This research involves the continuation of a fundamental research program in seismic tomography. Scattered wave information will be incorporated into ongoing investigations of upper mantle structure in the western Pacific. The effects of wave scattering on global inversions of long period S wave travel times will be investigated using previously developed algorithms. Reliable estimators for the resolution and covariance of tomographic images will be developed using approximate generalized inverses based on back-projection. These estimators will be incorporated into schemes for reparametrization that minimize the artifacts of resolution heterogeneity in tomographic images. Finite frequency effects in body wave travel times will be extended to include the "headwaves" Pn and Sn, with the ultimate aim to combine Pn and Sn travel times with waveform constraints on upper mantle structure. New algorithms will be tested beyond the Born approximation (currently the scheme used) in modeling more complicated amplitude anomalies, such as caused by strong focusing and diffraction. The goals are to make significant improvements in the imaging of structural heterogeneity at short and intermediate wavelengths, both through a better quantification of the statistical properties of imaging errors, and by increasing the resolving power through a more correct interpretation of waveform amplitudes.
