Effect of submarine canyons on tsunami propagation: A case study of the biobio canyon, Chile

The 2010 Chile tsunami had different effects along the Chilean coast. Seawater surged hundred meters into many rivers, though field surveys showed that the 2 km wide Biobio River did not experience any flooding. In a similar manner, the coastal zones south of the river had an inundation height of less than 2 m. To ascertain why these areas were not greatly affected by the event, the behavior of tsunami waves propagating over a submarine canyon was investigated by means of numerical simulations over a simplified and idealized bathymetry. The main variables which define the size of the canyon were varied, and three different tsunami wave lengths were tested. The results show that submarine canyons have a strong influence on tsunami propagation and run-up such that there is a spatial variation of wave amplitude along the coast and this behavior is very sensitive to the canyon size. The run-up directly behind the canyon is lower than in the case without the canyon, while there are zones of wave amplification at both sides of the canyon. These idealized results compare well with what happened during the 2010 Chile tsunami, and provide a useful insight into the behavior of tsunamis around other submarine canyons in other regions of the world.