HR: 0800h
AN: T51B-0444    [Abstracts]
TI: Large-Scale Model of the Electrical Conductivity in the Crust
AU: * Lau, B W
EM: blau@science.sjsu.edu
AF: San Jose State University, Department of Physics, San Jose, CA 95192-0106 United States
AU: * Lau, B W
EM: blau@science.sjsu.edu
AF: NASA Goddard Space Flight Center, GEodynamics Branch MS 921, Greenbelt, MD 20771 United States
AU: Takeuchi, A
EM: takeuchi@science.sjsu.edu
AF: San Jose State University, Department of Physics, San Jose, CA 95192-0106 United States
AU: Takeuchi, A
EM: takeuchi@science.sjsu.edu
AF: NASA Goddard Space Flight Center, GEodynamics Branch MS 921, Greenbelt, MD 20771 United States
AU: Freund, F
EM: ffreund@core2.gsfc.nasa.gov
AF: San Jose State University, Department of Physics, San Jose, CA 95192-0106 United States
AU: Freund, F
EM: ffreund@core2.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, GEodynamics Branch MS 921, Greenbelt, MD 20771 United States
AU: Freund, F
EM: ffreund@core2.gsfc.nasa.gov
AF: NASA Ames Research Center, Earth System Science and Technology, MS 242-4, Moffett Field, CA 94035-1000 United States
AB: Pre-earthquake electromagnetic signals have been linked to large currents (10$^{6}$ A) and large propagation distances (100 km). From physical principles, such signals require charge motion. Once generated, the charges must be able to move in the ground. This motion is governed by the electrical conductivity in the source volume of the charges and in its vicinity. There are different proposed contributions to the conductivity of the crust. These include interconnected pore water, conductive minerals like magnetite, sulfides, and other impurities, and partial melts. The intrinsic conductivity of the rocks is generally thought to be too low to make an important contribution. In order to build a proper model, the scale of the phenomenon must be considered. We consider situations where contributions from two materials dominate. The conductors are saline solutions and the igneous rocks themselves. The model considers thick layers of rocks and thin sheets of brine-filled fissures oriented in vertical planes. The two primary axes of conduction are normal and parallel to the planes. The conduction problem is thus reduced to that of series and parallel resistors whose total conductivity is related to the volume of each constituent. In addition the conductivity is depth-dependent. The upper crust tends to be crisscrossed by brine-filled fissures, while the deeper crust tends to be fluid-free due to retrograde mineral reactions, which consume water. Depending on the density of fissures, the conductivity of the upper crust can be dominated by either the electrolytic conductivity of brine-filled fissures or by the intrinsic conductivity of the rocks. The conductivity of the deeper crust will be dominated by the intrinsic conductivity of the rocks.
DE: 8045 Role of fluids
DE: 8164 Stresses--crust and lithosphere
DE: 5109 Magnetic and electrical properties
DE: 3210 Modeling
DE: 1645 Solid Earth
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting