integrated electrical resistivity tomography ert and self potential sp techniques for assessing hydrological processes within glacial lake moraine dams moraine dams can be inherently unstable but effective assessment strategies remain poorly identified we integrate electrical resistivity tomography ert with electrical self potential sp and lake level measurements to investigate the structure of and hydrological processes within a moraine dam complex adjacent to miage glacier italy this complex separates two meltwater lakes characterized by an efficient subterranean hydraulic connection our ert data reveal a continuous free surface within the complex whose morphology reflects the topography of the moraine complex akin to unconfined groundwater aquifers sp data were corrected for spatial changes in the thickness of the upper unsaturated layer using principles of electrography the residual streaming potential map is consistent with darcian flow of lake waters through the moraine complex characterized by a negative to positive potential change from 70 mv these electrical signatures are consistent with those generated by water seepage through earth dams in various non glacial settings integrated electrical geophysical methods thus provided an inexpensive and unobtrusive evaluation of the hydrological properties of and processes within the moraine complex since spatio temporal patterns of subsurface water flow critically affect the strengths of moraine sediments such methods promise to be powerful in assessing the long term stability of moraine dammed glacial lakes

crosshole ip imaging for engineering and environmental applications induced polarization ip imaging is a promising tool in engineering and environmental studies application of this technique for near surface investigations has previously been limited by incomplete understanding of the physicochemical controls on the ip response together with a lack of appropriate methods for data inversion as laboratory studies have shown description of ip in terms of complex electrical conductivity enables access to various structural characteristics pertinent to practical issues such as subsurface lithology definition hydraulic permeability estimation or hydrocarbon contaminant mapping in particular analysis in terms of real and imaginary conductivity components offers improved lithological characterization since surface polarization effects are separated from electrolytic and surface conduction effects an occam type ip inversion algorithm based on complex algebra is described which accounts for these advances in ip interpretation by directly solving for complex conductivity results from crosshole applications at two case study sites demonstrate the suitability of the ip imaging approach for subsurface characterization in the first case study the imaging results correlate with the observed complex sequence of quaternary sediments at a waste disposal site characterization of the polarizability of these sediments offers significant value in lithological differentiation in the second case study the results of ip imaging at a hydrocarbon contaminated site illustrate the potential of the method in environmental studies the hydrocarbon location is clearly evident from the ip image and a markedly different response is observed at an uncontaminated region of the site by adopting empirical structural electrical relationships images of textural and hydraulic properties are estimated as a step toward improved quantitative characterization the success of the method for these contrasting applications supports further investigation into understanding the physical and chemical processes that control observed ip

layered and laterally constrained 2d inversion of resistivity data in a sedimentary environment quasi layered models often can represent the actual geology more accurately than smooth minimum structure models we present a 2d inversion scheme with lateral constraints and sharp boundaries lci for continuous resistivity data all data and models are inverted as one system producing layered solutions with laterally smooth transitions the models are regularized through lateral constraints that tie interface depths or thicknesses and resistivities of adjacent layers a priori information used to resolve ambiguities and to add for example geological information can be added at any point of the profile and migrates through the lateral constraints to parameters at adjacent sites similarly information from areas with well resolved parameters migrates through the constraints to help resolve areas with poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result a simple synthetic model proves the need for a quasilayered 2d inversion when compared with a traditional 2d minimum structure inversion a 2d minimum structure inversion produces models with spatially smooth resistivity transitions making identification of layer boundaries difficult a continuous vertical electrical sounding field example from sweden with a depression in the depth to bedrock supports the conclusions drawn from the synthetic example a till layer on top of the bedrock hidden in the traditional inversion result is identified using the 2d lci scheme furthermore the depth to the bedrock surface is easily identified for most of the profile with the 2d lci model which is not the case with the model from the traditional minimumstructure inversion

induced polarization detection and mapping of contaminant plumes several laboratory and scaled model investigations suggest that organic contaminants affect the surface electrical properties of exposed soils rocks and therefore produce measurable induced polarization ip signatures however there is little field evidence of an ip methodology for contaminant mapping a2d time domain ip method is developed for mapping the fs12 contaminant plume at the massachusetts military reservation mmr located in cape cod massachusetts the fs 12 plume consists of approximately 265 m 3 of fuel that erupted from a broken underground pipeline in the early 1970s benzene and ethylene dibromide edb are the primary contaminants at fs 12 with concentrations exceeding the allowed maximum concentration levels mcl while other constituents of the plume did not exceed their mcl therefore the contaminants of interest are benzene and edb partly because of their health risk and partly because they present the highest concentrations 2400 and 1000 g l respectively among the plume constituents and are therefore more likely to be related to the polarization source ip data were acquired along a survey line that partially transects the plume extending over contaminated and uncontaminated zones and were inverted to give 2d resistivity and chargeability plots to 100 m depth and a horizontal extent of 400 m by separately inverting ip data derived from time windows located at short and long decay times a timedomain gross spectral chargeability difference is produced both the chargeability and gross spectral chargeability difference show good agreement with the known location of the plume from monitoring wells with the ip chargeability section suggesting contaminant distribution detail that cannot otherwise be inferred from the sparse borehole distribution

resistivity and induced polarization monitoring of salt transport under natural hydraulic gradients we demonstrate the use of resistivity induced polarization ip monitoring of salt transport under natural hydraulic loads electrical monitoring of saline tracer transport during forced injection has been demonstrated previously detection of tracer transport under natural hydraulic loading is difficult because neither the hydraulic load nor the tracer resistivity can be controlled in one study we identify the electrical response to salt transport in a dynamic beach environment resistivity ip imaging resolved the structure of the saltwater freshwater interface and evidence for tide induced groundwater transport resistivity increases in the near surface and at depth upbeach of the high tide mark accompanied by tidal transgression we attribute this to desaturation and decreasing salinity in the near surface and to decreasing salinity at depth despite tidal transgression monitoring of groundwater levels indicates a phase lag between the tide level and groundwater level supporting the electrical da

incorporating geological dip information into geophysical inversions geological bodies are often linear structures that have well defined strike direction and dip angle we develop a new model objective function that allows this important information to be incorporated into geophysical inversions a rotation matrix is applied to the horizontal and vertical derivatives of the model so that the derivative in an arbitrary direction is obtained a model objective function that measures the flatness with respect to the rotated derivatives favors models that have elongated features with the specified strike and dip angle formulations for both 2 d and 3 d cases are presented and they are illustrated using examples from dc resistivity and induced polarization ip problems synthetic and field examples show that an inversion carried out using known dip information produces a model that has higher resolution and provides a better representation of the true structure

joint inversion of seismic refraction and resistivity data using layered models applications to groundwater investigation we developed a method for joint inversion of seismic refraction and resistivity data using sharp boundary models with few layers typically three we demonstrated the usefulness of the approach v

three dimensional resistivity tomography in extreme coastal terrain amidst dense cultural signals application to cliff stability assessment at the historic d day site summary pointe du hoc overlooking the english channel in normandy france was host to one of the most important military engagements of world war ii but is vulnerable to cliff collapses that threaten important german fortifications including the forward observation post op and rudder s command post the objective of this study is to apply advanced 3 d resistivity tomography towards a detailed site stability assessment with special attention to the two at risk buildings 3 d resistivity tomography data sets at pointe du hoc in the presence of extreme topography and dense cultural clutter have been successfully acquired inverted and interpreted a cliff stability hazard assessment scheme has been designed in which regions of high resistivity are interpreted as zones of open dry fractures with a moderate mass movement potential regions of low resistivity are zones of wet clay filled fractures with a high mass movement potential the op tomography results indicate that the highest mass movement hazard appears to be associated with the marine caverns at the base of the cliff that are positioned at the point of strongest wave attack these caverns likely occupy the future site of development of a sea arch that will threaten the op building the mass movement potential at the rudder s command post area is low to moderate the greatest risk there is associated with soil wedge failures at the top of the cliffs

application of time lapse ert imaging to watershed characterization time lapse electrical resistivity tomography ert has many practical applications to the study of subsurface properties and processes when inverting time lapse ert data it is useful to proceed beyond straightforward inversion of data differences andtakeadvantageofthetime lapsenatureofthedata weassess various approaches for inverting and interpreting time lapse ertdataanddeterminethattwoapproachesworkwell thefirst approachismodelsubtractionafterseparateinversionofthedata from two time periods and the second approach is to use the inverted model from a base data set as the reference model or prior information for subsequent time periods we prefer this second approach data inversion methodology should be considered when designing data acquisition i e to utilize the second approach it is important to collect one or more data sets for which the bulk of the subsurface is in a background or relatively unperturbed state athird and commonly used approach to time lapse inversion invertingthedifferencebetweentwodatasets localizes the regions of the model in which change has occurred however varying noise levels between the two data sets can be problematic to further assess the various time lapse inversion approaches weacquiredfielddatafromacatchmentwithinthedry creek experimental watershed near boise idaho u s a we combined the complimentary information from individual static ertinversions time lapseertimages andavailablehydrologicdatainarobustinterpretationschemetoaidinquantifyingseasonalvariationsinsubsurfacemoisturecontent

time lapse ert monitoring of an injection withdrawal experiment in a shallow unconfined aquifer toquantifyperformanceof3dtime lapseelectricalresistivity tomography ert a sequential injection withdrawal experiment was designed for monitoring the pump and capture remediation of a conductive solute in an unconfined alluvial aquifer prior information is incorporated into the inversion procedure via regularization with respect to a reference model according to threeprotocols 1independentregularizationinvolvingasingle reference model 2 background regularization involving a referencemodelobtainedviainversionofpreinjectiondata and3 time lapseregularizationinvolvinganevolvingreferencemodel obtained via inversion of data from previous experimental stages emplacementandsequentialwithdrawalofthesoluteisclearly imaged for all protocols time lapse regularization results in greater amounts of model structure while providing significantcomputationalsavings ert estimatedelectricalconductivity is used to predict solute concentration and solute mass in the aquifer at any experimental stage we are able to estimate total solute mass in the aquifer with a maximum accuracy of 60 85 depending on regularization protocol and survey geometry wealsoestimatethewithdrawnsolutemassforeveryexperimentalstagethechangeinmassbetweenexperimentalstages withdrawn mass estimates are more reliable than total mass estimates and do not exhibit systematic underprediction or dependence on regularization protocol withdrawn mass estimates areaccurateforchangesinmassbelow2 4 kgofpotassiumbromide kbr for horizontal and vertical dipole dipole surveys respectively estimating the withdrawn solute mass does not require background subtraction and thus does not require backgrounddata

geoelectrical mapping for improved performance of suds in clay tills many cities of the northern hemisphere are covered by low permeable clay tills posing a challenge for stormwater infiltration practices however clay tills range amongst the most heterogeneous types of sediments and infiltration rates can vary by several orders of magnitude this study evaluates if a 2d geoelectrical system can reveal such heterogeneity at field scale and thus be used to optimize the hydraulic performance of stormwater runoff infiltration systems the assessment is based on a field study where data from non invasive geoelectrical data are compared with data from invasive geological methods including borehole soil sample descriptions one excavation description and a near surface spear auger mapping project the experiments returned a significant correlation of geoelectrical and spear auger mapped surface sediments furthermore a highly permeable oxidized fracture zone in greater depths could be revealed on the 2d geoelectrical profiles the successful determination of highly permeable zones harbors potential for improved hydraulic performance of infiltration suds sustainable urban drainage systems

variation in groundwater salinity in a tidal salt marsh basin north inlet estuary south carolina abstract groundwater flow of freshwater from upland forests into salt marshes is influenced by hydrologic forces that operate over a wide range of temporal scales including storm events tidal fluctuations seasonal variations in rainfall and evapotranspiration et groundwater salinity can be a useful first order indicator of the balance between these flow processes a dipole dipole electrical resistivity survey was conducted approximately monthly during 2005 to measure groundwater salinity across a portion of crabhaul creek a tidal salt marsh basin at the boundary of the upland forest and the north inlet marsh in south carolina the monthly electrical resistivity surveys were designed to provide a detailed spatially continuous measurement of subsurface conductivity to a depth of 4 m in order to further investigate the seasonal variation in groundwater salinity resistivity models were corroborated by simultaneous measurements of salinity in nearby piezometers the freshwater brackish water interface was clearly imaged by the resistivity movement of this interface occurs on a timescale of months rather than a regular seasonal variation the average salinity in the marsh basin is highest in late summer july august when et is highest and lowest during the winter november december the position of the brackish freshwater interface changes but is not well correlated to local rainfall or tidal cycles except under specific circumstances a steady state hydrological model correctly predicts the average position of the freshwater brackish interface and suggests a linear relationship between the height of the water table and the location of the interface these results suggest a complex relationship between precipitation events and groundwater flow from the forest into the marsh

