1. Station-Specific Traveltime Tables In a 3D earth

2. Goal: improve earthquake locations while minimizing computation effort through precomputation

3. Three-D earth model elliptical earth model ½ degree resolution, tetrahedral splines based on available structural information Crust 2.0 Pn tomography Surface wave tomography

4. Overall organization into interfaces Small-scale organization into tetrahedra Linear interpolation within tetrahedra implying rays that are circular arcs

5. First Cut at building a 3-d MODEL Simplified, 2-layer-crust version of Crust 2.0 on top of AK135 mantle with sub-Moho velocities adjusted to match Crust 2.0 Pn velocities

9. Strategy Compute differential traveltimes between 3D model and reference vertically-stratified model one traveltime calculation for each station gives traveltime correction for earthquake anywhere in the US to that station

10. Examples Crust2 minus AK135 differential traveltimes

13. Shadow zone

17. Sensitivity Test Test grid of earthquake hypocenters Current US station configuration Traveltimes for 3D model Location using AK135 Assess location error

18. Stations east of California

19. Location Errors: = 0.5 degree Note: this preliminary calculation used data from a limited number of stations