Earthquake Lights: Mechanism of Electrical Coupling of Earth's Crust to the Lower Atmosphere

Earthquake lights are an atmospheric luminous phenomenon occurring before, during, and occasionally after earthquakes. In the present work we assume that strong electric currents are produced inside the Earth during earthquakes and model the current and field distribution inside and above the Earth to find the conditions where electrical discharges can appear. The simulation results quantify the effects of various configurations of current dipoles inside the Earth. The results are supported by approximate formulations allowing effective solution of the same problems using an analytical theory. It is shown that a large-scale dipole with poles located in Earth's crust at 5 and 15 km beneath the Earth's surface requires energy significantly higher than the total seismic wave energy in major earthquakes. The more likely setup to produce earthquake lights is found to be when the upper pole of the source current dipole is shifted close to the Earth's surface, in particular, when locations of current dipoles are tens of meters beneath Earth's surface.