Co-seismic Earthquake Lights: The Underlying Mechanism

Earthquake lights (EQLs) have long been considered mysterious natural phenomena, for which no good physical explanation seemed to be available. Crucial to understanding EQLs, in particular the intense flashes of light bursting out of the ground while S waves propagate, is the presence of peroxy defects in igneous rocks, in particular in gabbroic rocks that typically fill the subvertical dykes in regions of past extensional tectonics. The peroxy defects tend to locate along grain boundaries or may even link adjacent mineral grains, making them highly susceptible to ever so slight displacements of mineral grains. Thus, the passage of an S wave will instantly activate peroxy bonds. If the number density of the stress-activated peroxy is so high that their delocalized wave functions overlap, the entire rock volume must instantly expand, supported from within by an electronic degeneration pressure. This process will be followed by a momentary dissociation of the peroxy defects, generating e′ and h· charge carriers, causing the volume to instantly contract again, at least partly. If an electric discharge can burst out from the top of the dyke, removing some of the charge carriers and generating an EQL, an additional volume contraction can be expected occur.