The role of fluids in generating electric fields associated with seismogenic processes from an electrokinetic perspective

Electrokinetic signals generated by fluid flow or stress loading in seismogenic zones have been proposed as potential earthquake precursors. However, the relative contributions of fluid-driven versus stress-driven mechanisms remain poorly understood. In this study, we extend the quasi-static electrokinetic theory to simultaneously account for both mechanisms and implement it within a modified Luco-Apsel-Chen generalized reflection and transmission method. Simulations of a porous half-space model reveal that fluid injection can generate a vertical electric field up to 33 times stronger than that from shear stress. Under tensile stress conditions, where both stress-driven and fluid-driven mechanisms are included, fluid flow, whether externally imposed or induced by stress, becomes a significant contributor to the generation of electric signals. Importantly, the permeability of the seismogenic layer significantly influences the dominant mechanism, with a transition from stress-dominated to fluid-dominated responses occurring at a permeability threshold of approximately 10 −14.5 m 2 . In a multilayer model incorporating realistic heterogeneity, horizontal electric fields are significantly amplified compared to those from the half-space model. This enhancement arises from a low-permeability barrier above the seismogenic zone, which impedes vertical fluid flow and promotes lateral fluid redirection, a behavior that aligns with the “fault valve” model. These results underscore the importance of accounting for both stress-driven and fluid-driven sources, as well as geologic structure, when interpreting pre-earthquake electrokinetic phenomena. Our findings provide a physically grounded basis for improving the detection and interpretation of geoelectric signals related to the seismogenic process.