electrical impedance variation with water saturation in rock we measured the electrical impedances of 22 sandstone samples during oil driving water tests using the two electrode method experiments show that the imaginary part x of the impedance r ix of rock may respond well to water saturation in the frequency range 100 hz 15 mhz we found that the maximum x values and their corresponding interfacial polarization frequencies are linear with water saturation the lower critical frequency is found to vary with water saturation in an unclear relationship with the characteristic length of rock the dissipation factor at the interfacial polarization frequency remains quite stable and may be an indicator of the pore structure of rock we used an equivalent circuit to explain the dispersive behavior of rock more than one interfacial polarization frequency in the impedance argand plot is predicted and can be observed if the measurement frequency range is wide enough

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

high resolution characterization of vadose zone dynamics using cross borehole radar characterization of the dynamics of moisture migration in the unsaturated zone of aquifers is essential if reliable estimates of the transport of pollutants threatening such aquifers are to be made electrical geophysical investigation techniques such as ground penetrating radar offer suitable methods for monitoring moisture content changes in the vadose zone moreover these tools permit relatively large measurement scales appropriate for hydrological models of unsaturated processes and thus they offer a distinct advantage over conventional measurement approaches ground penetrating radar when applied in transmission mode between boreholes can provide high resolution information on lithological and hydrological features the technique may be applied in tomographic mode and in a much simpler vertical profile mode both modes of measurement have been utilized using two boreholes 5 m apart located at a field site in the uk sherwood sandstone aquifer radar transmission measurements have been used to characterize the change in moisture content in unsaturated sandstone due to controlled water tracer injection continual monitoring of cross borehole radar measurements over an 18 month period has also permitted determination of travel times of natural loading to the system and has revealed the impact of subtle contrasts in lithology on changes in moisture content over time the time series of inferred moisture contents show clearly wetting and drying fronts migrating at a rate of approximately 2 m month 1 throughout the sandstone

localization and characterization of cracks in clay rocks using frequency and time domain induced polarization induced polarization ip is a geophysical method that is potentially sensitive to the presence of cracks in porous rocks and therefore to damage we performed time domain and frequency domain ip measurements at the tournemire underground research laboratory url aveyron france in areas where different types of cracks are observed these cracks correspond to both tectonic fractures and new cracks associated with stress release and desiccation resulting from the excavation of a gallery these measurements were performed both in eastern and northern galleries of the test site the eastern gallery was excavated in 1996 while the northern gallery was excavated recently in 2008 this gives us the opportunity to study the electrical characteristics of the excavation damaged zone surrounding the galleries with respect to the age of the excavation longitudinal profiles were performed along the floor of the galleries with 48 cu cuso4 electrodes separated by a distance of 20 cm chargeability and resistivity were inverted using a gauss newton iterative approach assuming an isotropic heterogeneous clay rock material the resulting ip tomograms show a correlation between high values of chargeability and the presence of calcite filled tectonic fractures x ray analysis indicates that the presence of pyrite in these fractures is a potential source of the observed ip signals the cracks associated with the mechanical damage of the formation exhibit low values of chargeability on the same order of magnitude than the chargeability of the clay rock matrix and are therefore hardly observable a smaller ip response associated with the presence of these cracks is observed in the older gallery and this observation is qualitatively related to the desaturation process associated with these cracks in a specific area of one of the galleries the presence of calcareous nodules is observed to be an important source of anomalous chargeability this signature seems to be associated with the presence of pyrite

controls on induced polarization in sandy unconsolidated sediments and application to aquifer characterization resistivity and induced polarization ip measurements 0 1 1000 hz were made on clay free unconsolidated sediments from a sandy alluvial aquifer in the kansas river floodplain the sensitivity of imaginary conductivity a fundamental ip measurement to lithological parameters fluid conductivity and degree of saturation was assessed the previously reported power law dependence of ip on surface area and grain size is clearly observed despite the narrow lithologic range encountered in this unconsolidated sedimentary sequence the grain size relationship is effectively frequency independent between 0 1 and 100 hz but depends on the representative grain diameter used for the sediments examined here d90 the grain diameter of the coarsest sediments in a sample is well correlated with the distribution of the internal surface in the well sorted sandy sediments investigated here is such that most of the sample weight is likely required to account for the majority of the internal surface we fin

complex conductivity imaging for the understanding of landslide architecture abstract geophysical methods are widely used for landslide investigation to delineate depth and geometry of the sliding plane in particular electrical resistivity tomography ert is often used because both porosity and water saturation control the electrical resistivity of the subsurface materials and are critical for slope stability moreover ert can be employed to monitor changes in pore fluid pressure which is an important factor triggering landslides however the interpretation of ert results in clay rich landslides can be challenging considering that high electrical conductivity values may not only be related to an increase in saturation but also to the surface conduction mechanism which becomes dominant in the presence of clays recently environmental investigations have demonstrated an improved subsurface characterization through induced polarization ip imaging an extension of the ert method which permits to gain information about electrical conductive and capacitive i e polarization effect properties of the subsurface as the polarization effect is mainly controlled by surface charge which is large in clays ip images are expected to improve the lithological interpretation and overcome the limitations of the ert method additionally measurements collected over a broad frequency bandwidth the so called spectral ip sip have been successfully used in laboratory experiments to quantify textural and hydrogeological parameters however the application of sip field measurements for the delineation of hydrogeological structures in landslides has not been addressed to date to fill this gap in this study we present sip imaging results for data collected at the la valette landslide south east french alps where an existing geotechnical model of the landslide is available for evaluation moreover our study provides a detailed revision on the collection and processing of sip datasets as well as a description of the diverse sources of error in ip surveys to stress the importance of data error quantification for a quantitative application of the sip method our results demonstrate that adequate data processing allows obtaining consistent results at different frequencies and independently of the measuring protocol furthermore the frequency dependence of the complex conductivity obtained in the field scale sip survey is consistent with earlier laboratory experiments in conclusion our study shows the potential of the sip method to improve our understanding of subsurface properties and an improved delineation of the contact between the mobilized material and the bedrock as well as variations in the clay content within the landslide and the bedrock

radar frequency dielectric dispersion in sandstone implications for determination of moisture and clay content 1 the relationship between dielectric permittivity water saturation and clay content for the sherwood sandstone from ne england was characterized as part of a wider study of the vadose zone moisture dynamics and pollution vulnerability of this aquifer dielectric permittivity was measured over the full range of saturation levels for various lithologies ranging from clean medium grained sandstone to fine grained sandstone containing up to 5 clay using a specially constructed dielectric cell dielectric constant kr is largely independent of frequency between 350 mhz and 1000 mhz below 350 mhz kr of fine grained clay rich sandstone shows frequency dispersion tests on physical models of the sandstone consisting of a fine fraction of ottawa sand and montmorillonite clay indicate that the clay minerals within the sandstone are responsible for its frequency dispersive behavior these tests also show that increasing pore fluid salinity increases dielectric dispersion at the lower end of the frequency range which indicates that this arises from the interfacial maxwell wagner mechanism associated with platy clay particles water saturated sand clay mixtures show very low dielectric constants at high frequencies over 650 mhz this effect is independent of salinity and probably results from the layered geometric arrangement of solids bound and free water within the swelling clay the complex refractive index method crim with a mineral dielectric constant of about 5 provides a good match to the water saturation versus dielectric constant data for all sherwood sandstone lithologies at frequencies between 350 and 1000 mhz and for clay poor sandstone at lower frequencies below 350 mhz the presence of a few percent of clay in some sherwood sandstone lithologies raises their crim best fit mineral dielectric constant substantially

rooted brooks range ophiolite implications for cordilleran terranes modeling of gravity and magnetic data shows that areally extensive mafic and ultramafic rocks of the western brooks range alaska are at least 8 km thick and that gabbro and ultramafic rocks underlie basalt in several places the basalt gabbro and ultramafic rocks have been considered parts of a far traveled ophiolite assemblage these rocks are the highest structural elements in the brooks range thrust belt and are thought to be hundreds of kilometers north of their origin this requires these rocks to be thin klippen without geologic ties to the continental shelf sedimentary rocks that now surround them the geophysically determined thick and interleaved subsurface character of the basalt gabbro and ultramafic rocks is inconsistent with this interpretation an origin within an extensional setting on the continental shelf could produce the required subsurface geometries and explain other perplexing characteristics of these rocks early mesozoic alaska from the north slope southward to the interior may have had many irregular extensional basins on a broad distal continental shelf this original tectonic setting may apply elsewhere in cordilleran type margins where appropriate mafic and ultramafic analogs are present

relevance of induced polarization to quantitative formation evaluation abstract the role of electrical induced polarization ip in the petrophysical estimation of shaliness and permeability remains uncertain in the wake of widely varying degrees of optimism within the literature of the past 30 years therefore there is no general agreement on the potential usefulness of ip methods within the framework of formation evaluation a refinement of the broad scatter of data previously indicated by ip shaliness permeability correlations has been accomplished through new empirical relationships involving time domain ip parameters it is demonstrated that chargeability can be related smoothly and definitively to excess conductivity or intergranular permeability these relationships are based upon measurements of water saturated sandstones over a wide range of electrolyte conductivity their field application is viable provided that three formation constants have been determined from laboratory measurement in the light of these developments the possible contribution of induced polarization measurements to petrophysical evaluation is briefly re examined with more confidence than has been justifiable up to now in so doing particular attention is paid to those precautionary procedures of core preparation and data acquisition which must be followed if the ip approach is to be beneficial from a quantitative standpoint

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

changes in remanence coercivity and domain state at low temperature in magnetite abstract submicron magnetite crystals with mean sizes of 0 037 0 10 and 0 22 m undergo major changes in hysteresis properties and domain states in crossing the verwey transition t v 120 k the 0 037 m crystals are single domain sd both in the cubic phase at room temperature t 0 and in the monoclinic phase below t v the 0 10 and 0 22 m crystals have a mixture of sd and two domain 2d states at room temperature t 0 but mainly sd structures below t v in agreement with micromagnetic calculations coercive force h c increases on cooling through t v by a factor 3 5 in the submicron magnetites and 40 in a 1 3 mm single crystal because of the high crystalline anisotropy and magnetostriction of monoclinic magnetite as a result domain walls and sd moments are so effectively pinned below t v that all remanence variations in warming or cooling are reversible however between 100 k and t 0 remanence behavior is variable saturation remanence sirm produced in monoclinic magnetite at 5 k drops by 70 100 in warming across t v with minor recovery in cooling back through t v ultimate levels at 5 k of 23 37 for the submicron crystals and 3 for the 1 3 mm crystal in contrast sirm produced in the cubic phase at 300 k decreases 5 35 submicron or 95 1 3 mm during cooling from 300 to 120 k due to continuous re equilibration of domain walls but there is little further change in cooling through t v itself however the submicron magnetites lose a further 5 15 of their remanence when reheated through t v these irreversible changes in cycling across t v and the amounts of the changes have potential value in determining submicron magnetite grain sizes the irreversibility is mainly caused by 2d sd transformations on cooling through t v which preserve or enhance remanence while sd 2d transformations on warming through t v cause remanence to demagnetize

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

estimation of hydraulic parameters of shaly sandstone aquifers from geoelectrical measurements electrical and hydraulic conductivities of shaly sandstones are described using a capillary approach for a granular clay bearing material the clays are assumed to occur as shale shells uniformly coating the insulated sand grains the real and imaginary components of the complex electrical conductivity for this material model are written in terms of a unique solid matrix conductivity treated as a volumetric property above a critical salt concentration the conductive contribution of the shells is independent of the electrolyte salinity under this condition the equation for the bulk conductivity of the sandstone can be expressed in a simplified form however below the critical concentration the matrix conductivity is dependent on the conductivity of the water saturating the shaly component and can be expressed only by the complete equation the hydraulic conductivity for this model is expressed by a modified kozeny carman equation a new semi empirical equation relates the hydraulic conductivity for such rocks to their porosity formation resistivity factor and the electrical conductivity of its solid matrix these combined properties are described as the lithoporosity factor in this new formulation the petrophysical parameters involved are easily determined from the electrical geophysical measurements the performance of this equation is firmly tested with experimental laboratory data available in the literature its application is then extended to estimate the hydraulic parameters of a shaly sandstone aquifer in bahia brazil using either the borehole or the surface geoelectrical data examples are given to emphasize the combined use of electrical resistivity and induced polarization measurements in computing hydraulic properties

normal and reverse unroofing sequences in syntectonic conglomerates as evidence of progressive basinward deformation when a new mountain belt is generated by tectonics the denudation of the mountain front may cause the development of alluvial fans at its base the retreat of the mountain front by denudation processes and a widening of the drainage network in the source area create adjacent alluvial fan conglomerates with an inverted vertical clast distribution this vertical clast distribution represents a normal unroofing sequence renewed uplift of a previous inverted vertical clast distribution can produce a reverse unroofing sequence if continued shortening occurs in the same area a rejuvenation of the source area and basin margin may produce a new generation of clasts from the source area and a partial or total reworking of previously deposited conglomerates to supply second generation clasts if this type of reworking process is repeated as fault uplift steps basinward several new inverted and stratigraphic vertical clast distributions may arise

