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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS009 Oral Presentation 2038
Instabilities, electric currents and earthquake precursors associated with
volcanic activity
Prof. Friedemann Freund
Earth Science Division, Code SGE NASA Ames Research Center IAGA
Michelle Mcmillan, John Keefner, Joshua J. Mellon, Rachel Post
Deviatoric stresses can activate electronic charge carriers that normally lie dormant in rocks1. The
existence of these charge carriers was previously unknown. We studied electric currents flowing down
strain gradients and temperature gradients2. The charge carriers in question are defect electrons in the
oxygen anion sublattice known as positive holes or pholes for short. They are introduced into the matrix
of minerals during cooling when hydroxyl pairs (due to traces of dissolved water) split off hydrogen
molecules and convert to peroxy links. The two oxygens in the peroxy links convert from the 2- to the
1- valence state. When deviatoric stresses act on cool rocks or when temperatures rise above ~500C,
peroxy links dissociate activating pholes and loosely bound electrons. The pholes are capable of
streaming out of the stressed or hot rocks (source) into the surrounding less stressed or cool rocks,
generating potentially powerful currents. Whether or not these currents develop, when and how they
flow depends on whether or not the electrons can also flow out of the source and recombine with the
pholes, thereby closing the electric circuit. The interplay between pholes and electrons is expected to
control the magnitude of dipoles, the intensity of the transient currents and of their associated EM
fields. Understanding these processes may help us interpret EM signals generated by dynamically
evolving feeder systems beneath volcanoes. 1 Freund et al. 2006, Phys. Chem. Earth 31, 389-396;
Freund and Sornette, 2007, Tectonophys. 431, 33-47. 2 McMillan and Freund, AGU 2006 Fall Mtg,
MR21A-0001
Keywords: electric currents, electromagnetic emissions, instabilities