Top panel: comparison of cut at a latitude of 30° north computed from different frequencies as a function of distance. The frequencies used in this comparison are 3.0, 3.1, 3.2, and 3.3 mHz (see legend). A 30°-wide arc-to-arc geometry is implemented. The flow model used is MC1. Bottom panel: differences between the travel-time shifts shown in the top panel. We note that the differences increase rapidly as the travel distance decreases, and are on the order of hundredths of a second for the shortest distance (Δ = 6°) used in this work. Also, the smaller the frequency used in the ray approximation, the steeper the decline in the derived travel-time shift with increasing travel distance