The mechanisms of seismo-electromagnetic phenomena remain largely unexplained. To address this issue, we introduce a fault model that takes account of a coupled interaction between earthquake nucleation and deep Earth gases. This interaction causes a negatively electrified gas flow due to an exo-electron attachment reaction, as the gases pass through fractured asperities. This transient activity may be regarded to be a pressure-impressed electric current generator. In the model, the current and frequency are formulated as functions of earthquake parameters. The estimated current is sufficient to explain the seismic electromagnetic signals observed at ground level. A physical model of how current generation is coupled with ionospheric electromagnetic disturbances is explained in terms of magnetic induction coupling for strong offshore earthquakes, which may provide a plausible explanation of observed ionospheric electron enhancement prior to some recent offshore earthquakes. The model also suggests that geomagnetic observations close to an epicentre of a strong offshore earthquake may provide an effective means of detecting clear and identifiable precursor signals.