Global Anelastic Waveform Tomography

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Seismic Attenuation

Understanding the distribution of seismic attenuation in the mantle is important for: 1. Discriminating between chemical and thermal heterogeneity; 2. Interpreting models of elastic structure derived from data at different frequencies.

Yet, while mapping of the 3D elastic structure of the upper mantle has benefited from approximate first-order perturbation techniques, modeling of the 3D distribution of seismic attenuation has lagged behind due to difficulties in accounting for purely elastic effects of scattering at sharp interfaces and (de)focusing, which can obscure the anelastic signal.

At present, Ved Lekic is working on combining forward modeling using the coupled spectral element method cSEM with the use of approximate finite-frequency kernels NACT in the inversion to construct a higher resolution 3D Q model of the upper mantle.


Existing Model QRLW8

QRLW8 is an anelastic 3D model of the upper mantle from full seismogram waveform inversion developed by Yuancheng Gung, Barbara Romanowicz. Read more about the model, and the interesting implications it raises.

The figure below shows our most recent upper mantle Q model, QRLW8 (Gung and Romanowicz, 2004): 1. Derived from long period seismograms in the time domain, comprising both fundamental mode surface waves and overtones; 2. Used an iterative waveform inversion technique, in which we solve for elastic and anelastic structure in successive steps; 3. Employed non-linear asymptotic mode coupling theory as the theoretical framework for both the forward and inverse parts of our inversions (Romanowicz, 1987; Li and Romanowicz, 1996).

QRLW8.gif

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