chronology of ophiolite crystallization detachment and deeper parts of subduction zones emplacement evidence from the brooks range alaska sup 40 ar sup 39 ar data from early middle jurassic ophiolites 187 184 ma in the western brooks range alaska indicate that detachment related metamorphism occurred approximately 20 m y after crystallization and approximately 20 m y before emplacement onto the arctic alaska margin high temperature metamorphic rocks along the basal surfaces of many ophiolites have ages that are contemporaneous with ophiolite crystallization suggesting that detachment and thrust faulting occur while the lithosphere is young lt 10 ma and relatively hot from these relations it has been generally assumed that detachment and initial overthrusting of oceanic lithosphere occur near the site of generation such as a marginal basin or mid ocean ridge the new data from the brooks range ophiolites confirm previous indications that some ophiolites have much longer intervals between crystallization thrust related metamorphism and emplacement on the basis of these new results and data from other ophiolites the authors propose that ophiolites originating within large ocean basins will generally have longer crystallization to emplacement intervals than the more commonly recognized marginal basin type ophiolites

effects of fluid displacement pattern on complex electrical impedance in berea sandstone over frequency range 104 106 hz to better understand the effect of fluid distribution on the electric response of rocks saturated with oil and brine we conducted experimental studies on the complex electrical impedance in a berea sandstone together with in situ acquisitions of oil distribution images employing a high resolution medical x ray computed tomography we performed two tests of brine displacement by oil under high 10 mpa and low 5 mpa pressures which were accompanied by fingering and stable displacement patterns respectively the measured complex impedance data were fitted to the cole model to obtain the resistance capacitance peak frequency of the imaginary impedance and the exponent of the rock fluid system with increasing oil saturation the resistance showed an increasing trend whereas the other three parameters decreased the fingering displacement exhibited lower resistance and capacitance than the stable displacement the analysis of the resistance changes using a simple parallel connection model indicates that there are more components of residual brine in parallel connections in the fingering pattern than in the stable displacement pattern at the same saturation we also interpreted the normalised changes in the capacitance or apparent dielectric constant with respect to the oil saturation via an analysis of the shape factor of fluid distribution based on the maxwell wagner brugermann hanai model the changes in the shape factor suggest that the pinch off of the brine in parallel connection by the oil is a dominant mechanism reducing the capacitance in the stable displacement most of the connections in the brine phase are immediately pinched off by oil displacement front at a local oil saturation of 65 conversely in the fingering displacement there is a transition from the bulk or layered brine to the pinched off at a local oil saturation below 60 the analyses indicate that the difference in the fluid distribution under different fluid conditions is responsible for the non archie behaviour

mapping oil contaminated sand and till with the spectral induced polarization sip method the laboratory and field results from an environmental application of the spectral induced polarization sip method are presented the phase spectra of the resistivity of uncontaminated glacial till silt sand and gravel were measured in the laboratory the effects of waste oil and motor oil on the phase and amplitude spectra of the resistivity were studied using artificially contaminated sand and till samples and mineral soil samples from real waste sites field ip and sip measurements were also made at the waste sites the laboratory phase spectra of sands and tills were straight or slightly concave upwards in a log log plot the phase angle varies between 0 1 and 20 mrad at 1 hz frequency and increases towards higher frequencies with a slope of 0 15 0 25 in laboratory tests motor oil and waste oil changed the phase and amplitude spectra of sand and till at first the amplitude and phase decreased due to oil contamination later during continued maturation both the amplitude and phase increased after a few days or weeks of maturation some of the contaminated samples showed a convexupwards phase spectrum the features observed in artificially contaminated samples were also detected in the sample material from real waste sites furthermore the in situ results from the waste sites were in agreement with the laboratory results in laboratory tests the phase spectra of clean sand and till remained stable with time whereas the phase spectra of oil contaminated samples changed with increasing maturation time this together with the field results suggests that differences between the spectra of clean and polluted soils and also changes occurring in the phase spectra of contaminated soils with time can be indicative of contamination

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

paleomagnetism of the mesozoic asik mountain mafic complex in northern alaska implications for the tectonic history of the arctic composite terrane at least three mutually exclusive hypotheses exist for the origin of the arctic composite terrane and its mesozoic location relative to the stable craton of north america the most widely accepted hypothesis calls for counterclockwise rotation of the arctic composite terrane as it rifted from the arctic archipelago a second hypothesis calls for no relative movement and a third places the arctic composite terrane on the kula plate as a part of a separate ribbon shaped microcontinent all three hypotheses predict unique positions for the arctic composite terrane with respect to rotation and translation since the middle of the mesozoic paleomagnetic and susceptibility studies were conducted on rocks from 15 sites in the 160 ma k ar cooling age asik mountain mafic to ultramafic complex in the western part of the arctic composite terrane coherent data from 11 sites yielded a direction of dec 255 1 inc 82 1 19 3 95 9 6 63 5 6 contact and fold tests were not possible but the direction differs distinctly from the modern magnetic direction the anisotropy of magnetic susceptibility revealed a well developed oblate fabric of variable orientation the orientation of the fabric was not related to the regional stress regime so we conclude that the rocks were not deformed and metamorphosed during thrusting and thus the magnetic remanence direction obtained is most likely primary the direction yields a pole position at long 166 8 e lat 59 8 n a95 18 4 a63 10 7 that is discordant to the expected 160 ma reference direction for north america counterclockwise rotation of the arctic composite terrane would yield a perfect fit to the 160 ma reference pole with an allowance for up to 5 of northward translation this result combined with previous paleomagnetic data makes a convincing argument that the arctic composite terrane has not remained fixed in its current orientation with respect to north america however the data are not sufficient to differentiate between the two hypotheses that suggest movement of the arctic composite terrane relative to north america

