scaling laws between seismo electric magnetic fields and earthquake magnitude the mechanisms generating the charges potentials and abnormal electromagnetic radiation that accompany earthquakes have been discussed based on observational theoretical and laboratory studies in particular over the last few decades we previously conducted stick slip tests using precut granite cores with a contact electrode on the sample side and proposed that surface charges released from charge trapping centres on sheared asperities are a possible source of the above mentioned charges or potentials here we discuss seismo electric and magnetic fields formed by the surface charges and derive their scaling laws with the earthquake magnitude at a distance according to our model detectability of these fields at a point on the ground surface depends strongly on wet dry condition at a fault zone sheared asperities

comment on self potential signals associated with preferential groundwater flow pathways in sinkholes by a jardani j p dupont and a revil jardani et al 2006a hereinafter referred to as jdr present a self potential survey showing circular anomalies associated with shallow sinkholes in a chalk karst they perform various finite element modelings and data analysis and in particular use a three dimensional 3 d version of the so called dipole occurrence probability doi tomography iuliano et al 2002a

possible electrokinetic origin of large magnetic variations at la fournaise volcano abnormal time variations of the geomagnetic field related to volcanic activity have been reported for several decades1 10 two main candidates have been considered for the source mechanism of these volcanomagnetic variations piezomagnetism and electro kinetic effects we considered both of these mechanisms in our attempts to interpret the most spectacular volcanomagnetic variations observed on piton de la fournaise volcano reunion island 11 but now new analysis of the latest data which covers a time span of more than three years leads us to think that water circulation is the main agent of the strong magnetic signals observed on the volcano in addition to the signals that we correlated with the volcano activity11 12 longer period components also exist as shown here with amplitudes and characteristics that have not been reported before we propose that these magnetic variations are generated by electrokinetic effects in which case the water circulation system into this massif would be a sensor for detecting stress changes linked to the volcano activity

anomalous diffusion of electromagnetic eddy currents in geological formations controlled source electromagnetic em induction in some geological formations isshown here to be compactly described by an anomalous subdiffusion process such aprocess which is not universal is governed by a fractional diffusion equation oralternatively the convolutional form of ohm s law a subdiffusing eddy current vortex or electromagnetic smoke ring propagates in such a way that its position of medianintensity overruns its position of peak intensity this behavior is not allowed in classicaldiffusion but is a simple consequence of diffusion within a stationary fractal medium a similar analysis has been applied to understand heavy tailed traveltime distributions thatappear in certain hydrological time series the tell tale signature of anomalouselectromagnetic diffusion is a slope b of the magnetic zero crossing moveout curve that isconstant with transmitter receiver rx offset and significantly different from unity neither lateral heterogeneity nor unixial anisotropy can generate such a constant slopemoveout curve with an economy of model parameters controlled source em data fromtwo sites in texas and one in new mexico are used in this study to test the eddy currentsubdiffusion hypothesis

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

modification of streaming potential by precipitation of calcite in a sand water system laboratory measurements in the ph range from 4 to 12 spontaneous potentials associated with volcanic activity are often interpreted by means of the electrokinetic potential which is usually positive in the flow direction i e zeta potential of the rock is negative the water rock interactions in hydrothermal zones alter the primary minerals leading to the formation of secondary minerals this work addresses the study of calcite precipitation in a sand composed of 98 quartz and 2 calcite using streaming potential measurements the precipitation of calcite as a secondary mineral phase inferred by high calcite saturation indices and by a fall in permeability has a significant effect on the electrokinetic behaviour leading to a significant reduction in the zeta potential in absolute value and even a change in sign the measured decrease in zeta potential from 16 mv to 27 4 mv takes place as the ph rises from 4 to 7 while it remains constant at 25 1 mv as the ph increases from 8 to 10 5 for ph higher than 10 5 calcite precipitates and is expected to coat the quartz surface the measured zeta potential vary from 17 to 8 mv for ph ranging from 10 6 to 11 7 depending on the amount of precipitated calcite indicated by the decrease in permeability the observed change in sign of the electrical surface potential rules out the usual qualitative interpretation of sp anomalies in order to determine fluid circulations even at ph lower than 9 if calcite is widely present as a secondary mineral phase since the electrical surface potential of calcite depends also on co2 partial pressure and ca2 therefore sp anomalies as measured in hydrothermal field without mineralogical analyses of hydrothermal deposits and without geochemical fluid survey should be interpreted with caution

synthetic rough fractures in rocks natural fractures serve a very important function in the transport of fluid through rocks as well as in the flow of electrical charge and heat the creation of numerically synthesized fractures can aid the study of the physical processes connected with fractures synthetic fracture is the term used to describe fractures that are created numerically in such a way that they share the same mean geometrical characteristics as specific natural fractures measured by profiling by a process known as tuning we have modified methods for producing synthetic rough surfaces whose geometric properties are tuned to mimic natural fracture surfaces in rocks in order to create synthetic fractures that are statistically identical to those found in rocks one important such modification has been the incorporation of a method that allows the surfaces to be matched at long wavelengths and unmatched at short wavelengths with the degree of matching varying smoothly in between as it does for real fractures we have compared numerically synthetic fractures created using the new method with fractures created using an existing technique that uses a mismatch wavelength as a sudden discontinuity between matched and unmatched behavior as well as data from fractures in real rocks this comparison has shown that the new technique provides much more realistic numerically synthesized fractures than previous methods synthetic fractures created with the new method have been used in normal closure and fluid flow modeling and the results are reported in a companion paper

streaming potential measurements 1 properties of the electrical double layer from crushed rock samples the potential has been inferred from streaming potential measurements with crushed rock samples as a function of ph and electrolyte concentration for various salts the value obtained for crushed fontainebleau sandstone at ph 5 7 and a kcl solution with a resistivity of 400 m is 40 5 mv where the error is dominated by sample to sample variations the sensitivity of the potential to the electrolyte resistivity for kcl is given experimentally by f 0 23 0 014 where f is the electrolyte resistivity the point of zero charge pzc is observed for ph 2 5 0 1 and the potential is positive for ph pzc for ph 5 the variations of the potential with ph can be approximated by ph 5 7 1 0 068 0 004 ph 5 7 for f 100 m the potential has been observed to be sensitive to the valence of the ions and is approximately reduced by the charge of the cation unless specific adsorption takes place like in the case of al 3 the experimental results are well accounted for by a three layer numerical model of the electrical double layer and the parameters of this model can be evaluated from the experimental data the sensitivity of the potential to the rock minerals has also been studied the potential obtained for granitic rocks is comparable to that obtained for fontainebleau sandstone but can be reduced by a factor of 2 4 for sandstones containing significant fractions of carbonates or clay to take into account the effect of the chemical composition of the electrolyte a chemical efficiency is defined as the ratio of the potential to the potential measured for kcl this chemical efficiency is measured to be 80 for typical groundwater but can be as low as 40 for a water with a high dissolved carbonate content the set of empirical laws derived from our measurements can be used to assess the magnitude of the streaming potentials expected in natural geophysical systems

magmatology of mt pelee martinique f w i iii fractional crystallization versus magma mixing the mineralogical and chemical compositions of the magmas emplaced during the three successive stages of mt pelee s activity ca 0 4 0 2 ma ca 0 1 ma 19 500 y b p 13 500 y b p remained relatively constant all magmas are cogenetic in a broad sense and result from the combination of two major petrogenetic processes fractional crystallization witnessed by gabbroic and dioritic cumulates fichaut et al 1989 this issue and magma mixing evidenced by textural mineralogical and chemical heterogeneities gourgaud et al 1989 this issue the study of heterogeneous eruptions e g the ash and scoria flows second stage and the 1902 1929 block and ash flows demonstrates that the basic and acid magmas involved have small but significant geochemical differences the distribution of compatible mg sc co and hygromagmaphile th la ta hf elements indicates that fractional crystallization played a dominant role in the genesis of the second stage products whereas magma mixing was dominant in the 1902 1929 lavas geological mineralogical and geochemical constraints are used to propose models of magma chambers the second stage deposits are considered to be the result of the discharge of the magmas stored in a chemically stratified ca 2 3 km3 magma chamber tentatively described as a cylinder or a parallelepiped of large vertical extent tens of km but small horizontal section some hundreds of meters by contrast the young 13 500 y b p deposits of mt pelee are thought to originate from a small 1 km3 and shallow ca 10 km in depth chamber filled with andesitic to dacitic magmas the periodic intrusion of basic magmas presumably from a deeper chamber causes magma mixing which triggers the eruption of heterogeneous and hybrid products

