Pacific Coastal and Marine Science Center
Tsunamis and Earthquakes
Persistence of Tsunami Waves
Do tsunamis stop after they first strike land? No!
Part of the tsunami energy is reflected back to the open ocean and scattered by sharp variations in the coastline. In addition, a tsunami can generate a particular type of coastal trapped wave called edge waves that travel back-and forth, parallel to shore. These effects result in many arrivals of the tsunami at a particular point on the coast rather than a single wave.
Because of the complicated behavior of tsunami waves near the coast, the first amplitude and surge of a tsunami is often not the largest, emphasizing the importance of not returning to a beach many hours after a tsunami hits.
To illustrate this phenomena, the simulations below show tsunami wave behavior along the northern California coastline. For visualization purposes, tsunami wave amplitudes are exaggerated and 2.5 hours of elapse time has been compressed into 30 seconds of animation time.
View to the south-east. Download .mov file 3.5 MB
View to the north-east. Download .mov file 2.1 MB
The simulations below show tsunami wave behavior long the central California coastline. For visualization purposes, tsunami wave amplitudes are exaggerated and 70 minutes of elapse time has been compressed into 20 seconds of animation time.
View to the south-east. Download .mov file 3.6 MB
View to the north-east. Download .mov file 2.0 MB
Resonance within harbors and estuaries is not shown in these simulations, but it is another important aspect that contributes to the persistence of tsunami waves.