delineation of subsurface variability in clay rich landslides through spectral induced polarization imaging and electromagnetic methods abstract although commonly triggered by heavy or long lasting precipitation events landslides in clay rich formations are hardly predictable as their triggering mechanisms are still not fully understood hence detailed information about the internal structure of landslides with high spatial resolution is fundamental for an improved understanding of triggering mechanisms and management in this context electrical resistivity tomography ert is a well established method used for the delineation of lithological interfaces in landslides and changes in water content however the quantitative interpretation of the ert images can be challenging particularly for clay rich landslides considering that the electrical signatures are dominated by the variations in the clay fraction rather than saturation moreover large scale investigations also demand the development of faster surveying techniques hence in this study we discuss the combined investigation of a landslide with low induction number electromagnetic emi mapping and induced polarization ip imaging we investigate the application of such methods to assess subsurface variability across different scales near surface emi mapping and their correlation with geomorphological data whereas ip images are used to investigate the extension at depth from the shallow structures measurements are performed at a shallow clay rich landslide in lower austria austria characterized by lithological structures of the flysch and gresten klippen zone with both formations known to be highly susceptible to landsliding the interpretation of the imaging results for data collected along 15 profiles is performed using separately acquired hydrogeological and geotechnical data we observe a relationship between the electrical properties and geotechnical parameters which permits to delineate areas associated to different weathering stages controlling the groundwater flow moreover spectral induced polarization sip data collected along one transect shows sensitivity to changes in textural composition such as the fraction of clay minerals the study shows the suitability of an integrated investigation with emi mapping and ip imaging in combination with extensive geotechnical data for an improved characterization of subsurface variability and thus understanding of clay rich landslides

electrical properties of partially saturated sandstones novel computational approach with hydrogeophysical applications 1 electric and electromagnetic geophysical tools are suitable methods for investigating moisture content transport and storage properties of the subsoil with noninvasive surveys interpretation of field data is still based on empirical or semiempirical equations which must be calibrated with complex time consuming laboratory measurements in this paper we develop pore scale models suitable for computing the effective electric conductivity and the effective permittivity of partially saturated porous media on the basis of simple structural parameters grain size distribution and porosity we compute the electrical conductivity with three approaches that model the conductivity of the shell of coating clay around solid grains of shaly sandstones using different assumptions we compare the simulated results with experimental data from sherwood sandstone uk and discuss the effect of these assumptions on the effective conductivity simulations performed using a modeling approach that accounts for interaction between volume and surface conduction show an excellent agreement with experimental data we also model the effective permittivity of the same porous medium at several saturation values and obtain a good match with laboratory measurements

determining pore throat size in permo triassic sandstones from low frequency electrical spectroscopy 1 hydraulic conductivity or permeability a knowledge of which is vital in modelling the movement of hydrocarbons in reservoir rocks and contaminants in aquifers is strongly related to the intergranular pore throat size in sandstones for many years attempts have been made to determine permeability from the electrical properties of rocks but with little success here we have measured the complex electrical conductivity of permo triassic sandstone samples over the frequency range 0 0001 1000 hz and show how parameters determined from the characteristic shape of the spectra correlate closely to pore throat size determined from mercury injection measurements

evaluation of transport and storage properties in the soil and groundwater zone from induced polarization measurements1 spectral induced polarization as well as complex electrical measurements are used to estimate on a non invasive basis hydraulic permeability in aquifers basic laboratory measurements on a variety of shaly sands silts and clays showed that the main feature of their conductivity spectra in the frequency range from 10 3 to 103 hertz is a nearly constant phase angle thus a constant phase angle model of electrical conductivity is applied to interpret quantitatively surface and borehole spectral induced polarization measurements the model allows for the calculation of two independent electrical parameters from only one frequency scan and a simple separation of electrical volume and interface effects the proposed interpretation algorithm yields the true formation factor the cation exchange capacity and the surface area to porosity ratio which corresponds to the inverse hydraulic radius using a kozeny carman like equation the estimation of hydraulic permeability is possible

resistivity of partially saturated triassic sandstone the variation in resistivity with saturation of poorly cemented triassic sandstone samples from a site in the english midlands has been measured the measurements were obtained using an adapted four electrode technique which utilizes conductive gelling agents between electrodes avoiding the need to sputter electrodes directly on to samples a difficult process with such friable samples the measurements provide important information regarding the way in which resistivity varies with saturation in the triassic sandstone the resulting variation in the observed resistivity versus saturation curves indicates the presence of significant pore scale variation between samples measurements have also been conducted on fully saturated samples these indicate significant variation in the matrix conductivity between samples the results have important implications for field scale monitoring of the unsaturated zone

magnetometric resistivity a new approach and its application to the detection of preferential flow paths in mine waste rock dumps the injection of a low frequency electrical current in the ground between two electrodes a and b generates a magnetic field that can be measured at the ground surface with sensitive magnetic sensors the map of the magnetic field measured at the frequency of the injected current can be used to determine the paths of the current through the ground when the current is channelled along preferential conductive paths the magnetometric resistivity mmr method can be used to detect these paths conductive current paths can be associated with preferential flow paths of groundwater when the two electrodes a and b are in the direction of the flow and when the flow path is highly electrically conductive with respect to the background we first review the background equations for the magnetic field in mmr then we provide the kernel of the problem using biot and savart law to connect the components of the observed magnetic field to the current density distribution we also develop a simple approach to invert the magnetic field in terms of electrical current paths to illustrate how the method works we develop five synthetic models to test the sensitivity of the method to the properties of the conductive targets channelling the electrical current the targets are characterized by different shapes sizes depths and conductivity contrasts with the background then we proceed with a case study for which the mmr method is used to identify and map preferential groundwater flow paths bypassing a mine waste rock dump drainage collection trench into the tailings pond in this case the conductivity of the flow paths is much stronger than the background conductivity due to the high mineralization of the ground water along these paths the method underlines the 3 d architecture of these flow paths

dielectric spectroscopy of sedimentary rocks a physiochemical model for the complex dielectric response of sedimentary rocks is used to invert broadband dielectric spectra for effective grain size distributions the complex dielectric response of each grain within the water wet granular matrix is obtained by superimposing the polarization of the electrochemical double layer which is assumed to surround each grain with the complex dielectric response of the dry mineral grain the effective complex dielectric response of the water wet matrix grains and surface phase is obtained by volume averaging over the entire distribution of particle sizes the complex dielectric response of the total mixture water wet matrix and bulk pore solution is obtained using the bruggeman hanai sen effective medium theory studies of berea sandstone show that the grain size distribution obtained by inverting the real part of the complex dielectric spectra is similar to the grain size distribution obtained from optical images of the sample in thin section the current model however does not account for surface roughness effects or the polarization of counterions over multiple grain lengths therefore the grain size distribution obtained by dielectric spectroscopy is broader than the image derived distribution the dielectric derived grain size distribution can be fit with two separate power laws that crossover at r 1 m which corresponds to a relaxation frequency of 2 khz the low frequency dielectric response f 2 khz is primarily controlled by the clay size grains and surface roughness which has a fractal dimension of d 2 48 0 07 at very low frequencies f 0 1 hz the dielectric response appears to be controlled by the electrochemical polarization of counterions over multiple grain lengths a more general model should account for the effects of surface roughness and grain interactions on the dielectric response it would also be useful to develop a simplified version of this model perhaps similar in form to the empirically derived cole cole response which could be more easily used to model and interpret electrical geophysical field surveys e g induced polarization ground penetrating radar and time domain reflectometery measurements

hierarchical bayesian method for mapping biogeochemical hot spots using induced polarization imaging author s wainwright hm flores orozco a bucker m dafflon b chen j hubbard ss williams kh abstract 2015 american geophysical union all rights reserved in floodplain environments a naturally reduced zone nrz is considered to be a common biogeochemical hot spot having distinct microbial and geochemical characteristics although important for understanding their role in mediating floodplain biogeochemical processes mapping the subsurface distribution of nrzs over the dimensions of a floodplain is challenging as conventional wellbore data are typically spatially limited and the distribution of nrzs is heterogeneous in this study we present an innovative methodology for the probabilistic mapping of nrzs within a three dimensional 3 d subsurface domain using induced polarization imaging which is a noninvasive geophysical technique measurements consist of surface geophysical surveys and drilling recovered sediments at the u s department of energy field site near rifle co usa inversion of surface time domain induced polarization tdip data yielded 3 d images of the complex electrical resistivity in terms of magnitude and phase which are associated with mineral precipitation and other lithological properties by extracting the tdip data values colocated with wellbore lithological logs we found that the nrzs have a different distribution of resistivity and polarization from the other aquifer sediments to estimate the spatial distribution of nrzs we developed a bayesian hierarchical model to integrate the geophysical and wellbore data in addition the resistivity images were used to estimate hydrostratigraphic interfaces under the floodplain validation results showed that the integration of electrical imaging and wellbore data using a bayesian hierarchical model was capable of mapping spatially heterogeneous interfaces and nrz distributions thereby providing a minimally invasive means to parameterize a hydrobiogeochemical model of the floodplain

