electrokinetic experimental study on saturated rock samples zeta potential and surface conductance summary it is important to know the electrokinetic properties of crustal rocks for interpreting the conductivity mechanisms and seismoelectric phenomena during earthquakes and seismoelectric well logging in this study electrokinetic experiments are conducted using a special coreholder by employing an ac lock in technique a series of experiments are conducted on 10 sandstone samples to measure the streaming potentials and streaming currents and the experiments on each sample are done at six different salinities the streaming potential coefficient and streaming current coefficient are calculated from the measured streaming potentials and streaming currents the experimental results show that streaming potential coefficient and streaming current coefficient decrease as the salinity increases the dependence of these two coefficients on permeability and pore radius are analysed and compared with previous works at low salinities the streaming potential coefficient and streaming current coefficient increase with the increasing permeability and pore radius at high salinities the streaming potential coefficient streaming current coefficient almost share a same value for 10 different samples this conclusion indicates that the differences of rock parameters can only be well recognized at lower salinities and the electrokinetic signals are invalid at high salinities which offers a restrictive condition for using the amplitude of electrokinetic signals to estimate rock parameters the zeta potential have also been estimated through combined measurements of streaming potential and streaming current the surface conductivity and its contribution to electrokinetic effects are determined from a comparison of zeta potentials by two different methods and then the validation of the helmholz smoluchowski equation for a capillary tube is tested in rocks we also compare our date with theoretical and experimental works and set up an expression about the relationship between zeta potential and salinity which fits the experimental data well

fracture anisotropy characterization in crystalline bedrock using field scale azimuthal self potential gradient the potential for the geophysical characterization of fractured rock bulk anisotropy using azimuthal self potential gradient aspg method was investigated at four fractured rock field sites in the new jersey highlands njh province a visual from polar plots and empirical from linear regression of cross plots correlation exists between aspg measurements and dominant fracture strike orientations mapped at three of the four study sites with the magnitude of the sp signal positively correlated to the number of fractures n along the same azimuth this result is consistent with recent electrokinetic theory that invokes a dependence of the streaming potential coupling coefficient on microgeometry in addition to hydraulic gradient based on local surface drainage patterns and regional fracture orientations the direction of the positive lobe of the aspg signal appears indicative of the likely flow direction within fracture sets three repeat measurements at one site over a one year period consistently reproduced the aspg lobes along major and minor fracture sets although the magnitude of the self potential varied along the major strike set possibly due to variable rates of groundwater flow whereas aspg captured hydraulic anisotropy at three of four sites resistivity anisotropy only dominated azimuthal resistivity surveys ars data at one site our results suggest that aspg is a surprisingly simple effective tool for characterization of fracture dominated media in addition to defining the fracture induced hydraulic anisotropy the direction of fracture controlled flow is evident from the polarity of the sp signal

variations of self potential and unsaturated water flow with time in sandy loam and clay loam soils abstract accurate assessment of soil water fluxes is essential in soil physics due to its direct implications in environmental agronomical or hydrological applications field estimations of soil water fluxes by classical hydraulic methods are often difficult to obtain moreover water fluxes are highly variable in space and time the obtainment of a reasonable estimate for this variable would require numerous measurement sites however such a requirement is rarely met thony et al cr acad sci paris earth planetary sci 325 1997 317 presented the experimental evidence of a linear relationship between the self potential sp and the unsaturated soil water flux therefore this relationship would allow the indirect assessment of the water flux using electrical measurements such an approach would appear much more flexible and easier to perform than the current hydraulic measurements the aim of this study is to experimentally investigate the existence and robustness of the flux sp relationship for different soil types and pedoclimatic conditions the soil water fluxes and the sp were monitored in a long term experiment involving two types of soils contrasting in hydraulic and electric properties the soils were placed in lysimeters which were instrumented with tensiometers and tdr probes for monitoring hydraulic heads and moisture content respectively unpolarizable sp electrodes temperature sensors and suction cups for collecting pore water were also installed in the lysimeters the sp and the fluxes were measured or calculated in the 30 40 cm depth section results show that the variations of the sp with time were clearly linked to both rainfall events and evaporation however in the long term the linear relationship between the unsaturated water flux and the sp evolves from strongly correlated to almost not correlated the slope sensitivity of the flux sp relationship varies with the soil type decreasing with more electrically conductive soil taking into account a varying soil electrode contact greatly improves the flux sp relationship at the scale of the rainfall event particularly when considering infiltration and drainage phases separately nevertheless at the scale of a year with alternated rainfalls and evaporation phases the robustness of the relationship decreases i e the coefficients of the relationship vary between events this variability could be related to time variations in electrical conductivity not so much to that of the soil water but rather to that of the water from the salted soil mud added to the sp electrodes at the time of installation this study points out methodological problems associated with the measurement of sp in shallow unsaturated soils over the long term and the need for designing specific electrodes for this purpose however in deep soils beneath the root zone environmental conditions generally vary slowly and lightly in comparison to surface horizons in this case and with our present set of sp measurement devices the flux sp relationship could be more stable than in the surface soil horizons and useful for examining aquifer recharge capillary rises or contaminant transfer

impact of water saturation on seismoelectric transfer functions a laboratory study of coseismic phenomenon s u m m a r y seismic waves propagating in a porous medium under favourable conditions generate measurable electromagnetic fields due to electrokinetic effects it has been proposed following experimental and numerical studies that these so called seismoelectromagnetic couplings depend on pore fluid properties the theoretical frame describing these phenomena are based on the original biot s theory assuming that pores are fluid filled we study here the impact of a partially saturated medium on amplitudes of those seismoelectric couplings by comparing experimental data to an effective fluid model we have built a 1 m length scale experiment designed for imbibition and drainage of an homogeneous silica sand the experimental setup includes a seismic source accelerometers electric dipoles and capacitance probes in order to monitor seismic and seismoelectric fields during water saturation apparent velocities and frequency spectra in the kilohertz range are derived from seismic and electrical measurements during experiments in varying saturation conditions amplitudes of seismic and seismoelectric waves and their ratios i e transfer functions are discussed using a spectral analysis performed by continuous wavelet transform the experiments reveal that amplitude ratios of seismic to coseismic electric signals remain rather constant as a function of the water saturation in the s w 0 2 0 9 range consistently with theoretically predicted transfer functions

experimental and theoretical basis of self potential phenomena in volcanic areas with reference to results obtained on mount etna sicily abstract self potential anomalies observed on volcanoes may be closely associated with thermoelectric electrochemical or electrokinetic couplings calculations based on irreversible thermodynamics and on laboratory measurements of streaming potentials allow us to estimate the amplitude of the anomalies generated by each mechanism in order to obtain realistic results values of the parameters used in the calculations or used to draw conclusions from the streaming potential measurements were chosen according to in situ tests or laboratory measurements with samples of volcanic origin results show clearly the pronounced predominance of the streaming potentials effects 300 mv upon thermoelectric 30 mv and electrochemical 10 mv couplings

