Dependence of shear wave seismoelectrics on soil textures: a numerical study in the vadose zone

LAURENCE JOUNIAUX; ZYSERMAN, FABIO IVÁN; LEONARDO MONACHESI

le Corum , Montpellier, France

Congreso; 43rd IAH Congress, Montpellier, Francia ?Groundwater and society: 60 years of IAH?; 2016

IAH- International Association of Hydrogeologists

The seismo-electromagnetic method can be used for non-invasive subsurface exploration. This method is appopriate for detecting fluids such as water, oil, gas, CO2, or ice, and also helps to better characterise the subsurface in terms of porosity, permeability, and fractures. The seismoelectromagnetic method combines seismic and electric methods, with the resolution of the seismics and the sensitivity of the electromagnetic methods to the fluids. However, the challenge of this method is the low level of the induced signals. The purpose of this work is to study seismoelectric conversions generated in the vadose zone, when this region is traversed by a pure SH wave. We assume that the soil is a partially saturated one-dimensional porous media and we use the van Genuchten [1]constitutive model to describe the water saturation profile. Correspondingly, we extend Pride´s formulation [2] as suggested by Warden et al. [3] to deal with partially saturated media, introducing two substantially different saturation dependent functions into the electrokinetic coupling coefficient linking the poroelastic and the electromagnetic wave equations. In order to study the influence of different soil textures we perform a numerical analysis considering, among other relevant properties, the electrokinetic coupling coefficient and coseismic responses (Cos) and interface responses (IR). We observe that the Cos are consistent with analytical results. Moreover, the IR are several order of magnitude stronger than the Cos, and markedly depend on the soil texture and the chosen coupling model. The results obtained suggest that seismoelectric prospection using shear waves could be developed as an useful tool for vadose zone characterization studies. References 1.aa L. Richards, Capillary conduction of liquids through porous mediums. Physics 1, 318?333, 1933. 2.aaS. Pride, Governing equations for the coupled electromagnetics and acoustics of porous media. Phys. Rev. BCondens.Matter 50, 15678?15695, 1994. 3.aaS. Warden, S. Garambois, L. Jouniaux., D. Brito, P. Sailhac, C. Bordes, Seismoelectric wave propagation numerical modeling in partially saturated materials. Geophys. J. Int. 194, 1498?1513, 2013.