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Conversions sismo-électromagnétiques en milieux poreux

Sheldon Warden 1
1 IPGS-GE - Géophysique expérimentale (IPGS)
IPGS - Institut de physique du globe de Strasbourg
Abstract : A seismic wave passing through a uid-containing porous medium creates a relative motion between the uid and solid phases. By moving the excess ions in the electrical double layer, this relative motion creates a streaming current. This electrokinetic phenomenon, occurring at the micro scale, generates at least two types of seismoelectro- magnetic conversions that can be measured at the macro-scale. On one hand, it gives birth to coseismic electromagnetic elds accompanying the seismic disturbance. On the other hand, when a seismic wave crosses an interface between two media of di erent mechanical, electrical or hydrological properties, it creates a streaming potential imbalance at the interface, acting as a dipolar electromagnetic source. The resulting interface reponses travel at electromagnetic velocities and are measured almost simultaneously by all receivers. This thesis aims to improve our understanding these phenomena and develop geophysical imaging techniques based on seismoelectromagnetic conversions. Two areas of work are explored. The rst encompasses seismoelectromagnetic data processing, especially the extraction of interface responses, which may provide information about the subsurface at depth. We compare the in uence of several ltering techniques on the amplitudes and waveforms of the interface responses. We also introduce a new wave separation technique in the curvelet domain, taking advantage of the similarity between seismic and coseismic data. Furthermore, the theory for the coupled propagation of seismic and electromagnetic waves is restricted to saturated porous media. We extend it here to partially saturated media for the case of a water/air mixture, deriving the e ective mechanical properties of the medium and expressing the electrical conductivity, the dielectric permittivity and the seismoelectric coupling as a function of water saturation. We adapt a seismoelectromagnetic wave modelling program based on the general re ectivity method to unsaturated conditions. Abstract : Keywords : Near surface geophysics - Seismoelectromagnetic signals - Porous media - Wavelets - Wave separation - Numerical modelling - Unsaturated media
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Submitted on : Friday, October 11, 2013 - 12:17:00 PM
Last modification on : Friday, April 5, 2019 - 8:22:15 PM
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  • HAL Id : tel-00872157, version 1

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Sheldon Warden. Conversions sismo-électromagnétiques en milieux poreux. Géophysique [physics.geo-ph]. Université de Strasbourg, 2012. Français. ⟨tel-00872157⟩

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