anti torque systems of electromechanical cable suspended drills and test results abstract to prevent spinning of the upper non rotated part of the electromechanical drill an anti torque system has to be included in the downhole unit at the same time the anti torque must allowthe drill to move up and down the borehole during drilling and tripping operations usually the anti torque system has a blade form of various designs that engages with the borehole wall and counteractsthe torque from the stator of the driving motor this paper presents a review of the different anti torquesystems and test results with selected designs leaf spring skate and u shaped anti torque systems experiments showed that the skate anti torque system can provide the maximal holding torque between67 and 267 n m 1 depending on the skates outer diameter and ice temperature while the leaf springanti torque system can provide only 2 5 40 n m 1 in case of straight contact between the ice and theleaf springs the total resistance force to axial movement of the skate anti torque system lies in therange 209 454 n if the system is vibrating for the leaf spring anti torque system the total axialresistance force is far less 19 243 n keywords

deep massive sulphide exploration using 2d and 3d geoelectrical and induced polarization data in skellefte mining district northern sweden geoelectrical and induced polarization data from measurements along three profiles and from one 3d survey are acquired and processed in the central skellefte district northern sweden the data were collected during two field campaigns in 2009 and 2010 in order to delineate the structures related to volcanogenic massive sulphide deposits and to model lithological contacts down to a maximum depth of 1 5 km the 2009 data were inverted previously and their joint interpretation with potential field data indicated several anomalous zones the 2010 data not only provide additional information from greater depths compared with the 2009 data but also cover a larger surface area several high chargeability low resistivity zones interpreted as possible massive sulphide mineralization and associated hydrothermal alteration are revealed the 3d survey data provide a detailed high resolution image of the top 450 m of the upper crust around the maurliden east north and central deposits several anomalies are interpreted as new potential prospects in the maurliden area which are mainly concentrated in the central conductive zone in addition the contact relationship between themajor geological units e g the contact between the skellefte group and the j orn intrusive complex is better understood with the help of 2010 deep resistivity chargeability data the bottommost part of the vargfors basin is imaged using the 2010 geoelectrical and induced polarization data down to 1 km depth

laterally filtered 1d inversions of small loop frequency domain emi data from a chemical waste site we made a study in the backyard of an agrochemical plant using a small loop frequency domain electromagnetic induction emi system such systems are very sensitive to conductive structures buried at shallow depths frequently they are only used to locate and delimit these structures by direct observation of data however much more information can be obtained by applying numerical modeling techniques to the data first we mapped an anomalous zone that indicates the possible presence of buried waste or some other underground contamination by visualizing data then we applied a 1d inversion method to the data from this zone by joining 1d inversion results this method builds 2d images of the subsoil structure below survey lines because the code applies smoothness constraints to the 1d inversions the subsoil properties in these 2d images change gradually with depth the code does not impose any correlation between the data or 1d models corresponding to neighboring points so sharp lateral changes can appear several of them do not represent real features of the subsoil we designed and applied two spatial filters to smooth the spurious lateral variations in our models one correlates the data acquired at adjacent points prior to inversions the other applies an analogous correlation to the inverse models obtained from the original data both filters greatly improve the quality of the 2d images compiling these results we obtained a 3d model of the subsoil that characterizes the anomalous structure excavations made later at the site confirmed the results

cooperative constrained inversion of multiple electromagnetic data sets abstractwe evaluated a method for cooperatively inverting multiple electromagnetic em data sets with bound constraints to produce a consistent 3d resistivity model with improved resolution field data from the antonio gold deposit in peru and synthetic data were used to demonstrate this technique we first separately inverted field airborne time domain em aem controlled source audio frequency magnetotellurics csamt and direct current resistivity measurements each individual inversion recovered a resistor related to gold hosted silica alteration within a relatively conductive background the outline of the resistor in each inversion was in reasonable agreement with the mapped extent of known near surface silica alteration variations between resistor recoveries in each 3d inversion model motivated a subsequent cooperative method in which aem data were inverted sequentially with a combined csamt and dc data set this cooperative approach was first applied to a synthetic inversion over an antonio l

transdimensional change point modeling as a tool to investigate uncertainty in applied geophysical inference an example using borehole geophysical logs recently developed methods for inferring abrupt changes in data series enable such change points in time or space to be identified and also allow us to estimate noise levels of the observed data the inferred probability distributions of these parameters provide insights into the capacity of the observed data to constrain the geophysical analysis and hence the magnitudes and likely sources of uncertainty we carry out a change point analysis of sections of four borehole geophysical logs density neutron absorption sonic interval time and electrical resistivity using transdimensional bayesian markov chain monte carlo to sample a model parameter space the output is an ensemble of values which approximate the posterior distribution of model parameters we compare the modeled change points borehole log parameters and the variance of the noise distribution of each log with the observed lithology classes down the borehole to make an appraisal of the uncertainty characteristics inherent in the data our two examples one with well defined lithology changes and one with more subtle contrasts show quantitatively the nature of the lithology contrasts for which the geophysical borehole log data will produce a detectable response in terms of inferred change points we highlight the different components of variation in the observed data due to the geologic process dominant lithology changes that we hope to be able to infer geologic noise due to variability within each lithology and analytical noise due to the measurement process this inference process will be a practical addition to the analytical tool box for borehole and other geophysical data series it reveals the level of uncertainties in the relationships between the data and the observed lithologies and would be of great use in planning and interpreting the results of subsequent routine processing

