River Basin Of Wyoming.
Authors David Phillips, Robert Grimm and Bart Hoekstra“Weathered-layer” corrections to seismic-reflection travel times for deep hydrocarbon exploration are often made
using shallow refracted arrivals on the reflection records. There has been recent interest in using these “refractionstatics”
solutions to provide depth-to-bedrock maps for environmental or engineering applications as a by-product of
the deep seismic survey. We show that the depth to bedrock and bedrock velocities produced by automatic
refraction-statics processing of a three-dimensional seismic survey of a gas field in Wyoming differ significantly
from those determined from an engineering survey. Manual reprocessing of the refraction statics produced some
improvement, but is still inferior to refraction data taken for the specific purpose of determining depth to bedrock.
Automatic refraction statics provide adequate travel-time adjustments to reflection records due to a shallow lowvelocity
layer, but such solutions should not be taken to represent explicit depth to bedrock.
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Neural Network Interpretation Of High-Frequency Electromagnetic Ellipticity Data
Authors RaIf A. Birken and Mary M. PoultonThis paper focuses on the detection of three dimensional (3D) small conductive targets from high-frequency
electromagnetic elliptic@ data using neural networks. For environmental investigations it is necessary to provide
as much information on the location of shallow buried conductive objects or the electrical properties of possible
contaminants. The networks are trained with one-dimensional (ID) forward models to estimate the resistivity and
dielectric constant structure of the ground. The input is given by elliptic@ sounding curves from eleven discrete
frequencies in binary steps in a range from 32 kHz to 32 MHz. Halfspace and layered earth neural networks will
provide reasonable fit to sounding curves even if they are influenced by shallow conductive 3D objects. We show
that a detailed inspection of elliptic@ profiles over targets such as a 5 m by 3 m aluminum sheet (depth of 1 m), a
5%gallon barrel (depth of 0.63 m), and two metal desk (depth of approximately 1 m) can help to detect these
anomalies. Piecewise halfspace neural network are capable of enhancing the anomalies in resistivity depth sections
and provide additional information for the detection and possible localization of the object. The visualization of
the results is very important since small targets will show up as subtle anomalies. Based on observations of
elliptic@ sounding curves and profiles we can train a neural network to classify target responses versus
background responses for specific sites, assuming that enough soundings are available to train the neural networks.
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Joint Seismic And Electrical Tomography
Authors Jie Zhang and F. Dale MorganSeismic and electrical properties in the earth are not directly associated with each other. If a large seismic
velocity contrast occurs across a geological interface, certain change of the corresponding electrical properties
may also take place, but not necessarily. To seek solutions with maximum structure coherency between
the two physical parameters in the earth, we develop a joint seismic and electrical tomography method
that simultaneously reconstructs seismic velocities and electrical resistivities with cross constraints on the
normalized structure curvatures.
The joint approach applies a 2D nonlinear refraction traveltime tomography method and a 2.5D d.c.
resistivity tomography method in a joint process. It includes a wavefront raytracing method for rapid
traveltime calculation, and a transmission-network method for electrical potential calculation. A Conjugate
Gradient (CG) approach is applied to solve an inverse problem that minimizes the seismic traveltime and
the electrical potential misfits, and meanwhile maximizes coherency of their normalized structure curvatures
by the way of Tikhonov regularization.
We demonstrate the performance of the joint tomography technique with a numerical example. A geological
structure is characterized with three zones in terms of seismic and electrical properties. Applying
the joint inversion method takes advantages of both geophysical approaches and automatically reconstructs
consistent structures.
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