Impact of water saturation on seismoelectric transfer functions: a laboratory study of coseismic phenomenon

Clarisse Bordes (1) , P Sénéchal (1) , Julien Barrière (1) , Daniel Brito (1) , Eric Normandin (2) , Damien Jougnot (3)

1 LFCR - Laboratoire des Fluides Complexes et leurs Réservoirs
2 IPREM - Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux
3 METIS - Milieux Environnementaux, Transferts et Interactions dans les hydrosystèmes et les Sols

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.

Mots clés: Electrical properties; Hydrogeophysics; Wave propagation

Domaines: Géophysique [physics.geo-ph]

Clarisse Bordes, P Sénéchal, Julien Barrière, Daniel Brito, Eric Normandin, et al.. Impact of water saturation on seismoelectric transfer functions: a laboratory study of coseismic phenomenon. Geophysical Journal International, 2015, pp.1317-1335. ⟨10.1093/gji/ggu464⟩. ⟨hal-01147905⟩