A large earthquake occurred along a fault and a smaller earthquake occurred at the same location the next day. A seismograph station 300 km away recorded both events. True or false: P-waves would have traveled to the station more quickly after the larger earthquake?

• A. True
• B. False
• C. Not enough information
• D. They would arrive at the same time

Answer: (B)

P-waves move at speeds set by the rocks they travel through, not by how large the earthquake is. Since both events originate at the same location, the path to the station is the same and the P-wave velocity is essentially the same. The arrival time depends on when the earthquake starts plus that fixed travel time, not on the earthquake’s magnitude. So the P-waves would not travel more quickly after the larger quake—they would move at about the same speed, and the larger quake’s waves would simply arrive earlier in absolute time if it happened first. For example, with crustal P-waves around 6 km/s, 300 km takes roughly 50 seconds, regardless of quake size.