%0 Journal Article
%T Experimental Validation of the Electrokinetic Theory and Development of Seismoelectric Interferometry by Cross-Correlation
%A F. C. Schoemaker
%A N. Grobbe
%A M. D. Schakel
%A S. A. L. de Ridder
%A E. C. Slob
%A D. M. J. Smeulders
%J International Journal of Geophysics
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/514242
%X We experimentally validate a relatively recent electrokinetic formulation of the streaming potential (SP) coefficient as developed by Pride (1994). The start of our investigation focuses on the streaming potential coefficient, which gives rise to the coupling of mechanical and electromagnetic fields. It is found that the theoretical amplitude values of this dynamic SP coefficient are in good agreement with the normalized experimental results over a wide frequency range, assuming no frequency dependence of the bulk conductivity. By adopting the full set of electrokinetic equations, a full-waveform wave propagation model is formulated. We compare the model predictions, neglecting the interface response and modeling only the coseismic fields, with laboratory measurements of a seismic wave of frequency 500£¿kHz that generates electromagnetic signals. Agreement is observed between measurement and electrokinetic theory regarding the coseismic electric field. The governing equations are subsequently adopted to study the applicability of seismoelectric interferometry. It is shown that seismic sources at a single boundary location are sufficient to retrieve the 1D seismoelectric responses, both for the coseismic and interface components, in a layered model. 1. Introduction The first observation of coupling between electromagnetic and mechanical effects (also known as electroosmosis, which is one of the electrokinetic effects) dates back to the beginning of the 19th century. In 1809, Reuss [1] was the first to report on an experiment where a direct current was applied to a clay-sand-water mixture. The experiment was performed with a U-tube, filled with quartz at the bottom. Application of an electric current caused the water to rise in the leg containing the negative electrode [2]. The electrokinetic effect works as follows. In a fully fluid-saturated porous medium, a charged nanolayer at the solid-liquid interface is present (see Figure 1). The origin of this charged nanolayer lies in the presence of an aqueous solution, typically a negatively charged silane grain surface. The resulting interface potential is called the zeta-potential, which is typically negative and on the order of a few tens of millivolts [9]. The counterions in the fluid reorganize in a layer that is bound to the surface by electrostatic forces (Stern layer) and a diffuse layer that is free to flow. In the diffuse layer two types of physical phenomena are competing, the electrostatic forces between the ions and the Brownian motion of the particles. This effectively results in an exponentially
%U http://www.hindawi.com/journals/ijge/2012/514242/