experience from two resistivity inversion techniques applied in three cases of geotechnical site investigation the combination of in situ geotechnical testing and continuously measured geophysical data can be a powerful tool in geotechnical site investigation in two cases from sweden and one case from denmark electric resistivity surveys are used successfully in geotechnical site investigations the main contribution of resistivity results is the possibility to interpret continuous geological models an improved methodology combines two dimensional 2d smooth inversion and 2d laterally constrained inversion 2d lci to significantly increase interpretability the 2d smooth inversion has high horizontal resolution and 2d lci high vertical resolution the possibility to add a priori information from for example drill log data to constrain the 2d lci increases the confidence in the inverted model and limits ambiguity in a site investigation for a railway trench in southern sweden a geotechnical data set is used as a priori data to increase the reliability of the inversion of the resistivity data from this combined survey a complex quaternary geology is described in detail a slope stability study from south of stockholm sweden employed resistivity data together with refraction seismic and geotechnical drill log data the result gives necessary geometrical information for the important geological units for example for stability calculations both these surveys were performed with a multielectrode system in the third case a pulled array resistivity survey was used to map the uppermost 15 20 m to estimate the distribution of the geological formations for freeway construction in denmark the result enables a more accurate estimate of the total freeway construction costs

methods for calculating frechet derivatives and sensitivities for the non linear inverse problem a comparative study1 a fundamental step in the solution of most non linear inverse problems is to establish a relationship between changes in a proposed model and resulting changes in the forward modelled data once this relationship has been established it becomes possible to refine an initial model to obtain an improved fit to the observed data in a linearized analysis the frechet derivative is the connecting link between changes in the model and changes in the data in some simple cases an analytic expression for the frechet derivative may be derived in this paper we present three techniques to accomplish this and illustrate them by computing the frechet derivative for the id resistivity problem for more complicated problems where it is not possible to obtain an expression for the frechet derivative it is necessary to parameterize the model and solve numerically for the sensitivities partial derivatives of the data with respect to model parameters the standard perturbation method for computing first order sensitivities is discussed and compared to the more efficient sensitivity equation and adjoint equation methods extensions to allow for the calculation of higher order directional and objective function sensitivities are also presented finally the application of these various techniques is illustrated for both the 1d and 2d resistivity problems

the use of reference models from a priori data to guide 2d inversion of electrical resistivity tomography data clay rich till plains cover much of the uk such sites are attractive locations for landfills since clay aquitards lower the risk of landfill leachate entering groundwater however such tills often contain sand and gravel bodies that can act as leachate flow routes such bodies may not be detected by conventional site investigation techniques such as drilling boreholes and trial pitting a method of guided inversion where a priori data are used to construct structural reference models for use in inverting electrical resistivity tomography data was proposed as a tool to improve the detection of sand and gravel bodies within clay rich till sequences following a successful 2d guided inversion synthetic modelling study a field study was undertaken wenner 2d electrical resistivity tomography lines resistivity cone penetrometry bores and electromagnetic induction ground resistivity data were collected over a site on the east yorkshire coast england where sand and gravel lenses were known to exist from cliff exposures a number of equally valid geoelectrical models were constructed using the electromagnetic and resistivity cone data these were used as structural reference models in the inversion of the resistivity tomography data blind inversion using an homogenous reference model was also carried out for comparison it was shown for the first time that the best solution model produced by 2d inversion of one data set with a range of structural reference models could be determined by using the l2 model misfit between the solution models and associated reference models reference misfit as a proxy for the l2 misfit between the solution models and the synthetic model or best guess geoelectrical model true misfit the 2d methodology developed here is applicable in clay rich till plains containing sand and gravel bodies throughout the uk

an algorithm for fast 3d inversion of surface electrical resistivity tomography data application on imaging buried antiquities in this work a new algorithm for the fast and efficient 3d inversion of conventional 2d surface electrical resistivity tomography lines is presented the proposed approach lies on the assumption that for every surface measurement there is a large number of 3d parameters with very small absolute jacobian matrix values which can be excluded in advance from the jacobian matrix calculation as they do not contribute significant information in the inversion procedure a sensitivity analysis for both homogeneous and inhomogeneous earth models showed that each measurement has a specific region of influence which can be limited to parameters in a critical rectangular prism volume application of the proposed algorithm accelerated almost three times the jacobian sensitivity matrix calculation for the data sets tested in this work moreover application of the least squares regression iterative inversion technique resulted in a new 3d resistivity inversion algorithm more than 2 7 times faster and with computer memory requirements less than half compared to the original algorithm the efficiency and accuracy of the algorithm was verified using synthetic models representing typical archaeological structures as well as field data collected from two archaeological sites in greece employing different electrode configurations the applicability of the presented approach is demonstrated for archaeological investigations and the basic idea of the proposed algorithm can be easily extended for the inversion of other geophysical data

explicit expressions and numerical calculations for the frechet and second derivatives in 2 5d helmholtz equation inversion in order to perform resistivity imaging seismic waveform tomography or sensitivity analysis of geophysical data the frechet derivatives and even the second derivatives of the data with respect to the model parameters may be required we develop a practical method to compute the relevant derivatives for 2 5d resistivity and 2 5d frequency domain acoustic velocity inversion both geophysical inversions entail the solution of a 2 5d helmholtz equation first using differential calculus and the green s functions of the 2 5d helmholtz equation we strictly formulate the explicit expressions for the frechet and second derivatives then apply the finite element method to approximate the green s functions of an arbitrary medium finally we calculate the derivatives using the expressions and the numerical solutions of the green s functions two model parametrization approaches constant point and constant block are suggested and the computational efficiencies are compared numerical examples of the derivatives for various electrode arrays in cross hole resistivity imaging and for cross hole seismic surveying are demonstrated two synthetic experiments of resistivity and acoustic velocity imaging are used to illustrate the method

estimating depth of investigation in dc resistivity and ip surveys in this paper the term depth of investigation refers generically to the depth below which surface data are insensitive to the value of the physical property of the earth estimates of this depth for dc resistivity and induced polarization ip surveys are essential when interpreting models obtained from any inversion because structure beneath that depth should not be interpreted geologically we advocate carrying out a limited exploration of model space to generate a few models that have minimum structure and that differ substantially from the final model used for interpretation visual assessment of these models often provides answers about existence of deeper structures differences between the models can be quantified into a depth of investigation doi index that can be displayed with the model used for interpretation an explicit algorithm for evaluating the doi is presented the doi curves are somewhat dependent upon the parameters used to generate the different models but the results are robust

