Multi-grid and Resolution Full-wave Tomography and Moment Tensor

There is a general consensus that 3D reference models can be used to isolate effects of wave propagation and thus help in improving characterization of seismic sources. Advances in computation and numerical method have made it possible to capture increasingly broadband, full wave generation and propagation in 3D earth models. The main objectives of this project are to construct hierarchical, multi-grid (resolution) joint P and S velocity models and the corresponding finite-difference strain Green’s tensors (FDSGT) for rapid seismic moment determination. In the first year of a three-year project, we collected and processed up to 21 years continuous seismic data from broadband seismic stations in the eastern hemisphere (latitude 55S-55N; longitude 30W-157E). Empirical Green’s functions derived from ambient seismic noise show clear Rayleigh waves over a broad frequency range. We measured over ~10,000 phase delays in 6 period bands ranging from 50 s to 600 s, which provide new constraints on the entire upper mantle, including the upper mantle transition zone. Several iterations of full-wave tomographic inversion have been carried out to obtain a joint P and S velocity model. Preliminary results clearly show high-velocity anomalies associated with plate subduction beneath Indonesia, southern Tibet, Iran, and the Hellenic arc. The African cratons and the west Australian craton appear as prominent high-velocity features. The eastern African Rift and Afar have deep-rooted low-velocity anomalies. Future work includes integration of earthquake arrivals and ambient noise data. 2011 Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies 178 Approved for public release; distribution is unlimited.