Earthquake Lights and Estimates of Electric Fields and Currents

Luminous phenomena were observed during a number of earthquakes, e.g. the 1995 Kobe earthquake in Japan. Estimates based on the eyewitness's reports show that to produce lightning-type and corona-type discharges in the air the electric charge delivered to the ground surface should be of the order of several Coulomb. We assume that this charge was formed and transported by "mechanically produced current" flowing through the fault. The most difficult problem is why these charges survive in the highly conductive soil. The electric conductivity may drastically decrease due to heating and evaporation of water, but only in a thin central part of the fault, while the width of the luminous zone, and thus the width of the zone with high electric field strengths is of the order of hundred meters or even several km. So we propose the mechanism of charge localization - the so-called skin effect. Spreading of the currents and charges is described by a system of diffusion-type electromagnetodynamic equations. There are various models of rupturing during earthquakes. In the wrinkle-like self-healing pulse model the porosity and hydraulic and electric conductivity increase at the leading edge of the ruptured segment and decrease at the trailing edge. Assuming the electrokinetic mechanism as the most effective one we find that the charged fluid flows from these wedge-like ends of the ruptured segment to its center. The two currents flowing in the opposite direction produce magnetic fields with opposite rotation and reconnection due to magnetic diffusion decreases magnetic signals at large distances from the source region. Co-seismic electric and magnetic signals obtained during the Kobe earthquake at two stations at distances of about 100 km from the epicenter do not contradict our estimates and 3D numerical simulations based on our model of electric currents, magnetic fields and mechanical processes of rupturing. We suggest that similar current system may be formed even in the cases when earthquake lights are absent. So investigation of electromagnetic phenomena may give insight into the mechanical processes.