HR: 1340h
AN: T33A-1359    [Abstracts]
TI: A new global P wave model
AU: Li, C
EM: changli@mit.edu
AF: Chang Li, 54-510, 77 Mass. Ave., cambridge, MA 02139 United States
AB: Using data from different seismic phases and improved tomography codes we have constructed a new model of 3-D variations in P-wavespeed in Earth's mantle. First, we have improved data coverage by adding to the large volume of routinely processed ISC catalog (P, pP, PKP ) data, as reprocessed by Engdahl et al. (BSSA98), several sets of differential travel times that have been measured by waveform cross correlation. These data include PKP-Pdiff (Wysession) and various PKP branches (Creager and McSweeney), which help improve resolution of structure in the lowermost mantle, and PP-P (Bolton and Masters), which greatly improves the mapping of structure in the upper mantle away from belts of high seismic activity. Second, we follow Karason et al. (JGR01) and use 3-D sensitivity kernels to account for the fact that the data are measured at different frequency, and in different ways. The kernels allow low frequency data (e.g., PP-P, Pdiff) to constrain long wavelengths without preventing short period data (P, PKP) to resolve small scale structure. We use approximate kernels since our research has shown that for this application the precise shape of the kernels is less important than effects of parameterization and regularization. Third, the localization of sensitivity is further aided by the use of a grid that is adapted to sampling density, so that small scale structure can be resolved in regions of dense data coverage. Fourth, for the ray geometry part we use 3-D ray tracing to account for the non-linear effects of heterogeneity on ray geometry. Finally, we correct for 3-D variations in crust structure, using CRUST2.0, which helps reduce the artificial smearing of shallow structure along steep ray paths. We present the new model, along with resolution tests, and discuss improvements over previous efforts.
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting