Rethinking Electrokinetic Signals Before Earthquakes: Insights from Finite-Fault Modeling

Summary Electrokinetic signals generated by coupled stress–fluid processes are increasingly recognized as indicators of fault-zone dynamics prior to earthquakes. However, their interpretation is often limited by the common reliance on point-source approximations, which neglect the inherently distributed nature of stress accumulation and fluid migration along fault planes. Here, we develop a quasi-static finite-fault electrokinetic framework in which coupled stress and fluid perturbations are represented as spatially distributed, time-evolving sources. The approach combines an extended Luco–Apsel–Chen generalized reflection and transmission method with a point-source superposition scheme, enabling efficient simulation of electrokinetic responses to area sources in layered porous media. Numerical results reveal that the horizontal components of geoelectric fields in the coupled stress–fluid system are highly sensitive to fluid-source geometry, whereas vertical components primarily reflect stress loading. Spatial variability in initiation time, arising from finite-rate fluid migration, further introduces waveform complexity, amplitude modulation, and multi-stage temporal evolution in surface signals. Notably, we find that the directional variations of the geoelectric field provide a robust diagnostic for distinguishing fluid-driven from stress-induced signals, with angular misalignments reaching up to 16.6°. These results establish a quantitative framework for interpreting near-fault electrokinetic signals and for guiding monitoring strategies aimed at constraining fault-zone fluid pathways and stress evolution.