THE EFFECT OF A SUBMARINE CANYON ON TSUNAMI PROPAGATION IN THE GULF OF ARAUCO, CHILE

Abstract

The 2010 Chile tsunami affected the entire coast of the Biobio Region, where several bays were flooded, and seawater surged hundreds of meters into rivers. However, no inundation occurred in the 2km wide Biobio River, located at the northern entrance of the Gulf of Arauco. Likewise, minimal inundation (less than 2m) was found on the gulf’s eastern coast, just south of the river mouth. The study was done by means of numerical simulation with TUNAMI code. Four (4) nested grids with 81”, 27”, 9” and 3” resolution were defined. Several scenarios were simulated, including the 1730, 1835, 1960 and 2010 events. The first two scenarios considered only a uniform rupture zone, while the others were defined using non-uniform initial condition. Another set of simulations were run without the presence of the island and with a modified bathymetry, so that its effect on tsunami propagation could be studied. It can be concluded that the Biobio canyon is very important in tsunami propagation in the Gulf of Arauco. There is a mitigation effect on the eastern side of the Gulf due to the refraction and dispersion generated by its presence. The change in wave direction is enhanced due to wave diffraction generated by the Santa María Island, causing the wave fronts to move in a north-south direction, preventing severe damage to the eastern side. However a direct impact of the tsunami in the southern end of the Gulf can be observed.