2009 Samoan Islands Tsunami
Introduction
At 6:48 local time on September 29, 2009 (local time, UTC-11), a large earthquake of magnitude Mw 8.1 took place, which generated a large tsunami. This tsunami struck the coastal areas of the Independent State of Samoa, American Samoa, and Tonga.
Field Survey
The field survey was conducted on Upolu island in Samoa and Tutuila island in American Samoa, from October 28 to 31, 2009. Our survey team consisted of members from Waseda University and the National University of Samoa. The major findings obtained from this survey are described below.
- Tsunami height exceeded 5m in a wide area of Upolu and Tutuila Islands and the maximum run-up height was over 20 m in Poloa, American Samoa.
- The Samoan Islands, especially Upole Island, have a wide coral reef platform in front of them. Many people saw the wave breaking on top of it and quickly became aware of the approaching tsunami. Wave breaking on the coral reef decreased the kinetic energy of the tsunami in one of the surveyed villages.
- Due to widespread education concerning tsunami disasters, and regardless of whether the tsunami warning arrived (Ulutogia) or not (Satitoa, Poloa), many people said that they felt danger when the tsunami passed over the coral reef and decided to evacuate. Thus it was clear to the survey team that the effect of tsunami education is spreading, following the Indian Ocean Tsunami in December 2004.
- The social structure of the islands is very strong and the Matai (the chief of the village) has great authority in Samoa. This social condition influenced the residents' decision making process after the tsunami disaster. The residents in Poloa, American Samoa and Ulutogia, Samoa already decided to relocate to higher location around one month after the tsunami attack.
References
- Shibayama, T., Mikami, T., Matsumaru, R., Takagi, H. & Latu, F. (2010): Field Survey and Analysis of Tsunami Disaster in the Samoan Islands, Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering), 66(1), 1376-1380. (in Japanese with English abstract) [doi:10.2208/kaigan.66.1376]
- Mikami, T., Shibayama, T., Matsumaru, R., Takagi, H., Latu, F. & Chanmow, I. (2011): Field survey and analysis of tsunami disaster in the Samoan Islands 2009, 6th International Conference on Coastal Structures, Yokohama, Japan, 1325-1336.