Understanding the seismoelectric interface response is important for developing seismoelectric field methods for oil exploration and environmental/engineering geophysics. The existing seismoelectric theory has never been validated systematically by controlled experiments. We have designed and developed an experimental setup in which acoustic-toelectromagnetic wave conversions at interfaces are measured. An acoustic source emits a pressure wave that impinges upon a porous sample. The reflected electric-wave potential is recorded by a wire electrode. We have also developed a full-waveform electrokinetic theoretical model based on the Sommerfeld approach and have compared it with measurements at positions perpendicular and parallel to the fluid/porous-medium interface.We performed experiments at several salinities. For 10 -3 and 10 -2 M sodium chloride (NaCl) solutions, both waveforms and amplitudes agree. For 10 -4 M NaCl, however, amplitude deviations occur. We found that a single amplitude field scaling factor describes these discrepancies. We also checked the repeatability of experiments. The amplitudes are constant for the duration of an experiment (1-4 hours) but decrease on longer time scales $24 hours ð Þ . However, the waveforms and spatial amplitude pattern of the electric wavefield are preserved over time. Our results validate electrokinetic theory for the seismic-to-electromagnetic-wave conversion at interfaces for subsurface exploration purposes.

A full-waveform seismoelectric numerical model incorporating the directivity pattern of a pressure source is developed. This model provides predictions of coseismic electric fields and the electromagnetic waves that originate from a fluid/porous-medium interface. An experimental setup in which coseismic electric fields and interface responses are measured is constructed. The seismoelectric origin of the signals is confirmed. The numerically predicted polarity reversal of the interfacial signal and seismoelectric effects due to multiple scattering are detected in the measurements. Both the simulated coseismic electric fields and the electromagnetic waves originating from interfaces agree with the measurements in terms of travel times, waveform, polarity, amplitude, and spatial amplitude decay, demonstrating that seismoelectric effects are comprehensively described by theory.

We designed and developed an experimental setup in which acoustic to electromagnetic (EM) wave conversions at interfaces can be measured. Theoretical results are obtained with an electrokinetic full-waveform theoretical model, where use was made of the Sommerfeld approach. Using bimodal samples, different luid-solid interface effects and saturating luids were investigated. The contrast between water and water-saturated porous glass samples is larger than the contrast between water and oil-saturated porous glass samples. The contrast between water and water-saturated Fontainebleau sandstone is larger than the contrast between oil and watersaturated Fontainebleau sandstone.Abbreviations: EM, electromagnetic; EDL, electric double layer.When luid low occurs in a luid-saturated porous medium, electrokinetic efects can occur. he origin of these efects lies in a charged nanolayer that is present at the solid-liquid interface: the electric double layer (EDL) (Stern, 1924). Silane molecules at the grain surfaces are subject to deprotonization when brought in contact with an electrolyte, and the grain surface thus becomes negatively charged. he excess charge in the luid is redistributed. We can distinguish the so-called Stern layer, consisting of counterions in the luid that are bound to the grain surface by electrostatic forces, and a difuse layer that is free to low (for more details, see, e.g., Overbeek, 1952;Davis et al., 1978). A socalled zeta potential (z) is formed at the interface of the EDL and the bulk luid, which is typically on the order of a few tens of millivolts (Lowrie, 2007). he potential Y in the bulk luid decreases exponentially when one moves away from the interface (Pride, 1994). he characteristic decay length in the luid is the Debye length, describing the balance between electrostatic forces and thermal difusivity (Masliyah and Bhattacharjee, 2006). For reasons of convenience, Y = z is usually deined at the solid-liquid boundary instead of on the EDL-bulk luid interface. When no pressure forces are applied, the system is in equilibrium. However, when, for example, a compressional wave propagates through a luid-saturated porous medium, pressure gradients will be created on the scale of the wavelength. he resulting hydraulic low will transport the counter ions relative to the immobile, bound charge. In this way, counter ions accumulate in pressure troughs and bound charge becomes exposed in pressure peaks. his creates the so-called co-seismic EM ield that propagates along with the seismic wave. We note that within a propagating compressional wave in a homogeneous material, there is no net electric current. he electric ield generated by the relative motion of the counter ions with respect to the bound charge drives a conductive current that exactly balances the electric current induced by the hydraulic low. For interfaces, however, this is no longer the case. When a compressional or shear wave traverses an interface with a contrast in electrical or mechanical properties, an electric current imbalance is...

Coupled seismic and electromagnetic (EM) wave effects in fluid-saturated porous media are measured since decades. However, direct comparisons between theoretical seismoelectric wavefields and measurements are scarce. A seismoelectric full-waveform numerical model is developed, which predicts both the fluid pressure and the electric wavefields in a fluid in which a porous disc is embedded. An experimental setup, in which pressure and electric signals in the fluid are simultaneously measured, is presented. The setup allows the detection of the EM field that is generated when an acoustic wave crosses the interface between the fluid and the thin porous disc, without interference of electrical fields that are present within seismic body waves. The predicted pressure wavefield agrees well with the measurements in terms of acoustic wave travel times, waveforms, and amplitudes. The electric wavefield predictions agree with the recordings in terms of travel times, waveforms, and spatial amplitude decay. A discrepancy in amplitude of the converted EM signal is observed. Theoretical amplitudes that are smaller than the measurements were also reported in previous literature. These results seem to validate seismoelectric theory.