Seismic waves in the Earth. Surface seismic waves generated by an earthquake arrive at a distant observer after the arrival of P waves and S waves (Fig. 12.27B), partly because surface waves travel more slowly than both P and S waves. Even if all these waves had the same velocities, however, the surface waves would still arrive last. Explain why.

Figure 12.27B

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P S Surface waves 1000 2000 3000 4000 5000 Time (s) Seismic signal at observer