Planetary Geodynamics Laboratoy Science Highlight
NASA GSFC Planetary Geodynamics 698

SCIENCE HIGHLIGHT

Planetary Geodynamics Laboratory, Code 698

January 2005

Stress on Rocks Generates Electric Currents

Freund Leads Effort Connected to Possible Earthquake Precursor Signals

Earthquakes are the result of stresses that build up in the crust of the Earth, most often associated with plate motion. Stresses on rock may produce other observable phenomena in advance of the actual rupture (earthquake). One of these observables may be caused by weak currents generated in the rock by increased pressure associated with the build up of stress. This has been the focus of research by Friedemann Freund and co-workers. They have approached this problem from both a theoretical and experimental basis, and recently conducted a series of benchmark experiments which show that stresses on igneous rocks (like granite) convert mechanical energy into electric current. This results from the activation of charge carriers (including positive "defect electrons" formed within the stressed rock). The figure below shows the experimental apparatus recently used. If a circuit is available, the flow is out of the stressed rock into its surroundings, and lasts for hours even after the stresses are no longer increased.

Experimental apparatus for measuring the currents generated by stressing rocks Experimental apparatus for measuring the currents generated by stressing rocks. The experiments were carried out using the facilities at the Department of Civil Engineering, University of Maryland, College Park, and the Department of Civil Engineering, San Jose State University.

Picture of Friedemann Freund Friedemann Freund is a University of Maryland Baltimore County (UMBC) Visiting Scientist in the Planetary geodynamics Laboratory, on sabbatical from San Jose State University. He also holds an adjunct appointment at the Ames Research Center. He has developed a theoretical model to explain the physical basis for some electromagnetic precursory phenomena associated with earthquakes and is now carrying out experimental tests of that model.

Contacts: Friedemann Freund, GSFC Code 698, ffreund@core2.gsfc.nasa.gov

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Responsible NASA official: Dr. Herbert Frey

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Last modified on February 18, 2005