Dr. Aranguiz-Muñoz, Rafael

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.

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.

In the case of a near-field tsunami event, coastal residents must quickly become aware of the potential danger of a tsunami taking place and start taking actions to evacuate. The present paper aims to show which types of evacuation triggers worked amongst coastal residents with different characteristics and backgrounds by conducting a comparative analysis of four recent near-field tsunami events. The results of the analysis showed that basic knowledge about tsunamis had been spreading throughout the areas studied, which triggered many people to evacuate soon after feeling ground motion, almost regardless of how frequently each area had experienced tsunami events in the past. Educational activities and community-based efforts appear to be some of the reasons that can explain this finding. However, because some people in areas with fewer past experiences only evacuated after noticing last-minute signs and there is a nonnegligible number of visitors present in the coastline of certain communities, continuous efforts toward developing tsunami awareness are still needed. The results of the analysis also showed that in areas with fewer past experiences, people were more likely to wait for messages from the authorities to decide to evacuate. This finding highlights the importance of teaching local residents and visitors how a tsunami can reach a given area in a relatively short period of time.

On September 28, 2018 significant tsunami waves, which are considered to have been generated by submarine landslides, struck the shorelines of Central Sulawesi, Indonesia. One month after the event, the authors conducted a questionnaire survey of the affected areas (Donggala Regency and Palu City) to collect information on the evacuation behaviour and tsunami awareness of local residents. In the present study, in addition to summarising the overall trend of the survey results using descriptive statistics, a chi-squared test was applied to analyse the significance of the relationship between tsunami awareness and evacuation behaviour and the demographic characteristics of respondents. The analysis of the results demonstrates that although the respondents generally have a high level of tsunami awareness, younger people and Donggala Regency residents have an overall lower understanding of the phenomenon. It was also found that 82.5% of the population evacuated after witnessing others evacuating during the event. As there was no official warning to residents before the arrival of the tsunami, this social trigger played a significant role in prompting evacuation and decreasing the number of casualties. The present study also revealed that many people faced congestion while evacuating (especially in Palu City). This highlights the need to introduce additional tsunami disaster mitigation strategies to ensure that all residents can swiftly evacuate during such incidents.

The September 28 2018 Palu tsunami surprised the scientific community, as neither the earthquake magnitude nor its strike-slip mechanism were deemed capable of producing the wave heights that were observed. However, recent research has shown that the earthquake generated several landslides inside Palu bay. The authors conducted a post-disaster field survey of the area affected to collect spatial data on tsunami inundation heights, nearshore and bay bathymetry, and carried out eyewitness interviews to collect testimonies of the event. In addition, numerical simulations of the tsunami generation and propagation mechanisms were carried out and validated with the inferred time series. Seven small submarine landslides were identified along the western shore of the bay, and one large one was reported on the eastern shore of Palu City. Most of these landslides occurred at river mouths and reclamation areas, where soft submarine sediments had accumulated. The numerical simulations support a scenario in which the tsunami waves that arrived at Palu city 4–10 min after the earthquake were caused by the co-seismic seafloor deformation, possibly coupled with secondary waves generated from several submarine landslides. These findings suggest that more comprehensive methodologies and tools need to be used when assessing probabilistic tsunami hazards in narrow bays.

Water level oscillations induced by the ground motion of an earthquake have occasionally been observed in a closed or partially enclosed water system. The generated water disturbances can induce localized flooding, boat collisions, breakage/damage of moored cables due to water disturbances, or even the capsizing of vessels. In this study, the authors focused on cases of seismic water level oscillations in canals and attempted to investigate the potential hazards of and effective countermeasures against them through numerical simulations. The proposed numerical simulation model was first validated by reproducing the water level oscillation that was actually observed at a canal in Mexico City (Xochimilco Canal) during the 2017 Central Mexico Earthquake. The method was then applied to one of the canals in Tokyo (Keihin Canal) to clarify the potential water level fluctuations that can take place due to this phenomenon. The results indicate that while the risks of local inundation would be low, small boats, which can be found in many places in the canal, are at risk of capsizing. Finally, the use of wave-dissipating blocks was found to be an effective countermeasure to decrease the potential for a significant seismic water level oscillation to take place in this canal.