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

earthquake source nucleation a physical model for short term precursors abstract ohnaka m 1992 earthquake source nucleation a physical model for short term precursors in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 149 178 this paper deals with a quasistatic leading to a quasidynamic at a later time nucleation process that precedes the earthquake dynamic rupture and models of the earthquake source nucleation are put forward based on physical principles a quasistatic to quasidynamic rupture nucleation process is an intrinsic part of the ensuing earthquake dynamic rupture in other words the nucleation process itself is an short term or immediate precursor that occurs in a localized zone during the earthquake nucleation premonitory slip proceeds in the localized nucleation zone and shear stress also decreases gradually in the zone since slip weakening occurs during the nucleation immediate foreshock activity is a part of the nucleation process leading to the mainshock dynamic rupture therefore hypocentral locations of foreshocks are necessarily restricted to lie near the mainshock hypocentre onset of the mainshock rupture whether or not foreshocks occur during the mainshock nucleation depends on how the rupture growth resistance varies on a local to small scale since patches of greater rupture growth resistance are considered to prevail on a local to small scale in the fault zone carrying immediate foreshocks would be one of the major characteristics of earthquakes that nucleate within the brittle seismogenic layer when a mainshock earthquake nucleates within the brittle seismogenic layer and its hypocentre is located near the base of the seismogenic layer immediate foreshocks for this mainshock are necessarily restricted to lie within a localized region shallower than hypocentral depth of the mainshock by contrast the nucleation process below the base of the seismogenic layer is aseismic in nature so that carrying no conspicuous foreshocks would be a common characteristic of interplate earthquakes that nucleate below the base of the brittle seismogenic layer the breakdown strength p the breakdown stress drop b and the critical slip displacement dc are indicative of the rupture growth resistance to estimate depth variations of these parameters the effects of the normal stress n and temperature t on those parameters are examined using available data so far published the combined effects of n and t on p in the brittle to semibrittle regime are found to be represented empirically by p n t po n 1 cosh 50 t 40 sinh 50 t exp 2000 t where po n 135 7 0 750 n and t is measured in k and n in mpa it is found that dc increases sharply with t but is insensitive to n above 300 c while dc depends on n but is insensitive to t below 300 c on the basis of these results variations in p dc and b at mid crustal depths are estimated for quartzo feldspathic rocks for a given geothermal gradient

hydrothermal circulation beneath mount pelee inferred by self potential surveying structural and tectonic implications abstract self potential sp surveys were made on mount pelee volcano martinique island french west indies in 1991 and 1992 in order to recognize its hydrothermal system the associated groundwater channeling and the main superficial structures of the massif almost 70 km of profiles were carried out with an average sample spacing of 50 m measurements essentially reveal negative sp anomalies down to 1700 mv with high gradients 1 83 mv m due to the infiltration of meteoric water into the massif rims of summit calderas morne macouba and etang sec present sharp negative sp anomalies on the western northern and eastern flanks negative sp anomalies indicate no upward water flow beneath mount pelee summit on the southwestern volcano flank a 3 5 6 km horseshoe shaped structure corresponding to a southwest flank collapse event older than 25 000 years bp is clearly identified by the sp mapping high gradients border the inner southern rim from morne calebasse to st pierre town and the caribbean sea along the northern rim of the horseshoe shaped structure the negative sp anomalies give place to a positive sp anomaly up to 200 mv of sw ne trend this zone covers the area of two active hot springs sources chaudes and puits chaud 40 65 c marine magnetic surveys and bathymetry show that the horseshoe shaped structure spreads into the caribbean sea up to about 10 km from the coast buried structural discontinuities are evidenced inside the flank collapse structure the upper one deviates the groundwater flow coming from the summit toward the south flank where the flow finds an indentation to expand again downwards this discontinuity is either an old hypothetical caldera rim partly destroyed by the collapse of the south southwestern flank and covered by recent pyroclastic deposits or more probably the trace of a bulge landslide a circulation model of the hydrothermal waters is proposed rainfall 5 6 m year is partly drained inside the summital calderas and the flank collapse zone through pyroclastic flows down to an impermeable basement there the groundwater constitutes perched aquifers at the contact of the bulge landslide or of the hypothetical old caldera rim along the inner northern border of the flank collapse structure the phreatic water is reheated warm groundwater flows along the northern avalanche structure rim and discharges near the coast in ground and marine outcrops of medium temperature finally the main part of the meteoric water is channeled along the old caldera rim or along the bulge landslide towards the south flank of mount pelee where some gaps in the rim exist there the groundwater finds again a subhorizontal gravitational circulation along mount pelee slopes into the caribbean sea

transient electrical activity accompanying rock under indentation loading abstract enomoto y and hashimoto h 1992 transient electrical activity accompanying rock under indentation loading in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 337 344 laboratory experiments have been conducted to investigate the geoelectrodynamics associated with rock fractures in the earth s crust that is when rocks were subjected to indentation fracturing in two ways the electric charges generated were detected namely 1 a direct charge collection method using an electroconductive indenter serving as the collecting electrode referred to as near field test and 2 an indirect collection method in which an electrode was placed on rocks at a specific distance from the indentation fracture zone referred to as far field test as near field test results higher electric charge signals were detected during the loading cycle when cracking occurred around the indent on granite and on moist andesite also in the far field test the charge signal propagating through the rock during fracturing could be detected the signal intensity decreased as the distance between the indent and electrode increased possible mechanisms for fracture induced charge generation and their propagation through rock media are discussed

a semi analytical solution for transient streaming potentials associated with confined aquifer pumping tests we consider the transient streaming potential response due to pumping from a confined aquifer through a fully penetrating line sink confined aquifer flow is assumed to occur without fluid leakage from the confining units however since confining units are typically clayey and hence more electrically conductive than the aquifer they are treated as non insulating in our three layer conceptual model we develop a semi analytical solution for the transient streaming potentials response of the aquifer and the confining units to pumping of the aquifer the solution is fitted to field measurements of streaming potentials associated with an aquifer test performed at a site located near montalto uffugo in the region of calabria in southern italy this yields an average hydraulic conductivity that compares well to the estimate obtained using only hydraulic head data specific storage is estimated with greater estimation uncertainty than hydraulic conductivity and is significantly smaller than that estimated from hydraulic head data this indicates that specific storage may be a more difficult parameter to estimate from streaming potential data the mismatch may also be due to the fact that only recovery streaming potential data were used here whereas head data for both production and recovery were used the estimate from head data may also constitute an upper bound since head data were not corrected for pumping and observation wellbore storage estimated values of the electrical conductivities of the confining units compare well to those estimated using electrical resistivity tomography our work indicates that where observation wells are unavailable to provide more direct estimates streaming potential data collected at land surface may in principle be used to provide preliminary estimates of aquifer hydraulic conductivity and specific storage where the latter is estimated with greater uncertainty than the former

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

nature of surface electrical conductivity in natural sands sandstones and clays the electrical conductivity of rocks results from conduction through the bulk solution occupying the pores and from surface conduction occurring at the fluid grain interface the nature of the surface electrical conductivity of shaly and clean sands and sandstones is examined surface conduction is characterized by the specific surface conductance which is the sum of three contributions i conduction within the electrical diffuse layer which makes a negligible contribution to the total specific surface conductance ii conduction in the stern layer which is shown to vary significantly with the salinity of the pore fluid at low salinities 10 6 to 10 3 mol 1 1 but becomes independent of salinity at higher salinities iii a mechanism operating directly on the mineral surface independent of salinity and perhaps associated with proton transfer at salinities higher than 10 3 mol 1 1 and at 25 c the specific surface conductance of quartz and clays is equal to 8 9 10 9 s and 2 5 10 9 s respectively equations describing the influence of surface conductivity and microstructure upon the macroscopic electrical conductivity of sands sandstones and shales are also developed

