Development of a Tool for Single Station Locations of Small Seismic Events Using Regional Three-Dimension Velocity Models

70141 In regions with relatively few seismic stations and small-to-intermediate magnitude events, traditional network location methods cannot be depended upon to provide the location accuracy required for nuclear test monitoring. This project will develop practical location algorithms based upon observations made at single stations and/or arrays. Phase I will develop an efficient algorithm to locate small seismic events with single stations or arrays, based on ray tracing of both Lg and Pn through the WINPAK3D velocity model for the India/Pakistan region. In particular, an efficient algorithm to calculate accurate travel times for the Lg phase in 3-D velocity models will be developed, along with a model-based approach to accurately locate small-to-intermediate size events using single stations and/or arrays. The method will be applied to events with high-quality ground truth locations in order to establish the success rate. Phase II will include additional secondary phase arrivals, automate the algorithm, and examine the method¿s transportability to additional regional three-dimensional velocity models. Commercial Applications and Other Benefits as described by the awardee: The model-based single-station location algorithm should offer the DOE nuclear monitoring program a tool for accurately determining epicenters for small-to-intermediate magnitude events in complex tectonic regimes that are only recorded on one or a few seismic stations.