HR: 1340h
AN: T13A-0448    [Abstracts]
TI: Shear-Wave Splitting Beneath the Arabian Shield and Red Sea
AU: * Hansen, S E
EM: shansen@es.ucsc.edu
AF: University of California, Santa Cruz, Earth Science Dept. and IGPP 1156 High St., Santa Cruz, CA 95064 United States
AU: Schwartz, S Y
EM: sschwartz@es.ucsc.edu
AF: University of California, Santa Cruz, Earth Science Dept. and IGPP 1156 High St., Santa Cruz, CA 95064 United States
AU: Rodgers, A
EM: rodgers7@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., L-205, Livermore, CA 94551 United States
AU: Al-Amri, A
EM: amsamri@ksu.edu.sa
AF: King Saud University, Department of Geology Seismic Studies Center P.O. Box 2455, Riyadh, 11451 Saudi Arabia
AB: The Red Sea Rift zone is composed of distinct geologic provinces in close proximity to one another resulting from the rifting and rotation of the African plate relative to the Arabian plate. Since the rift zone is a prototype of a newly formed oceanic basin, understanding of its geodynamic framework will provide important constraints on how seafloor spreading initiates and how continental rifting evolves. Our goal is to extend previous studies of this complex tectonic environment to generate a more complete characterization of the lithospheric structure in the Red Sea region. As part of this work, shear-wave splitting analysis, following the method of Silver and Chan (1991), has been employed to measure seismic anisotropy near the Red Sea Rift. This allows us to compare the anisotropic signature obtained with different candidate models of continental rifting to investigate mantle deformation and rifting mechanics. Data for our study comes from both the eight stations of the PASSCAL Saudi Arabia Broadband Array, which operated from November 1995 to March 1997, as well as the 25 broadband stations of the Saudi Arabian National Digital Seismic Network (SANDSN). Data from the SANDSN are uniquely available to us through collaboration with the King Abdulaziz City for Science and Technology. Splitting parameters, including fast polarization directions and delay times, have been determined for S, SKS, and other core refracted phases recorded at the Saudi Arabian stations. Stations along the eastern margin of the Red Sea display little variation with back azimuth and generally indicate a rift-parallel fast polarization direction. This is consistent with a single anisotropic layer model with hexagonal symmetry and a horizontally oriented fast axis. However, stations extending into the central region of the Arabian Peninsula display more pronounced back azimuth dependence. This may be associated with either lateral variations across the study area or with more complicated anisotropic structure, such as dipping or multiple layer anisotropy. These findings have important implications in that they do not support a "passive" rifting model, where the entire lithosphere below the rift extends and forms a rift-perpendicular fast direction. Instead, these results may indicate the presence of more "active" rifting processes, where the lithosphere is thinned through small scale convection, resulting in more complex anisotropy. In addition, the effects of fossilized anisotropy from previous tectonic events or the alignment of magmatic cracks along the rift zone may also play an important role in the observed anisotropic signature. Additional modeling, using an approach similar to Hartog and Schwartz (2000, 2001), will allow us to further examine these variations and resolve the anisotropic structure beneath the Red Sea and the Arabian Shield.
DE: 7203 Body waves
DE: 7218 Lithosphere (1236)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8105 Continental margins: divergent (1212, 8124)
SC: Tectonophysics [T]
MN: Fall Meeting 2005