Dr. Aranguiz-Muñoz, Rafael

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.

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.