electromagnetic emissions during dilating fracture of a rock abstract a lot of experiments on electromagnetic emissions emes have been reported under axial compressive fracture shear fracture indentation fracture and stick slip friction in lab and blasting in situ but there are rare reports on the in lab experimental work on emes during dilating fracture of a rock which is helpful in studying and understanding emes related to slow earthquakes and the earthquakes due to volcanic activities and water level changes of reservoirs therefore in the present paper in order to check whether there are detectable emes during dilating fracture of a rock in lab dilating fracture experiments were conducted the dry cuboid specimens of initially intact granodiorite and limestone were tested inside magnetic field free space mffs at room temperature we arranged evenly 20 eme antennas whose resonance frequencies range from 2 5 khz to 540 khz close to rock specimens our experimental results strongly indicate that detectable emes could generate during dilating fracture of a rock they were recorded only associated with some but not all phases of fracture their waveforms often took on the trend that a peak arrived at first and then attenuated sharply and followed by a series of low amplitude oscillations the electromagnetic em signals after eliminating the effects of eme antennae via deconvolution had the maximum peak to peak amplitudes of about 80 0 mv and 40 5 mv for granodiorite and limestone respectively their main spectral components often concentrated in the band of several khz to 60 khz and of several khz to 280 khz the emission of electrons and charged particles from fracture surfaces and or micro fracture electrification could be possible mechanisms for our experimental results

fractal measurements of sandstones shales and carbonates measurements were made of the fractal properties of sandstones shales and carbonates using a statistical analysis of structural features on fracture surfaces fractal behavior is associated with power law behavior for the number of features as a function of the feature size on the pore rock interface only one sedimentary rock a novaculite was found not to have a fractal structure the fractal dimensions range from 2 27 to 2 89 and the long length limits to the fractal regime range from 2 m to over 50 m in all cases the fractal behavior extends to less than 0 2 m which is the measurement resolution the porosity associated with the fractal pore rock interface can be calculated from the fractal parameters some of the samples have additional porosity not associated with power law behavior photographs and other evidence are used to show that the fractal structures are the result of diagenesis fractal diagenetic structures include euhedral quartz overgrowths druse quartz calcite dolomite clays and chert

stable isotope analyses of carbonate complicated by nitrogen oxide contamination a delaware basin example abstract whole rock subsurface samples from the cherry canyon formation delaware basin were used to document the presence of a contaminant gas affecting the isotopic composition of acidified carbonate the whole rock material when reacted in purified phosphoric acid using the mccrea 1950 method produces a contaminant mass 46 gas nitrogen dioxide no2 this mass 46 gas contributes to the 18o 16o ratio mass 46 44 artificially enriching the 18o value and masking the true isotope signature of the co2 derived from the carbonate minerals acidified whole rock samples containing low carbonate 18o pdb values some greater than 30 conversely samples with higher carbonate 5 have 18o values ranging from 5 to 8 hence diluting the effects of the contaminant gas on the mass 46 44 ratio after purifying the co2 produced by the mccrea 1950 method with a reduction furnace all of the 18o values fall in the range of 0 to 12 regardless of carbonate content th 16c pdb values remain unchanged after reduction furnace purification indicating no effect on mass 45 44 ratio the inferred source of the contaminant no2 gas is from inorganic ammonium adsorbed to interlayer sites of alumina silicates such as illite and mica this source is supported by the detection of ammonium and clays in the whole rock material and the lack of correlation between percent organic carbon and 18o values influenced by no2 to eliminate the effect of the contaminant gas on 18o values we describe a simple procedure that removes the contaminant no2 gas yielding the true isotopic signal from the carbonate minerals in whole rock material

the effect of diagenesis on oxygen isotope ratios of biogenic phosphates the effect of diagenesis on the oxygen isotope composition of ancient biogenic phosphates was evaluated by measuring different types of material from middle triassic localities in the southern alps dentin bone and tooth enamel of different taxa hosted by different rock types and metamorphosed to differing degrees were analyzed for their 18 o and 13 c values using a new microanalytical gc irmms technique the 18 o values of the majority of bone and bulk tooth samples were 18 to 19 permil smow with three samples below this range and one close to 20 permil in contrast samples of tooth enamel were 19 4 to 20 7 permil significantly higher than bone and bulk tooth without the enamel data the 18 to 19 permil data could be misinterpreted as primary only when the higher 18 o values of the enamel are considered is it apparent that the bulk data have undergone diagenesis and temperature estimates are 5 c lower than would otherwise be calculated alteration of bulk tooth is also seen in a miocene shark tooth where 18 o values of enamel are 3 permil higher than those of bulk tooth although enamel is routinely analyzed for paleoclimate work of herbivorous mammals bulk bone teeth or shells are almost exclusively used for older marine samples the results of the present study indicate that bulk data should be treated with caution

laboratory studies of electrical potential during rock failure we have investigated electrical potential and acoustic emissions signals associated with rock deformation five rock types were studied clashach bentheim and darley dale sandstones all quartz rich and a seljadur basalt and portland limestone both quartz free both air dry and the rocks were tested in distilled water shallow crustal conditions were simulated in a triaxial rock deformation cell with a confining pressure simulating depth of 40 mpa pore pressures ranging 5 35 mpa and strain rates 10 7 10 4 s 1 precursory electric potential signals prior to failure were observed in both saturated and dry samples of the quartz rich sandstones but only observed in the water saturated quartz free rocks co seismic electrical signals were obtained in all tests providing strong evidence that two of the main sources for precursory and co seismic signals are the piezoelectric and electrokinetic phenomena lowering the strain rate resulted in an increase in the number of acoustic emissions the pore volume changes during compaction and dilatancy remained approximately constant for all strain rates streaming potential generated by fluid flow across the sample was also measured at different stages of deformation the potential signals increased with the pore pressure gradient c 2005 elsevier ltd all rights reserved

complex resistivity measurements of confined rock complex resistivity was measured for samples of westerly granite and berea sandstone saturated with 0 01 m kclaq a four electrode technique was employed to make measurements over a frequency range of 10 3 to 106 hz and a confining pressure range of 0 2 to 200 mpa when the electrical response was analyzed in terms of equivalent conductivity and relative permittivity k both of these quantities varied more with confining pressure for the granite samples than they did for the sandstone in addition both rock types exhibited large low frequency dispersion of permittivity while previous studies have measured the response of near dc conductivity to changes in pressure measurements of pressure dependence of the full complex resistivity provide greater insight into earthquake related phenomena as well as induced polarization measurements and other remote sensing techniques

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

the retention of primary oxygen isotope compositions of fossil elephant skeletal phosphate fossil elephant remains from sediments of plio pleistocene age in the vicinity of lake turkana kenya provide insights into the ability of the phosphate oxygen system to preserve original 18o values 18op in the depositional environment individual fossil specimens exhibit systematic variations in the 18op values of their various tooth and bone components differences in 18op values between these skeletal components can be as high as 3 6 despite the fact that equivalent phases for individual modern elephants have 18op values which vary by less than 0 6 xrd traces of the different skeletal phases of modern and fossil samples also infer differential preservation of primary apatite crystallinities among the various fossil phases fossil samples of dentine cementum and bone have x ray spectra with sharper and more intense peaks compared to their modern counterparts but little change in crystallinity is observed for fossil enamel samples a model based on the premise that the enamel phase preserves primary isotope signatures and that the accompanying skeletal phases are partially re equilibrated with the fluids associated with the microbial decomposition of the elephant s carcass is consistent with the features of the 18op dataset this isotopic evidence in conjunction with the physical and chemical attributes of enamel has led us to postulate that enamel could be preserving primary isotope signatures while other skeletal components are affected to varying degrees by alteration processes in the burial environment

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

reply to comment by a revil and n linde on streaming potential dependence on water content in fontainebleau sand revil and linde recently commented our paper concerning streaming potential sp measurements in unsaturated sand during drainage experiments this comment suggests that the approach used to infer sp coefficients was inappropriate for unsaturated conditions and therefore yielded wrong conclusions and unphysical results regarding the behaviour of the relative sp coefficient this reply argues that even if in allegre et al we neglected some secondary electrokinetic sources the resulting conclusions are still representative of the behaviour of the true sp coefficient and that the remarks of revil linde arose from a misunderstanding of the drainage experiment conditions we also find support for our results from a comparison between our observations and previous experimental studies