light reflection and transmission by a temperate snow cover an understanding of the reflection and transmission of light by snow is important for snow thermodynamics hydrology ecology and remote sensing snow has an intricate microstructure replete with ice air interfaces that scatter light spectral observations of light reflection and transmission from 400 to 1000 nm were made in temperate snowpacks under cold and under melting conditions the optical observations were made using a dual detector spectroradiometer one detector was placed above the snow surface to monitor the incident and reflected solar irradiance and the second detector was placed at the base of snow cover to measure downwelling irradiance the optical measurements were supplemented by a physical characterization of the snow including depth density and an estimate of grain size in general transmitted light levels were low and showed a strong spectral dependence with maximum values between 450 and 550 nm for example a 10 cm thick snow layer reduced visible transmission 500 nm to about 5 of the incident irradiance and infrared transmission 800 nm to less than 1 extinction coefficients were in the range 3 30 m 1 and tended to decrease slightly as the snow aged and increase as snow density increased

permeability dependence of streaming potential in rocks for various fluid conductivities streaming potentials have been measured on sandstone and limestone samples in a large range of permeabilities the electrokinetic coupling coefficient increases with permeability and we explain this effect by the related variation of surface conductivity a model is proposed to study this effect for various fluid conductivities and it is shown that the dependence of the electrokinetic coupling coefficient on permeability is stronger for high fluid resistivity and is weaker for lower fluid resistivity when fluid resistivity is below 1 m permeability and streaming potential are no more related

the 2004 parkfield earthquake test of the electromagnetic precursor hypothesis 1 a controversy has existed for 30 years concerning the possibility of earthquake prediction using electromagnetic precursors long term electromagnetic monitoring prior to during and after the m6 0 earthquake at parkfield california on 28 september 2004 now provides a definitive test of this hypothesis during the earthquake our instruments recorded clearly documented electrical signals from an earthquake impulsive changes of up to 2 5 mv at an electrode located 250 m from the rupture zone followed by a transient decay lasting at least 3 1 4 hours similar signals 1 5 mv were recorded with the only two m 5 aftershocks but their transient decays lasted for only 17 min these signals are unambiguously a result of the earthquake and can be useful in studies of fluid flow in faults a major current topic in earthquake physics patterns in the distribution of transient voltages differ from static stress changes but are consistent with a small coseismic pressure drop on the fault and fluid flow inward signals at a distance of 1 km from the fault are less than 1 mv and are statistically no different from zero in our analysis transient voltages for the aftershocks have opposite polarity from those recorded with the main shock and are again maximal close to the fault suggesting subsequent outward flow from the fault finally there is no evidence of any precursory signal strongly calling into question previously suggested signals preceding smaller or more distant earthquakes

theory of electrokinetic effects occurring at the final stage in the preparation of a tectonic earthquake crustal deformation processes occur with relative rapidity when short term precursors appear at the final preparatory stage of a tectonic earthquake this paper contains calculations of crustal bulk strain before an earthquake based on the model of a rigid inclusion the data give initial conditions for the problem of fluid percolation in a two phase medium accompanied by electrokinetic effects the solution provides a description of systems of currents arising in the vicinity of the source region an analysis of this theoretical evidence yields information on the behaviour of short term precursors in telluric currents and the geomagnetic field

seismic electric signals ses and earthquakes a review of an updated van method and competing hypotheses for ses generation and earthquake triggering abstract electromagnetic phenomena are sometimes associated with seismic events but earthquake prediction using seismic electric signals ses has not been seriously considered since the early 1990s there are several causes 1 false alarms that have created panics in greece and 2 a strong critique of the varotsos alexopoulos nomicos van method used there an updated van method that includes time series analysis has made successful medium range predictions and short range predictions when coupled with seismic time series analysis four types of potential mechanisms to create precursory ses relying on deformation effects temperature effects ore mineral movement or groundwater variation are reviewed data relevant to each are insufficient to favor a single mechanism records of the number of false positive and missed events for an updated van method have not been well maintained false positives appear to be abundant and render the method unusable co seismic groundwater fluctuations are addressed and two novel hypotheses of earthquake trigger mechanism are also presented ionospherically induced electric and resultant magnetic fields to weaken rock thereby causing failure and volatiles liberated from minerals additionally promoting rock failure recommendations for further study are included

experimental studies of seismoelectric conversions in fluid saturated porous media when seismic waves generate a relative fluid solid motion in a fluid saturated porous medium the moving charges streaming current in the electric double layer induce an electromagnetic em field this paper first experimentally confirms that the coupling between the seismic wave and the electromagnetic field in the kilohertz range is electrokinetic in nature seismoelectric signals are measured in homogeneous cylindrical porous rock samples and multilayered models the seismoelectric signals in homogeneous rock are electric fields that move along with the acoustic wave the mechanism of the seismoelectric conversion is completely different from the piezoelectric effect of quartz grains the seismoelectric sensitivity with respect to salinity of the saturant has been experimentally determined the amplitude of seismoelectric signals increases as the saturant conductivity decreases the seismoelectric effects are generated by two different mechanisms both the em radiation and the electric potential generated at an interface and within a porous medium respectively were measured as the p wave at ultrasonic frequencies passes through the layered models our experimental results demonstrate that seismoelectric effects exist and are measurable in the kilohertz range the paper concludes with a comparison of experimental data and modeled data in a three layer porous model seismoelectric measurements could be an effective means of obtaining transport coefficients such as hydraulic permeability and other porous rock properties

streaming potential measurements 2 relationship between electrical and hydraulic flow patterns from rock samples during deformation streaming potential and resistivity measurements have been performed on fontainebleau sandstone and villejust quartzite samples in a triaxial device during compaction uniaxial compression and rupture measurements on individual samples do not show any clear intrinsic dependence of the streaming potential coefficient with permeability an apparent dependence of the streaming potential coefficient with permeability is however observed during deformation the effect of surface conductivity is taken into account and is small compared with the observed changes in the streaming potential coefficient the observed dependence is therefore interpreted in terms of a difference in the evolution of the electrical and hydraulic connectivity patterns during deformation this effect causes the streaming potential coefficient and consequently the inferred potential to be reduced by a geometrical factor r g representing the electrical efficiency of the hydraulic network estimates of the r g factor varying between 0 2 and 0 8 for electrolyte resistivity larger than 100 m are obtained by comparing the values of the potential inferred from intact rock samples with the values obtained from crushed rock samples where the geometrical effects are assumed to be negligible the reduction of the streaming potential coefficient observed during compaction or uniaxial compression suggests that the tortuosity of the hydraulic network increases faster than the tortuosity of the electrical network before rupture an increase in the streaming potential coefficient associated with the onset of dilatancy was observed for three samples of fontainebleau sandstone and one sample of villejust quartzite the changes in streaming potential coefficient prior to failure range from 30 to 50 during one experiment an increase in the concentration of sulfate ions was also observed before failure these experiments suggest that observable streaming potential and geochemical variations could occur before earthquakes

waveform joint inversion of seismograms and electrograms for moment tensor characterization of fracking events electromagnetic signals have been observed in association with fracking experiments in the laboratory and in the field we have developed a seismoelectric forward modeling approach to produce synthetic seismograms and electrograms generated by fracking events using the finite element method with perfect matched layer boundary conditions the poroelastodynamic equations are solved in the frequency domain using a formulation based on the solid phase displacement and the pore pressure these results are used to compute the electrical field disturbances of electrokinetic nature three types of electrical signals are generated type i disturbance is associated with the seismic source itself type ii disturbance corresponds to seismoelectric conversions and type iii corresponds to coseismic signals this model is applied to simulate the seismic and electrical signals corresponding to the occurrence of a fracking event in a two layers system we perform a stochastic joint inversion of the seismograms and electrograms using the adaptive metropolis algorithm ama to obtain the posterior probability density functions of the parameters characterizing the seismic source assuming that the velocity model is perfectly known the joint waveform inversion is performed on synthetic noise free data and the ama algorithm is successful in retrieving the true values of the unknown parameters the proposed approach is then tested on the same synthetic data after being contaminated with 15 random noise with respect to the maximum amplitude of the signals the model parameters are better determined for the joint inversion of seismic and electrical data by comparison with the inversion of the seismic time series alone we also propose a deterministic tomographic algorithm that is successful in locating the in situ source current density distribution for types i and ii anomalies from the electrical data alone

experimental measurements of the sp response to concentration and temperature gradients in sandstones with application to subsurface geophysical monitoring exclusion diffusion potentials arising from temperature gradients are widely neglected in self potential sp surveys despite the ubiquitous presence of temperature gradients in subsurface settings such as volcanoes and hot springs geothermal fields and oil reservoirs during production via water or steam injection likewise with the exception of borehole sp logging exclusion diffusion potentials arising from concentration gradients are also neglected or at best it is assumed that the diffusion potential dominates to better interpret these sp sources requires well constrained measurements of the various coupling terms we report measurements of thermoelectric and electrochemical exclusion diffusion potentials across sandstones saturated with nacl brine and find that electrode effects can dominate the measured voltage after correcting for these we find that hittorf transport numbers are the same within experimental error regardless of whether ion transport occurs in response to temperature or concentration gradients over the range of nacl concentration investigated that is typical of natural systems diffusion potentials dominate only if the pore throat radius is more than approximately 4000 times larger than the diffuse layer thickness in fine grained sandstones with small pore throat diameter this condition is likely to be met only if the saturating brine is of relatively high salinity thus in many cases of interest to earth scientists exclusion diffusion potentials will comprise significant contributions from both ionic diffusion through and ionic exclusion from the pore space of the rock however in coarse grained sandstones or sandstones saturated with high salinity brine exclusion diffusion potentials can be described using end member models in which ionic exclusion is neglected exclusion diffusion potentials in sandstones depend upon pore size and salinity in a complex way they may be positive negative or zero depending upon sandstone rock texture expressed here by the pore radius r and salinity

numerical simulation of electrokinetic potentials associated with subsurface fluid flow a postprocessor has been developed to calculate space time distributions of electrokinetic potentials resulting from histories of underground conditions pressure temperature vapor saturation concentrations of dissolved species flow rate etc computed by unsteady multidimensional geothermal reservoir simulations electrokinetic coupling coefficients are computed by the postprocessor using formulations based on experimental work reported by ishido and mizutani 1981 the postprocessor was applied to both numerical modeling of natural self potential sp anomalies in geothermal fields and production induced sp changes the essential features of the sp anomalies and sp changes which have actually been observed in real geothermal fields are reproduced reasonably well in these calculations for both single phase liquid and two phase vapor liquid geothermal reservoirs the postprocessor was also applied to predicting the magnitude of electrical earthquake precursory signals caused by dilatant strains taking place within a narrow vertical fault zone if the rate of porosity increase is high enough to induce substantial pore pressure decrease two phase flow develops in the fault zone and produces observable signals at the ground surface if a high conductivity channel connects the near surface region and the deep fault zone

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

observed vertical redistribution of black carbon and other insoluble light absorbing particles in melting snow 1 light absorbing impurities in snow reduce snow albedo producing a positive radiative forcing warming the surface air and snowpack and accelerating snow melt as the snow melts black carbon bc and other insoluble light absorbing particulate impurities ilap are retained at the snow surface because their scavenging efficiency with meltwater is 100 so concentrations of ilap in surface snow increase with snow melt further reducing snow albedo the magnitude of this positive feedback depends on the scavenging efficiency of bc and other ilap with snow meltwater we present results from field measurements of the vertical distribution of bc and other ilap in snow near barrow alaska the dye 2 station in greenland and tromso norway during the melt season amplification factors due to melt are calculated for the concentrations in surface snow of bc and all ilap at barrow and dye 2 melt scavenging rates are estimated melt amplification appears generally to be confined to the top few centimeters of the snowpack where it increases concentrations of bc and other ilap by up to a factor of about five scavenging fractions of ilap due to percolation of meltwater are estimated at 10 30 with the rates for bc being comparable or a few percent lower the lack of distinction may result from the particles in snow being internal mixtures of both bc and other ilap so that scavenging efficiencies for these internally mixed particles are determined by the total particle size and hydrophobicity rather than being different for individual particle components

a simple model of snow albedo decay using observations from the community collaborative rain hail and snow albedo cocorahs albedo network the albedo of seasonal snow cover plays an important role in the global climate system due to its influence on earth s radiation budget and energy balance volunteer community collaborative rain hail and snow albedo cocorahs albedo observers collected 3249 individual daily albedo snow depth and density measurements using standardized techniques at dozens of sites across new hampshire usa over four winter seasons the data show that albedo increases rapidly with snow depth up to 0 14 m multiple linear regression models using snowpack age snow depth or density and air temperature provide reasonable approximations of surface snow albedo during times of albedo decay however the linear models also reveal systematic biases that highlight an important non linearity in snow albedo decay modeled albedo values are reasonably accurate within the range of 0 6 0 9 but exhibit a tendency to overestimate lower albedo values and underestimate higher albedo values we hypothesize that rapid reduction in high albedo fresh snow results from a decrease in snow specific surface area while during melt events the presence of liquid water in the snowpack accelerates metamorphism and grain growth we conclude that the cocorahs albedo volunteer observer network provides useful snow albedo depth and density measurements and serves as an effective model for future measurement campaigns

