streaming potential observations using geothermal wells and in situ electrokinetic coupling coefficients under high temperature abstract in an attempt to detect streaming potentials induced by subsurface water flows we have observed the horizontal electric field self potential variations across stationary electric dipoles near geothermal wells in the takinoue geothermal area japan we observed variations of self potential which seem to be associated with the water flows in the aquifer induced by turning on and off the flow of the wells amplitudes of the variations are 3 5 mv across 60 200 m dipoles and can be explained well with a proposed electrokinetic model the streaming potential coefficient of 15 mv bar and or the potential of 50 to 100 mv in the aquifer are appropriate to explain the observed data by the model the obtained electrokinetic coupling coefficients are in situ ones and determined for crustal rock water system under high temperature 200 c condition the present results together with a laboratory study by ishido and mizutani 1981 give fundamental information on electrokinetic coupling coefficients in the earth s interior and are very important when we make quantitative interpretations of self potentials generated by geothermal activity on the basis of electrokinetic effects

correction to strong ferrimagnetic resonance signal and magnetic susceptibility of the nojima pseudotachylyte in japan and their implication for coseismic electromagnetic changes 1 pseudotachylyte is a glassy fault rock providing certain evidence of ancient seismic fault movement i examine the nojima pseudotachylyte found along the nojima fault which caused the 1995 kobe earthquake m 7 2 in japan using the electron spin resonance technique the nojima pseudotachylyte has a strong ferrimagnetic resonance fmr signal derived from bulky trivalent iron ions in ferrimagnetic iron oxides this fmr signal appears by heating the surrounding fault gouge that is the source material of the nojima pseudotachylyte furthermore the magnetic susceptibilities of the nojima pseudotachylyte are 10 2 10 3 times larger than those of the surrounding fault gouge and are proportional to the fmr signal intensities here i reconstruct the magnetization process of fault gouge during ancient seismic fault slip using the fmr signal the results indicate that the instantaneous magnetization of the nojima fault gouge may have induced instantaneous geomagnetic changes and that the instantaneous geomagnetic changes may have further induced geoelectric changes by electromagnetic induction

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

near bed mass flux profiles in aeolian sand transport high resolution measurements in a wind tunnel vertical profiles of the streamwise mass flux of blown sand in the near bed 17 mm region are analysed from high resolution measurements made using an optical sensor in a wind tunnel this analysis is complemented by detailed measurements of mass flux and mean velocity profiles throughout the boundary layer depth 0 17 m using passive chambered sand traps of small dimensions and armoured thermal anemometers respectively the data permit a preliminary analysis of the relations between the observed forms of the profiles of near bed fluid stress and horizontal mass flux within a carefully conditioned boundary layer profiles of mass flux density are found to be characterized by three regions of differing gradient with transitions at about 2 mm and 19 mm above the bed the exponential decay of mass flux with height is confirmed for elevations above 19 mm and when plotted as a function of u 2 g a parameter of mean vertical trajectory height in saltation the gradient of mass flux in this region scales with the wake corrected friction velocity u where u 0 30 m s 1 a separate near bed region of more intense transport below 19 mm is identified which carries 80 per cent of the total mass flux this region is evident in some previous field and wind tunnel data but not in profiles simulated by numerical models ventilated passive sand traps underestimate mass flux in this region by 37 per cent at slow or moderate wind speeds a third significant region below 2 mm is observed these regions are likely to be related to grain populations in successive saltation low energy ejections and intermittent bed contact respectively optical measurements reveal locally high grain concentrations at some elevations below 5 mm these heights scale with transport rate mass flux gradient and wind speed copyright 1999 john wiley sons ltd

numerical modelling of self potential signals associated with a pumping test experiment summary the study of electrical signals associated with groundwater flow is a powerful method to determine in a non invasive way the distribution of hydraulic heads in aquifers hence the distribution of the hydraulic conductivity and storativity experimental hydraulic heads and electrical self potential sp signals associated with a pumping test in an unconfined aquifer were reproduced with a numerical model based on the finite difference method for simplicity we assumed axial symmetry around the pumping well we assessed the equivalent hydraulic conductivity and specific storage of the aquifer by fitting the piezometric levels obtained in the course of the pumping against synthetic hydraulic heads produced by the model the current coupling coefficient is obtained from the best fit between the experimental and modelled sp signals at the end of the pumping phase then keeping the previously determined hydraulic parameters the relaxation of both the hydraulic heads and the sp signals were modelled and found to be consistent with the measured values the data show almost linear relationships between the hydraulic heads in the aquifer and the electrical signals recorded at the ground surface these results show that sp signals allow monitoring subsurface flow in the course of pumping experiments

