HR: 11:20h
AN: S12B-05    [Abstracts]
TI: A Comparison of Downslope Propagation, Rough Boundary Effects, and Shear in T-phase Excitation
AU: * Odom, R I
EM: odom@apl.washington.edu
AF: Applied Physics Laboratory University of Washington, 1013 NE 40th Street, Seattle, WA 98105
AU: Soukup, D J
EM: dsoukup@apl.washington.edu
AF: Applied Physics Laboratory University of Washington, 1013 NE 40th Street, Seattle, WA 98105
AU: Park, M
EM: minkyu@kordi.re.kr
AF: Korea Ocean Research and Development Institute, Anson P.O. Box 29, Seoul, 425-600 Korea, Republic of
AB: We compare and contrast different aspects of T-phase excitation. Employing a modal description of the seismic wavefield, it is apparent that if the Earth were a plane-layered, semi-infinite halfspace or a radially symmetric sphere, T-phases would not exist. Even shallow earthquakes are too deep to directly excite the low order modes carrying the T-phase signal. Some mechanism is required to break the strict modal orthogonality and scatter energy into the low order modes. Downslope propagation and a rough ocean bottom can accomplish this. These are in a sense the same process. If the bottom is treated purely as a random rough surface with some characteristic spatial spectrum, the continental or near-island slopes are just long wavelength components of the roughness spectrum. They also have a large correlation length scale. Rough surface scattering is weaker for longer correlation length scales. The actual contribution to the T-phase signal depends on the steepness and length of the slope, and may provide a greater or lesser contribution to the T-phase energy depending on the overall roughness. An additional feature is that if the Earth did not support shear, T-phases would not exist. This is not because a fluid Earth would have smooth boundaries. Rather a fluid Earth will not support interface (Stoneley/Scholte) waves, which seem to be essential for T-phase excitation.
DE: 7220 Oceanic crust
DE: 4259 Ocean acoustics
DE: 3025 Marine seismics (0935)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting