To derive an analytical prestack-migration traveltime equation in the space-time domain, I will start by casting the prestack migration in the Fourier (frequency-wavenumber) domain, where the traveltime shifts are described analytically. Such a migration is commonly referred to as phase-shift migration Gazdag (1978); Yilmaz (1979). The prestack version of this migration for anisotropic media is described in detail by Alkhalifah (1997b).