[S-CG10_2AM1] Microcracks preceding ruptures in the crust related to earthquakes, volcanic eruptions and landslide

★ [SCG10-03] Seismoelectric phenomena of electrokientic nature associated with the formation of cracks in porous media

*Andre REVIL¹ (1.Colorado School of Mines, department of Geophysics)

Keywords:electrokinetic, streaming current, self-potential, moment tensor, source localization, electromagnetic phenomena

I will describe the physics of the generation of electromagnetic disturbances associated with the formation of cracks in porous media. The mechanism is electrokinetic in nature (i.e., associated with the flow of the pore water with respect to the solid phase of a porous material). I will describe the occurrence of these electromagnetic signals and how they can be inverted jointly with seismic signals to determine the position of the hydromechanical disturbance and its moment tensor. I will also demonstrate that electrical fields of electrokinetic nature are associated with the formation of crack through a set of laboratory experiments (see figure below showing the fluctuation in the electrical potential on the surface of the block and the amount of recorded acoustic emissions). The associated electrical field fluctuations can be remotely monitored and the resulting signals used to localize their causative source. The technique is similar to what is performed in electroencephalography (in the medical world) in which an electrical field (associated with the opening of ionic channels at the synapses between the neurons) can be measured on the scalp of a patient and inverted to localize and monitor brain activity. A laboratory experiment shows how these electrical fields can be recorded at the surface of a cement block during the fracking of the block. The measurements are performed with a research-grade medical electroencephalograph and inverted using the genetic algorithm to localize the causative source of electrical current and therefore localize the evolution of the crack. Two snapshots of electrical signals are used to show how the breakage evolves over time. A second experiment is performed to see if we could localize a pulse water injection from a shallow well in field conditions and in the case of a heterogeneous subsurface.