Orbital period ratio of Neptune and Uranus P_N/P_U (top panel) and survival ratio of the original population (bottom panel) during fast (orange) and slow (blue) migrations. The orbital period ratio of which the short-period terms are eliminated by the low-pass filter is indicated by the red line. The horizontal lines indicate the locations of the 15:8, 11:6, 9:5, 7:4, and 5:3 MMRs between Neptune and Uranus. Two important moments for fast migration, 0.70 τ and 1.08 τ, and two important moments for slow migration, 0.22 τ and 0.80 τ, are indicated by the vertical lines. Only the period ratio for slow migration is shown in the top panel, and that for fast migration is almost the same.