Studies of Global Seismicity and Earth Structure

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This research is a 5-year continuation of investigations carried out under two former grants dealing with earthquake source analysis and earth structure. Topics include 1) continuation of the ongoing Centroid Moment Tensor (CMT) analysis; 2) refining the CMT analysis procedure through the combined use of waveforms and travel time observations; 3) extending the CMT procedure to the analysis of smaller events by the use of teleseismic surface waves; 4) using SKKS and SKS observations, in conjunction with 3D mantle models, to constrain outer core structure; 5) using combined data sets to obtain improved spherically symmetric reference Earth models; 6) performing joint inversions for the P and S 3D-velocity structure of the mantle; 7) performing modeling experiments based on joint inversion of seismic and geodynamic data, as well as exploring the geodynamic implications of the 3D velocity models; 8) including higher frequency data in the 3D earth structure modeling experiments in order to improve radial and lateral resolution; 9) developing procedures for hybrid region/global model parameterizations which will allow for proper inversions for large- scale regional structure; 10) investigation of mantle anisotropy and lateral variation in attenuation and how these phenomena may be accounted for in the 3D modeling experiments. The service provided by these efforts to the world seismological community, especially the CMT catalog, is widely used in determination of earth structure, tectonics, and earthquake analysis. This research is a component of the National Earthquake Hazard Reduction Program.