HR: 16:00h
AN: S14A-01    [Abstracts]
TI: Whole Mantle 1-D Structure From Short-period Body Waves
AU: Shearer, P
EM: pshearer@ucsd.edu
AF: IGPP/Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92122, United States
AU: * Oki, S
EM: soki@ucsd.edu
AF: IGPP/Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92122, United States
AB: Modeling Earth's anelastic structure as well as elastic structure is important for several reasons: (1) the depth dependence of attenuation and the shear-to-bulk Q ratio constrain the physical state of the deep Earth including its melt content, (2) attenuation can be a strong indicator of temperature variations because they have a larger effect on attenuation than on elastic velocity, and (3) attenuation causes physical dispersion of seismic velocities, which must be taken into account when interpreting travel time data. However, attenuation studies have proven challenging because of the typically large scatter in attenuation measurements and the difficulty in separating out source and elastic propagation effects from the intrinsic attenuation signal. We describe a new 1-dimensional Q model for short-period body waves. It is modeled from a dataset of 15,000 differential t^* measurements of teleseismic P and S waves recorded in broadband seismograms. The S waveform is synthesized from the observed P wave and then cross-correlated to the observed S wave. The t^* that gives the best correlation coefficient provides an estimate of attenuation along the ray path. To avoid biases from multipathing and other propagation path effects, we perform the cross- correlation only on the first half swing of the waveform. An advantage of our dataset is that it is little affected by the source-time function or instrument response, since the P and S waves are recorded at the same station from the same event. We invert our t^* measurements for a 3-layer Q_μ model (2 in upper mantle and 1 in lower mantle). Our new Q model has higher Q values (less attenuation) compared to existing Q models derived from longer period datasets, especially in the lower mantle. This is consistent with frequency dependence of Q as has been suggested both from laboratory experiments and previous seismic observations. The attenuation is strongest in the upper mantle and we examine regional variations in Q by computing station and event terms (i.e., by averaging the t^* residuals). These results show correlations with tectonics that are generally consistent with regional attenuation studies.
DE: 3909 Elasticity and anelasticity
DE: 5144 Wave attenuation
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8103 Continental cratons
SC: Seismology [S]
MN: 2007 Fall Meeting