cratered cobbles in triassic buntsandstein conglomerates in northeastern spain an indicator of shock deformation in the vicinity of large impacts comment and reply comment ernstson et al 2001 1 interpreted pitted and fractured quartzite cobbles of lower triassic conglomerates as new evidence in support of the existence of two large impact structures in the iberian chain azuara and rubielos de la cerida fig 1 2 in this discussion we disagree with their

reactive flow models of the anarraaq zn pb ag deposit red dog district alaska the red dog ore deposit district in the brooks range of northern alaska is host to several high grade shale hosted zn pb deposits due to the complex history and deformation of these ore deposits the geological and hydrological conditions at the time of formation are poorly understood using geological observations and fluid inclusion data as constraints numerical heat and fluid flow simulations of the anarraaq ore deposit environment and coupled reactive flow simulations of a section of the ore body were conducted to gain more insight into the conditions of ore body formation results suggest that the ore body and associated base metal zonation may have formed by the mixing of oxidized saline metal bearing hydrothermal fluids 200 c with reducing hs rich pore fluids within radiolarite rich host rocks sphalerite and galena concentrations and base metal sulfide distribution are primarily controlled by the nature of the pore fluids i e the extent and duration of the hs source forward modeling results also predict the distribution of pyrite and quartz in agreement with field observations and indicate a reaction front moving from the initial mixing interface into the radiolarite rocks heuristic mass calculations suggest that ore grades and base metal accumulation comparable to those found in the field 18 zn 5 pb are predicted to be reached after about 0 3 my for initial conditions 30 ppm zn 3 ppm pb 20 deposition efficiency

a state space bayesian framework for estimating biogeochemical transformations using time lapse geophysical data 1 we develop a state space bayesian framework to combine time lapse geophysical data with other types of information for quantitative estimation of biogeochemical parameters during bioremediation we consider characteristics of end products of biogeochemical transformations as state vectors which evolve under constraints of local environments through evolution equations and consider time lapse geophysical data as available observations which could be linked to the state vectors through petrophysical models we estimate the state vectors and their associated unknown parameters over time using markov chain monte carlo sampling methods to demonstrate the use of the state space approach we apply it to complex resistivity data collected during laboratory column biostimulation experiments that were poised to precipitate iron and zinc sulfides during sulfate reduction we develop a petrophysical model based on sphere shaped cells to link the sulfide precipitate properties to the time lapse geophysical attributes and estimate volume fraction of the sulfide precipitates fraction of the dispersed sulfide encrusted cells mean radius of the aggregated clusters and permeability over the course of the experiments results of the case study suggest that the developed state space approach permits the use of geophysical data sets for providing quantitative estimates of end product characteristics and hydrological feedbacks associated with biogeochemical transformations although tested here on laboratory column experiment data sets the developed framework providesthe foundation neededfor quantitative field scale estimation of biogeochemical parameters over space and time using direct but often sparse wellbore data with indirect but more spatially extensive geophysical data sets

on the complex conductivity signatures of calcite precipitation 1 calcite is a mineral phase that frequently precipitates during subsurface remediation or geotechnical engineering processes this precipitation can lead to changes in the overall behavior of the system such as flow alternation and soil strengthening because induced calcite precipitation is typically quite variable in space and time monitoring its distribution in the subsurface is a challenge in this research we conducted a laboratory column experiment to investigate the potential of complex conductivity as a mean to remotely monitor calcite precipitation calcite precipitation was induced in a glass bead 3 mm packed column through abiotic mixing of cacl2 and na2co3 solutions the experiment continued for 12 days with a constant precipitation rate of 0 6 milimole d visual observations and scanning electron microscopy imaging revealed two distinct phases of precipitation an earlier phase dominated by well distributed discrete precipitates and a later phase characterized by localized precipitate aggregation and associated pore clogging complex conductivity measurements exhibited polarization signals that were characteristic of both phases of calcite precipitation with the precipitation volume and crystal size controlling the overall polarization magnitude and relaxation time constant we attribute the observed responses to polarization at the electrical double layer surrounding calcite crystals our experiment illustrates the potential of electrical methods for characterizing the distribution and aggregation state of nonconductive minerals like calcite advancing our ability to quantify geochemical transformations using such noninvasive methods is expected to facilitate our understanding of complex processes associated with natural subsurface systems as well as processes induced through engineered treatments such as environmental remediation and carbon sequestration

