Earth Planets Space, Vol. 58 (No. 2), pp. 233-241, 2006
Gerassimos A. Papadopoulos1, Riccardo Caputo2, Brian McAdoo3,4, Spyros Pavlides5, Vassilios Karastathis1, Anna Fokaefs1, Katerina Orfanogiannaki1, and Sotiris Valkaniotis5
1Institute of Geodynamics, National Observatory of Athens, 11810 Athens, Greece
2Deptartment of Structural Geology, University of Basilicata, Macchia Romana Campus-85100 Potenza, Italy
3Institute of Geology, ETH Zentrum, Sonneggstrasse 5CH8092 Zurich, Switzerland
4Department of Geology and Geography, Vassar College, Box 735, Poughkeepsie, NY 12604, USA
5Department of Geology, Aristotelian University of Thessaloniki, 54006 Thessaloniki, Greece
(Received July 15, 2005; Revised December 28, 2005; Accepted January 17, 2006; Online published February 17, 2006)
Post-event field surveys were conducted and measurements were taken in Sri Lanka and Maldives about two weeks after the catastrophic Indian Ocean tsunami of 26 December 2004. The measurements taken were cross-checked after interviewing with local people. In the southwest, south and east coastal zones of Sri Lanka maximum water levels ranging from h = 3 m to h = 11 m a.m.s.l. were estimated. The highest values observed were in the south of the island: Galle h ~ 10 m, Hambantota h ~ 11 m. Maximum inundation of d ~ 2 km was observed in Hambantota. The heavy destruction and thousands of victims caused in coastal communities, buildings and infrastructure, like railways and bridges, is attributed not only to physical parameters, like the strength of the tsunami hydrodynamic flow, coastal geomorphology and the wave erosional action in soil, but also to anthropogenic factors including the increased vulnerability of the non-RC buildings and the high population density. Local people usually described the tsunami as a series of three main waves. The leading wave phase was only a silent sea level rise of h 1.5 m and d 150 m, while the second wave was the strongest one. The first two waves occurred between 09:00 and 09:30 local time, depending on the locality. It is well documented that near Galle, southern part, the strong wave arrived at 09:25:30. In the west coast the third wave was a late arrival which possibly represents reflection phases. In Maldives, three waves were also reported to arrive between 09:00 and 09:30 local time. Maximum water level was only h ~ 3 m in Laamu Atoll, which is interpreted by the wave amplitude damping by the coral reef to the east of the island complex as well as to that the tsunami did not arrived at high tide time. Damage was observed in several islands of Maldives but this was minimal as compared to the heavy destruction observed in Sri Lanka. About 25 Greek eyewitnesses, who happened to experience the tsunami attack in Padong and Blue Lagoon Port of Phuket island as well as in Maya Bay, Phi-Phi islands, Thailand, were interviewed on the basis of a standard questionnaire. The first sea motion was a retreat of at least 100 m. Then, two main waves arrived, the first being the strong one occurring at about 09:55-10:05 local time, with h ~ 6 m in Padong causing significant destruction and human victims. The collected information clearly indicates that the tsunami propagated as the leading crest wave to the west side, e.g. in Sri Lanka and Maldives, and as the leading trough wave to the east, e.g. in Thailand.
Key words: Sumatra earthquake, Indian Ocean tsunami, field observations, eyewitness accounts, Sri Lanka, Maldives Is., Thailand.