# Reconstructing the 26 June 1917 Samoa Tsunami Disaster
## 1 Introduction  
More than 700 million people live in island states, most of them developing countries, and low-lying areas at the coast are under constant risk from tsunamis, storm surges, or severe fluctuations of sea levels. In the Pacific, small island developing states (SIDS) represent a collection of remote island communities with developing economies that are often at elevated risk from climate change, sea level rise, coastal erosion, and both natural and anthropogenic hazards [1, 2]. It is often the case that due to their geography and the relatively small size of these islands, a significant proportion of the population, infrastructure, and commercial and industrial activity are concentrated in low lying areas, typically in a strip close to the coasts, which render them at considerable risk from coastal inundation from tsunamis [3]. The central south Pacific region is frequently affected by tsunamis generated from earthquakes centred on the Tonga Kermadec Trench, including 39 events between 1837 and 2009 that included the 1917 and 2009 tsunamis that affected the Samoa islands [4]. These two nearly identical events suggest that tsunamis in this region are relatively common, and, as a consequence, the SIDS in this area are exposed not only to global tsunamigenic events, but also to frequent locally derived tsunamis triggered by earthquakes, volcanic eruptions, and submarine landslides [5]. Indeed, the recent submarine volcanic eruption of Hunga-Tonga Hunga-Ha'apai (HTHH) in Tonga on 14 January 2022 [6; 7], and the resulting tsunami along with potential inferred predecessors (e.g., [8]), illustrate that there is a high degree of residual risk to these islands from local tsunami generating events. Local tsunamis with less than 30 min impact time are extremely hazardous to the island communities, due to the limited warnings and response times between the triggering event (earthquake or eruption, for example), and the tsunami wave making landfall. Consequently, when trying to understand current tsunami risks and the nature and extent of exposure to these islands, it is common to use data or records from historical events to constrain the likely intensity (inundation extent and flow depths, for example), and then use this within a scenario-based context to understand the present-day exposure if such an event was to occur today. The focus of this study is to reconstruct the 1917 tsunami that struck the islands of Samoa, which was the second most deadly tsunamigenic event on record to affect this region after the fatal 2009 tsunami that devastated the southeast coast of Upolu [9; 10] (Figure 1). Although the 2009 event provides a benchmark to help plan for and mitigate the impacts of local tsunamis sourced at the Northern Tonga Trench (NTT) in Samoa, areas that experienced little or no impact give rise to a public perception that these areas are at minimal threat from tsunamis. This is particularly the case for coastal areas in Savai'i island to the west of Upolu. However, very little is known about the impacts of the 1917 tsunami predecessor, despite the earthquake source magnitude being the largest ever recorded in this region [11]. Figure 1: Location of the 1917 earthquake epicentre (star) and 2009 earthquakes (circles) relative to Samoa. The 1917 earthquake epicentre was located along the transform segment of the NTT margin about 100 km south of west Savai'i, and approximately 150 km west of the 2009 earthquake. Preliminary modelling by [PERSON] et al. (2011) [12] suggests a focusing of tsunami flux northwards toward the west and southern areas of Savai'i. This implies that these areas would have been severely impacted compared with what they had experienced in the 2009 event. Paradoxically, the evidence presented in [12] does not seem commensurate with the lack of documented impacts for the event, which led them to hypothesize that the scale of impacts was masked by the impacts of the 1918 influenza pandemic, which occurred approximately 1 yr later.