# Reconstructing the 26 June 1917 Samoa Tsunami Disaster
## 4 Results
### Comparison with the 2009 Tsunami  
The 2009 event is the most devastating tsunami to have affected Samoa in recent history. Occurring on 29 September, at 06:48 a.m. local time, two earthquakes only minutes apart shook the ground and caused large waves to travel quickly through the ocean, which caused major destruction and loss of life in less than 30 min after the earthquake rupture [26,38,39]. As the 1917 event can be considered a historical predecessor to the 2009 event in terms of source region [12], a comparison between the two events is made.  
Apart from the obvious differences in instrumental monitoring quality in 1917 compared with 2009 [26,40], the main differences between the two events in terms of the distribution of affected coast are highlighted in Figure 10. The main energy beam for the 1917 tsunami was focused towards west and south Savai'i, whereas for the 2009 event, energy was focused towards American Samoa and southeast Upolu, which reflects the proximal epicentral locations of the generating earthquakes, respectively, which were about 150 km apart.  
Figure 7: Inundation on Upolu in close-ups (10 m res.). The map shows the 10 m resolution run-up on Upolu (**a**) and in Apia (**b**), with the most severe inundation in Upolu close to Gagío’olevao (**c**).  
Figure 8: _Cont_.  
These hazard characteristics help to explain the observed variations in exposure impact distributions between the modelled 1917 and benchmark 2009 events. A larger proportion of people would be exposed in Savai'i island (71% of the total exposure) compared with Upolu island if a characteristic 1917-type event were to occur. In contrast, coastal areas in southeast and east Upolu were most severely affected in the 2009 event, which reflects the epicentral location of the generating earthquake at the subducting bend of the NTT terminus and main direction of tsunami flux east/northeast towards southeast Upolu. The 1917 epicentre 150 km to the west at the transform segment of the NTT results in the main direction of tsunami flux northward towards Savai'i. This implies that the distribution of the relative exposure of elements at risk to NTT-sourced tsunamis depends on the location of earthquake origin along the subduction zone bend of the NTT.  
Notwithstanding the spatial differences in exposure relative to the location of tsunami origin at the NTT, of note is the time of day that each event occurred. Both events struck either in the morning (2009 tsunami) or in the evening (1917 tsunami) during times when the residential population was not at maximum capacity. Had they occurred in the middle of the night, for example, then the scale of human losses might have been significantly greater in each event; this is a key consideration in resilience planning for future NTT sourced tsunamis.  
Figure 8: (**a**) Present-day buildings categories on Savai’i and Upolu. (**b**) Exposure of buildings in Savai’i and Upolu to the 1917 modelled scenario event. (**c**) Close up of Sala’ilua village on southwest Savai’i showing the modelled tsunami inundation and exposed buildings.  
Figure 9: Number of people affected in residential buildings in the six damage states on: (**a**) Upolu, and (**b**) Savai’i.