Pre-earthquake signals: Underlying physical processes

Prior to large earthquakes the Earth sends out transient signals, sometimes strong, more often subtle and fleeting. These signals may consist of local magnetic field variations, electromagnetic emissions over a wide range of frequencies, a variety of atmospheric and ionospheric phenomena. Great uncertainty exists as to the nature of the processes that could produce such signals, both inside the Earth's crust and at the surface. The absence of a comprehensive physical mechanism has led to a patchwork of explanations, which are not internally consistent. The recognition that most crustal rocks contain dormant electronic charge carriers in the form of peroxy defects, O3Si/(oo)\ SiO3, holds the key to a deeper understanding of these pre-earthquake signals from a solid state physics perspective. When rocks are stressed, peroxy links break, releasing electronic charge carriers, h(.), known as positive holes. The positive holes are highly mobile and can flow out of the stressed subvolume. The situation is similar to that in a battery. The h(.) outflow is possible when the battery circuit closes. The h(.) outflow constitutes an electric current, which generates magnetic field variations and low frequency EM emissions. When the positive holes arrive at the Earth's surface, they lead to ionization of air at the ground-air interface. Under certain conditions corona discharges occur, which cause RF emission. The upward expansion of ionized air may be the reason for perturbations in the ionosphere. Recombination of h(.) charge carriers at the surface leads to a spectroscopically distinct, non-thermal IR emission. (C) 2010 Elsevier Ltd. All rights reserved.