electric potential changes prior to shear fracture in dry and saturated rocks electric potential changes before shear rupture were measured using darley dale sandstone quartz rich and icelandic basalt quartz free on both dry specimens and in the presence of pore fluid we find that electric potential changed markedly just prior to dynamic rupture in dry and saturated sandstones and saturated basalt but we did not detect precursory signals in dry basalt the absence of signals in dry basalt provides strong evidence that the piezoelectric effect and electrokinetic effect are dominant sources for precursory signals moreover we find that the amplitude of the precursory signals due to electrokinetic effect in saturated sandstone were as large as the coseismic signals we propose that this signal is caused by accelerating evolution of dilatancy as cracks grow in the rock before rupture resulting in water flow into the dilatant region with an electric current produced concurrently

detection of fluid flow variations at the nankai trough by electric and magnetic measurements in boreholes or at the seafloor detection of changes in the flow rate of expelled fluids in accretionary prisms by monitoring of electric and magnetic fields is discussed a numerical model of the electric and magnetic fields associated with fluid flow variations at the nankai trough is presented which gives a numerical solution of the coupled system of electric convection currents and conduction currents that directly determines the magnetic anomaly itself measurements in a borehole located between two vents are shown to be well adapted to detection of fluid flow variations using the vertical gradient of the electric potential and the horizontal magnetic field the vertical electric field is about 10 mv km up to 500 m depth where there is a lithologic reflector and about 50 mv km below this reflector the horizontal gradient of the magnetic field is 2 nt km at the seafloor modelization with a lower fault conductivity and a larger decollement thickness has also been modeled the vertical gradient of the horizontal magnetic field is 5 to 15 nt km a variation of 3 mv and 1 5 to 3 nt at 600 m depth in a borehole could reveal a fluid flow rate variation of 20 which is a reasonable fluid flow change based on some observations at short scale time since a 1 5 to 3 nt anomaly seems easier to detect than a 3 mv anomaly it is likely that the variation of the magnetic field would more sensitively reveal fluid flow variations when monitoring the magnetic field at the seafloor a change of 0 4 nt km in the horizontal gradient could reveal a fluid flow rate variation of 20

zeta potential estimation of volcanic rocks on 11 island arc type volcanoes in japan implication for the generation of local self potential anomalies 1 from streaming potential measurements we deduced the zeta potential of 73 volcanic rock samples collected in 11 volcanoes where self potential sp surveys had also been conducted experiments with crushed rock samples and 0 001 mol l nacl solution showed a large variation in streaming potential coefficient which ranged from 2860 to 2280 mv mpa deduced zeta potential ranged from 45 1 to 37 2 mv among the 73 samples 9 samples showed positive values and 11 samples showed small absolute values less than 10 mv even in a volcano the zeta potential values of rocks were sometimes highly variable to investigate the reason for the variation in zeta potential we performed x ray fluorescence xrf measurements on the rock samples however no significant correlations between zeta potential or isoelectric point and weight percentage of major elements were found implying that the zeta potential of the volcanic rocks is not controlled by chemical composition but by mineralogical composition or crystalline structure in volcanic areas rocks with positive or small absolute values of zeta potential which are considered to be unusual frequently exist in areas along with local positive sp anomalies although positive sp anomalies are usually interpreted as an indication of hydrothermal upflow this correlation suggests that in addition to the groundwater flow pattern the polarity of zeta potential should also be considered for interpretation of sp data therefore in cases where detailed zeta potential measurements have not been conducted local positive sp anomalies should be interpreted with caution

three dimensional modelling of streaming potential summary the self potential sp method responds to the electrokinetic phenomenon of streaming potential and has been applied to hydrogeologic and engineering investigations to aid in the evaluation of subsurface hydraulic conditions to enable the study of variably saturated flow problems of complicated geometry a 3 d finite volume algorithm is developed to evaluate the sp distribution resulting from subsurface fluid flow the algorithm explicitly calculates the distribution of streaming current sources and solves for the sp given a model of hydraulic head and prescribed distributions of the streaming current cross coupling conductivity and electrical conductivity the forward solution is verified by comparing it with an analytical solution for a point source of flow and measured data taken at the surface of a homogeneous embankment we apply the forward model to a synthetic pumping well example to illustrate that heterogeneous physical property distributions can result in significant charge accumulation the sign and magnitude of this secondary charge is determined by the physical property and potential gradients at the interface and can complicate the interpretation of sp data when a single primary flow source is assumed the 3 d character of the sp response to seepage through an embankment and foundation is illustrated in a preliminary study of sp data collected at a dam site in british columbia

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

fluid flow monitoring in oil fields using downhole measurements of electrokinetic potential downhole measurements of electrokinetic potential are a promising new technology for hydrocarbon reservoir monitoring usinga3dfinite elementmodelcombiningbothmultiphase flow and electrokinetic components we investigated the behavior of electrokinetic streaming potential during oil production in a range of reservoir environments we found that streamingpotential signals originate at fluid fronts and at geologic boundaries where fluid saturation changes as water encroaches on an oil production well the streaming potential signal associated with the water front encompasses the well even when the front is up to 100 m away so the potential measured at the well starts to change significantly relative to a distant reference electrode variations in the geometry of the encroaching water front can be characterized using an array of electrodes positioned along the well but a good understanding of the local reservoir geology is required to identify signals caused by the front the streaming potential measured at a well is maximized in low permeability reservoirsproducedatahighrateandinthickreservoirswithlow shale content however considerable uncertainties remain particularly relating to the nature of electrokinetic coupling at high salinity and during multiphase flow our results suggest that the streaming potential at low salinity 10 3 10 4 mol l is large 100 1000 mv but might become too small to resolve 0 1 mv at high salinity 0 5 2 mol l depending on how the available data for the electrokinetic coupling at low salinity are extrapolated into the high salinity domain more work remains to determine the behavior of electrokinetic coupling andthereforetheutilityofthistechniqueathighsalinity

laboratory measurements anomalous 0 1 0 5 hz streaming potential under geochemical changes implications for electrotelluric precursors to earthquakes streaming potentials resulting from flow of various salt solutions in rock were measured on saturated sediments fontainebleau sandstones the streaming potential v was found to be proportional to the driving pore pressure p pulses of amplitude 15 40 mv in the frequency range of 0 1 to 0 5 hz were observed when the conductivity of the injected water was decreased and the fluid flow rate was relatively low corresponding to a darcian velocity of 17 to 30 cm h the amplitudes of these pulses are 47 to 133 of the corresponding steady components of the v values such geochemically induced effects may possibly be responsible for the frequency signals from 0 1 to 0 5 hz that were sometimes observed before an earthquake

measurement of streaming potential coupling coefficient in sandstones saturated with high salinity nacl brine 1 we present measurements of the streaming potential coupling coefficient in intact sandstone samples saturated with nacl brines at concentrations up to 5 5 moll 1 the values we record at low salinity are consistent with those reported previously as brine salinity increases the coupling coefficient decreases in magnitude but is still measureable up to the saturated concentration limit the magnitude of the zeta potential also decreases with increasing salinity but approaches a constant value at high salinity this behaviour is not captured by current models of the electrical double layer our results suggest that streaming potential measurements may be used to monitor flow in saline subsurface environments such as deep saline aquifers and hydrocarbon reservoirs however they were obtained at laboratory temperature future work will focus on the effect of elevated temperatures at high salinity

