![]() ![]() For our starting model, we use a simplified two layer crustal model derived from the Crust 2.0 model over a uniform AK135 mantle. (2009), which incorporates variable resolution in both the geographic and radial dimensions. The model is represented using the triangular tessellation system described by Ballard et al. Reduction in the total number of ray paths is > 55%. To prevent over-weighting due to ray path redundancy and to reduce the computational burden, we cluster rays to produce representative rays. Our model is derived from the latest version of the Ground Truth (GT) catalog of P and more » Pn travel time picks assembled by Los Alamos National Laboratory. In this paper, we present the most recent version of our model, SALSA3D (SAndia LoS Alamos) version 1.4, and demonstrate its ability to reduce mislocations for a large set of realizations derived from a carefully chosen set of globally-distributed ground truth events. To test the hypothesis that high quality 3D Earth models will produce seismic event locations which are more accurate and more precise, we are developing a global 3D P wave velocity model of the Earth's crust and mantle using seismic tomography. This framework produces fast travel-time and uncertainty predictions and overcomes the ray-tracing algorithm hurdle because the lookup tables can be generated using the exact ray-tracing algorithm that is preferred for a model. We demonstrate and test a framework to create first-P and first-S 3D travel-time correction surfaces using an open-source framework ( PCalc + GeoTess, ) that easily stores 3D travel-time and uncertainty data. Attempting to use a different algorithm than the one used to develop a model usually results in poor travel-time prediction. Additionally, comparing location more » accuracy for 3D seismic velocity models tends to be problematic, as each model is determined using different ray-tracing algorithms. The computational requirements of these 3D models tend to make their operational use prohibitive. ![]() Higher-dimensional (i.e., three-dimensional-3D) seismic velocity models are becoming readily available and provide more accurate event locations over 1D models. These travel-time lookup tables are extremely fast to use and this fast computational speed makes them the preferred type of velocity model for operational needs. 1D models are generally used as travel-time lookup tables, one for each seismic phase, with travel-times pre-calculated for event distance and depth. ![]() Abstract Location algorithms have historically relied on simple, one-dimensional (1D) velocity models for fast seismic event locations. ![]()
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