Electromagnetic emission accompanying fracture of quartz‐bearing rocks

Abstract

Fracture of quartz‐bearing rocks and other hard piezoelectric materials is associated with radio frequency (RF) electromagnetic emission that can be readily detected in the laboratory. Using a standard RF coil and a transient recorder it was found that small cracks in quartz and tourmaline single crystals produce exponentially‐decaying RF transients with a time constant of about 10−5 s. Failure of quartz‐bearing rocks generates longer and more complex transients, presumably due to interference of radiation emitted by numerous piezoelectric crystals as a result of the sudden drop in piezoelectric field accompanying the release of stress. The spectral content of these transients depends on grain size, shifting to higher frequencies as grain size decreases. This fracture‐related emission has a variety of potential geophysical applications ranging from monitoring cracks in rock deformation experiments to studies of electromagnetic effects associated with earthquakes, hydraulic fracture and mine failure. Copyright 1977 by the American Geophysical Union.