electric potential changes associated with slip failure of granite preseismic and coseismic signals electric potential changes were measured for stick slip events in granite samples with a three block direct shear arrangement at 8 mpa normal stress two electrodes were mounted on the left and right hand blocks and the electric potential difference between each electrode and the ground was measured with a high input impedance recording system of frequency range from dc to 100 hz as well as coseismic electric signals of about 1 5 v which appeared the moment of the dynamic slip event preseismic signals were detected just before the slip event the coseismic signal rises stepwise with opposite polarities at the two electrodes and exponentially decays with a time constant of e s where e is the permittivity and s is the conductivity of the rock sample we conducted a simple test of rapid stress drop without slipping and observed almost the same electric signal as the coseismic signal this suggests that the electric signal is generated by the piezoelectric effect we proposed a generation model based on the piezoelectric effect and the resultant relaxation process and obtained a theoretical frequency response which is in agreement with experimental data the preseismic signal appears about 2 3 s before the dynamic event with an amplitude of about 50 mv the local strains along two sliding surfaces were also measured to monitor the growth of the rupture nucleation zone when the growth of the rupture nucleation zone occurred on the left sliding surface a clear preseismic signal was detected at the electrode mounted on the left granite block when the growth occurred on the right hand surface a signal was detected at the electrode on the right block this shows that the preseismic electric signal is caused by stress change in the rupture nucleation zone these preseismic and coseismic signals were also detected with an antenna which was placed away from the sample surface

self potential observations during hydraulic fracturing 1 the self potential sp response during hydraulic fracturing of intact sierra granite was investigated in the laboratory excellent correlation of pressure drop and sp suggests that the sp response is created primarily by electrokinetic coupling for low pressures the variation of sp with pressure drop is linear indicating a constant coupling coefficient cc of 200 mv mpa however for pressure drops 2 mpa the magnitude of the cc increases by 80 in an exponential trend this increasing cc is related to increasing permeability at high pore pressures caused by dilatancy of microcracks and is explained by a decrease in the hydraulic tortuosity resistivity measurements reveal a decrease of 2 prior to hydraulic fracturing and a decrease of similar to 35 after fracturing an asymmetric spatial sp response created by injectate diffusion into dilatant zones is observed prior to hydraulic fracturing and in most cases this sp variation revealed the impending crack geometry seconds before failure at rupture injectate rushes into the new fracture area where the zeta potential is different than in the rock porosity and an anomalous sp spike is observed after fracturing the spatial sp distribution reveals the direction of fracture propagation finally during tensile cracking in a point load device with no water flow a sp spike is observed that is caused by contact electrification however the time constant of this event is much less than that for transients observed during hydraulic fracturing suggesting that sp created solely from material fracture does not contribute to the sp response during hydraulic fracturing

streaming potential during drainage and imbibition total are thanked for partially funding jackson under the total chairs programme at imperial college london and for funding vinogradov shell are thanked for funding leinov the department of earth science and engineering at imperial college london are thanked for supporting zhang with a janet watson scholarship damien jougnot frederic perrier and an anonymous reviewer are thanked for their careful and thorough reviews the data for this paper are available in supporting information or by contacting the corresponding author m d jackson imperial ac uk

noise reduction in long term self potential monitoring with travelling electrode referencing the long term monitoring of the electric self potential sp in geophysical systems is affected by electrode degradation and drift this error contribution can be reduced if the electrodes of measuring dipoles are referenced to the same accessory electrode moved in turn at each pole the benefit of this travelling electrode referencing scheme ter has been evaluated in a dedicated experiment performed from march 2000 to march 2001 at tribhuvan university nepal two prototype monitoring points separated by 55 m have been instrumented with pairs of lead lead chloride petiau electrodes installed in buckets filled with salted bentonite at a depth of 1 and 2 meters the electrical potential at 1 and 2 meters depth was also accessible from the surface by pipes filled with salted bentonite over one year the measurement error defined as the standard deviation of the difference between the measured potential and the true sp at a given time is estimated to be 5 mv this error value is reduced to less than 1 mv with ter after correction a smooth annual variation with amplitude of 10 to 15 mv is observed and is interpreted as streaming potentials associated with the monsoon and subsequent drying these results provide significant guidelines for precision long term sp monitoring in particular in tropical volcanic or tectonically active regions

electromagnetic emissions from dry and wet granite associated with acoustic emissions 1 triaxial deformation experiments were performed to compare electromagnetic emissions emes from dry and wet granite specimens associated with acoustic emissions aes cylindrical specimens of initially intact granite were tested at room temperature we measured both high frequency 10 khz to 1 mhz and low frequency dc to 500 hz components of the electric potential variations in general it is difficult to detect emes in wet conditions because wet rock has very short electric relaxation time which is proportional to its electric resistivity however in the wet experiment using a granite specimen saturated with distilled water under a constant pore pressure emes in the high frequency range were detected and accompanied with aes although emes in the low frequency range were not observed in contrast in the dry granite experiment emes were detected in both the high frequency and low frequency ranges in the high frequency range the dry specimen generated eme more frequently than the wet specimen the generation mechanism can be explained based on piezoelectricity and compensation charges the difference in the eme generation from wet and dry granite is attributed to the difference of electric relaxation time also electromagnetic fields due to an electric polarization in a dielectric and conductive medium are discussed including the frequency dependence of the skin depth

evidence of the theoretically predicted seismo magnetic conversion summary seismo electromagnetic phenomena in porous media arise from seismic wave induced fluid motion in the pore space which perturbs the equilibrium of the electric double layer this paper describes with details the original experimental apparatus built within the ultra shielded chamber of the low noise underground laboratory of rustrel france we measured seismo magnetic conversions in moist sand using two induction magnetometers and a pneumatic seismic source to generate the seismic wave propagation we ensured to avoid the magnetometer vibrations which could induce strong disturbances from induction origin interpretation of the data is improved by an analytical description of phase velocities for fast pf and slow ps longitudinal modes transverse mode s as well as the extensional mode due to the cylindrical geometry of the sample the purpose of this paper is to provide elements to measure correctly coseismic seismomagnetic fields and to specify their amplitude the seismic arrivals recorded in the sample showing a 1200 1300 m s 1 velocity have been associated to p and extensional waves the measured seismo magnetic arrivals show a velocity of about 800 m s 1 close to the calculated phase velocity of s waves therefore we show that the seismo magnetic field is associated to the transverse part of the propagation as theoretically predicted by pride 1994 but never measured up to now moreover the combined experimental and analytical approaches lead us to the conclusion that the measured seismo magnetic field is probably about 0 035 nt for a 1 m s 2 seismic source acceleration 0 1 g