an introduction to the tectonophysics special issue geodynamics and environment in east asia tribute to jacques angelier 1947 2010

shape of the shallow aquifer at the fresh water sea water interface on a high energy sandy beach abstract inland aquifers are connected to the ocean through permeable coastal sediments the mixing zone between sea water and fresh groundwater forms a so called subterranean estuary the dynamics and the shape of this interface influence fluxes of fresh water to the coastal zone on tidal sandy beaches tide and waves actions lead to the formation of an intertidal saline circulation cell that complements the structure of the subterranean estuary between sea water and fresh water the upper beach corresponds to the recharge zone where large volumes sea water penetrate the sediment at high tide whereas the lower beach corresponds to the discharge zone of older pore water that remains in the sand for several tidal cycles the objective of our study was to characterize the shape and the evolution of this saline cell in a high energy macro tidal beach the truc vert beach sw france in order to assess the distribution of saline brackish and fresh water in this high energy beach aquifer we conducted electrical resistivity tomography ert measurements from the lower beach face to the sand dune in winter 2012 2013 we also measured water table elevation and salinity in three piezometers situated at the base of the dune and in pore waters at low tide on tidal cross shore transects results show that the intertidal saline plume can be identified and localized with the ert method the fresh saline water interface is almost vertical in the upper beach the saline circulation cell occupies the upper part of the tidal beach over a thickness of 5 m deep below this saline cell a brackish water flows to the ocean about 30 of fresh water was found in pore water in the lower part of the beach shifting of the vertical front between saline and fresh waters of about 2 5 m occurred during the spring neap tidal cycle this migration is small relative to the beach size suggesting that the transition zone is relatively stable the variations in salinity of the circulation cell suggest that the position of the saline plume is controlled by the spring tide level our results differ slightly from studies based on modelling and piezometric measurement made in less exposed micro tidal sandy beaches our data would allow to better constrain numerical models that would enable to quantify water residence time and solute fluxes in subterranean estuaries of high energy beaches

a 2d numerical study of the effect of particle shape and orientation on resistivity in shallow formations surficial heterogeneous soils such as till alluvial fans or slope deposits are difficult to characterize by geotechnical tests because of the presence of decimeter to meter sized pebbles or rocks the effective resistivity of such two component media composed of a percentage of resistive particles embedded in a conductive matrix is given by the bussian s equation the application of this equation allows the concentration of resistive particles to be determined if the resistivity values of each component and of the mixture as well as the cementation exponent m are known however previous theoretical and experimental studies have shown that the effective resistivity is affected by the shape of the particles the objective of this study is to numerically determine the 2d effects of particle shape and orientation on the resistivity two configurations have been considered in the finite element fe modeling laboratory like measurements and field layout for circular particles the numerical results fi

comparing induced polarization responses from airborne inductive and galvanic ground systems lewis ponds new south wales we have evaluated the mapping of polarizable material using a cole cole model to fit second order effects in concentric loop airborne electromagnetic system responses at lewis ponds in new south wales an inverted ground dipole dipole array data has accurately imaged in 3d disseminated sulfide extending above and around ore grade massive sulfides the polarizable zone is present in the near surface where from modeling airborne systems may have sensitivity to the small inductive induced polarization effects although the inverted chargeability measured from galvanic current injection into the ground was spatially coincident with the mineralized target the estimated chargeabilities from induced polarization effects in an airborne versatile time domain electromagnetic survey were substantially displaced to the east the airborne induced polarization response may be associated with finer grained mineralization in the hanging wall of the sulfide deposits or have a quite different source such as clays associated with faulting

a survey of current trends in near surface electrical and electromagnetic methods electricalandelectromagnetice emmethodsfornearsurface investigations have undergone rapid improvements over the past few decades besides the traditional applications in groundwater investigations natural resource exploration and geological mapping a number of new applications have appeared these include hazardous waste characterizationstudies precision agricultureapplications archeological surveys and geotechnical investigations the inclusion of microprocessors in survey instruments development ofnewinterpretationalgorithms andeasyaccesstopowerful computers have supported innovation throughout the geophysical community and the e em community is no exception most notable are development of continuous measurement systems that generate large dense data sets efficiently these have contributed significantly to the usefulness of e em methods by allowing measurements over wide areas without sacrificing lateral resolution the availability of theseluxuriantdatasetsinturnspurreddevelopmentofinterpretation algorithms including laterally constrained 1d inversionaswellasinnovative2d and3d inversionmethods taken together these developments can be expected to improve the resolution and usefulness of e em methods and permit them to be applied economically the trend is clearly towarddensesurveyingoverlargerareas followedbyhighly automated post acquisition processing and interpretation to provide improved resolution of the shallow subsurface in a cost effectivemanner

time lapse imaging of subglacial drainage conditions using three dimensional inversion of borehole electrical resistivity data we recorded electrical resistivity data at the base of four boreholes drilled through haut glacier d arolla switzerland the data were acquired repetitively every hour over two diurnal hydrological cycles in the late melt season separated by 10 days constrained three dimensional 3 d data inversion allowed reconstruction of hourly variations in bulk resistivity in the subglacial sediment layer inverted resistivity models reflect the establishment of channelized subglacial drainage in the study area between the two hydrological cycles in agreement with previous work daily variations in bulk and water resistivity are in phase and bulk resistivity amplitudes decrease away from the subglacial channel using selected electrical hydraulic relationships we estimate metre scale changes in the hydraulic conductivity and porosity of the subglacial sediment layer accounting for increasing clay content and decreasing median grain radius with distance from the channel hydraulic conductivity and porosity were respectively calculated to decrease from 6 4 2 1 10 2 m s 1 and 0 34 0 01 at the channel to 3 3 2 2 10 2 m s 1 and 0 26 0 01 at a distance of 5 m from it the hydraulic conductivity estimates are in agreement with previously inferred values and the porosity estimates fall within the expected range for unlithified subglacial sediments we conclude that collection and inversion of repeat 3 d subglacial resistivity data is feasible and has the capacity to generate multidimensional images of subglacial hydraulic processes and properties

