measurement of the seismoelectric response from a shallow boundary field experiments carried out at a site near vancouver canada have shown that a shallow lithologic boundary can be mapped on the basis of its seismoelectric response as seismic waves cross the boundary between organic rich fill and impermeable glacial till they induce electric fields that can be measured at the surface with grounded dipole receivers sledgehammer and blasting cap seismic sources positioned up to 7 m away from the interface have produced clear seismoelectric conversions two types of seismoelectric signals are observed the primary response is distinguished by near simultaneous arrivals at widely separated receivers its arrival time is equal to the time required for a seismic p wave to travel from the shotpoint to the fill till boundary on the surface its maximum amplitude about 1 mv m is measured by dipoles located within a few meters of the shotpoint at greater distances the amplitude of the primary arrival decays rapidly with offset and secondary seismoelectric arrivals become dominant they differ from the primary response in that their arrival times increase with dipole offset and they appear to be generated in the immediate vicinity of each dipole sensor our studies show that the responses cannot be attributed to piezoelectricity or to resistivity modulation in the presence of a uniform telluric current we infer that seismically induced electrokinetic effects or streaming potentials are responsible for the seismoelectric conversion and a simple electrostatic model is proposed to account for the two types of arrivals although our experiments were small in scale the results are significant in that they suggest that the seismoelectric method may be used to map the boundaries of permeable formations

borehole electrokinetic responses in fracture dominated hydraulically conductive zones electrokinetic borehole logging experiments conducted in fracture dominated devonian metasediments and carboniferous limestone boreholes containing dissolu tion discontinuities indicate a strong relative amplitude correlation between a downhole electrokinetic response and previously obtained hydrogeological data for the respective boreholes voltages in the range 0 2 1 5 volt were recorded per mpa of gauge pressure induced in the borehole fluid a relationship between fracture aperture and the frequency content of the electrical data has also been observed

impact of indus river discharge on productivity and preservation of organic carbon in the arabian sea over the twentieth century marine high productivity zones along the continents are of great economic importance and they account for most organic carbon burial the carbon cycle in many coastal zones is influenced by the sediments and dissolved nutrients introduced by rivers however there is little direct evidence for a regional marine response to changes in river dynamics here we present a suite of high resolution records of organic and inorganic paleoceanographic proxies which together demonstrate that past changes in indus river discharge have strongly affected productivity patterns in the coastal northeastern arabian sea anthropogenic activity including the building of dams and irrigation facilities during the past century has drastically decreased the discharge rate of the indus river between a d 1890 and 1998 the period over which this reduction occurred primary productivity off the pakistan coast seems to have decreased by more than one third over the same period the regional oxygen minimum zone weakened increasing the supply of oxygen to the sediments leaving the expected imprint on a suite of redox sensitive elements and reducing the preservation of organic matter

numerical analysis of seismoelectric wave propagation in spatially confined geological units using numerical modelling we investigate the evolution of seismoelectric effects induced by seismic excitation in spatially confined lithological units typical geometries represent clay lenses embedded in an aquifer or petroleum deposits in a host rock in fluid saturated rocks seismic waves can generate electromagnetic fields due to electrokinetic coupling mechanisms associated with such processes in the vicinity of the fluid mineral interface two seismoelectric phenomena are investigated 1 the co seismic field associated with the seismic displacement at each point in a subsurface and 2 the interface response generated at layer boundaries our modelling uses a simplified time domain formulation of the coupled problem and an efficient 2d finite element implementation to gain insight into the morphogenetic field behaviour of the seismoelectric effects several numerical simulations for various target geometries were treated accordingly we varied both the thickness of the confined units and the value of the electrical bulk conductivity in porous media analysis of these effects shows differences between interface responses for electrically conductive versus resistive units so the pertinent contrast in electrical bulk conductivity controls the shape and structure of these seismoelectric conversion patterns moreover the seismoelectric interface response captures both the petrophysical and geometrical characteristics of the geological unit these models demonstrate the value of using seismoelectric interface response for reservoir characterization in either hydrogeological or hydrocarbon exploration studies

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

vertical seismoelectric profiling in a borehole penetrating glaciofluvial sediments 1 seismoelectric signals have been measured as a function of depth in a borehole penetrating glaciofluvial sands silts and glacial till using a broadband surface seismic source and a downhole electrode array transient electric field pulses with amplitudes of 1 to 4 v m accompanied the arrival of seismic p waves at the electrodes but no simultaneous interfacial signals were observed above the noise floor of approximately 0 2 v m the co seismic effect was strongest in a sand and gravel layer where its amplitude is consistent with the predictions of a simplified theoretical model normalization of the amplitude logs by measurements of seismic particle velocity and electrical conductivity enhanced their sensitivity to changes in lithology and porosity the results of this experiment suggest that co seismic seismoelectric effects show potential as a porosity permeability logging tool in the borehole environment