electrokinetic signature of the nankai trough accretionary complex preliminary modelling for the kaiko tokai program abstract fluid flow in the nankai trough accretionary complex has been observed during the previous phases of the kaiko project to be of order 100 m year 1 in small scale high permeability conduits and 10 m year 1 where shallow detachment faults intersect the seafloor the rate of flow was also variable increasing up to 30 over a month monitoring the fluid flow will be one of the principal objectives of the next phase of the kaiko program known as kaiko tokai one method is to measure the electric and magnetic fields generated by the electrokinetic phenomena or streaming potential resulting from fluid flow in the porous sediments this paper describes modelling of fluid flow in the accretionary prism and the resulting electrokinetic signals which may be observed from sensors on the seafloor or in shallow boreholes a two dimensional finite difference model is used to study the hydrogeology of a realistic section of the nankai trough with constraints from seismic reflection data and ocean drilling program boreholes fluid sources owing to porosity reduction in the prism and of distant external origin are modelled we find that porosity reduction alone is insufficient to reproduced the observational estimates of excess pore pressure and fluid flux additional fluid source terms are therefore required along a low angle decollement or detachment fault which separates the deformed prism sediments from the undeformed underthrust sediments beneath the decollement must be significantly more permeable than the adjacent sediments our models suggest by approximately four orders of magnitude and is probably anisotropic parallel to the main structural trends from the hydrogeological model the electric potential and electric and magnetic fields within the ocean and sediments were calculated from the electrokinetic phenomena seafloor electric potentials are found to be of the order of a few millivolts with seafloor horizontal and vertical electric fields of the order of 0 5 vm 1 close to the deformation front as the electric potential rises significantly with depth through the sediments boreole measurements may be particularly useful we conclude with some comments about noise sources and experimental logistics for the kaiko tokai program

streaming potential properties of westerly granite with applications this paper reports on laboratory measurements of the streaming potential properties of common minerals and in particular of westerly granite data are presented for these solids in contact with simple electrolytic solutions and in one case for temperature variation in the range 5 70 c for 1 1 electrolytes the ratio of the streaming potential coupling coefficient to fluid resistivity was approximately 4 mv atm m and for 2 1 electrolytes 2 mv atm m the effect of temperature was small 0 05 mv c temperature increase and indicates that the zeta potential was independent of temperature preliminary experimental results using mixed electrolytic solutions nacl cacl2 and two phase fluid flow are also described two phase flow can enhance streaming potentials by as much as a factor of 3 or 4 the laboratory data are used to interpret streaming potentials in geological problems such as earthquake prediction geothermal prospecting using the self potential method and surface conductivity contribution to the electrical resistivity of rocks

a review on modeling inversion and interpretation of self potential in mineral exploration and tracing paleo shear zones abstract this study discusses the improvements of different modeling and inversion approaches to self potential sp anomaly associated with shallow and deep subsurface imaging the study also focuses on the fundamental foundations of self potential which have been advanced with time and event cause system and application in different investigation fields in addition a point by point forward modeling of different subsurface idealized geological bodies is discussed various sp techniques utilized for interpretation have likewise been examined for each use of sp anomaly besides the uncertainty associated with the understanding of self potential interpretation has also been discussed additionally the above studies were used to examine the diverse subsurface idealized geologic bodies deciphered from different inversion and elucidation strategies combinations of 17 real field illustrations were examined and a similar investigation was conducted for different interpretation strategies moreover a similar study was carried out to gain insights to mineralized bodies associated with different subsurface structures and the depth of the ore body and the rest of the model parameters are also discussed a correlation between the field information and the interpreted model information is shown considering different elucidation techniques wherever information was available the significance of this type of study is its multi purpose application in investigating various subsurface problems related to mineral exploration and tracing paleo shear zones this study would be very useful to scientists investigating the use of self potential in mineral ore investigation and in tracing paleo shear zones in continental crust

convection current generated prior to rupture in saturated rocks laboratory experiments were performed to study the generation mechanism of electric signals during deformation and rupture of rock with the focus on the effects of pore water movement we have developed a triaxial apparatus that is specially designed for this purpose within the framework of the international frontier program on earthquake research of the institute of physical and chemical research riken this apparatus can deform a rock specimen that is electrically isolated from the surroundings at a very slow strain rate using a cylindrical specimen of intact rock inada granite makabe granite muroto gabbro and fujieda sandstone saturated with distilled water we carried out triaxial deformation tests under a constant pore pressure at room temperature during a deformation test we continuously measured the electric current generated in the specimen in addition local strains pore pressure and pore fluid movement from the intensifier were recorded at a sampling frequency up to 1 khz the volume change due to dilatancy was obtained from the average of the local strain measurements at four positions we found that the convection current flowed before the main fracture showing good correlation with the dilatancy rate and the water flow rate the current density of the signal was about 1 ma m2 this result demonstrated that the electric current is caused by an electrokinetic effect due to the water flow associated with accelerating evolution of dilatancy before the fracture

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

permeability dependence of streaming potential coefficient in porous media in theory the streaming potential coefficient depends not only on the zeta potential but also on the permeability of the rocks that partially determines the surface conductivity of the rocks however in practice it is hard to show the permeability dependence of streaming potential coefficients because of the variation of zeta potential from sample to sample to study permeability dependence of streaming potential including the effects of the variation of the zeta potential and surface conductance due to the difference in mineral compositions between samples we perform measurements on 12 consolidated samples including natural and artificial samples saturated with 7 different nacl solutions to determine the streaming potential coefficients the results have shown that the streaming potential coefficients strongly depend on the permeability of the samples for low fluid conductivity when the fluid conductivity is larger than than 0 50 s m for the natural samples or 0 25 s m for the artificial ceramic samples the streaming potential coefficient is independent of permeability this behavior is quantitatively explained by a theoretical model

fluid flow near reservoir lakes inferred from the spatial and temporal analysis of the electric potential electric self potential sp variations have been monitored continuously from 1995 to 1998 at 14 points on a ridge separating the roselend and la gittaz reservoir lakes in the french alps the lakes have level variations of at least 50 m over yearly cycles seasonal variations of sp associated with lake level variations are observed on five points of the array for three points located on the banks of the lakes a positive correlation to the lake level variations is observed with a maximal amplitude of about 180 mv corresponding to an average response of 2 4 mv per meter of water for two points located on the bottom of each lake the correlation is negative with a maximal magnitude of about 50 mv corresponding to an average response of 1 1 mv per meter of water two independent temporary electrical arrays located on the banks of each lake confirm these measurements and allow a better spatial characterization of the sources associated with the observed sp variations in particular near the roselend lake the electrical response to lake level variations is increasing for decreasing altitude the measured sp variations are proposed to result from the electrokinetic coupling associated with a vertical groundwater flow connecting a constant pore pressure source to the bottom of the lakes numerical modeling indicates that the spatial variation of the response and the nonlinear response observed at one point can be explained by leakage currents in the conductive lake water the values of the streaming potential coefficient spc measured in the laboratory with crushed rock samples from the site range from 14 to 50 mv 0 1 mpa for an electrolyte resistivity of 40 m and are compatible to first order with the magnitude of the observed seasonal sp variations a detailed quantitative electrokinetic modeling is currently limited mainly by the poor knowledge on the contribution of electrical leakage currents and the local variability of the spc this experiment indicates that spatial and temporal variations of the electric potential are promising tools to characterize and monitor shallow groundwater flow and provide practical data for the investigation of groundwater flow associated with volcanic or tectonic activity

