HR: 1340h
AN: T33A-1346    [Abstracts]
TI: Anisotropic Seismic Structure along the trace of the Dead Sea Rift
AU: * Levin, V
EM: vlevin@rci.rutgers.edu
AF: Department of Geological Sciences, Rutgers University, Piscataway, NJ 08854 United States
AU: Henza, A
EM: ahenza@eden.rutgers.edu
AF: Department of Geological Sciences, Rutgers University, Piscataway, NJ 08854 United States
AU: Rogers, A
EM: rogers7@llnl.gov
AF: Earth and Environmental Science Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94551 United States
AU: Park, J
EM: jeffrey.park@yale.edu
AF: Department of Geology and Geophysics, Yale University, New Haven, CT 06520 United States
AB: How the motion on a transform plate boundary is accommodated in the upper mantle is not very well known. A notion of a narrow zone of deformed mantle rock associated with the transform is intuitive, however such specifics as the width of this zone, the intensity of deformation etc. have been probed at a few locations only. Deformation of upper mantle rocks should result in the formation of fabric that makes of seismic wave velocity anisotropic, and thus studies of seismic anisotropy indicators hold considerable promise in improving the understanding of continental transform fault behavior. The Dead Sea Rift is a left-lateral transform boundary between the Arabian and African plates, with over 100 km of offset accumulated since $\sim$15Ma. It cuts through the former shield, and thus is modifying a lithosphere that has experienced numerous episodes of rock-fabric formation prior to the inception of the transform. The challenge in understanding the accommodation of this transform at depth is thus in discriminating rock fabric imparted by the modern motion from other signatures that have likely been left behind by previous tectonic episodes. We investigate depth dependence of seismic anisotropy along the trace of the Dead Sea Rift. We use observations of birefringence in $SKS$ phases from permanent and temporary observatories. In preliminary analysis we found considerable variation in values of effective splitting parameters (fast directions and delays), both with the propagation direction, and between sites. Such variations are likely when anisotropic structures are either stratified or laterally variable. We devise depth-dependent models of anisotropy and evaluate their relative merit using group inversion methodology of Menke and Levin (2003). Sets of azimuthally distributed observations are inverted together for models of different classes (single layer of anisotropy, single layer with inclined axis, two layers of anisotropy etc.) and their respective fits are compared. Models with best performance are then interpreted in the context of both the modern plate motion and the past tectonic episodes in the region.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting