Earthquake location programs for events recorded at regional to teleseismic distances have traditionally used travel-time tables such as the J-B tables (Jeffreys and Bullen, 1958), which were based on ray tracing in a laterally homogeneous spherical earth (e.g.,Boyd et al., 1984). Such travel-time tables may not give accurate locations for events located using stations at local to near-regional distances because of regional variations in the crustal and upper-mantle velocity structure—the regions of the Earth in which the first-arrival P and S waves spend most of their time for such events. Until recently, it was a...

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