modeled and observed variations in storm divergence and stratiform rain production in southeastern texas abstractstorm divergence profiles observed by an s band doppler radar are compared to ensemble simulations of 10 disparate precipitating systems occurring in warm season weakly baroclinic and strongly baroclinic environments in southeastern texas eight triply nested mesoscale model simulations are conducted for each case using single and double moment microphysics with four convective treatments i e two convective parameterizations and explicit versus parameterized convection at 9 km observed and simulated radar reflectivities are objectively separated into convective stratiform and nonprecipitating anvil columns and comparisons are made between ensemble mean echo coverages and levels of nondivergence lnds in both the model and observations storms occurring in less baroclinic environments have more convective rain area less stratiform rain area and more elevated divergence profiles the model ensemble and observations agree best for well organized leading line trailing stratiform systems

plausibility of long distance electrotelluric precursors to earthquakes a systematic analysis of the plausibility of different classes of models which could account for low frequency precursory electrotelluric signals observable at large distances from a large earthquake is carried out first we consider linear models for which either a stationary electrical field is generated by a current dipole in the source volume or a static deformation field results from a precursory strain in the source volume linearly inducing a streaming potential effect near the electrode in the former case only the conjunction of very favorable circumstances may lead to an electrical field larger than 10 mv km at more than 100 km with the constraint that no anomaly exceeds a few volts per kilometer in the source area it indeed requires a powerful electrical dipole current 104 a length 1 km which might be produced by a streaming potential effect associated with the connection of nonhydrostatic fluid reservoirs pore pressure difference up to 100 mpa a two dimensional channeling of the electrical currents from the source to the electrode area which would result from high conductivity horizontal layers and finally a local amplification factor of typically 100 near the electrodes which might be produced by a narrowing of the conductive channel for an elastic long distance interaction an electric field of 10 mv km at a distance 10 times the source length 100 km away from a m 6 earthquake requires a precursory deformation larger than the coseismic deformation if no strong local amplification is considered alternatively nonlinear models are proposed and discussed assuming that the crust is stuffed with small scale local instabilities fractures and nonhydrostatic fluid reservoirs among which a number are close to their instability threshold these instabilities may follow their own evolutionary process inducing sporadic fluid flow and hence streaming potential effect in the vicinity of the electrodes without any relation to a remote tectonic activity however these instabilities may be sensitive to very small changes in the stress field and hence be triggered by the elastic precursory deformation of a remote seismic source this requires that the precursory deformation near the instability is at least larger than the tidal strain 10 7 this necessary condition is met at a distance of up to 10 times the source dimension when the precursory strain source is only 10 of the coseismic deformation provided that the strain source is double the size of the seismic fault itself this model could account for the absence of self potential anomalies related to the earthquake itself as a large proportion of the available instabilities could have been swept away by the precursory strain furthermore with such a model a precursory strain in the source area could induce a detectable change in the background seismic activity over a vast area which may give a new interpretation of the times of increased probability observations for short distances the triggering of fluid instabilities by strain perturbation and the associated streaming potential effect may well be a promising model for explaining low frequency electric and magnetic precursors

streaming potential and permeability of saturated sandstones under triaxial stress consequences for electrotelluric anomalies prior to earthquakes the streaming potential due to fluid circulation in rock was measured on saturated sediments fontainebleau sandstones the electrokinetic coupling coefficient which is the ratio of the streaming potential and the excess pore pressure is proportional to the fluid resistivity additionally for a fluid conductivity of 10 3 s m the electrokinetic coupling coefficient varies from 10 to 6642 mv 0 1 mpa for sample permeability in the range of permeabilities from 0 15 10 15 to 1220 10 15 m2 the different values of the electrokinetic coupling coefficient have been explained by the effect of increasing surface conductivity which becomes nonnegligible compared to fluid conductivity for low permeability when the sample is deformed under triaxial stress up to failure the vertical permeability along the principal stress drops by about 0 20 0 1 mpa when failure occurs the typical variation of the electrokinetic coupling coefficient is a large increase beginning with the onset of the localization of the shear band at about 75 of the yield stress and stopping at the failure this increase of the electrokinetic coupling coefficient is due to an increase of potential in the shear zone when new surfaces are created and connected possible consequences of our results are given concerning the electrical fields which could appear during the preparation of an earthquake it is shown that in some cases self potential anomalies reported in the deformed zone preceding an earthquake occurrence could be due to an increase of the electrokinetic coupling coefficient from 75 of the yield stress to rupture in the vicinity of one of the electrodes any variation of fluid resistivity or permeability in the vicinity of one electrode could change the electrokinetic coupling coefficient inducing a surface electrokinetic potential anomaly in regard to the interpretation of the electrokinetic effect which occurs at large distance from the epicenter a larger electrokinetic potential anomaly could be measured between electrodes situated along a vertical fluid flow for instance in a shallow borehole an electrokinetic potential anomaly up to 30 mv for a fluid conductivity of 0 01 s m and a rock permeability of 10 12 m2 could be observed with a change of the underground water table level as slight as 50 cm 50 mbar moreover if the permeability between the electrodes is increased by a factor of 8 103 the electrokinetic coupling coefficient could be enhanced by a factor up to 650

streaming potential in volcanic rocks from mount pelee streaming potential and electric conductivity have been measured in a laboratory on 11 consolidated samples coming from five deposits of the different evolutionary stages of mount pelde volcano the streaming potential coupling coefficient ranges from 35 to 4905 mv mpa 1 and increases with increasing permeability this increase is mainly due to the dependency of rock effective conductivity with permeability the permeability of the samples varies from 0 146x10 12 to 34x10 12 m 2 the zeta potential at ph 7 and water conductivity of 2 1x10 4 s m l is relatively small for the majority of the samples it ranges from 4 to 19 rev according to water conductivity analysis on mount pel e streaming potential coupling coetficients of 25 to 406 mv mpa 1 can be expected for this volcano

active boulder movement at high martian latitudes lobate stony landforms occur on steep slopes at high latitudes on mars we demonstrate active boulder movement at seven such sites submeter scale boulders frequently move distances of a few meters the movement is concentrated in the vicinity of the lobate landforms but also occurs on other slopes this provides evidence for a newly discovered common style of activity on mars which may play an important role in slope degradation it also opens the possibility that the lobate features are currently forming in the absence of significant volumes of liquid water

