HR: 1340h
AN: S53B-1109    [Abstracts]
TI: When the Earth Speaks
AU: * Freund, F T
EM: ffreund@core2.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Planetary Geodynamics Laboratory, Greenbelt, MD 20771 United States
AU: * Freund, F T
EM: ffreund@core2.gsfc.nasa.gov
AF: San Jose State University, Department of Physics, San Jose, CA 95192-0206 United States
AB: Earthquake forecasting is an elusive goal, not only for seismology. It has been reported that, before major earthquakes, the Earth sends out signals. Most of these signals point to transient electric currents in the Earth's crust. To search for the cause of such currents attention has focused - for decades, but in vain - on piezoelectricity, a property of quartz, an abundant mineral in certain rocks. The fact that no generally accepted, physics-based mechanism for the generation of large currents was available has caused considerable confusion. As part of a program to study electrical signals during rock deformation we have made an amazing discovery: when we squeeze one end of a 1.2 m long slab of granite (or quartz-free rocks such as anorthosite or gabbro), we record two electric currents. The currents flow out of the stressed rock without any externally applied voltage. One current, carried by electrons, flows from the stressed rock volume directly to ground. The other current, carried by defect electrons or holes, flows through the full length of the unstressed rock and out the far end. The two currents are of equal magnitude and opposite sign. They are coupled and fluctuate. We understand where the currents come from, how the two types of electronic charge carriers are activated by stress, and how they propagate through the rocks. The discovery of these currents offers a physical basis to re-evaluate a range of electric and electromagnetic signals that have long been reported in connection with impending earthquake activity but seemed to be so difficult, if not impossible, to explain. It offers the opportunity to re-evaluate non-seismic (and non-geodesic) pre-earthquake signals as tools to forecast impending earthquake activity.
DE: 3904 Defects
DE: 3914 Electrical properties
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8164 Stresses: crust and lithosphere
DE: 8168 Stresses: general
SC: Seismology [S]
MN: Fall Meeting 2005