Electrification of the Atmosphere by the Underground Sources Causing Lightnings and Corona Discharges

An estimate of the electric charges, fields and currents at the atmosphere/Earth boundary and near it is given basing on the analyses of the published data gathered during and after the 17 January 1995 strong (magnitude 7.2) and shallow (17.2 km) earthquake in Kobe, Japan: on the luminous effects (lightnings and luminous volumes expanding and rising from the ground); measurements of electric conductivity across the fault; determination of strength and porosity of the samples obtained by drilling the ground down to the depth of about 1.8 km and some other. Numerical simulations are based on the specially developed 3D code taking into account nonuniform conductivity and mechanical separation of charges in the fault zone and motion of ions both in the ground and in the atmosphere under the action of transient electric fields. The existence of high electric fields for about 1-100 seconds (in spite of high conductivity in the ground, especially in a wide "crushed" zone around the central part of the fault) is the continuous generation and separation of electric charges during the continuous or "start-stop" type displacement the fault walls with the duration of each charging pulse of about 1-10 ms. The width of this zone with high electric fields, sufficient for production of lightnings and corona discharges in the atmosphere, is about several km. It is defined by processes of electric diffusion of the electric charges (upwards along the fault and in the lateral directions from the fault) through the ground and production of new and motion of preexisting atmospheric ions above the ground. The length of this zone is the length of the fault (i.e. in that case about 10-30 km). The estimated charge at the ground surface before lightning discharge is about several Coulombs, that is the value typical for a small thundercloud. In our case the lightnings and other types of earthquake lights are ignited by the underground sources.