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

statistical analysis of ulf seismomagnetic phenomena at kakioka japan during 2001 2010 to clarify and verify the ultralow frequency ulf seismomagnetic phenomena we have performed statistical studies on the geomagnetic data observed at the kakioka kak station japan during 2001 2010 we investigated the energy of ulf geomagnetic signals of the frequency around 0 01 hz using wavelet transform analysis to minimize the influences of artificial noises and global geomagnetic perturbations we used only the geomagnetic data observed at nighttime lt 2 30 a m to 4 00 a m and utilized observations from a remote station kanoya as a reference statistical results of superposed epoch analysis have indicated that ulf magnetic anomalies are more likely to appear before sizable earthquake events es 108 rather than after them especially 6 15 days before the events further statistical investigations show clearly that the ulf geomagnetic anomalies at kak station are more sensitive to larger and closer events finally we have evaluated the precursory information of ulf geomagnetic signals for local sizable earthquakes using molchan s error diagram the probability gain is around 1 6 against a poisson model the above results have indicated that the ulf seismomagnetic phenomena at kak clearly contain precursory information and have a possibility of improving the forecasting of large earthquakes

self potential signals associated with variations of the hydraulic head during an infiltration experiment 1 a field experiment was performed to monitor the variations of the hydraulic head in the vicinity of a ditch during a water infiltration experiment and using the self potential method the coupling between electric and hydraulic flows is electrokinetic in nature the electrical signals are measured at the ground surface with a set of ten non polarisable petiau pb pbcl2 electrodes over a section perpendicular to the ditch the electrical potential is linearly related to the depth of the water table which is here quite shallow between 1 to 2 m a rough estimate of the electrokinetic coupling coefficient obtained in the field is 10 mv per meter of hydraulic head 1000 mv mpa 1 of pore fluid pressure the order of magnitude of this estimate agrees with a laboratory experiment performed with a soil sample from the test site the good correlation found between electrical potential and hydraulic head variations opens the door to direct tomography of hydraulic head fluctuations with many innovative applications in hydrogeology especially because the potential depth to which this method could be applicable is high several hundred meters

electromagnetic and acoustic emission associated with rock fracture abstract to understand the physical mechanism of the anomalous electromagnetic emissions observed before earthquakes we carried out some laboratory experiments on electromagnetic and acoustic emission from a rock granitic samples were loaded at a constant strain rate and electromagnetic and acoustic emission were simultaneously recorded during deformation of the sample ten to 20 of the acoustic emissions detected during the experiment are associated with electromagnetic emission the onset time of electromagnetic emission is found to coincide with the origin time of the acoustic emission this demonstrates that the emission of electromagnetic waves is truly associated with microcracking in the sample the efficiency of generating electromagnetic emission seems to be higher in tensile cracks than in shear cracks the frequency spectrum of the electromagnetic emission obtained with five coil antennae of different frequency responses indicates that the main power of the electromagnetic emission is in the frequency range 0 5 mhz a possible mechanism of electromagnetic emission is electrification of a fresh surface created by subcritical cracking in a rock if this interpretation is correct production of new cracks is a necessary condition for generation of electromagnetic emissions although we do not completely understand how a natural earthquake occurs it is generally considered to be a result of shear faulting that connects pre existing small cracks therefore it is reasonable to expect anomalous electromagnetic emission associated with small tensile cracks before an earthquake and to expect that the anomalous electromagnetic emission will be observed only before an earthquake but not at the main shock which may not be very efficient for creation of a fresh surface

theory of transient streaming potentials in coupled unconfined aquifer unsaturated zone flow to a well a semianalytical solution is presented for transient streaming potentials associated with flow to a pumping well in an unconfined aquifer taking into account the effect of flow in the unsaturated zone above the water table flow in the unsaturated zone is modeled with a linearized form of richards equation using an exponential model for soil moisture retention and unsaturated hydraulic conductivity archie s law is invoked for unsaturated electrical conductivity the unsaturated electrokinetic coupling coefficient is modeled with a decaying exponential where the maximum value is at and below the water table the coupled flow and electrokinetic problem is solved using laplace and hankel transforms the results of the model predicted behavior are presented and compared to that observed in laboratory simulations of pump ing tests the early time polarity reversal predicted the model is observable in the experiments other non monotonic streaming potential behaviors predicted by the model are also evident in experimental measurements the model is used to estimate hydraulic parameters from sp data and these compare well to those obtained from drawdown data for example a hydraulic conductivity of 3 6 3 10 24 m s is obtained from sp data compared to 3 4 3 10 24 m s from drawdown data

rock magnetic properties related to thermal treatment of siderite behavior and interpretation detailed analyses of rock magnetic experiments were conducted on the oxidation products of high purity natural crystalline siderite that were thermally treated in air atmosphere susceptibilities increase sharply between 400 and 530 c indicative of some new ferrimagnetic mineral phase generation both a drop between 540 and 590 c on the heating cycle and a dramatic increase from 590 c to 520 c on the cooling cycle occurred and are well consistent with the characteristic of magnetite a distinct hopkinson type susceptibility peak indicates that hematite is the terminal product if siderite is heated to 700 c over and over it has been revealed in detail that the original inverse magnetic susceptibility fabric contributed by the crystalline anisotropy of siderite in siderite bearing specimens is changed to a normal magnetic fabric during incremental heating over 410 490 c this is a result of dominant contributions from the distribution anisotropy of newly transformed ferromagnetic minerals a strong chemical viscous remanent magnetization could be produced during siderite oxidation in an external field rock magnetic experimental results show that magnetite maghemite and hematite are the transformation products of high temperature oxidation of siderite in air maghemite was not completely inverted to hematite even at temperature as high as 690 c during incremental thermal treatments the mineral transformation processes were confirmed by conventional optical microscopic observation x ray diffractometry and mossbauer spectroscopic analyses these results indicate that the rock magnetic methods used here are reliable and highly sensitive in detecting very small magnetic phase changes in rocks we conclude that these temperaturedependent variations of magnetic properties can be used as criteria for identification of siderite in rocks and sediments furthermore it is clear that great care should be exercised in thermal demagnetization of siderite bearing rocks in paleomagnetic magnetic anisotropy and rock magnetic studies

the volcano electric effect 1 the formation of a magmatic intrusion at depth is responsible for the formation of various thermohydromechanical thm disturbances including the upsurge of shock waves and diffusion of pressure fronts in the volcanic system we couple electromagnetic theory maxwell equations and thermoporoelasticity biot equations to look at the ground surface electrical signature of these thm disturbances the nature of this coupling is electrokinetic i e associated with water flow relative to the mineral framework and the drag of the excess of charge located in the vicinity of the pore water mineral interface the groundwater flow disturbance being related here to the thm disturbances in drained conditions a new set of laboratory data shows that the electrokinetic coupling is very substantial in fractured basaltic and volcaniclastic materials and in scoria with several hundreds of millivolts of electrical potential gradient produced per megapascal of pore fluid pressure variations our theoretical analysis predicts the diffusion of electromagnetic disturbances and quasi static electrical signals these signals can be used as precursors of a volcanic eruption indeed electromagnetic phenomena recorded at the ground surface of a volcanic system once properly filtered to remove external contributions provide a direct and quasi instantaneous insight into the thm disturbances occurring in the heart of the volcanic structure prior and during a volcanic event tomography of the quasi static electrical field is discussed and applied to self potential profiles performed at the piton de la fournaise volcano during the preparation phase of the march 1998 eruption

theory of transient streaming potentials associated with axial symmetric flow in unconfined aquifers summary we present a semi analytical solution for the transient streaming potential response of an unconfined aquifer to continuous constant rate pumping we assume that flow occurs without leakage from the unit below a transverse anisotropic aquifer and neglect flow in the unsaturated zone by treating the water table as a moving material boundary in the development of the solution to the streaming potential problem we impose insulating boundary conditions at land surface and the lower boundary of the lower confining unit we solve the problem exactly in the double laplace hankel transform space and obtain the inverse transforms numerically the solution is used to analyse transient streaming potential data collected during dipole hydraulic tests conducted at the boise hydrogeophysical research site in 2007 june this analysis yields estimates of aquifer hydraulic parameters the estimated hydraulic parameters namely hydraulic conductivity transverse hydraulic anisotropy specific storage and specific yield compare well to published estimates obtained by inverting drawdown data collected at the field site

oxygen isotope analyses of co existing carbonate and phosphate in biogenic apatite a way to monitor diagenetic alteration of bone phosphate abstract the oxygen isotopic composition of phosphate 18 op and structural carbonate 18 oc of hydroxylapatite was determined in 31 bone and tooth samples of modern mammals from different countries these two variables are highly correlate r 2 0 98 and the calculated best fit of linear regression is very similar to the equation calculated from the phosphate and carbonate palaeotemperature equations 1 2 according to previous measurements 3 6 on fossils of different ages from different areas it seems quite improbable to find isotopically altered skeletal remains showing a good correlation between 18 op and 18 oc as is the case with modern samples it therefore seems possible at least in some cases to use these measurements for monitoring fossil bone and tooth diagenetic alteration when a set of points lie on the equilibrium line or close to it the 18 o values could be considered close to the original values in contrast when the points lie to the left or to the right of this line this probably means that the values are diagenetically modified due to interaction with meteoric water or 18 o enriched water respectively

