JpGU-AGU Joint Meeting 2020

Presentation information

[E] Poster

S (Solid Earth Sciences ) » S-SS Seismology


convener:Luca Urpi, Yusuke Mukuhira(Institute of Fluid Science, Tohoku University), Bogdan Enescu(Department of Geophysics, Kyoto University), Francesco Grigoli(ETH Zurich Swiss Federal Institute of Technology Zurich)

[SSS09-P06] Seismoelectromagnetic conversions generated by a double-couple source in
partially saturated media.

*Sheldon Dwight Warden1, Pascal Sailhac2, Stéphane Garambois3 (1.Hyperion Geophysical Services, 7 rue de Châtenois, 67100, Strasbourg, France., 2.GEOPS (Geosciences Paris Sud), Université de Paris Saclay, 15 Rue Georges Clemenceau, 91400, Orsay, France., 3.ISTerre (Institut des Sciences de la Terre), Université de Grenoble Alpes, 1381 rue de la piscine, 38400, Saint Martin d'Heres, France.)

Keywords:Electrokinetic conversions, Seismoelectric imaging, Induced seismicity monitoring

Seismoelectromagnetic conversions of electrokinetic origin have triggered new interest since

the theory for the coupled propagation of seismic and electromagnetic (EM) waves was

reformulated by Pride (1994). Over the last couple of decades, several modelling programs were

developed to simulate seismoelectromagnetic propagation. Most of these programs share in

common that they only allow to model point sources, well suited to simulate seismic surveys, but

inappropriate when attempting to simulate earthquakes, often described using a double-couple


In this work, we present a program allowing to model the seismoelectromagnetic waves triggered

by a double-couple source, based on the Synthetic Kennett Bouchon Program (SKBP) developed by

Garambois & Dietrich (2002); this program is modified to account for partial saturation conditions

(Warden et al., 2013) and high salinities (Vinogradov et al., 2010). We implement both M13+M31

and M12+M21 geometries. We validate our program by comparing its results with those obtained by

modelling a double-couple source through a numerical derivative and find excellent agreement

between both approaches. We then study the symmetry properties of the waves generated by this

new source type for a homogenous half-space.

We then perform a sensitivity study considering a simple tabular medium consisting of a

homogeneous layer overlying a homogeneous half-space. When considering a source of frequency

fpeak=40Hz of magnitude Mw=1, located 4km below the ground surface and 1.5km below the

boundary between both media, we model coseismic electric field amplitudes of the order of several

hundreds of μV.m−1. Analyzing these amplitudes in the light of magnetotelluric measurements

suggests that even a microearthquake could trigger a coseismic response large enough to be

measured at the ground surface.

We also study the characteristics of the interface response (IR) generated at the boundary between

the two homogenous media for a M13+M31 double-couple and show that this IR consists of a

conversion between an incident S wave and a converted EM wave; its amplitude variations can be

approximated by those of a horizontal dipole located at the boundary. We also quantify the

contributions of the SH and SV polarizations to the total converted amplitude and find that although

the SH waves are coupled to the Transverse Electric (TE) mode, they contribute to the Transverse

Magnetic (TM) mode component of the electric field through the IR.

We conclude our study by considering a more realistic model, designed to approximate the context

of a geothermal field. We also provide examples of possible coseismic signals observed in electric

and magnetic data acquired during geothermal monitoring experiments.