geophysical applications of electrokinetic conversion in volume 1 of geophysics 1936 r r thompson of humble oil and refining company proposed that the coupling of seismic and electrical energy can be used as an exploration tool subsequent efforts were directed toward using electric field antennas as geophones small scale studies concluded that antennas are not as sensitive as conventional geophones and their response is highly variable depending on the local soil conditions by 1959 martner and sparks of pan american petroleum reported in geophysics a systematic study of seismoelectric coupling using explosives at various depths their results were the first to show that the conversion of seismic to electromagnetic energy at the water table could be detected using surface antennas no studies have systematically explored the full potential of electroseismic methods using the same level of experimental sophistication used in seismic exploration

using borehole electroseismic measurements to detect and characterize fractured permeable zones in 1996 we measured stoneley wave induced electrical fields in an uncased water well drilled in fractured granite and diorite near hamilton massachusetts stoneley waves generated by sledgehammer blows to the surface casing produced a flow of pore fluid in permeable zones intersected by the borehole in turn this flow induced a streaming electrical field even though these electrical signals were very small tens of microvolts we were able to detect them using electrodes placed in the borehole after power line and telluric signals were canceled by remote referencing and notch filtering amplitude analysis of the electrical fields confirmed that they were induced by fluid flow in the fractured formation the normalized amplitudes of these electrical fields correlate with the fracture density log and agree with the theoretical model for this electroseismic phenomenon our biot theory based model predicts that borehole electroseismic measurements can be used to characterize permeable zones according t

active seismoelectric exploration of glaciers 1 repeatable and strong seismoelectric signals were recorded on glacier de tsanfleuron switzerland using a vertical sounding geometry electromagnetic waves are inferred to be generated by electrokinetic conversion of seismic energy within the snow pack and near the dry wet ice and ice bed interfaces a simple gradient based scheme allows such electrokinetic interface responses eirs to be isolated from noise eirs depend sensitively on the azimuthal orientation of the receiving array of electrical dipoles seismoelectric techniques promise to allow mapping even of thin water bearing strata within or beneath glaciers or frozen ground estimation of hydraulic or fluid properties of such strata as well as monitoring of ice fracturing or basal properties and processes at improved spatial resolution

anatomy of a seismoelectric conversion measurements and conceptual modeling in boreholes penetrating a sandy aquifer 1 conversions of compressional seismic waves to electric fields have been measured in two boreholes drilled in an unconfined sandy aquifer on the gnangara mound near perth australia the seismoelectric conversions at both field sites occurred in the vicinity of the water table at 13 m depth and yielded maximum amplitudes of 1 v m using a sledgehammer source on surface partially cemented layers inferred from geological and geophysical logs straddle the water table and may play a role in generating the conversion and influencing its amplitude distribution the dense vertical sampling used in these borehole experiments reveals spatial and temporal polarity reversals of the interfacial signal which provide new evidence in support of the conceptual model for seismoelectric conversions at interfaces we demonstrate that the growth rate of the source zone and its maximum vertical extent below the water table are encoded in the polarity of the interfacial signal these experiments confirm that vertical seismoelectric profiling can be used to gain further insight into seismoelectric conversions and characteristics of interfaces that makes them amenable to detection

electroseismic and seismoelectric measurements of rock samples in a water tank an electromagnetic em or seismic wave can induce seismic or em waves because of the electrokinetic conversion based on the electric double layer in a fluid saturated porous medium we tested a new method for observing electroseismic and seismoelectric conversions in rock samples our method is designed to overcome the shortcoming of previous attempts to separate signals generated by a continuous electric or seismic source in a small container we first observed acoustic fields around electrodes excited by an electric pulse in a water tank or in a water saturated porous sample in our approach we immersed rock samples in a water tank and measure the seismic or electric responses using electric or acoustic pulses conveyed through the immersed electrodes or hydrophone we measured electroseismic and seismoelectric frequency responses in berea sandstone and westerly granite samples at a frequency range of 15 150 khz the measurements clearly separate the effects of the electric source background noises

an analytical solution to assess the sh seismoelectric response of the vadose zone fil monachesi leonardo bruno universidad nacional de rio negro sede alto valle instituto de investigaciones en paleobiologia y geologia argentina consejo nacional de investigaciones cientificas y tecnicas argentina

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

seismoelectric imaging of the vadose zone of a sand aquifer we have acquired a 300 m seismoelectric section over an unconfined aquifer to demonstrate the effectiveness of interfacial signals at imaging interfaces in shallow sedimentary environments the seismoelectric data were acquired by using a 40 kg accelerated weight drop source and a 24 channel seismoelectric recording system composed of grounded dipoles preamplifiers and seismographs in the shot records interfacial signals were remarkably clear they arrived simultaneously at offsets as far as 40 m from the seismic source the most prominent signal was generated at the water table at a depth of approximately 14 m and had peak amplitudes on the order of 1 v m a weaker response was generated at a shallower interface that is interpreted to be a water retentive layer the validity of these two laterally continuous events and of other discontinuous events indicative of vadose zone heterogeneity is corroborated by the presence of reflections exhibiting similar characteristics in a ground penetrating rada

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