HR: 0800h
AN: S51E-1057    [Abstracts]
TI: Finite Frequency Group Velocity Sensitivity Kernels for Surface Wave Tomography
AU: Barmin, M P
EM: barmin@colorado.edu
AF: Center for Imaging of the Earth's Interior, Department of Physics, Campus Box 390, Boulder, CO 80309 United States
AU: Levshin, A L
EM: levshin@colorado.edu
AF: Center for Imaging of the Earth's Interior, Department of Physics, Campus Box 390, Boulder, CO 80309 United States
AU: * Ritzwoller, M H
EM: ritzwoller@colorado.edu
AF: Center for Imaging of the Earth's Interior, Department of Physics, Campus Box 390, Boulder, CO 80309 United States
AB: Surface wave tomography based on phase or group wave speeds have different strengths and limitations. Absolute phase speeds are strongly affected by source phase which may be poorly known and are subject to a 2-pi phase ambiguity, which together limit their use typically to periods above 40 sec. Group speeds do not suffer as strongly from these problems and measurements can be obtained to much shorter periods, but are harder to measure accurately and the sensitivity kernels are more complicated. In particular, group travel times depend both on the relative group speed perturbation and on the frequency derivative of the relative phase speed perturbation. Group velocity tomography as it has been performed to date has been based primarily on ray theory (e.g., Ritzwoller and Levshin, JGR, 103, 4839, 1998) or on truncated finite frequency sensitivity kernels (e.g., Ritzwoller et al., JGR, 107, 2335, 2002) of questionable theoretical justification. We describe an approximate form of the group velocity sensitivity kernel that is sufficiently accurate to act as a firm basis for group velocity tomography. The exact form of the sensitivity kernel, however, depends on many assumptions (e.g., choice of background elastic model, the resolution of the model parameterization, source radiation pattern) and the exact way in which the group speed measurements are made, particularly the interval of measurement chosen both in the time and frequency domains. Different approximations are likely to be made by different tomographers, but we believe the principal source of uncertainty remains the ad-hoc choice of damping in the tomographic inversion.
DE: 7255 Surface waves and free oscillations
DE: 7270 Tomography (6982, 8180)
DE: 7290 Computational seismology
SC: Seismology [S]
MN: Fall Meeting 2005