a wind tunnel investigation of the influences of fetch length on the flux profile of a sand cloud blowing over a gravel surface wind tunnel tests were conducted to examine the fetch effect of a gravel surface on the ux pro le of the sand cloud blowing over it using typical dune sand the results suggest that the ux pro le of blown sand over a gravel surface differs from that over a sandy surface and is characterized by a peak ux at a height above the surface while that over a sandy surface decreases exponentially with height the ux pro le of a sand cloud over a gravel surface can be expressed by a gaussian peak function q a b exp 0 5 h c d 2 where q is the sand transport rate at height h and a b c and d are regression coef cients the signi cance of the coef cients in the function could be de ned in accordance with the fetch length of the gravel surface and wind velocity coef cient c represents the peak ux height and increases with both wind velocity and fetch length implying that the peak ux height is related to the bounce height of the particles in the blowing sand cloud coef cient d shows a tendency to increase with both wind velocity and fetch length the sum of a and b representing the peak ux increases with wind velocity but decreases with fetch length the average saltation height derived from the cumulative percentage curve shows a tendency to increase with both the fetch length and wind velocity for any fetch length of a gravel surface the sand transport equation is expressed as q c 1 ut u g u3 where q is the sand transport rate u is the wind velocity ut is the threshold velocity measured at the same height as u g is the gravitational acceleration is the air density c is a proportionality coef cient that decreases with the fetch length of the gravel surface at a given wind velocity the sand transport rate over a gravel surface is only 52 68 per cent of that over a sandy surface the ux rate in true creep over a gravel surface increases with wind velocity but decreases with the fetch length whereas the creep proportion the ratio of creep ux to the sand transport rate decreases with both the wind velocity and fetch length two variable including fetch length and wind velocity equations were developed to predict the peak ux height average saltation height and transport rate copyright 2004 john wiley sons ltd

surface electric variations induced by deep hydraulic stimulation an example from the soultz hdr site 1 we carried out monitoring of surface electric potential variations at the soultz hot dry rock site france during a stimulation experiment where 23 000 m3 of water were injected in granite at 5 km depth we have observed a long period 9 10 days potential variation with a maximum amplitude of 5 mv thanks to the conductive well casing the start of this anomalous potential coincides with that of the water injection and its magnitude increases as more water is injected before returning toward its original value after shut in we interpret this anomalous potential as an electrokinetic effect which is caused by the injection of water circulating in deep fractures we modeled the pressure distribution during the stimulation and obtained the surface sp using electrokinetic coupling relationships we found that an in situ coupling coefficient of 1 mv mpa at the low end of laboratory values gives a good fit to the data

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

wind tunnel experiments on vertical distribution of wind blown sand flux and change of the quantity of sand erosion and deposition above gravel beds under different sand supplies wind tunnel experiments were carried out with respect to the vertical distributions of wind blown sand flux and the processes of aeolian erosion and deposition under different wind velocities and sand supplies above beds with different gravel coverage preliminary results revealed that the vertical distribution of wind blown sand flux was a way to determine whether the gobi sand stream was the saturated one or not it had different significances to indicate characteristics of transport and deposition above gobi beds whether bed processes are of aeolian erosion or deposition was determined by the sand stream near the surface especially within 0 6 cm height while the sand transport was mainly influenced by the sand stream in the saltating layer above the height of 6 cm the degree of the abundance of sand supply was one of the important factors to determine the saturation level of sand stream which influenced the characteristic of aeolian erosion and deposition on gravel beds given the similar wind condition the sand transport rates controlled by the saturated flow were between 2 and 8 times of the unsaturated one those bed processes controlled by the saturated flow were mainly of deposition and the amount of sand accumulation increased largely as the wind speed increased in contrast the bed processes controlled by the unsaturated flow were mainly of aeolian erosion meanwhile there was an obvious blocking sand ability within the height of 0 2 cm and the maximal value of sand transport occurred within the surface of 2 5 cm height

a large self potential anomaly on unzen volcano shimabara peninsula kyushu island japan self potential sp observation was carried out in the summit area of unzen one of the active volcanoes in kyushu island japan we found a positive sp anomaly in the vicinity of the newly extruded lava dome the potential difference across the anomaly exceeds 1000mv per 500m streaming potentials associated with subsurface hydrothermal convection seem to be the most reasonable mechanism for the positive anomaly in association with the first emergence of the lava dome a sharp increase of sp was detected which is considered to be a result of the growth of the hydro thermal system

comparison of measured wind tunnel and sweep simulated soil losses wind erosion estimates from the single event wind erosion evaluation program sweep model of the wind erosion prediction system weps were compared to wind tunnel experiments the influences of wind speed and soil texture were investigated from a previous study soil losses were measured directly in a wind tunnel using three soil types sandy loam loamy sand and sand each under three free stream wind speed conditions 10 18 and 26 m s 1 a different sand soil from another experiment was also tested under five wind speeds from 10 to 18 m s 1 over intervals of 2 m s 1 using a sediment trap and a flux profile estimating method the comparison of measured and estimated agricultural soil losses under non extreme winds less than 18 m s 1 in the wind tunnel was good the loamy sand comparison had an error less than 6 while the sandy loam soil had an error of about 35 sweep underestimated the amount of erosion with the sand soil however because the estimating equations used in sweep to predict soil parameters for agricultural soils are not directly applicable to pure sand surfaces this was expected when conducting sweep simulations it is recommended to use the actual aggregate size distribution asd data if available rather than relying on sweep s asd parameter values being estimated from other soil properties c 2013 elsevier b v all rights reserved

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

mechanisms linking active rock glaciers and impounded surface water formation in high mountain areas rock glaciers are slowly flowing mixtures of debris and ice occurring in mountains they can represent a reservoir of water and melting ice inside them can affect surface water hydrochemistry investigating the interactions between rock glaciers and water bodies is therefore necessary to better understand these mechanisms with this goal we elucidate the hydrology and structural setting of a rock glacier marginal pond system providing new insights into the mechanisms linking active rock glaciers and impounded surface waters this was achieved through the integration of waterborne geophysical techniques ground penetrating radar electrical resistivity tomography and self potentials and heat tracing results of these surveys showed that rock glacier advance has progressively filled the valley depression where the pond is located creating a dam that could have modified the level of impounded water a sub surface hydrological window connecting the rock glacier to the pond was also detected where an inflow of cold and mineralised underground waters from the rock glacier was observed here greater water contribution from the rock glacier occurred following intense precipitation events during the ice free season with concomitant increasing electrical conductivity values the outflowing dynamic of the pond is dominated by a sub surface seepage where a minor fault zone in bedrock was found characterised by altered and highly fractured rocks the applied approach is evaluated here as a suitable technique for investigating logistically complex hydrological settings which could be possibly transferred to wider scales of investigation

automatic fuzzy logic recognition of anomalous activity on long geophysical records application to electric signals associated with the volcanic activity of la fournaise volcano reunion island abstract for the mitigation of natural hazards geophysicists install more and more sensors in the field to enlarge the monitoring networks in volcanic and seismogenic areas unambiguous results can be obtained only if many parameters are continuously recorded and processed over very long time series several years overlapping an eruption or an earthquake on the other hand recent research has led to a sharp increase in the sampling rate of the data acquisition systems therefore manual data processing with a first step visual expertise becomes more and more difficult time consuming and at the same time less objective this paper introduces an alternative to manual signal recognition it includes the development of a specific anomaly recognition algorithm called difference recognition algorithm for signals dras and its application to self potential sp records obtained on the 10 channels of the electric stations located on la fournaise volcano before during and after the eruption of march 9 1998 the algorithm starts with the construction of rectification functionals examples are energy length zero crossing rate from the data over a running characteristic time window application of fuzzy set measures over the calculated functionals allows dras to identify in particular well spaced and time organised sp oscillations observed on the volcano up to 2 weeks before the march 9 1998 eruption based on the results obtained one can conclude that electric signals in the ulf band frequency

resistivity and self potential changes associated with volcanic activity the july 8 2000 miyake jima eruption japan abstract the miyake jima volcano abruptly erupted on july 8 2000 after 17 years of quiet and gave birth to a crater 1 km in diameter and 250 m deep this expected unrest was monitored during the years 1995 2000 by electromagnetic methods including dc resistivity measurements and self potential sp surveys beneath the 2500 yr old hatcho taira summit caldera audio magnetotelluric soundings made in 1997 98 identified a conductive medium 200 500 m thick within the 50 m isoline located at a few hundred metres depth it was associated with the active steady state hydrothermal system centred close to the 1940 cone and extending southward a dc resistivity meter set in a schlumberger array with 600 1000 and 1400 m long injection lines evidenced strong resistivity changes between september 1999 and july 3 2000 in the vicinity of the newly formed crater the apparent resistivity has reached about three times its initial values on the 1400 m long line and has lowered to about 20 on the 600 m line just prior to the july 8 2000 eruption sp mapping made inside the summit hatcho taira caldera revealed negative anomalies where positive ones had occurred during the previous tens of years the largest negative anomaly 225 mv in amplitude mainly took place above the 1940 cone which collapsed in the crater formation a permanent 1 km long sp line across the caldera suggests accelerating changes during the 3 months preceding the eruption on a larger scale the comparison between 1995 and 2000 surveys has shown a global increase of the hydrothermal activity beneath the volcano its source could have been 250 m to the south of the crater these observations suggest that the hydrothermal system was slowly disturbed in the months preceding the eruption while drastic changes have occurred during the 2 weeks before the summit collapse when tectonic and volcanic swarms have appeared

saltating particles over flat beds measurements of ejection and impact velocities trajectory lengths and maximum rise heights of sand grains median diameters 118 and 188 m in saltation over a flat sand bed in a wind tunnel have been obtained from the digitization of multiple image photo graphs the mean angle of ejection is found to be about 30 o from the horizontal rather than 90 o with mean vertical ejection velocity of about 2u where u is the friction velocity trajectories of saltating grains have been computed using the measurements of the initial ejection velocities and the mean velocity profile of the air flow

pattern of shallow ground water flow at mount princeton hot springs colorado using geoelectrical methods abstract in geothermal fields open faults and fractures often act as high permeability pathways bringing hydrothermal fluids to the surface from deep reservoirs the mount princeton area in south central colorado is an area that has an active geothermal system related to faulting and is therefore a suitable natural laboratory to test geophysical methods the sawatch range front normal fault bordering the half graben of the upper arkansas valley is characterized by a right lateral offset at mount princeton hot springs this offset is associated with the chalk cliffs of hydrothermally altered quartz monzonite because fault identification in this area is complicated by quaternary deposits including glacial and fluvial deposits we use dc electrical resistivity tomography and self potential mapping to identify preferential fluid flow pathways the geophysical data over 5600 resistivity and 2700 self potential measurements provide evidence of the existence of a dextral strike slip fault zone fault b responsible for the offset of the sawatch fault a segment of this dextral strike slip fault termed u1 is acting as the dominant vertical flow path bringing thermal waters to a shallow unconfined aquifer upwelling of the thermal waters is also observed at two zones u2 and u3 of an open fracture called fault a this fault is located at the tip of the sawatch fault and is likely associated with an extensional strain regime in this area self potential measurements are used to estimate the flux of upwelling thermal water the upflow estimate 4 1 10 3 m 3 day for the open segment of the fault b and 2 1 10 3 m 3 day for fault a from the geophysical data is remarkably consistent with the downstream mt princeton hot water production 4 3 4 9 10 3 m 3 day at approximately 60 86 c a temperature map indicates that a third upwelling zone termed u4 may exist at the southern tip of the sawatch fault

decomposition of multicomponent sea floor data into upgoing and downgoing p and s waves a method for decomposing multicomponent sea floor measurements into upgoing and downgoing p and s waves is presented we assume that a marine survey employing a marine source in the water layer is conducted over a plane layered medium from recordings of the pressure just above the sea floor and the particle velocity vector just below the sea floor decomposition filters can be determined by plane wave analysis the decomposition filter coefficients depend on the p and s wave velocities and the density at the sea bottom we show how to decompose the multicomponent measurements into upgoing and downgoing p and s vertical traction components vertical particle velocity components and horizontal particle velocity components the decomposition filters are applied with good results to synthetic data modeled in a plane layered medium

curvelet based seismoelectric data processing seismoelectromagnetic conversions are induced through electrokinetic phenomena occurring when passing seismic waves induce relative fluid to solid displacements information on porous material properties provided by the type i coseismic electric field accompanying surface and body waves is limited to the vicinity of the electrical receivers as opposed to the type ii electromagnetic interface response ir which can help detect porous contrasts and or fluid changes within the subsurface at depth for general field geometries the problem is that type ii disturbances exhibit lower amplitudes than type i fields and are difficult to access directly hence separating both types of waves is a critical step when processing seismoelectric data synthetic seismograms and electrograms generated with a full waveform seismoelectric forward modelling code written by garambois dietrich enabled us to study the behaviour of the ir s characteristic dipolar amplitude pattern recovered through filtering the definitive version is available at www blackwell synergy com to better preserve the ir amplitudes we have developed a new filtering strategy based on the fast discrete curvelet transform seismic or seismoelectric wave fronts can be optimall described using this multiscale decomposition over multidirectional anisotropic needle shape structures we have built a mask in the curvelet domain zeroing out seismoelectric samples corresponding to non zero samples from the accelerogram thus taking advantage of the relationship between seismic and seismoelectric waves for type i fields this mask consists of a threshold function combined with a gaussian distribution promoting horizontal i e zero slowness directions when applied to synthetic data this filter enabled to successfully extract the ir although less altering its dipolar radiation pattern than the conventional dip based techniques this strategy was successfully applied to a seismoelectric data set acquired in sedimentary deposits and permitted to isolate an ir generated at the water table

on the difficulty of detecting streaming potentials generated at depth in order to investigate how a streaming potential coefficient measured in the laboratory at a typical scale of 10 cm can be incorporated into a field model with a typical scale of 1 to 10 km we measured the electric field induced by water flows forced at 150 m depth through a 10 m wide granite fractured zone the water flows were obtained by pumping cyclically 10 m of water from a borehole that cut the fractured zone at depth and contemporaneously reinjecting it into another borehole located 50 m away after one day a steady state fluid flow regime was reached with pumping cycles lasting 45 minutes indicating a hydraulic conductivity of 10 5 m s 1 and a specific storage coefficient of 3 25 10 6 m 1 the expected self potential at the surface was an anomaly with two maxima of opposite sign and 2 v amplitude each both located 160 m away from the middle of the borehole heads the signal being divided by two 500 m away from the middle of the borehole heads in agreement with wurmstich and morgan 1994 instead we observed an electrical signal of 8 mv midway between the borehole heads and smaller than 5 mv 33 m away from the borehole heads the discrepancy observed between the data and the model can be explained by fluid flow leakages that occurred close to the water table head represented about 20 of the total water flow and activated smaller but closer electric sources this experiment thus illustrates the practical difficulty of detecting streaming potentials generated at depth it shows in particular that in fractured zones and hence in the vicinity of a major active fault small water flows located distantly from an energetic targeted source but close to some of the electrodes of the network can sometimes drastically distort the shape of the expected anomaly models of possible electrical earthquake precursors therefore turn out to be more speculative than expected

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

separation of upgoing and downgoing wavefields using the boundary element method summary the boundary element method has been applied for decomposing seafloor measurements into upgoing and downgoing waves two complementary solutions in the forms of a linear matrix system and a multiple multipole expansion are obtained without any assumptions about the subsurface if the elastic parameters below the seafloor are known these solutions are explicit they do not require any knowledge of the source signature basic components such as green s function computation can be replaced by alternative acoustic or elastic solutions results are useful for deghosting free surface multiple attenuation and p s splitting of ocean bottom cable data

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

estimating aquifer hydraulic properties from the inversion of surface streaming potential sp anomalies 1 electrokinetic effects of water flow during pumping tests have been shown to generate surface streaming potential sp anomalies of several tens of mv that are well correlated with the geometry of the water table it follows that sp measurements can be used to estimate aquifer hydraulic properties we have developed an inversion scheme for surface sp data generated by flow pumping and found that we are able to estimate the hydraulic conductivity and the depth and the thickness of the aquifer we applied our inversion scheme to the data from bogoslovsky and ogilvy 1973 and found a hydraulic conductivity of 10 5 m s 1 an aquifer thickness of roughly 28 m and an electrokinetic coupling coefficient of 1 mv m 1 these values are in the range of what is expected for this kind of environment

assessing the internal structure of landslide dams subject to possible piping erosion by means of microtremor chain array and self potential surveys abstract an integrated geophysical approach comprising microtremor chain array and self potential surveys was used to assess the internal structure of landslide dams subject to possible piping erosion in selected sites in japan and kyrgyzstan the non invasive geophysical approach is cost effective environmentally friendly and portable and hence it has proven to be valuable for the geotechnical assessment of landslide dams where piping can trigger failure of the dam while the microtremor chain array survey results revealed the internal structure of the landslide dam the self potential survey results indicated the path of anomalous seepage zones in the surveyed sites of long existing landslide dams the presence of a seepage path in the dam was confirmed by a good correlation between the areas of low phase velocity and large negative self potential anomalies in summary this integrated geophysical approach could be useful for the early risk assessment of landslide dams and prediction of landslide dam failure by piping

self potential modeling from primary flows this paper discusses a new method for the investigation of self potentials sp based on induced current sources the induced current sources are due to divergences of the convection current which is driven in turn by a primary flow either heat or fluid as a result of using this approach there is a shift in emphasis toward the vector flow field and its interaction with current cross coupling structure when compared with the total potential approach of nourbehecht 1963 which emphasized the primary flow potential and the voltage cross coupling this shift in emphasis is advantageous because it is analogous to the actual physical processes for example fluid flow in the ground gives rise to drag convection currents and the interaction of the convection currents with the electrical structure gives rise to the electrical potentials sp this simple physical picture should aid in developing a better intuitive understanding of the generation of sp effects the convective current approach is easily ada

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

deep water peg legs and multiples emulation and suppression this paper discusses a two step method for predicting and attenuating multiple and peg leg reflections in unstacked seismic data in the first step an observed seismic record is extrapolated through a round trip traversal of the water layer thus creating an accurate prediction of all possible multiples in the second step the record containing the predicted multiples is compared with and subtracted from the original the wave equation method employed to predict the multiples takes accurate account of sea floor topography and so requires a precise water bottom profile as part of the input information about the subsurface below the sea floor is not required the arrival times of multiple reflections are reproduced precisely although the amplitudes are not accurate and the sea floor is treated as a perfect reflector the comparison step detects the similarities between the computed multiples and the original data and estimates a transfer function to equalize the amplitudes and account for any change in waveform caused by the sea floor reflector this two step wave equation method is effective even for dipping sea floors and dipping subsurface reflectors it does not depend upon any assumed periodicity in the data or upon any difference in stacking velocity between primaries and multiples thus it is complementary to the less specialized methods of multiple suppression

dipolar self potential anomaly associated with carbon dioxide and radon flux at syabru bensi hot springs in central nepal the syabru bensi hot springs are located at the main central thrust mct zone in central nepal high carbon dioxide and radon exhalation fluxes reaching 19 kg m a2 d a1 and 5 bq m a2 s a1 respectively are associated with these hot springs making this site a promising case to study the relationship between self potential and fluids gas and water exhalation along a fault zone a high resolution self potential map covering an area of 100 m by 150 m that surrounds the main gas and water discharge spots exhibits a dipolar self potential anomaly with a negative peak reaching a180 mv at the main gas discharge spot the positive lobe of the anomaly reaching 120 mv is located along the terraces above the main gas and water discharge spots several electrical resistivity tomograms were performed in this area the resistivity tomogram crossing the degassing area shows a dipping resistive channel interpreted as a fracture zone channeling the gas and the hot water we propose a numerical finite difference model to simulate the flow pattern in this area with the constraints imposed by the electrical resistivity tomograms the self potential data the position of the gas vents and hot water discharge area this study provides insights on the generation of electrical currents associated with geothermal circulation in a geodynamically active area a necessary prerequisite to study using self potentials a possible modulation of the geothermal circulation by tectonic activity citation byrdina s et al 2009 dipolar self potential anomaly associated with carbon dioxide and radon flux at syabru bensi hot springs in central nepal

zeta potential measured for an intact granite sample at temperatures to 200 c 1 streaming potential was measured in an intact granite sample saturated with aqueous kcl solutions at three different concentrations at temperatures between 25 and 200 c the magnitudes of the streaming potential coefficient and of the surface conductance which dominates the sample conductivity both increase with increasing temperature using a capillary model we found that the magnitude of the zeta potential also increases with increasing temperature

rapid fluid disruption a source for self potential anomalies on volcanoes self potential sp anomalies observed above suspected magma reservoirs dikes etc on various volcanoes kilauea hawaii mount unzen japan piton de la fournaise reunion island miyake jima japan result from transient surface electric fields of tens of millivolts per kilometer and generally have a positive polarity these sp anomalies are usually attributed to electrokinetic effects where properties controlling this process are poorly constrained we propose an alternate explanation that contributions to electric fields of correct polarity should be expected from charge generation by fluid vaporization disruption as liquids are vaporized or removed as droplets by gas transport away from hot dike intrusions both charge generation and local increase in electrical resistivity by removal of fluids should occur we report laboratory observations of electric fields in hot rock samples generated by pulses of fluid water through the rock at atmospheric pressure these indicate the relative amplitudes of rapid fluid disruption rfd potentials and electrokinetic potentials to be dramatically different and the signals are opposite in sign above vaporization temperatures rfd effects of positive sign in the direction of gas flow dominate whereas below these temperatures effects of negative sign dominate this suggests that the primary contribution to observed self potential anomalies arises from gas related charge transport processes at temperatures high enough to produce vigorous boiling and vapor transport at lower temperatures the primary contribution is from electrokinetic effects modulated perhaps by changing electrical resistivity and rfd effects from high pressure but low temperature co 2 and so 2 gas flow ripping water molecules from saturated crustal rocks if charge generation is continuous as could well occur above a newly emplaced dike positive static potentials will be set up that could be sustained for many years and the simplest method for identifying these hot active regions would be to identify the sp anomalies they generate

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

self potential soil co2 flux and temperature on masaya volcano nicaragua we investigate the spatial relationship between self potential sp soil co sub 2 flux and temperature and the mechanisms that produce sp anomalies on the flanks of masaya volcano nicaragua we measured sp soil co sub 2 fluxes 1 to 5 0 x 10 sup 4 g m sup 2 d sup 1 and temperatures 26 to 80 c within an area surrounding a normal fault adjacent to comalito cinder cone 2002 2003 these variables are well spatially correlated wavelengths of sp anomalies are le 100 m and high horizontal sp gradients flank the region of elevated flux and temperature carbon isotopic compositions of soil co sub 2 delta sup 13 c 3 3 to 1 1 per thousand indicate a deep gas origin given the presence of a deep water table 100 to 150 m high gas flow rates and subsurface temperatures above liquid boiling points we suggest that rapid fluid disruption is primarily responsible for positive sp anomalies here concurrent measurement of sp soil co sub 2 flux and temperature may be a useful tool to monitor intrusive activity

decomposition of multicomponent seismic data into primary p and s wave responses1 inversion of multicomponent seismic data can be subdivided in three main processes 1 surface related preprocessing decomposition of the multicomponent data into primary p and s wave responses 2 prestack migration of the primary p and s wave responses yielding the angle dependent p p p s s p and s s reflectivity of the subsurface 3 target related post processing transformation of the reflectivity into the rock and pore parameters in the target this paper deals with the theoretical aspects of surface related preprocessing which consists of two steps 1 decomposition of the multicomponent data pseudo p and s wave responses into true p and s wave responses 2 elimination of the surface related multiple reflections and conversions

transient self potential anomalies associated with recent lava flows at piton de la fournaise volcano reunion island indian ocean self potential signals are sensitive to various phenomena including ground water flow streaming potential thermal gradients thermoelectric potential and potentially rapid fluid disruption associated with vaporization of water we describe transient self potential anomalies observed over recent 9 years lava flows at piton de la fournaise volcano reunion island indian ocean repeated self potential measurements are used to determine the decay of the self potential signals with time since the emplacement of a set of lava flow we performed a 9 km long self potential profile in february 2004 in the grand brule area this profile was repeated in july august 2006 the second repetition of this profile crossed eight lava flows emplaced between 1998 and 2005 during seven eruptions of piton de la fournaise volcano the self potential data show clear positive anomalies up to 330 mv and spatially correlated with the presence of recent lava flows the amplitude of the self potential anomalies decreases exponentially with the age of the lava flows with a relaxation time of not vert similar 44 months we explain these anomalies by the shallow convection of meteoric water and the associated streaming potential distribution but we cannot exclude possible contributions from the thermoelectric effect and the rapid fluid disruption mechanism this field case evidences for the first time transient self potential signals associated with recent volcanic deposits it can be also a shallow analogue to understand the variation of self potential signals in active geothermal areas and transient self potential signals associated with dike intrusion at larger depths the empirical equation we proposed can also be used to diagnose the cooling of recent lava flow on shield volcanoes

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

spatial heterogeneity of surface sediment grain size and aeolian activity in the gobi desert region of northwest china abstract studies have previously discussed characteristics of aeolian activity for different gravel densities on gobi surfaces however the significance of the spatial heterogeneity of its surface to sand flow over its surface and to dust emissions from the region has not been clearly demonstrated this is also the case for spatial variation in the aeolian environment accordingly this study established two observation transects both through the desert pavement area and the dune field in the gobi desert region of northwest china to measure surface sediment grain size wind speed and sand transport along these transects results showed that in areas where surface gravel content decreased and mobile sand dunes increased surface sediments were better sorted and grain size distribution changed from multimodal to roughly unimodal furthermore sand transport increased significantly and properties of aeolian activity varied markedly within a short distance this extreme variation in both grain size parameters and in sand transport indicated that strong spatial heterogeneity exists in the aeolian environment of the study area furthermore dune fields within gobi area are likely the main cause of sand flow over its surface as well as dust emissions from the region itself the findings in this study have universal applicability in gobi regions with uneven surface properties in other arid areas

modeling of streaming potential responses caused by oil well pumping the occurrence of streaming potentials is directly related to movement of fluids in the subsurface to investigate whether streaming potential measurements in boreholes and at the surface can be used to monitor subsurface flow and detect subsurface flow patterns in oil reservoirs we model streaming potential responses caused by oil well pumping in monitoring wells and at the earth s surface since the model parameters permeabilities cross coupling properties and electric conductivities depend on a few basic rock physics parameters such as brine conductivity amount of water saturation and porosity the model parameters are evaluated self consistently using rock physics models using a threedimensional 3 d finite difference algorithm the governing differential equations that are drawn from nonequilibrium thermodynamics are solved numerically in three self consistent steps solution of the hydraulic problem computation of the streaming current sources based on the principle of conservation of char

time evolution of hydraulic and electrokinetic parameters around the nojima fault japan estimated by an electrokinetic method abstract the nojima fault zone probe was designed to study the properties and healing processes of the nojima fault which is the surface fault rupture of the hyogo ken nanbu earthquake m7 2 of 1995 1995 kobe earthquake in this project water injection experiments were conducted in a borehole of 1800 m depth at the nojima fault we set up electrodes around the borehole and observed self potential variations to investigate the magnitude of electrokinetic and hydraulic parameters around the nojima fault zone in the 1997 experiment self potential variations were in the range of a few to about 20 mv across 320 450 m electrode dipoles with hydraulic pressure variations from 3 5 to 4 mpa in the 2000 experiment self potential variations were in the range of a few to about 85 mv across 160 260 m electrode dipoles with the hydraulic pressure variations from 3 to 4 5 mpa in the 2003 experiment self potential variations were in the range of a few to about 30 mv across 20 80 m electrode dipoles with hydraulic pressure of 4 mpa these observed self potential variations were explained well with an electrokinetic effect due to the underground flow of the injected water from the observed results we estimated that the ratio of hydraulic parameters permeability porosity and tortuosity to electrokinetic parameters zeta potential and dielectric constant decreased approximately 40 during eight years after the earthquake this result suggests that the healing process around the fault zone progress

hydraulic stimulation of geothermal reservoirs fluid flow electric potential and microseismicity relationships summary we have observed surface electric potential variations of several mv during a reservoir stimulation experiment run in 2000 at the soultz sous forets france hot dry rock site that we have interpreted as deep electrokinetic processes using data from another experiment run in 2003 at the same site we show here that the electrically conducting steel casing makes possible the measurement of surface sp anomalies even 5 km above the injection zone but obliterates any information about the geometry of the electrokinetic sources we also observed a slow temporal sp decay after the end of the that we interpret as large fluid flow persisting long after shut in at the edge of the stimulated area this persisting deep fluid flow explains why large induced microseismic events are recorded in this area long after the end of the stimulation experiment as fluid overpressures diffuse far away from the injection area this interpretation is consistent with the diffusive pattern of seismicity analysis of shapiro et al

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

geoelectric potential changes possible precursors to earthquakes in japan whether electromagnetic precursors to earthquakes eqs exist is an important question not only for eq prediction but also for understanding the physical processes of eq generation slow transient geoelectric potential changes have been observed before several recent eqs in japan in most cases they appeared 1 19 days before the eqs and their duration and intensity were several minutes to 1 h and 1 2 mv 100 m the changes appeared before five of all six eqs with magnitude 5 that occurred within 20 km of our stations during the observation period changes were also detected at greater epicentral distances up to 75 km before two other eqs including one eq of magnitude 4 7 which was preceded by a signal simultaneously recorded at three widely separated stations these geoelectric potential changes have been distinguished through the following criteria from a multitude of other changes which were noise of various origins i the selected changes were proportional in amplitude to the length of the recording station s short 100 m dipoles and were simultaneously detected also on long 1 10 km dipoles when the latter were in operation ii no such changes occurred during the observation period that were not followed by eqs although the eq precursory nature of these geoelectric potential changes is admittedly unproven it seems that the present results warrant continued serious research into the occurrence generation and transmission of these signals and their possible causal relationship to eqs

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

geothermal evolution of an intruded dike in the rift zone of kilauea volcano hawaii from vlf and self potential measurements abstract self potential sp and vlf measurements were made in 1973 1975 1995 1997 and 2012 across a basaltic dike that intruded into the koae fault zone of kilauea volcano hawaii in may 1973 the sp anomaly remained strong throughout in 2012 it was at about 60 of the strength it had in 1973 in contrast the vlf anomaly though diminished was still observable in 1995 1997 but by 2012 it had disappeared a hydrothermal dike model with parameters calibrated by modeling the solidification of kilauea iki lava lake is used to calculate temperatures and conductivity variation following jaeger s 1957 method we find that the time in years for a dike of width w m to solidify is 0 0075w2 thus a 1 m dike solidifies within the first few days and after 39 years is only tens of degrees above ambient given the orders of magnitude difference between the conductivities of wet and dry basalt we infer that after solidification the vlf anomalies were caused by induction in a localized veil of wet hot basalt enveloping the dike that was generated initially by condensation of steam and subsequently by condensation of evaporated water as temperatures reduced the conductivity anomaly persisted until the mid nineties by 2012 temperatures and condensation were too small for a vlf signal the persistent sp anomaly is attributed to localized fluid disruption with evaporation mainly at the water table and in the vadose zone streaming potentials are associated with evaporative circulation in the vadose zone next to the dike a positive potential is generated by upward flow of moisture laden air with a smaller negative potential on its flanks from downward infiltrating rainwater the analysis indicates that the combination of sp and vlf measurements can characterize the evolving geothermal regime of intrusions above the water table

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

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

characteristics of wind blown sand on gobi mobile sand surface the characteristics of wind blown sand on gobi mobile sand surface have been investigated through field observation and wind tunnel experiments on moving sand surface the pattern of wind speed profile in sand flow follows the power function overline u az b and its power exponent is about 0 20 while on gobi surface due to collision of sand grains with gravels the structure of sand flow differs from that on moving sand surface which decreases exponentially with height the height of blown sand activities on gobi surface is mainly concentrated below 20 cm in addition the structure of sand flow can reach a peak at a certain height and increases with inlet wind velocity