depth determinations of shallow hydrothermal systems by self potential and multi scale wavelet tomography in hydrothermal studies the depth of the hydrothermal system is always required but rarely known via traditional geophysical exploration techniques while previous studies have shown that continuous wavelet transform algorithms applied to self potential data can theoretically determine the depth of the hydrothermal fluids this study uses multi scale wavelet tomography with multiple wavelets field measurements and geophysical models to accurately determine this depth on stromboli waita and masaya volcanoes multi scale wavelet tomography of field measurements gives reproducible depth results supported by independent geophysical measurements and models and accurately locates the main water flow paths at shallow depths unlike other traditional geophysical methods multi scale wavelet tomography using self potential data is a low cost tool to rapidly determine depths of the shallowest hydrothermal structures this approach has the potential to significantly enhance our ability to locate geothermal systems and monitor active volcanoes

the fractal geometry of some stylolites from the calcare massiccio formation italy stylolites are serrated surfaces that form by stress enhanced dissolution though their geometry and morphology reflects their formation and evolution only a few studies have attempted to quantify them here we present results indicating that stylolites in limestone of the calcare massiccio formation jurassic italy are fractal over 4 5 orders of magnitude in spatial bandwidth with an average fractal dimension obtained by spectral and scaled windowed variance analyses clustering at 1 47 some stylolites from the skene cambrian usa and tamar cenomanian israel formations are fractal over 3 orders of magnitude with fractal dimensions of 1 26 and 1 43 these values are high relative to other natural surfaces and reflect the jagged topography of the stylolites preliminary results indicate that the fractal dimension and power are constant throughout the stylolite surface and are not orientation dependent furthermore we show that stylolite contours are fractal too the grain size does not register in our analyses implying that the grain is not a cutoff between processes rather stylolite generating processes operate similarly below and above the grain size our results suggest that the geometry of these stylolites especially at long wavelengths may not be sensitive to the immediate fabric surrounding them

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

time resolved study of charge generation and propagation in igneous rocks electrical resistivity changes ground potentials electromagnetic em and luminous signals preceding or accompanying earthquakes have been reported many times in addition to ground uplift and tilt and other parameters however no concept exists that would tie these diverse phenomena together into a physically coherent model using low to medium velocity impacts to measure electrical signals with microsecond time resolution it is observed that when gabbro and diorite cores are impacted at relatively low velocities 100 m s highly mobile charge carriers are generated in a small volume near the impact point they spread through the rocks causing electric potentials exceeding 400 mv em and light emission as the charge cloud spreads the rock becomes momentarily conductive when a granite block is impacted at higher velocity 1 5 km s the propagation of the p and s waves is registered through the transient piezoelectric response of quartz after the sound waves have passed the surface of the granite block becomes positively charged suggesting the same charge carriers as observed during the low velocity impact experiments expanding from within the bulk during the next 2 3 ms the surface potential oscillates indicating pulses of electrons injected from ground and contact electrodes the observations are consistent with positive holes e g defect electrons in the o2 sublattice traveling via the o 2p dominated valence band of the silicate minerals the positive holes propagate as charge clouds rather than as classical em waves before activation they lay dormant in form of electrically inactive positive hole pairs php chemically equivalent to peroxy links o3x oo xo3 with x si4 al3 etc phps are introduced into the minerals by way of hydroxyl o3x oh which all nominally anhydrous minerals incorporate when crystallizing in h2o laden environments the fact that positive holes can be activated by low energy impacts and their attendant sound waves suggests that they can also be activated in the crust by microfractures during the dilatancy phase depending on where in the stressed rock volume the charge carriers are activated they will form rapidly moving or fluctuating charge clouds that can account for earthquake related electrical signals and em emission wherever such charge clouds intersect the surface high fields are expected causing electric discharges and earthquake lights

experimental diagenesis exploratory results we conducted experiments in which a granular mixture of quartz and labradorite was deformed in compression at elevated temperatures 200 350 c and pressures 100 mpa in the presence of deionized water following initial consolidation of the material by application of the loads at room temperature a second hydrothermal phase of consolidation was observed when the temperature was increased with the loads fixed the strain rate during this hydrothermal consolidation decayed approximately exponentially with time and was accompanied by only minor porosity reduction the sample permeability decreased rapidly during the hydrothermal consolidation and continued to decrease following cessation of the deformation the rate of this self sealing process was a complex function of temperature scanning electron microscopy and microprobe analysis of the indurated post experimental material showed albitization of the feldspar especially in highly deformed regions analysis of post experimental fluids show that si in solution increased with increasing flow and temperature fluid rock equilibrium was not achieved within the short durations of the experiments 50 60 hours our interpretation is that deformation occured by grain boundary sliding aided by solution and reaction at high stress contacts and sealing occurred by precipitation in low stress regions in the throats of pores

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

radio emission associated with rock fracture possible application to the great chilean earthquake of may 22 1960 stress induced piezoelectric fields produce freely propagating electromagnetic radiation when microscopic rock fractures occur in quartz bearing rocks a laboratory study is presented which shows that electromagnetic emissions are produced when microfractures occur in westerly granite a detailed model is presented for the emission process which allows an estimate of the total radiated power from an individual microfracture on the basis of these results a case is presented that an unusual radio emission seen on several widely separated radio astronomy receivers in the northern hemisphere on may 16 1960 was due to a stress induced microfracture along the chilean fault this radio event occurred 6 days prior to the great chilean earthquake of may 22 1960 and may have been a precursor to one of the largest earthquakes of this century

growth of correlated pore scale structures in sedimentary rocks a dynamical model this report explores statistical models and geochemical observations to determine new insights into the formation of sedimentary rock

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

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

short time electrical effects during volcanic eruption experiments and field measurements laboratory experiments on the fragmentation and expansion of magmatic melt have been performed using remelted volcanic rock at magmatic temperatures as magma simulant a specially designed dc amplifier in combination with high speed data recording was used to detect short time electrostatic field effects related to the fragmentation and expansion history of the experimental system as documented by simultaneous force and pressure recording as well as by high speed cinematography it was found that 1 the voltage time ratio of electrostatic field gradients 100 to 104 v s reflects different physical mechanisms of fragmentation and expansion and 2 the maximum voltage measured in 1 m distance 0 1 to 180 v can be correlated with the intensity of the respective processes based on these experimental results a field method was developed and tested at stromboli volcano in italy a 0 8 m rod antenna was used to detect the dc voltage against local ground i e the electrostatic field gradient at a distance of 60 to 260 m from the respective vent upwind position of the detection site was chosen to prevent interference caused by contact of charged ash particles with the antenna a standard 8 hz geophone was used to detect the accompanying seismicity three types of volcanic activity occurred during the surveillance operation two of these could be clearly related to specific electrical and seismical signals a typical delay time was found between the electrical and the seismical signal corresponding to the seismic velocity within the crater deposits using a simple first order electrostatic model the field measurements were recalibrated to the laboratory scale comparison of field and laboratory data at first approximation revealed striking similarities thus encouraging the further development of this technique for real time surveillance operation at active volcanoes

