Electric dipoles perpendicular to a stick-slip plane

Stick-slip tests of pre-cut quartz pegmatite cylinders under tri-axial compression were conducted with a solenoid or toroidal coil near or surrounding the stick-slip plane. The solenoid coil detected damped oscillating signals during stick-slip events. The toroidal coil detected similar oscillations but on an exponential decay. The damped oscillating component is the induced electromotive force (emf) voltage due to piezoelectric polarizations of individual quartz crystals or due to the Earth's magnetostatic field when the coils vibrate. The exponentially decaying component is the induced emf voltage due to electric dipoles approximately perpendicular to the stick-slip plane. These perpendicular dipoles can be explained by the formation of surface charges on separate asperities. The exponential decay of the perpendicular dipoles is due to exponential diffusion and recombination of the separate charges. Electric dipoles on separated asperities may also exist on the geophysical scale: on fault planes during faulting. (c) 2006 Elsevier B.V. All rights reserved.