Skip to Main content Skip to Navigation
Theses

Etudes expérimentales et numériques de la propagation d'ondes couplées sismiques et électromagnétiques dans des matériaux saturés non consolidés

Abstract : The first few hundred meters of the subsurface is the seat of important issues related to fluids which society still has to face, such as the detection and monitoring of water ressources and pollution as well as the role of fluids in various types of hazard assessment or in geotechnics. This depth scale is highly complex and heterogeneous in terms of lithology and fluid content. Among the available geophysical methods, seismo-electric (or electro-seismic) coupling phenomena have the potential to emerge as a new high-resolution imaging technique, naturally sensitive to fluid contrasts. Two seismo-electric signals have been predicted and sometimes observed: co-seismic electric signals (high amplitude) and weak electromagnetic (EM) disturbances generated at depth when seismic waves cross an interface. This second phenomenon is the most promising in terms of imaging due to its sensitivity to original contrasts compared to seismic reflection. The emergence of the seismo-electric method was however slowed down due to difficulties in recording these weak seismo-electric signals. Based on the combination of experimental and numerical approaches, this PhD thesis aims at addressing practical questions concerning the acquisition and processing of seismo-electric and electro-seismic data.In the first part, in order to increase the signal-to-noise (S/N) ratio of seismo-electric signals, we theoretically and experimentally study their sensitivity to various electrode arrangements. For this, we developed a filter theory designed to assess the influence of complex electrode arrays for seismo-electric signals acquisition. This theory was successfully confronted to experimental seismo-electric data acquired using various electrode arrangements (namely the spacing between the electrodes, the number of the electrodes and the apparent seismic velocity) and to full waveform numerical simulations. This combined analysis shows that electrode configuration properties strongly influence seismo-electric amplitudes and waveforms. In particular, this approach explains the difficulty in recording depth-generated seismo-electromagnetic waves converted at an interface, when the conventional dipole configuration is used as receivers. We then promote the use of a 3-electrode configuration in seismo-electric measurements, since: 1) it reduces ubiquitous man-made electric noise, and 2) its filtering properties do amplify the EM waves originating from interfaces at depth with respect to dominant coseismic events.In the second part, we focus on the reciprocal electro-osmotic phenomena, i.e. the generation of seismic signals by an electric source in poroelastic saturated media. We first performed numerical investigations to assess the nature and properties of the different seismic arrivals generated by an electrical source in a homogeneous and an heterogeneous material, at the field scale. Then we tried to acquire electro-seismic laboratory data in a homogeneous material, data that we again confronted with numerical full waveform computations. The results show that electro-seismic waves can be observed and that they are locally generated around the electric source. We finally show that these electro-seismic signals are influenced by the fluid conductivity.
Document type :
Theses
Complete list of metadatas

https://tel.archives-ouvertes.fr/tel-01682910
Contributor : Abes Star :  Contact
Submitted on : Friday, January 12, 2018 - 3:47:11 PM
Last modification on : Wednesday, October 14, 2020 - 4:16:26 AM
Long-term archiving on: : Sunday, May 6, 2018 - 7:31:35 PM

File

DEVI_2017_archivage.pdf
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-01682910, version 1

Collections

Citation

Maureen Devi. Etudes expérimentales et numériques de la propagation d'ondes couplées sismiques et électromagnétiques dans des matériaux saturés non consolidés. Sciences de la Terre. Université Grenoble Alpes, 2017. Français. ⟨NNT : 2017GREAU022⟩. ⟨tel-01682910⟩

Share

Metrics

Record views

297

Files downloads

183