HR: 11:50h
AN: S32A-07    [Abstracts]
TI: Seismic waveform tomography in the time-frequency domain with applications to the Australian upper mantle
AU: * Fichtner, A
EM: fichtner@geophysik.uni-muenchen.de
AF: Department of Earth and Environmental Sciences - LMU, Munich, Theresienstrasse 41, Munich, 80333, Germany
AU: Bunge, P
EM: bunge@geophysik.uni-muenchen.de
AF: Department of Earth and Environmental Sciences - LMU, Munich, Theresienstrasse 41, Munich, 80333, Germany
AU: Igel, H
EM: igel@geophysik.uni-muenchen.de
AF: Department of Earth and Environmental Sciences - LMU, Munich, Theresienstrasse 41, Munich, 80333, Germany
AU: Kennett, B
EM: brian@rses.anu.edu.au
AF: Research School of Earth Sciences - ANU, Canberra, Bldg 61, Mills Road, Canberra, ACT 0200, Australia
AB: We present a novel approach to full waveform tomography based on misfits in the time-frequency domain and adjoint methods. Our focus is on theoretical developments and synthetic inversions for heterogeneities in the Australian upper mantle. The centrepieces of our methodology are envelope and instantaneous phase misfits defined on time-frequency transforms of the seismograms. These misfits allow us to extract the maximum robust information from seismograms for the purpose of high-resolution tomography. We derive Fréchet kernels for different definitions of the envelope and phase misfits using adjoint methods. The Fréchet kernels for instantaneous phase measurements agree with those obtained from waveform cross- correlation only in the special - though unrealistic - case of monochromatic waves. Examples of Fréchet kernels for data collected during the SKIPPY project are computed by means of a recently developed spectral element method. With synthetic inversions we demonstrate that lateral heterogeneities can be determined efficiently by using instantaneous phase measurements of S waves and surface wave trains without explicitly dissecting the seismograms. Special attention is given to the following questions relating to the inversion, i.e., the misfit minimisation algorithm: 1) determination of the optimal step length for gradient methods, 2) acceptance/rejection criteria for the updated models and 3) the pre-conditioning of the steepest descent direction. Finally, we examine the possibility of using enevelope or amplitude measurements and their corresponding Fréchet kernels for seismic waveform tomography.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7255 Surface waves and free oscillations
DE: 7260 Theory
DE: 7270 Tomography (6982, 8180)
DE: 7290 Computational seismology
SC: Seismology [S]
MN: 2007 Fall Meeting