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

electrical properties of zeolitized volcaniclastic materials 1 the interpretation of electromagnetic anomalies associated with volcanic activity requires a good understanding of two rock properties the electrical conductivity and the streaming potential coupling coefficient we measured these properties on 22 consolidated tuff samples containing clays and zeolites typically found in hydrothermal systems or in other areas of high water rock interactions associated with active volcanic areas these rocks exhibit unusually high surface conductivity and electrical cementation exponent 2 5 3 3 these features are explained by the highly complex texture of these rocks due to hydration dissolution processes of the volcanic glass and the formation of clay minerals and zeolites as alteration products at a pore fluid conductivity of 1 0 0 2 s m 1 the streaming potential coupling coefficient ranges from 3 55 to 10 7 mv mpa 1 the zeta potential a key electrochemical property of the pore water mineral interface determined from these measurements at t0 20 c and ph 6 7 and corrected for surface conductivity is 28 8 mv at 0 1 m nacl two clay free samples exhibit a zeta potential 16 5 mv a value associated with zeolites clinoptilolite the temperature dependence of the potential is rather strong with t t0 1 t t0 where 4 2 10 2 c 1 in the temperature range 20 60 c these data are applied to the understanding of large scale self potential anomalies located at the ground surface of miyake jima volcano

a geochemical and geophysical investigation of the hydrothermal complex of masaya volcano nicaragua abstract masaya volcano nicaragua is a persistently active volcano characterized by continuous passive degassing for more than 150 years through the open vent of santiago crater this study applies self potential soil co 2 and ground temperature measurements to highlight the existence of uprising fluids associated to diffuse degassing structures throughout the volcano the diffuse degassing areas are organized in a semi circular pattern and coincide with several visible and inferred surface volcanic structures cones fissure vents and likely consist of a network of buried faults and dykes that respectively channel uprising flow and act as barrier to gravitational groundwater flow water depths have been estimated by multi scale wavelet tomography of the self potential data using wavelets from the poisson kernel family compared to previous water flow models our water depth estimates are shallower and mimic the topography typically less than 150 m below the surface between 2006 and 2010 the depths of rising fluids along the survey profiles remained stable suggesting that hydrothermal activity is in a steady state this stable activity correlates well with the consistency of the volcanic activity expressed at the surface by the continuously passive degassing when compared to previous structural models of the caldera floor it appears that the diffuse degassing structures have an important effect on the path that shallow groundwater follows to reach the laguna de masaya in the eastern part of the caldera the hydrogeological system is therefore more complex than previously published models and our new structural model implies that the flow of shallow groundwater must bypass the intrusions to reach the laguna de masaya furthermore these diffuse degassing structures show clear evidence of activity and must be connected to a shallow magmatic or hydrothermal reservoir beneath the caldera as such the heat budget for masaya must be significantly larger than previously estimated

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

stick slip charge separation and decay measurements of charge separation in rock during stable and unstable deformation give unexpectedly large decay times of 50 sec time domain induced polarization experiments on wet and dry rocks give similar decay times and suggest that the same decay mechanisms operate in the induced polarization response as in the relaxation of charge generated by mechanical deformation these large decay times are attributed to electrochemical processes in the rocks and they require low frequency relative permittivity to be very large in excess of 105 one consequence of large permittivity and therefore long decay times is that a significant portion of any electrical charge generated during an earthquake can persist for tens or hundreds of seconds as a result electrical disturbances associated with earthquakes should be observable for these lengths of time rather than for the milliseconds previously suggested

experimental study on characteristics of surface potential and current induced by stress on coal mine sandstone roof abstract rocks generate voltage and current when subjected to load hence the study of their characteristics is critical to the prevention and management of mine dynamic disasters and their secondary impacts to investigate the characteristics of surface potential and current induced by stress on coal mine sandstone roof an experimental scheme for determining the mechanical electrical characteristics of rocks is constructed the aforementioned system tests the evolution rules of current and voltage generated by the coal mine sandstone roof at different loading rates the formation mechanism and coupling rules with mechanical properties of sandstone are also analysed experimental results show that although loading rates may differ the variations of pressure stimulated current psc and pressure stimulated voltage psv curves are similar throughout the loading process the psc is divided into three stages rapid growth slow growth and peak on the other hand the psv curve exhibits a double peak characteristic the loading rate changes the current and voltage growth rates and peak values when combined with mechanical properties it can be observed that the psc is related to the effective elastic modulus whereas the psv is related to micro crack and macro crack events in rocks the current and voltage generated by the coal mine sandstone roof subjected to load are consistent with stress the mechanical electrical properties of sandstone indicate that the change processes in the psc and psv result from the coupling effects of various mechanisms in the compaction stage these are mainly caused by the piezoelectric effect of sandstone in the elastic plastic deformation stage they are primarily generated by the electric dipoles formed by micro cracks in the sandstone fracture deformation stage the change processes are mainly caused by the crack tip discharge this study provide an experimental basis and practical results that reflect the microscale process and electrical precursors of sandstone fracturing

localized cultural denoising of high resolution aeromagnetic data we show how a denoising technique based on the wavelet transform can be used to deal with localized noise related to dc electrified railway lines this method which performs localized and sharp filtering of cultural noise was applied to high resolution aeromagnetic data acquired in the phlegrean volcanic area southern italy in 1999 and 2001 the helicopter borne survey was aimed at giving new detailed insights into the distribution of the magnetization of the area and therefore into the volcanological characteristics of the region the surveyed area is characterized by the presence of towns buildings and dc electrified railway lines whose magnetic effects influenced the measurements and were responsible for some of the measured anomalies this cultural noise has therefore to be minimized as much as possible in order to allow the data to be interpreted accurately due to the excellent space scale localization properties of the discrete wavelet transform the cultural disturbance was removed very precisely leaving the field in the adjacent areas unchanged

electromagnetic signals associated with stick slip of quartz free rocks abstract we recorded clear transients in the electric and magnetic fields upon sudden slip in stick slip experiments on dry cylindrically shaped quartz free rock specimens of basalt and peridotite with a 30 saw cut representing a fault at confining pressures of up to 120 mpa the amplitudes of the measured electric field signals were always higher at the electrode pair oriented parallel to the strike of the fault than at the pair oriented perpendicular this anisotropy suggests a preferred electric polarization normal to the slip surface the transients in the electric and magnetic fields were observed only when the fault slip occurred by stick slip mode not by a stable mode of the sliding and the amplitudes of the electric field signals increased with increasing stress drop it is suggested that the generation process of the electromagnetic signals is closely related to the characteristic behavior of the fault at the time of the initiation of slip during stick slip events probably with respect to the intensity of the signals we propose that one or both of the following two processes characteristic of the fault at the time of the initiation of slip during stick slip events are essential for the generation of detectable electromagnetic signals rapid slip along the simulated fault and separation of the rock masses across the fault

the hydroelectric problem of porous rocks inversion of the position of the water table from self potential data summary the self potential sp method is a fast and cheap reconnaissance tool sensitive to ground water flow in unconfined aquifers a model based on the use of green s functions for the coupled hydroelectric problem yields an integral equation relating the sp field to the distribution of the piezometric head describing the phreatic surface and to the electrical resistivity contrast through this phreatic surface we apply this model to sp data measured on the south flank of the piton de la fournaise volcano a large shield volcano located on reunion island indian ocean the phreatic surface inverted with the help of the simplex algorithm from the sp data agrees well with the available information in this area one borehole and electromagnetic em data this interpretation scheme which we call electrography has many applications to the crucial problem of water supply in volcanic areas where drilling is expensive

reply to the comment on implications of diagenesis for the isotopic analysis of upper miocene large mammalian herbivore tooth enamel from chad by l jacques n ogle i moussa r kalin p vignaud m brunet and h bocherens palaeogeography palaeoclimatology palaeoecology 266 2008 200 210 n their comment to our recent paper jacques et al 2008 zazzo et al 2009 this issue provide a correction regarding some technical features of one of the isotopic mass spectrometers used in our comparative study it appears that the system used to purify co2 in saskatoon was a dual inlet di and not a continuous flow cf as mistakenly stated as this system was considered as reliable as the other cf used in the comparative study zazzo et al 2009 this issue infer that the isotopic ratios previously measured on heavily contaminated material from a late miocene chadian site toros menalla tm with another di are reliable as well our reply will re evaluate the comparison between cf and di systems in the light of the correction for the system used in saskatoon and discuss the claim that previous isotopic measurements made on chadian material reflect biogenic signatures and were not affected by oxide contamination

implications of diagenesis for the isotopic analysis of upper miocene large mammalian herbivore tooth enamel from chad high resolution chemical and textural investigation of upper miocene mammalian tooth enamel from chad using electron microprobe and scanning electron microscope techniques provide direct evidence of extensive diagenetic alteration when compared with some modern and contemporaneous fossil specimens chemical and textural changes in chadian fossil enamel during fossilization include large amounts of secondary fe si mn and al bearing oxides both as coarse precipitation in cracks and permeating the apatite high fluorine contamination i e apatite alteration ca p cl na and mg depletion and sulphur contamination such diagenetic contamination significantly affects the oxygen and carbon isotope analysis of carbonate in apatite altering the delta o 18 and delta c 13 biogenic signals towards more positive values isotopic alteration is however greater for oxygen than for carbon indeed isotopic analysis of the heavily oxide and s contaminated chadian fossil tooth enamel samples on a classical dual inlet multiprep system versus three continuous flow irms mass spectrometers show great differences in both the delta o 18 and delta c 13 values while the multiprep dual inlet approach provides carbon and oxygen isotopic results that are indubitably altered and generally inconsistent with any biological values isotopic analysis on continuous flow systems which automatically filter out contaminating gases allow to attain or at least greatly approach primary isotopic signals some of the chadian fossil enamel samples analysed in this work come from the very important upper miocene tm266 fossil locality that yielded sahelanthropus tchadensis a k a toumai the oldest member of the hominid clade known so far at this site as in others a few or no other environmental proxies than isotopic analysis of biomaterials are available for palaeoenvironmental and palaeoecological reconstructions therefore to obtain reliable environmental information from the time of this ancient hominid recovering uncontaminated biogenic isotopic signals is crucial and from these results it is now technically possible c 2008 elsevier b v all rights reserved

a model of fossil tooth and bone diagenesis implications for paleodiet reconstruction from stable isotopes abstract diagenesis of structural carbonate in biogenic apatite in the postmortem environment is modeled as a process of water mineral interaction both closed and open system model calculations suggest that 13 c of structural carbonate in biogenic apatite is much more resistant to diagenetic modification than 18 o apatite structural carbonate retains an original 13 c signal in closed system diagenesis for open systems 13 c of biogenic apatite with very low porosity such as tooth enamel can survive most diagenesis and retain a primary isotopic signature on the hand 18 o of structural carbonate in biogenic apatite may not be a reliable indicator of the original isotopic ratios except in a diagenetic system with low temperature and very low water biomineral ratio application of the model to teeth and carbonate cement in sediments from the badlands south dakota illustrates that 13 c values of enamel samples preserve the original signal whereas 13 c values of dentine represent varying extents of diagenesis 18 o values of fossil teeth may record an early or late part of their water biomineral interaction history during diagenesis

short term earthquake prediction current status of seismo electromagnetics abstract loss of human lives as a result of earthquakes is caused overwhelmingly by the collapse of buildings within less than a few minutes of main shocks the most urgent countermeasure consists of two key elements one is strengthening of weak structures and the other is short term earthquake prediction short term prediction needs precursors although some promising precursors are reported the prevailing views in japan and elsewhere are overly pessimistic the pessimism largely roots in the fact that short term precursors are generally non seismic and tools developed for seismology are not designed to detect them nonetheless nationally funded large scale earthquake prediction programs always emphasize the need to reinforce seismometer networks they do not take into account the views of those in the science community who point to the importance of non seismic precursors while there are well founded causes to be skeptical the situation needs to be improved one reason for skepticism is that the observations of precursors have not yet been perfect enough and another is that some important fundamental aspects of non seismic precursors are still unresolved we review some of these problems

localization of self potential sources in volcano electric effect with complex continuous wavelet transform and electrical tomography methods for an active volcano 1 this study concerns the fluid flow circulation associated with magmatic intrusion during volcanic eruptions from electrical tomography studies the objective is to localize and characterize the sources responsible for electrical disturbances during a time evolution survey between 1993 and 1999 of an active volcano the piton de la fournaise we have applied a dipolar probability tomography and a multi scale analysis on synthetic and experimental sp data we show the advantage of the complex continuous wavelet transform which allows to obtain directional information from the phase without a priori information on sources in both cases we point out a translation of potential sources through the upper depths during periods preceding a volcanic eruption around specific faults or structural features the set of parameters obtained vertical and horizontal localization multipolar degree and inclination could be taken into account as criteria to define volcanic precursors

stable isotope compositions of mammoth teeth from niederweningen switzerland implications for the late pleistocene climate environment and diet abstract oxygen and carbon isotope compositions of well preserved mammoth teeth from the middle wurmian 40 70 ka peat layer of niederweningen the most important mammoth site in switzerland were analysed to reconstruct late pleistocene palaeoclimatic and palaeoenvironmental conditions drinking water 18o values of approximately 12 3 0 9 were calculated from oxygen isotope compositions of mammoth tooth enamel apatite using a species specific calibration for modern elephants these 18 o h 2 o values reflect the mean oxygen isotope composition of the palaeo precipitation and are similar to those directly measured for late pleistocene groundwater from aquifers in northern switzerland and southern germany using a present day 18 o h 2 o precipitation air temperature relation for switzerland a mean annual air temperature mat of around 4 3 2 1 c can be calculated for the middle wurmian at this site this mat is in good agreement with palaeotemperature estimates on the basis of middle wurmian groundwater recharge temperatures and beetle assemblages hence the climatic conditions in this region were around 4 c cooler during the middle wurmian interstadial phase around 45 50 ka bp than they are today during this period the mammoths from niederweningen lived in an open tundra like c3 plant dominated environment as indicated by enamel 13c values of 11 5 0 3 and pollen and macroplant fossils found in the embedding peat the low variability of enamel 13c and 18o values from different mammoth teeth reflects similar environmental conditions and supports a relatively small time frame for the fossil assemblage

identification of sources of potential fields with the continuous wavelet transform complex wavelets and application to aeromagnetic profiles in french guiana a continuous wavelet technique has been recently introduced to analyze potential fields data first we summarize the theory which primarily consists of interpreting potential fields via the properties of the upward continued derivative field using complex wavelets to analyze magnetic data gives an inverse scheme to find the depth and homogeneity degree of local homogeneous sources and the inclination of their magnetization vector this is analytically applied on several local and extended synthetic magnetic sources the application to other potential fields is also discussed then profiles crossing dikes and faults are extracted from the recent high resolution aeromagnetic survey of french guiana and analyzed using complex one dimensional wavelets maps of estimated depth to sources and their magnetization inclination and homogeneity degree are proposed for a region between cayenne and kourou

cross coupled flow modeling of coincident streaming and electrochemical potentials and application to subglacial self potential data 1 this study aims to demonstrate that self potential measurements can yield unique information about subglacial drainage conditions which has so far been doubtful at the bed of warm based glaciers arborescent and distributed drainage systems interact and streaming and electrochemical potentials coincide a key secondary aim of this study is therefore the development of a mathematical framework for the analysis of self potentials generated by such interacting flow systems we consider cross coupling between hydraulic electrical and chemical driving forces and apply the resulting model solution to self potential data recorded beneath haut glacier d arolla switzerland we find that 1 the streaming and electrochemical contributions to the total self potential signal can be separated mathematically 2 streaming potentials directly reflect the direction of water flow at the glacier bed 3 combination of streaming potentials with hydraulic conductivity estimates from slug tests allows estimation of in situ subglacial water flow velocities 4 the subglacial zeta potential calculated from estimated values of the streaming coupling coefficient is small 0 022 v due to systematic flushing of clay minerals from the channel area during the melt season and 5 uncertainties in exact electrode location in the borehole are unlikely to produce self potential noise self potential measurements may therefore yield unique information about subglacial drainage conditions and especially the direction and velocity of in situ subglacial water flow are difficult to obtain by other methods we further anticipate that our mathematical framework will be applicable to other areas of subsurface hydrology especially where spatially distributed seepage feeds preferential flow pathways

new insights into the kawah ijen hydrothermal system from geophysical data corentin caudron 1 2 3 guillaume mauri 4 glyn williams jones 5 thomas lecocq2 devy kamil syahbana 6 raphael de plaen 7 loic peiffer 8 alain bernard 3 ginette saracco 9 1 earth observatory of singapore nanyang technological university 50 nanyang av block n2 01a 15 singapore 639798 2 royal observatory of belgium seismology section 3 avenue circulaire 1180 uccle belgium 3 department of earth environmental sciences universite libre de bruxelles 50 ave roosevelt 1050 brussels belgium 4 center for hydrogeology and geothermics university of neuchtel neuchtel switzerland 5 department of earth sciences simon fraser university 8888 university drive burnaby british columbia v5a 1s6 canada 6 centre for volcanology and geological hazard mitigation geological agency ministry of energy and mineral resources jalan diponegoro 57 bandung 40122 indonesia 7 university of luxembourg faculte des sciences de la technologie et de la communication 6 rue richard coudenhove kalergi l 1359 luxembourg 8 instituto de energi as renovables universidad nacional auto noma de me xico privadaxochicalco s n centro 62580 temixco morelos mexico 9 cnrs umr7330 centre europeen de recherche et d enseignement en geosciences de l environnement cerege equipe modelisation aix marseille universite amu europole de l arbois bp 80 13545 aix en provence cedex 4 france ginet cerege fr corresponding author e mail corentin caudron gmail com abstract the magmatic hydrothermal system of kawah ijen volcano is one of the most exotic on earth featuring the largest acidic lake on the planet a hyper acidic river and a passively degassing silicic dome while previous studies have mostly described this unique system from a geochemical perspective to date there has been no comprehensive geophysical investigation of the system in our study we surveyed the lake using a thermocouple a thermal camera an echo sounderand co2 sensors furthermore we gained insights into the hydrogeological structures by combining self potential surveys with ground and water temperatures our results show that the hydrothermal system is self sealed within the upper edifice and releases pressurized gas only through the active crater we also show that the extensive hydrological system is formed by not one but three aquifers a south aquifer that seems to be completely isolated a west aquifer that sustains the acidic upper springs and an east aquifer that is the main source of fresh water for the lake in contrast with previous research we emphasize the heterogeneity of the acidic lake illustrated by intense subaqueous degassing these findings provide new insights into this unique hazardous hydrothermal system which may eventually improve the existing monitoring system

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

precipitation sealing and diagenesis 1 experimental results during burial and diagenesis of granular aggregates significant permeability reduction may be induced by the formation of low temperature authigenic minerals to quantitatively assess the importance of this process we have conducted a series of hydrothermal flow through experiments using deionized water and labradorite quartz sand all experiments were conducted in a modified triaxial apparatus configured to allow continuous permeability measurements under most of the conditions tested significant permeability reduction is observed with no concurrent decrease in porosity the overall permeability reduction sometimes exceeds 1 order of magnitude over 4 days and is positively correlated to temperature and deviatoric stress scanning electron microscope observations together with data from additional experiments show that the observed permeability reduction is entirely a result of secondary mineral growth si and al concentrations in the postexperiment fluids are also correlated to temperature and stress confirming the link between the chemical state of the system and permeability behavior in all experiments permeability reduction is fastest early and levels off in the late stages to explain the permeability behavior as a function of time a conceptual model is developed in which precipitation of authigenic minerals is rapid at early times while dissolution of quartz and labradorite is most active as the system approaches equilibrium the components necessary for secondary mineral formation are liberated at a lower rate thereby causing precipitation to slow although authigenic mineral formation does not reduce total pore space in these experiments there is a reduction in effective porosity which results in permeability reduction

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

tomography of self potential anomalies of electrochemical nature ore deposits and buried metals like pipelines behave as dipolar electrical geobatteries in which the source is due to 1 variation of the redox potential with depth 2 oxido reduction reactions acting at the ore body groundwater contact and 3 migration of electrons in the ore body itself between the reducing and oxidizing zones this polarization mechanism is responsible for an electrical field at the ground surface the so called self potential anomaly a new quick look tomographic algorithm is developed to locate electrical dipolar sources in the subsurface of the earth from the analysis of these self potential signals we applied this model to the self potential anomaly discussed by stoll et al 1995 in the vicinity of the ktb boreholes drilled during the continental deep drilling project in germany the source of this self potential signal is related to the presence of massive graphite veins associated with steeply inclined fault zones within the gneisses and observed in the ktb boreholes

diagenesis and the reconstruction of paleoenvironments a method to restore original δ18o values of carbonate and phosphate from fossil tooth enamel abstract intra tooth 18 o variations within the carbonate 18 oc and phosphate 18 op components of tooth apatite were measured for miocene and pliocene hypsodont mammals from afghanistan greece and chad in order to evaluate the resistance of enamel to diagenetic alteration application of water apatite interaction models suggest that the different kinetic behaviours of the phosphate water and carbonate water systems can be used to detect subtle oxygen isotope disequilibria in fossil enamel when intra individual variations are considered selective alteration of the oxygen isotope composition from the carbonate component of afghan and greek enamels suggests inorganic isotopic exchange processes microbially induced isotopic exchange for phosphate is demonstrated for the first time in enamel samples from chad in association with extensive recrystallization in chad 18 op values were derived from partial isotopic exchange with fossil groundwater during early diagenesis mass balance calculations using average carbonate content in enamel as a proxy for recrystallization and the lowest 18 op value of dentine as a proxy for the isotopic composition of the diagenetic fluid indicate that diagenesis can alter 18 op by as much as 3 in some enamel samples this diagenetic alteration is also responsible for a decrease in intra individual variations of up to 1 in affected specimens the effects of diagenesis on 18 op values of fossil enamel are not systematic however and can only be estimated if sequential 18 op and 18 oc analyses are performed on fossil enamel and dentine reconstruction of large temporal or spatial scale paleoclimates based on 18 op analyses from mammalian teeth cannot be considered valid if enamel has been affected by bacterial activity or if the data cannot be corrected for diagenetic effects

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

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

practical evaluation of steady heat discharge from dormant active volcanoes case study of vulcarolo fissure mount etna italy abstract from a theoretical approach combined with experimental study i propose a method to compute both sensible and latent heat transfer in a thermally active volcanic area this method is applied to a fumarolic thermal fissure located on the south flank on mount etna italy the method involves four steps 1 mapping of self potential sp to quickly identify thermal anomalies 2 mapping of ground temperature t at constant depth in the area defined by sp mapping 3 measurement of vertical t profiles at selected representative stations including the coldest and hottest and 4 direct measurements of vapor flow where the convective heat flux reaches the surface when heat flux values vary in the range 10 300 w m 2 t measurements at a depth equal to about 1 m are sufficient to estimate the absolute flux value to within an absolute error less than 30 and 10 for the relative value ground temperature measurement is an easy and accurate method for estimating heat discharge on a limited surface to define the fissure system monitor time variations of heat flux or to calibrate remote sensing results on the ground

correlating hydrothermal system dynamics and eruptive activity a case study of piton de la fournaise volcano la reunion abstract piton de la fournaise volcano la reunion island is a basaltic shield volcano which underwent an intense cycle of eruptive activity between 1998 and 2008 self potential and other geophysical investigations of the volcano have shown the existence of a well established hydrothermal system within the summit cone the present study investigates the relationship between changes in the hydrothermal system and eruptive activity at the summit cone of piton de la fournaise here we consider the depth of the hydrothermal activity section to be the area where the hydrothermal flow is the most intense along its path ten complete loop self potential surveys have been analyzed through multi scale wavelet tomography mwt to characterize depth variations of the hydrothermal system between 1993 and 2008 our mwt models strongly support the existence of six main hydrothermal flow pathways associated with the main edifice structure each of these pathways is part of the main hydrothermal system and is connected to the main hydrothermal reservoir at depth in both 2006 and 2008 around dolomieu crater based on our results the hydrothermal activity sections are located between 2300 and 2500 m a s l which correlate well with the elevation of the observed fumarole belt within the post 2007 collapse crater wall our results show that the depths of the local hydrothermal activity sections change substantially over the investigated period vertical displacement of the main potential generation area associated with these hydrothermal activity sections is observed on the order of several hundred meters at the transition between the period of quiescence 1993 1997 and the resumption of eruptive activity in 1998 and 2007 respectively from 1999 to march 2008 the hydrothermal system was consistently located at relatively shallow depths by quantitatively determining the vertical displacement of hydrothermal fluids over 16 years we identify a significant link between hydrothermal system and magmatic activity hydrothermal system depth below the surface is an indicator of the activity level pressurization depressurization of the volcano within the shallow magmatic systems thus when used in conjunction with long term volcano monitoring this approach can contribute substantially to detection of the precursory signals of changes in volcanic activity

analytic potentials for the forward and inverse modeling of sp anomalies caused by subsurface fluid flow classical interpretation techniques developed primarily for gravity and magnetic data have been adapted to electric self potential sp data from a recently developed wavelet based technique for potential field interpretation we propose a novel approach for the forward and inverse modeling of sp anomalies caused by subsurface fluid flow we use analytic signals and wavelets associated with the electric and fluid flow potentials fluid flow singularities have typical signatures in the wavelet domain sp data that can be used in the inversion scheme for cases where electrokinetics is unambiguously the origin of sp anomalies our interpretation method provides key parameters of the subsurface fluid flow e g position geometry flow rate to illustrate the theory we consider synthetic 2d flows for which analytic solutions exist and actual sp data acquired around the vulcarolo fissure on mount etna that show sources between 3 to 18 m depths

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