Independent sets of reflection seismic and seismoelectric data were collected, processed, and interpreted with the aim of generating and studying guided waves within a fault zone. While seismic surveys have recently been utilized to investigate fault zones, past and current seismoelectric experiments have been more focused on identifying lithological interfaces and the presence of fluids within the shallow subsurface. The utilization of a fault structure to study seismoelectric conversions associated with guided waves has not hitherto been reported in the literature. The purpose of this research is to investigate the capabilities of the seismoelectric geophysical method to image fault structures, and to compare these to the capabilities of the conventional reflection seismic technique. I hypothesize that the presence of subsurface fluids will enhance seismoelectric imaging of a fault system. My results show that seismoelectric data contribute significant new for fault zone characterization and subsurface. I collected seismic and seismoelectric data sets across a fault system in the Llano Uplift of central Texas. The seismic reflection data were collected with a Geometrics Strataview seismograph equipped with 36 geophones. The seismoelectric data utilized three Geometrics Geode seismographs, with electric fields recorded by stainless steel dipole pairs instead of geophones. A sledgehammer and an accelerated weight drop provided the seismic energy sources throughout the experiment. Elementary processing techniques were applied to both data sets to enhance the signal to noise ratio. Seismic reflection studies previously have been shown capable of identifying fault zones through the characterization of guided waves. The seismoelectric phenomenon has not yet been utilized for this purpose. Identification of fault-zone trapped waves within each data set was attempted separately before the two data types were qualitatively compared as to their relative capabilities for illuminating the fault zone. The seismic data revealed dispersive energy packets, indicative of guided waves, within the fault zone and absent in the surrounding lithologies. The seismoelectric data was able to produce comparable signals in the fault zone showing guided waves.

La propagation sismique dans les milieux poreux est classiquement associée à des phénomènes de dispersion et d’atténuation des ondes sous l’effet des mouvements fluides. Dans certaines conditions, celle-ci peut également être associée à une conversion d’énergie sismique en énergie électromagnétique dite « sismoélectrique ». La théorie des phénomènes sismoélectriques combinant la théorie de l’électrocinétique à la poroélasticité de Biot, repose en grande partie sur les développements de Pride (1994). Sur la base de ces développements théoriques, Pride et Haartsen (1996) relient le champ électrique cosismique à l’accélération sismique qui le génère par une fonction de transfert. Nous proposons une étude quantitative des couplages sismoélectriques en vue de valider la théorie de Pride et sa généralisation en milieu non saturé. Dans ce but, nous avons développé une expérience en laboratoire sur un sable de quartz non-consolidé, menée dans la gamme du kilohertz sur la base d’un dispositif d’acquisition électrique modulable. Deux méthodes de traitement des signaux sont proposées, l’une temporelle, l’autre spectrale, permettant d’obtenir une analyse complète des vitesses de phase, atténuations et fonctions de transfert. Les expériences réalisées se sont focalisées sur l’étude du rôle de la conductivité du fluide et de la saturation en eau dans le phénomène sismoélectrique cosismique. Une étude time-lapse a ainsi pu être réalisée dans des situations de changements de salinité et de teneur en eau. Dans tous les contextes, l’étude quantitative des rapports d’amplitudes des champs sismoélectriques et sismiques E/ü montre une bonne corrélation avec les prédictions théoriques. Par ailleurs, l’étude des variations de saturation dans une gamme allant de la saturation résiduelle en eau (Sw = 0.3) à la saturation totale, montre que: i) les atténuations et fonctions de transfert ont des comportements reliés à la distribution des fluides qui influencent fortement les propriétés mécaniques du milieu ; ii) une inversion de polarité du champ sismoélectrique peut être observée dans le cas très particulier des milieux non consolidés. / Seismic propagation within porous media is usually associated with wave attenuation and dispersion phenomena related to fluid flow. Under certain circumstances, it may also be correlated to a conversion of seismic into electromagnetic energy known as “seismoelectric”. The understanding of seismoelectric phenomena, combining the theory of electrokinetic to Biot’s poroelasticity, relies mainly on the formulation by Pride (1994). On basis of these theoretical developments, Pride and Haartsen (1996) defined a transfer function expressing the link between the coseismic seismoelectric field and the seismic acceleration at its origin. We propose a quantitative analysis of coseismic seismoelectric couplings with the purpose of validating Pride’s theory and generalizing it to partially saturated media. With this aim in view we developed a laboratory experiment involving an adjustable device for electric acquisitions, conducted within the kilohertz range on unconsolidated quartz sand. Experimental data were subsequently processed in both time and frequency domains, enabling a full analysis that embraces phase velocities, attenuations and transfer functions. The conducted experiments focused on the impact of fluid conductivity and water saturation with regard to the coseismic seismoelectric phenomenon. Time-lapse monitoring were accordingly run under varying salinity or water content. In all scenarios, the quantitative analysis of the electric-to-seismic amplitude ratio E/ü appeared in good agreement with theoretical projections. Moreover, investigations of saturation variations, ranging from the residual water saturation (Sw = 0.3) to full saturation, showed that: i) the behavior of attenuations and transfer functions are directly related to fluid distribution, that greatly impacts the mechanical properties of the medium; ii) in the very peculiar case of unconsolidated media, polarity inversion of the coseismic seismoelectric field may be experienced.