piecewise 1d laterally constrained inversion of resistivity data in a sedimentary environment layered models are often capable of representing the actual geology more accurately than smooth minimum structure models furthermore interval thicknesses and resistivities are often the parameters to which non geophysicist experts can relate and base decisions on when using them in waste site remediation groundwater modelling and physical planning we present a laterally constrained inversion scheme for continuous resistivity data based on a layered earth model 1d all 1d data sets and models are inverted as one system producing layered sections with lateral smooth transitions the models are regularized through laterally equal constraints that tie interface depths and resistivities of adjacent layers prior information e g originating from electric logs migrates through the lateral constraints to the adjacent models making resolution of equivalences possible to some extent information from areas with well resolved parameters will migrate through the constraints in a similar way to help resolve the poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result examples from synthetic 2d models show that the model recognition of a sublayered 2d wedge model is improved using the laterally constrained inversion approach when compared with a section of combined 1d models and when compared with a 2d minimum structure inversion case histories with data from two different continuous dc systems support the conclusions drawn from the synthetic example

electrical and gpr prospecting at palo blanco archaeological site northwestern argentina we conducted a geophysical survey at the palo blanco archaeological site located in catamarca argentina age estimates from radiocarbon dating indicate first occupation of the site around 1500 years ago the first description of thesite was done in 1960 at that time five residential units with different architectural arrangements were reported these structures had different levels of deterioration caused by exposure and human activities some of these original structures have become completely covered by sediments to aid in the design of efficient excavation plans detailed maps are required to locate the buried walls for this purpose we conducted geophysical surveys over one of the structures we had poor documentation about the structure at the time of the survey only one of the walls described in the earlier report was partially visible we used two geophysical methods ground penetrating radar gpr and electrical resistivity we performed 2d inversion of the resistivity data together with nu

combined application of surface geoelectrical methods for groundwater flow modeling a case history electrical methods electrical profiling and sounding induced polarization ip and self potential sp combined with geochemical and hydrochemical surveys were applied to characterize shallow sediments at a site contaminated by oil related brines the site is located within the romashkinskoye oil field tatarstan republic russian federation results of geochemical and hydrochemical surveys as well as those of electrical profiling revealed no individual haloes of contaminant in the soil and groundwater which suggests that the entire site is contaminated vertical electrical ip soundings ves ip allowed us to obtain the stratigraphic characteristics of the site and to distinguish a shallow aquifer among clayey aquitards interpretation of sp data on the basis of forward numerical modeling helped us to develop a groundwater flow model of the site to reduce ambiguities we kept fixed the values of layer resistivity derived from the inverted ves ip data boundary conditions on water head and water flow were based on drilling and sampling data we varied only the values of hydraulic conductivity to fit the calculated sp values to the measured sp values we found a strong misfit between the measured and calculated sp values for the one aquifer model by inferring a second deeper seated aquifer we computed a two aquifer model that produced a satisfactory sp fit

cross hole resistivity tomography using different electrode configurations this paper investigates the relative merits and effectiveness of cross hole resistivity tomography using different electrode configurations for four popular electrode arrays pole pole pole bipole bipole pole and bipole bipole by examination of two synthetic models a dipping conductive strip and a dislocated fault it is shown that besides the popular pole pole array some specified three and four electrode configurations such as pole bipole am n bipole pole am b and bipole bipole am bn with their multispacing cross hole profiling and scanning surveys are useful for cross hole resistivity tomography these configurations compared with the pole pole array may reduce or eliminate the effect of remote electrodes systematic error and yield satisfactory images with 20 noise contaminated data it is also shown that the configurations which have either both current electrodes or both potential electrodes in the same borehole i e pole bipole a mn bipole pole ab m and bipole bipole ab mn have a singularity problem in data acquisition namely low readings of the potential or potential difference in cross hole surveying so that the data are easily obscured by background noise and yield images inferior to those from other configurations

metalliferous mining geophysics state of the art in the last decade of the 20th century and the beginning of the new millennium the downturn in mining activity experienced during the 1990s did not preclude significant new developments in various areas of mining geophysics the methodology for acquiring and compiling data has kept pace with the latest technological developments from global positioning system navigation to raster displays and parallel computing wavelet transforms principal component analysis and fractals have begun to find successful applications in both processing and interpretation of geophysical data methods of quantitatively interpreting inverting anomalies in terms of 2 d and 3 d models of causative bodies are becoming common for the first time it is possible to make airborne gravity gradient measurements suitable for use in mineral exploration lower transmitter frequencies for airborne time domain electromagnetic em systems have enabled surveys in areas where conductive cover previously screened basement conductors the use of approximation algorithms has allowed the transformation of either time domai

challenges in geophysical mapping of glaciotectonic structures abstractglaciotectonic complexes have been recognized worldwide traditionally described on the basis of outcrops or geomorphological observations in the past few decades geophysics has become an integral part of geologic mapping which enables the mapping of buried glaciotectonic complexes the geophysical methods provide different types of information and degrees of resolution and thus a different ability to resolve the glaciotectonic structures we evaluated these abilities on the basis of an integrated application of four commonly used geophysical methods airborne transient electromagnetics high resolution reflection seismic geoelectrical and ground penetrating radar gpr we covered an area of 100 km2 in a formerly glaciated region in the western part of denmark the geologic setting was highly heterogeneous with glaciotectonic deformation observed in the form of large scale structures in the seismic and airborne transient electromagnetic data to small scale structures seen in the gpr and g

low load diamond drill bits for subglacial bedrock sampling electromechanical cable suspended drilling technology is considered one of the most feasible methods for subglacial bedrock drilling the outstanding feature of this technology is that the bit load produced by the drill weight is usually within the range 1 5 4 kn while the recommended load for diamond drilling is 10 30 kn or even more therefore searching for the diamond bits that can drill in extremely hard formations with minimal load and acceptable rates of penetration and torque is the necessary step to prove the feasibility of electromechanical subglacial drilling technology a special test stand has been designed and constructed to examine the impregnated surface set toothed and specially manufactured bionic drill bits the results of experiments with ten types of drill bits show that the toothed diamond drill bit has the highest penetration rate of 3 18 m h 1 in very hard and abrasive granite under a 3 kn load the torque 28 7 nm and power consumption 1 5 kw of toothed drill bits are acceptable for cable suspended drilling the penetration rates of bionic drill bits may also be considered suitable and fall within the range 1 0 1 69 m h 1 under the lowest tested load

