Why can several tsunami waves strike the same coast?

A tsunami is not a single wave but a train of progressive, oscillatory waves that radiate outward from a central disturbance, such as an earthquake or landslide. Because these waves have very long periods—ranging from five minutes to more than an hour—they arrive at a coastline as a series of successive crests and troughs separated by significant intervals of time.123

As these waves approach shallow water, they undergo complex interactions with the seafloor and the configuration of the coastline, which can cause them to be reflected and refracted. This process leads to multiple, often powerful, oscillations of the water level. Coastal areas may experience several of these major waves, with the intervals between them allowing for the characteristic rise and fall of water that can persist for hours or even days until the ocean surface reaches equilibrium. Consequently, the danger often persists well after the first wave has struck, as subsequent waves or the outflow of water can be just as destructive as the initial impact.13