Reassessment of long-term Tsunami hazards in Samoa based on sedimentary signatures

Abstract

Investigating tsunamis and cyclones from depositional records enables an understanding of the long-term hazards to coastal communities. In Samoa, whilst a long-term record of tsunamis and cyclones spanning the last few millennia has been previously suggested based on preliminary sediment core/trench studies, a detailed assessment of the characteristics distinguishing these events has not been presented. This study reevaluates the depositional evidence available for Samoa and offers a more robust interpretation of the temporal and spatial records of tsunami events preserved in the Samoan sedimentary record. Tsunami inundation and runup records of the 2009 South Pacific tsunami along with differences in depositional settings, and sedimentary and geochemical characteristics of the associated deposits provide modern analogies for interpreting comparable older event-type deposits deeper in the Samoan geological record. These are aided by the 1990/1991 Cyclones Ofa and Val deposits previously suggested at some sites, which provides a modern analogy for interpreting cyclone-related deposits. Available radiocarbon and radiometric dates for the core/trench sites provide time-indicators to identify contemporaneous events, which we use to interpret the long-term record of tsunamis in this island region.