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

plate tectonic development of the south west indian ocean a revised reconstruction of east antarctica and africa a revised sequence of reconstructions for east antarctica relative to africa is generated from published seafloor spreading and fracture zone anomalies these date from the cretaceous tertiary boundary to the late jurassic and lead to a revised predrift reconstruction for east and west gondwanaland euler pole 1 67 s 35 99 e rotation angle 53 43 this reconstruction derived wholly from marine data places east antarctica adjacent to the lebombo mountains and south of and subparallel to the sabi acid volcanic suite supporting the postulate that these rocks represent mesozoic plate boundaries this refit implies that part of the coastal plain of mozambique is underlain by oceanic or very highly extended continental crust the reconstruction is supported by the alignment of 1 the cape fold belt with its antarctic equivalents and 2 the western limit of pan african reactivation of the mozambique mobile belt with the western limit of the sverdrupfjella metamorphic suite antarctica initially moved along a transform fault lying immediately east of and subparallel to the lebombo mountains the eastern face of the tugela cone the southeastern face of the falkland plateau in its reconstructed position and the eastern flank of the agulhas plateau in its reconstructed position at m10 time a triple junction formed near the tip of the falkland plateau implying that the oldest lineated magnetic anomalies in the eastern weddell sea associated with this triple junction cannot predate m10 at m2 time the mozambique ridge rifted from the astrid ridge in a ridge jump episode such an event may also explain the presence of magnetic anomalies in the southern mozambique basin gunnerus ridge conrad rise and del cano rise are all tectonically associated with the madagascar ridge

3d crosshole ert for aquifer characterization and monitoring of infiltrating river water the hydrogeological properties and responses of a productive aquifer in northeastern switzerland are investigated for this purpose 3d crosshole electrical resistivity tomography ert is used to define the main lithological structures within the aquifer through static inversion and to monitor the water infiltration from an adjacent river during precipitation events and subsequent river flooding the river water resistivity increases as a consequence the electrical characteristics of the infiltrating water can be used as a natural tracer to delineate preferential flow paths and flow velocities the focus is primarily on the experiment installation data collection strategy and the structural characterization of the site and a brief overview of the ert monitoring results the monitoring system comprises 18 boreholes each equipped with 10 electrodes straddling the entire thickness of the gravel aquifer a multichannel resistivity system programmed to cycle through various four point electrode configurations of the 180 electrodes in a rolling sequence allows for the measurement of approximately 15 500 apparent resistivity values every 7 h on a continuous basis the 3d static ert inversion of data acquired under stable hydrological conditions provides a base model for future time lapse inversion studies and the means to investigate the resolving capability of our acquisition scheme in particular it enables definition of the main lithological structures within the aquifer the final ert static model delineates a relatively high resistivity low porosity intermediate depth layer throughout the investigated aquifer volume that is consistent with results from well logging and seismic and radar tomography models the next step will be to define and implement an appropriate time lapse ert inversion scheme using the river water as a natural tracer the main challenge will be to separate the superposed time varying effects of water table height temperature and salinity variations associated with the infiltrating water

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

electrical resistivity tomography of vadose water movement cross borehole electrical resistivity tomography ert was used to image the resistivity distribution before and during two infiltration experiments in both cases water was introduced into the vadose zone and the change in resistivity associated with the plume of wetted soil was imaged as a function of time the primary purpose of this work was to study the capabilities and limitations of ert to image underground structure and ground water movement in the vadose zone a secondary goal was to learn specifics of unsaturated flow in a complex geologic setting tomographs of electrical resistivity taken before infiltration image coarser well drained soils sands and gravels as more resistive zones whereas finer grained soils silts and clays which hold more water by capillarity are imaged as more conductive images of changes in resistivity during infiltration show growth of the water infiltration plume with time that is consistent with known geology in the ert images we see the effects of capillary barriers and infer differences between capillary driven flow through fine sediments and gravity driven flow through very permeable sediments images are consistent with numerical flow simulations using hydrological parameter values consistent with soil types inferred from well logs ert can be a useful tool to monitor movement of circuitous moisture fronts in a heterogeneous field setting that would go undetected by borehole measurements

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

soil creep in salt marshes a puzzling aspect of marsh morphodynamics is the occurrence of channel bank slumping despite the absence of channel widening and lateral migration an apparently unrelated conundrum is why the vertical accretion rate on the low marsh adjacent to channels is higher than the rate of relative sea level rise this sedimentation excess should not occur at steady state or in a regime of accelerated sea level rise here we suggest that lateral erosion and vertical sedimentation on channel banks are linked by creep the process by which soil is moved downslope by gravity the model presented herein predicts a dynamic equilibrium configuration for the cross section such that sedimentation excess on the channel banks is transferred by creep toward the channel where tidal flow erosion and suspended sediment transport directed toward the banks close the sediment budget this model predicts that bank slumping is an equivocal indicator of ongoing marsh loss and that high sedimentation rates on channel banks do not necessarily constitute a margin of resilience to accelerated sea level rise

vadose zone flow model parameterisation using cross borehole radar and resistivity imaging cross borehole geoelectrical imaging in particular electrical resistivity tomography ert and transmission radar tomography can provide high resolution images of hydrogeological structures and in some cases detailed assessment of dynamic processes in the subsurface environment through appropriate petrophysical relationships these tools offer data suitable for parameterising and constraining models of groundwater flow this is demonstrated using cross borehole radar and resistivity measurements collected during a controlled vadose zone tracer test performed at a field site in the uk sherwood sandstone both methods show clearly the vertical migration of the tracer over a 200 h monitoring period by comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two and three dimensional ert and cross borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0 4 m d such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site

dc resistivity mapping of internal landfill structures two pre excavation surveys geophysical investigations using 2 d dc resistivity were carried out on old parts of two similar landfills with waste of different ages the data sets which included high data density in both vertical and horizontal directions were interpreted with 2 d smoothness constrained inversion the landfills were excavated after the surveying the objective was to test the capability of the resistivity method as a pre characterization technique the objectives were only partially fulfilled first the moisture content was the parameter that appeared to exert the dominant control over the resistivity distribution of the landfill the most important potential information that can be recovered is therefore an indication of the waste piles hydraulics second it was neither possible to estimate the amount of recoverable soils nor to correlate the type of waste with the resistivity models however discrete anomalies were identified and if specific materials are searched for the resistivity models indicate possible places to search

three dimensional resistivity tomography of vulcan s forge vulcano island southern italy 1 9 525 dc resistivity measurements were taken along 9 profiles crossing the volcanic edifice of la fossa di vulcano the forge of god vulcan in ancient roman mythology vulcano island italy using a total of 958 electrode locations this unique data set has been inverted in 3d by minimizing the l2 norm of the data misfit using a gauss newton approach the true 3d inversion was performed using parallel processing on an unstructured tetrahedral mesh containing 75 549 finite element nodes and 398 208 elements to accurately model the topography of the volcanic edifice the 3d tomogram shows a very conductive body 0 1 s m comprised inside the pietre cotte crater with conductive volumes that are consistent with the position of temperature and co2 anomalies at the ground surface this conductive body is interpreted as the main hydrothermal body it is overlaid by a resistive and cold cap in the bottom of the crater the position of the conductive body is consistent with the deformation source responsible for the observed 1990 1996 deflation of the volcano associated with a decrease of hydrothermal activity

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

self potential signals associated with localized leaks in embankment dams and dikes abstract the self potential method can be used to detect and monitor anomalous seepages in dams and embankments in such a case an electrical field of electrokinetic nature i e associated with pore water flow can be measured using a set of non polarizable electrodes typically located at the ground surface or in some wells this field can be in turn related to the pattern of groundwater flow we built an experimental dam to investigate to which extent the self potential method can help characterizing seepages in dams we first use the finite element method to simulate the ground water flow in a heterogeneous porous and permeable material by solving the groundwater flow equation the resulting groundwater flow solution is then used to compute the electrical potential distribution by solving the corresponding elliptic partial differential equation in a preliminary experiment we could not measure any self potential anomaly associated with the infiltration of water in the dam our numerical simulations showed that the magnitudes of the self potential anomalies were controlled by 1 the nature of the flow regime viscous laminar versus inertial laminar flow regimes and 2 the presence of insulating polyvinyl chloride pvc tubes located at the end of the preferential flow channels in the structure of the dam thanks to these numerical simulations we added sand at the entrance of the infiltration area in order to reduce the effects of the pvc tubes and to restrain the flow regime to the viscous laminar flow regime new experiments allowed for detecting a self potential anomaly with an amplitude of around 9 mv consistent with that obtained through numerical modelling with a finite element simulator this comparison was used to test the accuracy of the modelling approach and define the strengths and weaknesses of the self potential method to determine preferential seepages in earth dam structures

