HR: 08:30h
AN: S21A-03 INVITED     [PDF]
TI: Modelling of 3D Attenuation Structure in the Mantle Using a Waveform Approach: Successes and Challenges
AU: * Romanowicz, B A
EM: barbara@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, Univ. of California at Berkeley, 215 Mc Cone Hall,, Berkeley, CA 94720 United States
AU: Gung, Y
EM: gung@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, Univ. of California at Berkeley, 215 Mc Cone Hall,, Berkeley, CA 94720 United States
AB: The study of lateral variations in Q in the upper mantle at the global scale is generally addressed using isolated phases in the seismogram (for example fundamental mode surface wave spectra), which limits the sampling and therefore the resolution of Q structure that can be achieved. The use of isolated phases has the advantage of working directly with amplitudes, thus making it easier to detect contamination of the anelastic attenuation signal by elastic focusing and scattering, a key problem in attenuation tomography. We here discuss recent progress on a waveform modeling approach, which allows us to work with entire seismograms and exploit the information contained both in fundamental mode surface waves, overtones and body waves. The method is based on a normal mode approach and proceeds iteratively. In the first step, we invert for 3D elastic structure using the NACT approach (Non-linear Asymptotic Coupling Theory; Li and Romanowicz, 1995), which aligns the phase part of the observed and synthetic seismograms. In the second step, we invert for Q. The crucial issue is how to account for elastic effects in the amplitudes (focusing)- we discuss asymptotic versus more exact methods to address this problem and illustrate the effects on the resulting models. We discuss prominent features in the lateral variations in Q in the upper mantle, their evolution with depth, and their relation with elastic structure, in particular from the point of view of resolving upwellings and the large scale signature of plumes.
DE: 7207 Core and mantle
DE: 7255 Surface waves and free oscillations
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting