Dr. Aranguiz-Muñoz, Rafael

On September 16, 2015 a magnitude Mw 8.3 earthquake took place off the coast of the Coquimbo Region, Chile. Three tsunami survey teams covered approximately 700 km of the Pacific coast. The teams surveyed the area, recording 83 tsunami flow depth and runup measurements. The maximum runup was found to be 10.8 m at only one small bay, in front of the inferred tsunami source area. However, it was observed that runup in other locations rarely exceed 6 m. Tsunami runup was larger than those of the 2014 Pisagua event, despite the similar earthquake magnitude. Moreover, tsunami arrival times were found to be shorter than those of previous tsunamis along the Chilean subduction zone. Numerical simulations of the tsunami event showed a good agreement with field data, highlighting that tsunami arrival time and the spatial variation of the tsunami amplitudes were strongly influenced by the bathymetry, coastal morphology and the slip distribution of the causative earthquake.

Tsunami resonance and coupled oscillation of shelf and bays modes has been reported to beimportant in tsunami wave amplification. The main objective of this work is to study the spatial pattern ofnatural oscillation modes and to analyze the influence of several resonators on the coast of the centralChile, which has a complex morphology with several bays, submarine canyons, and a wide continentalshelf. First, natural oscillation modes were computed by means of modal analysis of local and regionaldomains. Second, a dense network of tide gauges and pressure sensors was analyzed to obtain backgroundspectra inside bays. Third, tsunami spectra were computed from both tsunami records and numericalsimulations. The results show that the use of modal analysis and background and tsunami spectra iseffective for identifying natural oscillation modes. In addition, a dense network of tide gauges is useful tovalidate the spatial pattern of these natural modes. It was observed that larger resonators and the shelf areimportant in coupling oscillation with local bays, such that large amplification can be observed. Finally,this analysis allowed the diverse effects of 2010 and 2011 tsunamis in the bays of central Chile to beexplained, making it possible to better address tsunami mitigation measures and the preparedness ofcoastal communities.