relationship between spectral induced polarization and hydraulic properties of saturated and unsaturated sandstone there is growing interest in the use of geophysical methods for hydrological model parameterization empirical induced polarization ip hydraulic conductivity k relationships have been developed but these are only applicable to sediments in which the ip response shows limited variation with electrical current frequency here we examine the spectral ip response of samples taken from a uk sandstone aquifer and compare measured parameters with physical and hydraulic properties we demonstrate the limited value of existing ip k models due to the inherent ip frequency dependence of these samples our results show how the mean relaxation time is a more appropriate measure of ip response for these sediments a significant inverse correlation between the surface area to pore volume ratio and is observed suggesting that is a measure of a characteristic hydraulic length scale this is supported by a measured strong positive correlation between log and log k our measurements also reveal evidence of a relationship between and a dominant pore throat size which leads to postulations about the parallelism between the spectral ip behavior and unsaturated hydraulic characteristics additional experiments show how the relaxation time is affected by degree of fluid saturation indicating that saturation levels must be accounted for if our empirical relationships are applied to vadose zone studies our results show clear evidence of the potential value of frequency based ip measurements for parameterization of groundwater flow models

permeability prediction based on induced polarization insights from measurements on sandstone and unconsolidated samples spanning a wide permeability range abstractwe have compared various induced polarization ip models for permeability prediction of the same general form that were all based on two parameters the first being an electric substitute of effective porosity the formation factor and the second being an electric proxy of pore normalized surface area the imaginary part of electric conductivity these models empirically derived and based on mechanistic formulations were applied to an extensive database acquired on sandstones and unconsolidated sandy materials whereas previous studies on permeability prediction mainly concentrated on either sandstone or unconsolidated sediments we investigated a database composed of 94 samples including sandstones and unconsolidated material most of the samples in the database were saturated with a nacl solution with an electric conductivity close to 100 ms m samples with a saturating fluid that deviated from this composition were corrected using recently published relationships describing the ip depende

seasonal variation of moisture content in unsaturated sandstone inferred from borehole radar and resistivity profiles understanding the processes controlling recharge to aquifers is critical if accurate predictions are to be made on the fate of contaminants in the subsurface environment in order to understand fully the hydrochemical mechanisms in the vadose zone it is essential that the dynamics of the hydrology can be suitably characterised the correlation between moisture content and both bulk dielectric and resistivity properties of porous media is well established using suitably placed sensors in boreholes detailed depth profiles of dielectric and resistivity behaviour have been monitored over a period of two years at a triassic sherwood sandstone aquifer field site at hatfield england the borehole borehole transmission radar and borehole resistivity profiles show a significant correlation through appropriate petrophysical relationships derived from core samples seasonal dynamics of the vadose zone are seen to illustrate the migration of wetting and drying fronts over the monitoring period at a second field site in eggborough located 17 km from hatfield similar temporal changes in moisture content in the sandstone were observed using borehole radar profiles travel times of seasonal wetting fronts through the sandstone at both sites appear to be approximately 2 m per month the retardation of this front propagation in the top 3 m is also common to both sites suggesting that pollutant transport may be principally controlled by near surface sediments the results have important consequences to existing groundwater modelling programmes that are being utilised to predict transfer of agricultural chemicals through the vadose zone

an approach to the identification of fine sediments by induced polarization laboratory measurements time domain induced polarization ip laboratory measurements were performed on about 200 fine sediment samples with varying water content the results permitted an analysis of ip properties of clays loams silts and sands particular emphasis has been given to the analysis of the chargeability m as a function of lithotype and the water content by analyzing decay curves a new parameter was identified it is a statistically specific characteristic of the lithotype and is independent of the water content therefore it provides a diagnostic parameter for lithotype identification in association with the values of chargeability and electrical resistivity this parameter permits a reliable evaluation of water content and yields useful information about the porosity and permeability of the lithotype

electrical properties of artificial clay bearing sandstone rocks which contain clay minerals often display electrical properties which cannot be predicted by bulk electrical properties of the constituents cohen 1981 interactions between clay minerals and groundwater can produce polarization phenomena decreases in resistivity and supposed nonlinear behavior