Insights on the 2009 South Pacific tsunami in Samoa and Tonga from field surveys and numerical simulations

Hermann M. Fritz*, Jose C. Borrero, Costas E. Synolakis, Emile A. Okal, Robert Weiss, Vasily V. Titov, Bruce E. Jaffe, Spyros Foteinis, Patrick J. Lynett, I. Chi Chan, Philip L F Liu

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

38 Scopus citations

Abstract

An Mw≈8.1 earthquake south of the Samoan Islands on 29 September 2009 generated a tsunami that killed 189 people. From 4 to 11 October, an International Tsunami Survey Team surveyed the seven major islands of the Samoan archipelago. The team measured locally focused runup heights of 17m at Poloa and inundation of more than 500m at Pago Pago. A follow-up expedition from 23 to 28 November surveying the three main islands of Tonga's northernmost Niua group revealed surprising 22m runup and 1km inundation. We analyze the extreme tsunami runup and complex impact distribution based on physical and societal observations combined with numerical modeling. That an outer rise/outer trench slope (OR/OTS) event is responsible for a tsunami disaster in the Pacific calls for care in identifying and defining tsunami hazards. Evacuation exercises conducted in Samoa in the preceding year may have limited the human toll; however, cars were identified as potential death traps during tsunami evacuations. This event highlights the extreme hazards from near source tsunamis when the earthquake's shaking constitutes the de facto warning, and further underscores the importance of community based education and awareness programs as essential in saving lives.

Original languageEnglish (US)
Pages (from-to)66-75
Number of pages10
JournalEarth-Science Reviews
Volume107
Issue number1-2
DOIs
StatePublished - Jul 1 2011

Keywords

  • Earthquake
  • Samoa
  • South Pacific
  • Tonga
  • Tsunami

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

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