Dr. Aránguiz-Muñoz, Rafael

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.

On September 28, 2018, a large earthquake and its accompanying tsunami waves caused severe damage to the coastal area of Palu Bay, in the central western part of Sulawesi Island, Indonesia. To clarify the distribution of tsunami inundation and run-up heights, and damage to coastal communities due to the tsunami, the authors conducted a field survey 1 month after the event. In the inner part of Palu Bay tsunami inundation and run-up heights of more than 4 m were measured at many locations, and severe damage by the tsunami to coastal low-lying settlements was observed. In the areas to the north of the bay and around its entrance the tsunami inundation and run-up heights were lower than in the inner part of the bay. The tsunami inundation distance depended on the topographical features of coastal areas. The southern shore of the bay experienced a longer inundation distance than other shores, though generally severe damage to houses was limited to within around 200 m from the shoreline. The main lessons that can be learnt from the present event are also discussed.

The variability in obtaining estimates of tsunami inundation and runup on a near‐real‐time tsunami hazard assessment setting is evaluated. To this end, 19 different source models of the Maule Earthquake were considered as if they represented the best available knowledge an early tsunami warning system could consider. Results show that large variability can be observed in both coseismic deformation and tsunami variables such as inundated area and maximum runup. This suggests that using single source model solutions might not be appropriate unless categorical thresholds are used. Nevertheless, the tsunami forecast obtained from aggregating all source models is in good agreement with observed quantities, suggesting that the development of seismic source inversion techniques in a Bayesian framework or generating stochastic finite fault models from a reference inversion solution could be a viable way of dealing with epistemic uncertainties in the framework of nearly‐real‐time tsunami hazard mapping.

This work presents the analysis of long waves resonance in two of the main cities along the northern coast of Chile, Arica, and Iquique, where a large tsunamigenic potential remains despite recent earthquakes. By combining a modal analysis solving the equation of free surface oscillations, with the analysis of background spectra derived from in situ measurements, the spatial and temporal structures of the modes are recovered. Comparison with spectra from three tsunamis of different characteristics shows that the modes found have been excited by past events. Moreover, the two locations show different response patterns. Arica is more sensitive to the characteristics of the tsunami source, whereas Iquique shows a smaller dependency and similar response for different tsunami events. Results are further compared with other methodologies with good agreement. These findings are relevant in characterizing the tsunami hazard in the area, and the methodology can be further extended to other regions along the Chilean coast.

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.

We constructed a seismic source model for the 2015 MW 8.3 Illapel, Chile earthquake, which was carried out with the kinematic waveform inversion method adopting a novel inversion formulation that takes into account the uncertainty in the Green’s function, together with the hybrid backprojection method enabling us to track the spatiotemporal distribution of high-frequency (0.3–2.0 Hz) sources at high resolution by using globally observed teleseismic P-waveforms. A maximum slip amounted to 10.4 m in the shallow part of the seismic source region centered 72 km northwest of the epicenter and generated a following tsunami inundated along the coast. In a gross sense, the rupture front propagated almost unilaterally to northward from the hypocenter at \2 km/s, however, in detail the spatiotemporal slip distribution also showed a complex rupture propagation pattern: two up-dip rupture propagation episodes, and a secondary rupture episode may have been triggered by the strong high-frequency radiation event at the down-dip edge of the seismic source region. High-frequency sources tends to be distributed at deeper parts of the slip area, a pattern also documented in other subduction zone megathrust earthquakes that may reflect the heterogeneous distribution of fracture energy or stress drop along the fault. The weak excitation of high-frequency radiation at the termination of rupture may represent the gradual deceleration of rupture velocity at the transition zone of frictional property or stress state between the megathrust rupture zone and the swarm area.

On 1 April 2014, an earthquake with moment magnitudeMw8.2 occurred off the coast ofnorthern Chile, generating a tsunami that prompted evacuation along the Chilean coast. Here tsunamicharacteristics are analyzed through a combination of field data and numerical modeling. Despite theearthquake magnitude, the tsunami was moderate, with a relatively uniform distribution of runup, whichpeaked at 4.6 m. This is explained by a concentrated maximal slip at intermediate depth on the megathrust,resulting in a rapid decay of tsunami energy. The tsunami temporal evolution varied, with locations showingsustained tsunami energy, while others showed increased tsunami energy at different times after theearthquake. These are the result of the interaction of long period standing oscillations and trapped edgewave activity controlled by inner shelf slopes. Understanding these processes is relevant for the region,which still posses a significant tsunamigenic potential

A GIS analysis on the urbanization spread (1725 to present) in the Greater Concepcion Region demonstrates that increasing the tsunami disaster resilience of coastal communities is a pressing issue in Chile, due to the continuous presence of human settlements in tsunami-prone areas. This research assesses the contribution of “hard-infrastructure” for increasing disaster resilience within five coastal towns (Dichato, Coliumo, Tumbes, Penco and Talcahuano). Structures were considered beneficial to resilience-building if they had multi-functional properties which aided in the social and/or economic recovery of the affected community. The assessment was carried out through in-depth interviews with local inhabitants until the point of data-saturation. Results reveal that all surveyed coastal towns had hard-infrastructure that was built after 2010, in the form of promenades and elevated housing. The former structures contributed positively to building economic resilience in Dichato, Talchuano and Penco, through the promotion of tourism and small-scale fishing activities. However, the physical design of the elevated houses was found to only facilitate recovery of community economic functions in Tumbes, while causing strain on the social fabric and possibly hindering tsunami evacuation in all other study sites. The mixed contribution of hard-infrastructure to coastal resilience highlights the need for the de-centralization of planning and reconstruction processes for a successful contextualization of the issue.