inversion of nuclear well logging data using neural networks this work looks at the application of neural networks in geophysical well logging problems and specifically their utilization for inversion of nuclear downhole data simulated neutron and ray fluxes at a given detector location within a neutron logging tool were inverted to obtain formation properties such as porosity salinity and oil water saturation to achieve this the forward particle radiation transport problem was first solved for different energy groups 47 neutron groups and 20 ray groups using the multigroup code event a neural network for each of the neutron and ray energy groups was trained to re produce the detector fluxes using the forward modelling results from 504 scenarios the networks were subsequently tested on unseen data sets and the unseen input parameters formation properties were then predicted using a global search procedure the results obtained are very encouraging with formation properties being predicted to within 10 average relative error the examples presented show that neural networks can be applied successfully to nuclear well logging problems this enables the implementation of a fast inversion procedure yielding quick and reliable values for unknown subsurface properties such as porosity salinity and oil saturation

drilling comparison in warm ice and drill design comparison for the deep ice core drilling community the 2005 06 antarctic season was an exciting and fruitful one in three different antarctic locations dome fuji epica dml and vostok deep drillings approached bedrock the ice water interface in the case of vostok emulating what had previously been achieved at northgrip greenland summer 2003 and 2004 and at epica dome c2 antarctica season 2004 05 for the first time in ice core drilling history three different types of drill kems jare and epica simultaneously reached the depth of warm ice under high pressure after excellent progress at each site the drilling rate dropped and the drilling teams had to deal with refrozen ice on cutters and drill heads drills have different limits and perform differently in this comparative study we examine depth pressure temperature pump flow and cutting speed finally we compare a few parameters of ten different deep drills

relict landslide development as inferred from speleothem deformation tectonic data and geoelectrics abstract the direct dating of pre and postfaulting dislocated calcite speleothems afforded new insight into slope failure in the tatra mountains in southern poland a multi approach study of the karstic kalacka cave non crevasse type enabled us to infer the slope deformation structure which had been poorly preserved in ground surface topography using combined methods including geomorphological and structural mapping of cave and ground surfaces paleostress analysis near surface electrical resistivity tomography ert and induced polarization methods ip uranium series dating 234u 230th calcite microtexture analysis and stable isotope 18o and 13c analysis here slope deformation began with dilation between 280 7 ka and 265 8 ka and proceeded as deep seated gravitational slope deformations the final stage consisted of dilation rejuvenation and rockfall during the latest pleistocene or holocene post 35 4 ka additionally some dilations are evident beyond the extent of the landslide detected by ert indicating further progradation of slope failure since this failure was initiated during the climatic transition from mis 9 to mis 8 stable isotope analysis of calcite flowstone layers was applied to test climate factors the correlation of calcite microtexture and 18o and 13c compositional changes with the interval of dilation activity indicates that regional environment factors chiefly an increase in precipitation probably contributed to slope destabilization

3d geostatistical inversion of induced polarization data and its application to coal seam fires we applied the principal component geostatistical approach pcga to the inversion of time domain induced polarization data in terms of resistivity and chargeability distributions the pcga presents two major advantages over standard methods 1 it avoids the storage of the usually large covariance matrix which contains the geostatistical information by factorizing it in a product of low rank matrices 2 it does not assemble the jaco bian matrix per se we determine the robustness of this approach with three examples we first reconstruct the electrical conductivity and chargeability fields of two synthetic models generated using the geostatistical software stanford geostatistical modeling software the pcga approach performs better than the tikho nov based regularization approach when the true fields are very heterogeneous and the amount of data is limited the third example is devoted to a field study over the former lewis coal mine in colorado usa we perform a 3d localization of the burning front of this coal seam fire by applying our geostatistical inverse methodology to a time domain induced polarization data set in this case the horizontal components of the semivariogram are determined from a self potential map and the correlation length scale for the vertical component is determined from the known thickness of the coal bed the tomogram presents a high normalized chargeability associated with the burning front we evaluate the high normalized chargeability of the burning front in terms of the physical mechanism associated with the cation exchange capacity of the coal and the effect of temperature this demonstrates the potential of the geostatistical inversion and its suitabil ity for inverting geophysical data especially when the data density is sparse in the case of coal seam fires we determine the suitability of the induced polarization method to localize the burning front and the effect of temperature on the normalized chargeability

forward and inverse self potential modeling in mineral exploration natural self potential sp fields observed in the vicinity of conductive orebodies can be explained in terms of electrochemical reactions in which the conductors participate battery like models assume that a buried conductor creates an anode cathode pair by conveying a flow of electrons to oxidizing areas in the shallow subsurface from reducing areas at depth for conductors with invariant composition behaving as an inert electrode a quantitative formulation is already available numerical green s functions are used to allow one step evaluation of sp fields from an inert electrode model the model is used to simulate geoelectric targets in mineral exploration and to test a procedure to obtain current source terms by inverting an sp data set data inversion is constrained by charge conservation and prescribes source terms at the target surface a background resistivity model is assumed to be known and is used to recognize interfaces and evaluate numerical green s functions in forward and inverse modeling the inversion procedure is applied to interpret 2d data from two gold deposits of the yanacocha district peru

geophysical inversions applied to 3d geology characterization of an iron oxide copper gold deposit in brazil abstract mineral exploration dynamics often requires an efficient and objective means of evaluating a prospect in early exploration stages when few holes have been drilled in the case of deep prospects or prospects under cover this evaluation will mostly be based on geophysical data to develop an objective interpretation method capable of combining all the information available we have developed an integrated interpretation scheme of geophysical models and sparse geologic data our method is based on the relationship between recovered physical properties obtained from 2d and 3d inversions aiming to find patterns associated with geologic units such as iron formation copper ore and host rock the interpretation is guided by theoretical relations of the minerals of interest chalcopyrite and magnetite and the sparse geologic information available it is suitable for prospects in the initial stages of exploration when only limited mineralogical information is available from say one drillhole we h

