Abstract
Electrokinetic phenomena are believed to be the most likely origin of electromagnetic signals preceding or accompanying earthquakes. The intensity of the source current due to the electrokinetic phenomena is determined by the fluid flux and the electrokinetic coupling coefficient called streaming current coefficient; therefore, how the coefficient changes before rupture is essential. Here, we show how the electrokinetic coefficients change during the rock deformation experiment up to failure. The streaming current coefficient did not increase before failure, but continued to decrease up to failure, which is explained in terms of the elastic closure of capillary. On the other hand, the streaming potential coefficient, which is the product of the streaming current coefficient and bulk resistivity of the rock, increased at the onset of dilatancy. It may be due to change in bulk resistivity. Our result indicates that the zeta potential of the newly created surface does not change so much from that of the preexisting fluid rock interface.
Highlights
Electrokinetic phenomena occur when an electrolyte flows along charged solid surfaces
It is noted that the observed change in Cc indicates that the source current density did not increase during the deformation, and observed increase in Cp is attributed to bulk resistivity (see (8))
They measured the streaming potential, which was the product of the streaming current density and the specific resistivity of the specimen
Summary
Electrokinetic phenomena occur when an electrolyte flows along charged solid surfaces. For several decades, these phenomena have been of interest to geophysicists in many subfields. Observed self-potential has been associated with geothermal fields (e.g., [1, 2]), volcanic activity and topography (e.g., [3,4,5,6]), and shallow ground water flow (e.g., [7, 8]). Mizutani et al [14] first proposed a model: during dilatancy stage, which is assumed to precede earthquakes [15, 16], pore pressure in the dilatant region decreases and water flows into this region from the surrounding area, generating electromagnetic precursors to earthquakes due to electrokinetic phenomena
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