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| Titel |
Frequency-dependent sensitivity to mantle and core-mantle topography |
| VerfasserIn |
A. Colombi, T. Nissen-Meyer, L. Boschi |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067079
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| Zusammenfassung |
| We investigate the implications of lateral variations in the topography of global seismic
discontinuities, in the framework of high-resolution forward modeling and seismic
imaging.
We run 3D wave-propagation simulations accurate at periods of 10 s and longer, with
Earth models including core-mantle boundary (CMB) topography anomalies of ~1000 km
spatial wavelength and up to 10 km height with experimenting with a set of different
geographic patterns. We obtain very different waveform signatures for PcP (reflected) and
Pdiff (diffracted) phases supporting the theoretical expectation that the latter are sensitive
only to large-scale structure while the former only to small scale with respect to seismic
wavelength.
PcP at 10s is well suited to map such a small-scale perturbation while Pdiff at the same
frequency carries a faint signature that does not allow any tomographic reconstruction. Only
at higher frequency the signature becomes stronger.
We present a new algorithm to compute sensitivity kernels relating seismic travel times
(measured by cross-correlation of observed and theoretical seismograms) to the topography
of seismic discontinuities at any depth in the Earth using full 3D wave propagation.
Calculation of accurate finite-frequency sensitivity kernels is notoriously expensive, but we
reduce computational costs drastically by limiting ourselves to spherically symmetric
reference models, and exploiting the axial symmetry of the resulting propagating wave-field
that collapses to a 2D numerical domain.
We compute and analyze a suite of kernels for upper and lower mantle discontinuities that
can be used for finite frequency waveform inversion. For the travel-time residuals
calculated from 3D wave propagation, we compute using our efficient approach
the
PIC
matrix for various parameterizations and source-receiver distribution. Finally, upon the
choice of an adequate numerical scheme, we invert the residuals travel-time synthetics. |
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