fully coupled hydrogeophysical inversion of a laboratory salt tracer experiment monitored by electrical resistivity tomography 1 we perform a salt tracer experiment monitored by time lapse electrical resistivity tomography in a quasi two dimensional sandbox with the aim of determining the hydraulic conductivity distribution in the domain we use sodium chloride as a tracer together with cochineal red for visual monitoring the time series of observed resistance for each electrode configuration is characterized by its temporal moments we invert the mean arrival time of electrical potential perturbations and a few steady state hydraulic head measurements using the fully coupled hydrogeophysical approach recently introduced by pollock and cirpka 2010 this is the first application of the approach to experimental data the results obtained show a reasonable agreement between the estimated hydraulic conductivity field and the pattern of the actual sandbox filling using this estimation a transient simulation is performed to compute the propagation of the salt tracer plume through the sandbox the latter is compared to pictures taken during the experiment these results show an even better agreement indicating that the lenses of different sand types are not entirely homogeneous and some unexpected preferential flow paths are present we conclude that temporal moments of potential perturbations obtained during salt tracer tests provide a good basis for inferring the hydraulic conductivity distribution by fully coupled hydrogeophysical inversion

recent developments in the use of surface electrical methods for oil and gas exploration in the soviet union a great deal of interest has been expressed in western countries during recent years on possible applications of surface electrical methods in oil and gas exploration it has been reported that these methods are widely used in the soviet union but to date few technical details have been available in late 1979 the author visited the soviet union under the auspices of the australia ussr agreement on scientific cooperation with the purpose of studying recent developments in electrical and electromagnetic em methods this paper presents a summary of the use and applications of those methods in oil and gas exploration and includes a number of case histories the methods can be broadly classified as follows sounding for structural mapping sounding to measure the geoelectric properties of the oil bearing horizon and indirect methods which detect the presence of a geochemical plume or halo above the oil deposit the magnetotelluric mt method and transient sounding in the near zone zsbz are widely us

induced polarization of shaly sands equations have been developed that relate induced polarization ip in shaly sands to measurable petrophysical parameters the induced polarization process has been modeled in terms of two mechanisms clay counterion displacement and membrane blockage the resulting equations can be used to determine shaliness brine conductivity and oil saturation from in phase and out of phase conductivities laboratory measurements have confirmed the ip dependence on these variables as well as on temperature

comment on relative positions of africa and antarctica in the upper cretaceous evidence for non stationary behaviour of fracture zones by ph patriat j segoufin j goslin and p beuzart

hydraulic conductivity imaging from 3 d transient hydraulic tomography at several pumping observation densities 1 3 d hydraulic tomography 3 d ht is a method for aquifer characterization whereby the 3 d spatial distribution of aquifer flow parameters primarily hydraulic conductivity k is estimated by joint inversion of head change data from multiple partially penetrating pumping tests while performance of 3 d ht has been studied extensively in numerical experiments few field studies have demonstrated the real world performance of 3 d ht here we report on a 3 d transient hydraulic tomography 3 d tht field experiment at the boise hydrogeophysical research site which is different from prior approaches in that it represents a baseline analysis of 3 d tht performance using only a single arrangement of a central pumping well and five observation wells with nearly complete pumping and observation coverage at 1 m intervals we jointly analyze all pumping tests using a geostatistical approach based on the quasi linear estimator of kitanidis 1995 we reanalyze the system after progressively removing pumping and or observation intervals significant progressive loss of information about heterogeneity is quantified as reduced variance of the k field overall reduced correlation with slug test k estimates at wells and reduced ability to accurately predict independent pumping tests we verify that imaging accuracy is strongly improved by pumping and observational densities comparable to the aquifer heterogeneity geostatistical correlation lengths discrepancies between k profiles at wells as obtained from ht and slug tests are greatest at the tops and bottoms of wells where ht observation coverage was lacking

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

sea level driven marsh expansion in a coupled model of marsh erosion and migration coastal wetlands are among the most valuable ecosystems on earth where ecosystem services such as flood protection depend nonlinearly on wetland size and are threatened by sea level rise and coastal development here we propose a simple model of marsh migration into adjacent uplands and couple it with existing models of seaward edge erosion and vertical soil accretion to explore how ecosystem connectivity influences marsh size and response to sea level rise we find that marsh loss is nearly inevitable where topographic and anthropogenic barriers limit migration where unconstrained by barriers however rates of marsh migration are much more sensitive to accelerated sea level rise than rates of edge erosion this behavior suggests a counterintuitive natural tendency for marsh expansion with sea level rise and emphasizes the disparity between coastal response to climate change with and without human intervention

reply to the comment on relative positions of africa and antarctica in the upper cretaceous evidence for non stationary behaviour of fracture zones by a k martin

imaging and characterisation of subsurface solute transport using electrical resistivity tomography ert and equivalent transport models abstract we assess the usefulness of electrical resistivity tomography ert in imaging and characterising subsurface solute transport in heterogeneous unconfined aquifers a field tracer experiment was conducted at the krauthausen test site germany the spatial and temporal evolution of the injected nabr solute plume was monitored in a 2d ert image plane located downstream of the injection well for 90 days since ert maps changes in bulk electrical conductivity the reconstructed images at selected time intervals are first converted to solute concentration maps by postulating a linear relation the concentration maps are then analysed using an equivalent convection dispersion model cdm which conceptualises the aquifer as a homogeneous medium with a uniform mean flow velocity as demonstrated by associated synthetic model studies ert resolution in terms of recovered equivalent dispersivities is limited due to spatial smoothing inherent to the imaging algorithm since for heterogeneous media local concentrations within the plume deviate from those predicted by the equivalent cdm we also interpret the ert derived pixel breakthrough curves in terms of an equivalent stream tube model stm the stm represents transport in the aquifer by a set of 1d convection dispersion processes allowing the degree of mixing and the heterogeneity of transport within the plume to be quantified we believe that the observed tracer plume is satisfactorily described by the equivalent cdm probably because the tracer plume was small relative to the heterogeneity scale of the aquifer even though application of the stm revealed some deviation from the ideal homogeneous case the equivalent dispersivity in the stm matches the longitudinal dispersivity of the cdm closely consistent with predominantly homogeneous mixing however the stm analysis illustrates how ert results can be used to quantify the variability of parameters relevant to flow and transport in heterogeneous aquifers

thermoelectric self potential and resistivity data localize the burning front of underground coal fires abstractself potential signals and resistivity data can be jointly inverted or analyzed to track the position of the burning front of an underground coal seam fire we first investigate the magnitude of the thermoelectric coupling associated with the presence of a thermal anomaly thermoelectric current associated with a thermal gradient a sandbox experiment is developed and modeled to show that in presence of a heat source a negative self potential anomaly is expected at the ground surface the expected sensitivity coefficient is typically on the order of 0 5 mv c 1 in a silica sand saturated by demineralized water geophysical field measurements gathered at marshall near boulder co show clearly the position of the burning front in the electrical resistivity tomogram and in the self potential data gathered at the ground surface with a negative self potential anomaly of about 50 mv to localize more accurately the position of the burning front we developed a strategy based on two steps 1 we

application of electrical resistivity imaging to the development of a geologic model for a proposed edmonton landfill site electrical resistivity imaging eri was used to further characterize the geologic setting at the proposed aurum solid waste landfill site near edmonton alberta two bedrock channel aquifers the east and south channels exist in or near the site previous studies at the proposed site used borehole and pumping test data to determine that the two aquifers are separate and hydraulically disconnected by a sheet of ice thrust bedrock the three objectives of the eri were to resolve the sand channels and terrace sands resolve the top of the thrust bedrock and resolve the sand channels beneath the thrust bedrock the eri survey in combination with the borehole data presented a more detailed representation of the site s complex geology than borehole data alone the south channel has a long and even bottom steeply sloping sides and two levels the thrust bedrock occurs as irregular massive blocks throughout the site and the aquifers are hydraulically confined by the glacial till the bedrock surface is hi

the borehole fluid effect in electrical resistivity imaging fluid that fills boreholes in crosswell electrical resistivity investigations provides the necessary electrical contact between the electrodes and the rock formation but it is also the source of image artifacts in standard inversions that do not account for the effects of the boreholes the image distortions can be severe for large resistivity contrasts between the rock formation and borehole fluid and for large borehole diameters we have carried out 3d finite element modeling using an unstructured grid approach to quantify the magnitude of borehole effects for different resistivity contrasts borehole diameters and electrode configurations relatively common resistivity contrasts of 100 1 and borehole diameters of 10 and 20 cm yielded for a bipole length of 5 m apparent resistivity underestimates of approximately 12 and 32 when using ab mn configurations and apparent resistivity overestimates of approximately 24 and 95 when usingam bn configurations effects are generally more severe at shorter

improved hydrogeophysical characterization using joint inversion of cross hole electrical resistance and ground penetrating radar traveltime data appropriate regularizations of geophysical inverse problems and joint inversion of different data types improve geophysical models and increase their usefulness in hydrogeological studies we have developed an efficient method to calculate stochastic regularization operators for given geostatistical models the method which combines circulant embedding and the diagonalization theorem of circulant matrices is applicable for stationary geostatistical models when the grid discretization in each spatial direction is uniform in the volume of interest we also used a structural approach to jointly invert cross hole electrical resistance and ground penetrating radar traveltime data in three dimensions the two models are coupled by assuming at all points that the cross product of the gradients of the two models is zero no petrophysical relationship between electrical conductivity and relative permittivity is assumed but is instead obtained as a by product of the inversion the approach has been applied to data collected in a u k sandstone aquifer in order to improve characterization of the vadose zone hydrostratigraphy by analyzing scatterplots of electrical conductivity versus relative permittivity together with petrophysical models a zonation could be obtained with corresponding estimates of the electrical formation factor the water content and the effective grain radius of the sediments the approach provides greater insight into the hydrogeological characteristics of the subsurface than by using conventional geophysical inversion methods

a laboratory investigation of the thermoelectric effect abstractone contribution to self potential signals is the thermoelectric coupling associated with a temperature gradient in a porous material which causes mobile ions to diffuse from hot to cold regions we have developed 35 laboratory experiments to measure the value of the seebeck coefficient in two clean silica sands and two clayey sandstones fully saturated by nacl solutions to explore the influence of salinity upon the seebeck coefficient over four orders of magnitude in salinity the two sands are characterized by two distinct grain sizes coarse and medium and therefore two low values of surface conductivity portland sandstone rich in illite and kaolinite is characterized by a high surface conductivity and the berea sandstone is characterized by an intermediate surface conductivity the seebeck coefficient of the sands ranges from 0 4 at intermediate salinities to 0 5 mv c 1 at very low salinities for which surface conductivity associated with electromigration and electrodiffusion i

complex conductivity of volcanic rocks and the geophysical mapping of alteration in volcanoes abstract induced polarization measurements can be used to image alteration at the scale of volcanic edifices to a depth of few kilometers such a goal cannot be achieved with electrical conductivity alone because too many textural and environmental parameters influence the electrical conductivity of volcanic rocks we investigate the spectral induced polarization measurements complex conductivity in the frequency band 10 mhz 45 khz of 85 core samples from five volcanoes merapi and papandayan in indonesia 32 samples furnas in portugal 5 samples yellowstone in the usa 26 samples and whakaari white island in new zealand 22 samples this collection of samples covers not only different rock compositions basaltic andesite andesite trachyte and rhyolite but also various degrees of alteration the specific surface area is found to be correlated to the cation exchange capacity cec of the samples measured by the cobalthexamine method both serving as rough proxies of the hydrothermal alteration experienced by these materials the in phase real conductivity of the samples is the sum of a bulk contribution associated with conduction in the pore network and a surface conductivity that increases with alteration the quadrature conductivity and the normalized chargeability are two parameters related to the polarization of the electrical double layer coating the minerals of the volcanic rocks both parameters increase with the degree of alteration the surface conductivity the quadrature conductivity and the normalized chargeability defined as the difference between the in phase conductivity at high and low frequencies are linearly correlated to the cec normalized by the bulk tortuosity of the pore space the effects of temperature and pyrite content are also investigated and can be understood in terms of a physics based model finally we performed a numerical study of the use of induced polarization to image the normalized chargeability of a volcanic edifice induced polarization tomography can be used to map alteration of volcanic edifices with applications to geohazard mapping