inversion of induced polarization data we present an algorithm for inverting induced polarization ip data acquired in a 3 d environment the algorithm is based upon the linearized equation for the ip response and the inverse problem is solved by minimizing an objective function of the chargeability model subject to data and bound constraints the minimization is carried out using an interior point method in which the bounds are incorporated by using a logarithmic barrier and the solution of the linear equations is accelerated using wavelet transforms inversion of ip data requires knowledge of the background conductivity we study the effect of different approximations to the background conductivity by comparing ip inversions performed using different conductivity models including a uniform half space and conductivities recovered from one pass 3 d inversions composite 2 d inversions limited aim updates and full 3 d nonlinear inversions of the dc resistivity data we demonstrate that when the background conductivity is simple reasonable ip results are obtainable without using the best conductivity estimate derived from full 3 d inversion of the dc resistivity data as a final area of investigation we study the joint use of surface and borehole data to improve the resolution of the recovered chargeability models we demonstrate that the joint inversion of surface and crosshole data produces chargeability models superior to those obtained from inversions of individual data sets

internal structure and conditions of permafrost mounds at umiujaq in nunavik canada inferred from field investigation and electrical resistivity tomography a systematic approach was used for the interpretation of the electrical resistivity tomography carried out on two permafrost mounds at umiujaq in nunavik canada to assess their internal structure and conditions prior information under the form of a geocryologic model of the permafrost mounds was integrated in the inversion of the pseudo section of apparent electrical resistivity the geocryologic model was developed from the synthesis of previous field investigations including shallow and deep sampling temperature and electrical resistivity logging and cone penetration tests performed in the permafrost mounds values of electrical resistivity were ascribed to the different layers making of the geocryologic model to define a synthetic resistivity model of the permafrost mounds used as a reference model to constrain the inversion the constrained resistivity model clearly show the presence of ice rich cores in the permafrost mounds underscored by high resistivity values in excess of 30 000 m while t

electromagnetic dispersion and sensitivity characteristics of carbonate reservoirs abstractthe need to develop a new measurement method for the identification of favorable hydrocarbon producing zones in carbonate reservoirs is of great importance due to their complex pore structure and lithology we have evaluated fundamental experimental data acquired from carbonate formation samples in a buried hill reservoir to demonstrate the magnitude of the complex resistivity cr dispersion effect in oil saturated carbonate rocks and the possibility of identifying hydrocarbon bearing carbonate sections our experimental data set included cr measurements on four carbonate core samples with various degrees of oil saturation and at each saturation level cr measurements were acquired in a frequency range between 10 hz and 100 khz the experimental data indicated that the intensity of the cr dispersion effect increased with oil saturation above a specific critical excitation frequency the experimental spectra of the carbonate samples were fitted with the debye model and the cole cole model ccm

3d electrical imaging of an archaeological site using electrical and electromagnetic methods floridablanca is an 18th century archaeological site located in southern argentina archaeological investigations at the site began in 1998 and in 2000 we started a project to perform geophysical studies there in this paper we report the implementation of electrical and electromagnetic em methods in a sector of the site that corresponds to the settlers houses the objective of the project was to characterize the zone and the buried archaeological structures adobe walls tiles from a collapsed roof with 2d and 3d electrical and em techniques we first applied an em induction method covering a 600 m 2 area with a frequency ranging from 1000 to 19 000 hz a 3d visualization of the in phase and quadrature components gave an initial description of anomalies possibly associated with buried structures we then performed dipole dipole profiles and inverted the data to obtain the corresponding 2d and 3d electrical images finally after correlating the information obtained from the analysis of both em and electrical data we performed a more localized 3d dipole dipole mesh 25 m 2 to achieve the final electrical image of the most representative buried structure the combination of both techniques allowed us to map two entire houses and to identify three types of walls main separating and inner these results have been confirmed by an archaeological excavation

new geophysical and geological evidence for the present day southernmost active deformational front of the rif thrust and fold belt and the oceanic accretionary prism of cadiz the dhar doum lalla zahra fault northwestern atlantic coastal morocco combining the results from field observations high resolution 2d electric resistivity and high resolution seismic refraction tomography we have found new evidence for active faulting in the dhar doum area northwestern atlantic coast of morocco qualitative interpretation of the inverted resistivity and seismic refraction data reveals the presence of two thrust faults that cut the topographic surface and displace the most recent sedimentary deposits furthermore one of these seismically imaged faults strongly correlates with the dhar doum lalla zahra fault the steepening at the surface and the flattening with depth of this fault are likely to indicate an important strike slip component associated with a major reverse component if extended offshore to the west the dhar doum fault could be a continuation of the southernmost deformational front of the cadiz oceanic accretionary prism therefore this structure is very likely to represent the actual active southern deformational front of the oceanic accretionary prism as well as that of the rif fold and thrust belt the southward thickening of the growth strata composing the uppermost dune system and the occurrence of plio quaternary conglomerates north of the dhar doum lalla zahra fault suggest that the neotectonic activity may have started by the end of the pliocene and have continued to the present as indicated by the folding and faulting of the most recent sedimentary deposits and the presence of high scarps the identification of active faulting in the study area that may have a profound influence on seismic hazard analysis of the whole rif foredeep basin

large scale geophysical reconstruction of man made ground at former industrial iron furnace plantations blast iron furnace plantations were widespread throughout colonial and postcolonial america and therefore represent sites of specific archaeological interest because such plantations often were a really extensive historical reconstruction of a site is challenging using conventional archaeological field techniques alone therefore we appraise the usefulness of integrating magnetic gradiometer electrical resistivity tomography ert and electromagnetic em31 data in detecting and delineating buried structures related to former operation of the shade furnace a typical industrial plantation in 19th century pennsylvania the geophysical results were ground truthed in seven locations by archaeological excavation geophysical results demonstrated that 1 the distribution of remaining original soils could be mapped 2 waste materials e g slag used brick burned charcoal iron ore and broken up sandstone or limestone within or above the original soils could be detected and delineated whether the material occurred in pits or lenses or was dispersed across the ground surface and 3 the location and spatial extent of many former structures related to furnace operation could be identified such as building or bridge foundations and casting related structures e g the tapping channel or the casting floor and the former courses of a water canal raceway and a supply road we conclude that geophysical techniques can play a key role in reconstructing man made ground at former industrial furnace sites in north america