Earthquake lights: Mechanism of electrical coupling of Earth’s crust to the lower atmosphere

Co-seismic luminescence, commonly referred to as Earthquake lights (EQLs), is an atmospheric luminous phenomenon occurring before and during strong earthquakes. We utilize the assumption that strong 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 source currents for various configurations of current dipoles inside the Earth. The results are supported by approximate formulations allowing effective solution of the same problems using analytical theory. It is shown that a large scale dipole located in Earth’s crust 5 and 15 km beneath the Earth’s surface requires energy significantly higher than the total seismic wave energy in major earthquakes. The most likely setup to produce EQLs is found when the locations of sources are tens of meters beneath Earth’s surface.