a case study of resistivity and self potential signatures of hydrothermal instabilities inferno crater lake waimangu new zealand 1 inferno crater lake waimangu one of the largest hot springs in new zealand displays vigorous cyclic behavior in lake level and temperature it provides a natural small scale laboratory for investigating the geo electrical signature of fluid flows we measured self potential and electrical resistivity to see whether the huge variations of fluid volume approximately 60 000 m3 during a mean cycle period of 40 days could be detected electrical resistivity measurements revealed spectacular changes over time with the medium becoming more conductive as the lake receded this result is consistent with analog models where the vapor phase is replaced by liquid at recession the self potential survey did not detect temporal changes related to fluid movements this can be explained by the ph of the pore water 2 3 which is close to the point of zero charge of silica

2d electrical resistivity imaging of some complex landslides in lucanian apennine chain southern italy we use high resolution electrical resistivity imaging to delineate the geometry of complex landslides in the lucanian apennine chain of southern italy to identify the discontinuity between the landslide material and bedrock and to locate possible surfaces of reactivation the lucanian apennine chain is characterized by high hydrogeological hazard and shows a complete panorama of mass movements in this area all typologies of landslides markedly predisposed and tightly controlled by the geostructural characteristics are found rotational and translational slides rototranslational slides earth and mudflows as well as deep seated gravitational slope phenomena with a predominance of rototranslational slides evolving as earthflow slides three test sites characterized by complex geology and a high hydrogeologic hazard are studied the giarrossa and varco izzo earthflow slides are located to the west and east of the town of potenza whereas the latronico slide is located close to the town of latronico

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

characterization of a contaminated wellfield using 3d electrical resistivity tomography implemented with geostatistical discontinuous boundary and known conductivity constraints abstractcontinuing advancements in subsurface electrical resistivity tomography ert are increasing its capabilities for understanding shallow subsurface properties and processes the inability of ert imaging data to resolve unique subsurface structures and the corresponding need to include constraining information remains one of the greatest limitations yet provides one of the greatest opportunities for further advancing the utility of the method we propose a new method of incorporating constraining information into an ert imaging algorithm in the form of discontinuous boundaries known values and spatial covariance information we demonstrated the approach by imaging a uranium contaminated wellfield at the hanford site in southeastern washington state usa we incorporate into the algorithm known boundary information and spatial covariance structures derived from the highly resolved near borehole regions of a regularized ert inversion the resulting inversion provides a solution which fits the ert d

paleogeographic maps of the continents bordering the indian ocean since the early jurassic paleomagnetic data from the african plate from the early jurassic onward are critically re evaluated and updated resulting in a set of 30 paleopoles from which an apparent polar wander path is derived using 20 ma intervals this path is then used in conjunction with kinematic models of the indian and atlantic oceans to place other continents bordering the indian ocean eurasia india islands and plateaus madagascar seychelles mascarene and blocks involved in the collision of india with eurasia south tibet indochina in an absolute paleogeographic frame fixed with respect to africa paleogeographic maps are presented for the early jurassic pre breakup the jurassic cretaceous boundary anomaly ml5 the early cretaceous m2 the late cretaceous a 34 the cretaceous tertiary boundary a 29 the early eocene a 24 the middle eocene a 21 and the oligocene miocene boundary a 6 observed and predicted paleomagnetic directions for landmasses other than africa i e for western europe china korea india and australia which are not used in deriving the maps are found to be in very satisfactory agreement the quality of reconstructions as measured by rms discrepancies between observed and predicted paleolatitudes is of the order of 5 the main features of the paleogeographic maps are discussed with the aim of relating oceanic and on land geodynamic events the constraints provided by tibetan data on the india asia collision and the 20 ma reorganization of geology and plate boundaries in a band extending from the south china sea through tibet to the red sea system are discussed in more detail we emphasize the episodic nature of the breakup of gondwanaland and formation of the indian ocean and subsequent interaction with eurasia in which six major discrete events are identified separated by 30 ma phases of rather uniform plate motion

