HR: 0830h
AN: S21E-0349    [PDF]
TI: Global finite-frequency surface-wave tomography
AU: * Zhou, Y
EM: yingz@princeton.edu
AF: Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544 United States
AU: Nolet, G
EM: nolet@princeton.edu
AF: Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544 United States
AU: Dahlen, F
EM: fad@princeton.edu
AF: Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544 United States
AU: Laske, G
EM: gabi@igpp.ucsd.edu
AF: IGPP, University of California, San Diego, San Diego, CA 92093 United States
AB: We investigate finite-frequency effects in global surface-wave tomography. We compare two-dimensional phase-velocity maps inverted using ray theory and sensitivity kernels based on Born approximation. The same comparison is also made for three-dimensional upper mantle shear-wave velocity structures. The 3-D sensitivity kernels are computed using a fast kernel computation approach (Zhou et al, 2003). We incorporate the forward-scattering approximation, and take sidelobes fully into account when calculating the 2-D sensitivity kernels for phase-velocity perturbations. \\ The global phase-delay measurements used in this experiment has a frequency range from 3 mhz to 20 mhz (Laske \& Masters, 1996). The same local parameterization (average grid spacing $\sim 4^{\circ}$) is applied in both the ray theoretical inversion and the finite-frequency kernel inversion. In general, inversions based on ray theory and finite-frequency sensitivity kernels show similar large-scale geographic pattern, both in the 2-D phase-velocity maps and the 3-D shear-wave structures. However, the difference is significant in the amplitude of the anomalies and in the small-scale structures. In 2-D phase-velocity maps, the difference becomes more apparent at long periods, due to the increasing width of the Fresnel zone. Theoretically, finite-frequency kernels are expected to converge to ray theory whenever the scale of the anomaly is much larger than the wavelength. However, due to limited path coverage in tomographic practice, inversions based on ray theory often introduce considerable artifacts in both the amplitudes and locations of the anomalies even when the real structure is large in scale.
DE: 7200 SEISMOLOGY
DE: 7218 Lithosphere and upper mantle
DE: 7255 Surface waves and free oscillations
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting