Frequency Dispersion of the 1 April 2014 Iquique, Chile Tsunami

Abstract:

On 1 April 2014, a Mw 8.2 earthquake struck off the coast of Iquique, Chile. A tsunami was triggered by this earthquake and caused flooding along the northern coast of Chile. Time series of water surface elevations were recorded at tide gauges and DART (Deep-ocean Assessment and Report of Tsunamis) tsunami sensors in the Pacific Ocean. By comparing the wave spectra of the Iquique event with those of other historical events in this region, we notice the former are characterized with significantly higher energy concentration in high-frequency wave modes. This is an indicator of strong frequency dispersion effects, which can quickly reduce the amplitudes of the leading waves in open ocean. These effects are demonstrated through numerical simulations with a weakly dispersive Boussinesq model. The oceanic propagation of this tsunami is also simulated with MOST (Method of Splitting Tsunami), the numerical simulating tool of NO­AA’s tsunami forecast system, termed SIFT (Short-term Inundation Forecasting of Tsunamis). Though MOST is based on the nonlinear shallow-water theory, the numerical dispersion introduced by its finite difference scheme can be manipulated to compensate the neglected physical frequency dispersion, and makes it applicable to dispersive wave propagations.