relative positions of africa and antarctica in the upper cretaceous evidence for non stationary behaviour of fracture zones abstract new bathymetric and magnetic data have been collected in the enderby basin southern indian ocean during cruise md34 of the n o marion dufresne january february 1983 one can identify in this basin oceanic crust created along the same portion of the southwest indian ridge as the crust of the mozambique basin two sets of magnetic lineations with different amplitude split by a large offset fracture zone are localized in each basin and enable us to obtain accurate reconstructions of the africa antarctica plate boundary at the time of anomalies 34 33 and 32 the data west of prince edward fracture zone are taken into account to adjust the parameters of rotation these reconstructions of isochrons allow us to discuss the evolution of the geometry of accretionary plate boundaries and to emphasize the unstable behaviour of fractures zones in particular we give evidence for an important change in the spreading direction along prince edward fracture zone which demonstrates that stability of a pole of rotation is not guarantueed by major offset fracture zones

imaging and characterization of solute transport during two tracer tests in a shallow aquifer using electrical resistivity tomography and multilevel groundwater samplers 1 the relevance of aquifer heterogeneity for flow and transport is recognized broadly however its characterization is hampered by the inaccessibility of the subsurface time lapse electrical resistivity tomography ert offers the possibility of imaging noninvasively subsurface transport we present results of two tracer tests that were carried out successively in a shallow aquifer at the krauthausen test site germany the breakthroughs of an electrically conductive and a resistive tracer were monitored with ert and local multilevel groundwater samplers mls along two cross sections perpendicular to the mean flow direction sinking of the conductive salt tracer due to density effects was observed with ert we applied a stream tube model to characterize the spatially variable transport ert derived stream tube parameters showed similar patterns for the two tracer experiments reflecting the effect of aquifer heterogeneity on transport mls data did not show similar spatial patterns which indicates that these measurements may be prone to subtle changes of the flow field in the small sampling volume and mixing within screened wells between 50 and 10 of the tracer was recovered in the ert derived breakthrough curves compared with transport simulations in a homogeneous aquifer ert derived time integrated changes in electrical conductivity were locally larger but focused in a smaller area mls data indicated that in this area ert did not underestimate the tracer recovery the relatively low tracer recovery was attributed to undetected tracer breakthrough in regions with low ert sensitivity and in regions where the length of the tracer plume and the electrical conductivity contrast were small

inference of multi gaussian relative permittivity fields by probabilistic inversion of crosshole ground penetrating radar data abstractin contrast to deterministic inversion probabilistic bayesian inversion provides an ensemble of solutions that can be used to quantify model uncertainty we have developed a probabilistic inversion approach that uses crosshole first arrival traveltimes to estimate an underlying geostatistical model the subsurface structure and the standard deviation of the data error simultaneously the subsurface is assumed to be represented by a multi gaussian field which allows us to reduce the dimensionality of the problem significantly compared with previous applications in hydrogeology novelties of this study include an improvement of the dimensionality reduction algorithm to avoid streaking artifacts it is the first application to geophysics and the first application to field data the results of a synthetic example show that the model domain enclosed by one borehole pair is generally too small to provide reliable estimates of geostatistical variables a real data example based on two borehole pairs

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

three dimensional electrical conductivity and induced polarization tomography of a rock glacier three dimensional electrical resistivity and induced polarization data were collected on an unstable alpine rock glacier in val thorens vanoise massif france in addition to these field data we also performed induced polarization measurements during freeze and thaw using a soil sample and the poorly mineralized water both from this site in the tomograms the electrical conductivity and the normalized chargeability show very distinctly the presence of the rock ice mixture the chargeability itself is however quite constant over the entire investigated area with the exception of a small area associated with the presence of carboniferous rocks rich in graphite the background chargeability is close to the dimensionless number r 8x10 2 which is consistent with the prediction of the dynamic stern layer model for the polarization of porous media the theory implies that this dimensionless number r is independent on saturation and temperature in agreement with field observations a main implication of this observation is that the classical archie s law cannot be applied to describe the electrical conductivity in this type of environments with poorly mineralized pore water surface conductivity dominates the measured conductivity of the materials implying in turn that the electrical conductivity is related to both the water content and cation exchange capacity of the material we propose new equations for both the electric conductivity and the normalized chargeability in this type of environments plain language summary induced polarization is a geophysical method looking at imaging the 3d distribution of properties related to the ability of rocks to store reversibly electrical charges under the application of a primary electrical field this method has never been applied to rock glaciers a field application and a laboratory experiment demonstrate the usefulness of this method to characterize alpine rock glaciers and point up some shortcomings in the interpretation of electrical conductivity tomography done by previous authors in this type of environments