three dimensional inversion of self potential data used to constrain the pattern of groundwater flow in geothermal fields 1 we propose an algorithm to invert self potential signals measured at the ground surface of the earth to localize hydromechanical disturbances or to the pattern of groundwater flow in geothermal systems the self potential signals result from the divergence of the streaming current density groundwater flow can be either driven by topography of the water table free convection or deformation of the medium the algorithm includes the electrical resistivity distribution of the medium obtained independently by dc resistance tomography or electromagnetic methods or by coding the assumed geology in terms of distribution of the electrical resistivity accounting for the effect of the temperature and salinity distributions and possibly constraints from borehole measurements inversion of the distribution of the source current density from ground surface and borehole self potential measurements is achieved by solving the inverse problem using tikhonov regularization solutions that are compatible with the physics of the primary flow problem by introducing assumptions regarding the smoothness or the compactness of the source and the three dimensional distribution of the electrical resistivity of the system the inverse problem can be solved in obtaining the three dimensional distribution of the current source density in the ground however an annihilator can be added to the inverted source geometry without affecting the measured self potential field annihilators can be obtained from boundary conditions synthetic models and a sandbox experiment are discussed to demonstrate the validity of the algorithm an application is presented to the geothermal field of cerro prieto baja california mexico using literature data inversion of the self potential and resistivity data allows observing a plume of hot groundwater rising to the ground surface in the central part of the investigated area and discharging to the ground surface in the southwest part the temperature anomaly associated with the existence of this plume is independently observed by interpolating borehole temperature measurements we found a good agreement between the distribution of the temperature and the inverted source current density the proposed method appears therefore as a noninvasive method for remote detection and three dimensional mapping of subsurface groundwater flow

experimental measurements of seismoelectric signals in borehole models s u m m a r y an experimental system is built for the electrokinetic measurements with a small scaled seismoelectric detector and a high resolution digitizer 1 ms s 1 22 bits the acoustic and seismoelectric experiments are carried out in different boreholemodels at the high frequency of 90 khz in the laboratory all the localized seismoelectric signals that accompany compressional wave shear wave and stoneley wave are first clearly observed with a monopole source in sandstone boreholes that are saturated by tap water the amplitudes of these signals are measured in the range of 1 120 v which is useful for designing the seismoelectric logging instruments then the amplitude ratio of electric signal to acoustic pressure rep for each of the three waves is calculated and compared with the theoretical simulations based on the experimental data we find that seismoelectric logging signals as well as rep become stronger at the more permeable borehole model we also find that seismoelectric logging signals are more sensitive to permeability and porosity comparedwith acoustic logging signals therefore this study verifies the feasibility of seismoelectric well logging and further indicates that the seismoelectric logging technique might be a preferable method to estimate formation parameters in the field measurements

a transient method for measuring the dc streaming potential coefficient of porous and fractured rocks high quality streaming potential coupling coefficient measurements have been carried out using a newly designed cell with both a steady state methodology and a new pressure transient approach the pressure transient approach has shown itself to be particularly good at providing high quality streaming potential coefficient measurements as each transient increase or decrease allows thousands of measurements to be made at different pressures to which a good linear regression can be fitted nevertheless the transient method can be up to 5 times as fast as the conventional measurement approaches because data from all flow rates are taken in the same transient measurement rather than separately test measurements have been made on samples of berea and boise sandstone as a function of salinity approximately 18 salinities between 10 5 mol dm3 and 2 mol dm3 the data have also been inverted to obtain the zeta potential the streaming potential coefficient becomes greater more negative for fluids with lower salinities which is consistent with existing measurements our measurements are also consistent with the high salinity streaming potential coefficient measurements made by vinogradov et al 2010 both the streaming potential coefficient and the zeta potential have also been modeled using the theoretical approach of glover 2012 this modeling allows the microstructural electrochemical and fluid properties of the saturated rock to be taken into account in order to provide a relationship that is unique to each particular rock sample in all cases we found that the experimental data were a good match to the theoretical model

albedo model for shallow prairie snow covers a model for simulating the decrease in albedo of melting prairie snow covers is presented its application for calculating net radiation and establishing the time of melt is demonstrated it is expected the routine will find use in operational systems for synthesizing and forecasting streamflow runoff from snowmelt the model is based on point and aerial observations of incoming and reflected global radiation taken from february 1 to the end of ablation of the seasonal snow cover over a 14 year period in the open grassland area of western canada for complete snow covers not subject to frequent melt events the albedo depletion curve is approximated by three line segments of constant slope describing the periods of 1 premelt the months preceding the occurrence of active melt 2 melt the period of rapid ablation that leads to the disappearance of the seasonal snow cover and 3 postmelt the days following melt an algorithm of the model is developed and procedures for defining the start of melt and

electrical conductivity and streaming potential coefficient in a moderately alkaline lava series abstract coupled hydraulic and electrical problems are being investigated with renewed interest in geophysical applications in this study electrical conductivity and streaming potential coefficient spc have been measured in the laboratory for crushed oceanite hawaite and trachyte samples from an almost complete moderately alkaline lava series from the mururoa atoll french polynesia for ph varying from 7 to 9 5 and ionic strength varying from 0 1 to 100 mmol l despite the closely related mineralogy of the rocks contrasted results are obtained for the surface conductivity as defined by revil and glover 0 10 0 07 ms m 8 3 0 2 ms m and 1 05 0 16 ms m for oceanite hawaite and trachyte respectively and for the inferred potential 6 6 0 3 mv 26 3 0 5 mv and 14 6 0 3 mv respectively the higher values obtained with hawaite suggest that electrical properties are controlled by secondary and accessory minerals such as clay minerals and zeolites resulting from low temperature seawater alteration rather than by the magmatic differentiation furthermore a synthesis of results obtained with 20 rock samples indicates that signatures of the alteration process may emerge from the study of the potential as a function of surface conductivity the results with the lava series can be used to derive estimates of the scaling of basalt resistivity and associated spc as a function of permeability for permeability values smaller than 10 15 m 2 the value of the spc can be dramatically affected by the value of the surface conductivity at least in the brittle crust a better knowledge of the contributions of clay minerals and zeolites to surface conduction is therefore needed both for the interpretation of electrical conductivity profiles and for the estimation of electrical variations associated with groundwater flow as could be produced for example during volcanic or tectonic cycles

an overview of seasonal snow metamorphism the grains in seasonal snow undergo rapid and radical transformations in size shape and cohesion these grain characteristics affect all of the basic properties of snow snow is characterized as either wet or dry depending on the presence of liquid water wet snow is markedly different at low and high liquid contents dry snow is characterized as either an equilibrium form or a kinetic growth form that is it is either well rounded or faceted of course many snow grains display either transitional features between two of these categories or features which arise from other processes snow is classified depending on the dominant processes of its metamorphism