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

self potential improves characterization of hydraulically active fractures from azimuthal geoelectrical measurements 1 we examined the sensitivity of azimuthal self potential asp and azimuthal resistivity surveys ars to hydraulic anisotropy in a laboratory fracture block model both asp and ars measurements are influenced by anisotropy due to the strike of major fracture sets and heterogeneity due to variable fracture density of the block model the polarity of the self potential defines the flow direction and the self potential magnitude within a single fracture set is observed to increase with flow rate whereas the ars anisotropy is primarily controlled by fracture density connectivity and hence presumably hydraulic conductivity asp anisotropy appears diagnostic of 1 hydraulic gradient driving flow within fracture sets and 2 fracture density presumably controlling the strength of the streaming potential coefficient preliminary field data from the new jersey highlands illustrate that asp surveys can define hydraulic anisotropy in fractured rock environments our results suggest that combined interpretation of asp and ars can lead to improved geoelectrical characterization of fracture rock anisotropy

particle transport and adjustments of the boundary layer over rough surfaces with an unrestricted upwind supply of sediment abstract most natural surfaces containing non erodible roughness elements are considerably more complex than those studied in modelling exercises and wind tunnel simulations unlike idealized roughness elements which are uniform in size shape i e spheres or cylinders and spacing natural elements are challenging to measure in 3 dimensional space similarly most deflation lag surfaces such those as found on sandar and beaches are spatially heterogeneous open systems in which sediment transport from an external supply is very likely the development of irregular deflation lag surfaces and the transport of sediment over these surfaces from an upwind source of sediment was studied in a series of wind tunnel simulations surfaces prepared with crushed gravel and natural beach shingle respond conservatively in terms of the adjustment to the deflation and deposition of sediment deflation lag surfaces prepared with no spacing between the roughness elements i e close packed demonstrate little to no change in coverage with the introduction of particles from an upwind source neither the element type nor the friction velocity affect this outcome as the center to center element spacing increases to 60 mm infilling of the lag surface eventually is observed with the element coverage reduced by a factor between 2 and 4 for a given threshold ratio r t the roughness density is smaller than observed in previous simulation studies based on idealized roughness elements

the grain bed collision in sand transport by wind in the last decade much progress has been made toward the development of a comprehensive model of aeolian sediment transport in which the grain bed collision has been identified as having a significant role the grain bed collision has been studied by both physical experiments and numerical simulation a principal objective of these studies has been to gather sufficient data to characterize the collision in order that it may be represented as an empirical function in numerical models of the sand transport system thus the study of the exact physical mechanism of the collision has to some extent been neglected the transport of larger particles in saltation over a loose surface is known to promote the release of finer particles from that surface into suspension thus the precise physics of the grain bed collision become highly significant with regard to the physics of dust release from a surface this paper re examines previous collision data and compares them with a simple collision model this model proposed that the impinging grain strikes a single surface grain and rebounds an alternative mechanism might be that the impinging grain ploughs through the surface striking a number of bed grains before rebounding the collision data are shown to support the model first because the duration of the collisions observed on the high speed film supports a short contact time with the surface and second because the data fit well with the model

controlling windblown sand problems by an artificial gravel surface a case study over the gobi surface of the mogao grottoes abstract in arid regions gravel surfaces are usually known for protecting the soil from wind erosion trapping the sand and dust carried by the wind thereby forming a sink of sediment however gravel surfaces with a suitable gravel size and coverage density can also act as the source of sediment under unsaturated wind flow a dynamically equilibrated gravel surface can be built to prevent potential windblown sand problems in the dunhuang mogao grottoes in northwestern china unlike previous studies that suggested constructing a high coverage 50 or more gravel surface on the gobi land on top of the mogao grottoes a much lower value of 30 is recommended this kind of artificial gravel surface can protect the underlying sand materials from wind erosion and trap the invading westerly windblown sand at the same time the deposited sand over the artificial gravel surface can be transported to the western megadunes by the easterly wind under the multidirectional wind regime the gravel surface can remain from sand burial over the long term

witseg sampler a segmented sand sampler for wind tunnel test the flux profile of blowing sand is the reflection of a large number of sand particles moving in different trajectories to describe the function of the flux profile requires measuring the flux of blown sand at different heights a segmented sand sampler for wind tunnel study witseg sampler has been designed and evaluated in a wind tunnel the sampler is 0 6 m high and sectioned into 60 openings that can measure the flux profile of blowing sand at 10 mm intervals special attention was paid in designing the sampler to its practicability and efficiency for the convenience of use the leading edge with inlets sand chambers and side cover are removable to maximize the sampling efficiency the leading edge is wedge shaped so that the width of the inlets is 5 mm while the width of the sand chamber is 15 mm each sand chamber has two screened vents that are connected to a vertical vent to minimize the air pressure inside the sand chamber and maximize its efficiency wind tunnel evaluation shows that the sampler is good for measuring aeolian sand flux both the measured flux profile and total flux show a reasonably good agreement with the widely accepted flux profile function and sand transport equation it has an overall efficiency of 0 91 the witseg sampler that can measure the detailed variation of blown sand flux with height proves to be a good tool for studying the flux profile of blowing sand

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

reply to comment by revil on rapid fluid disruption a source for self potential anomalies by m j s johnston j d byerlee and d lockner