How do earthquakes change the Earth's surface over time?

During a large earthquake, one side of a fault may move upward, downward, or sideways relative to the other. The 1964 Alaska earthquake, for example, caused major vertical land changes along the coast. Over geologic time, repeated fault movement helps build mountains, create basins, and alter river courses. Earthquakes also can permanently raise or lower parts of the seafloor, affecting tsunamis and harbors. This is one way the slow movement of plates becomes visible in a single dramatic event.