TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 64 (No. 10), pp. 931-943, 2012

Sedimentary deposits left by the 2004 Indian Ocean tsunami on the inner continental shelf offshore of Khao Lak, Andaman Sea (Thailand)

D. Sakuna1,2, W. Szczuciński3, P. Feldens1, K. Schwarzer1, and S. Khokiattiwong2

1Institute of Geosciences Sedimentology, Coastal and Continental Shelf Research, University of Kiel, Otto-Hahn-Platz 1, D-24118 Kiel, Germany
2Oceanography and Environment Unit, Phuket Marine Biological Center, P.O. Box 60, Phuket 83000, Thailand
3Institute of Geology, Adam Mickiewicz University, Maków Polnych 16, 61-606 Poznań, Poland

(Received November 24, 2010; Revised May 3, 2011; Accepted June 15, 2011; Online published October 24, 2012)

Abstract: Tsunami waves leave sedimentary signatures both onshore and offshore, although the latter are hardly known. The objective of the present study is to provide new evidence for the 2004 Indian Ocean tsunami deposits left on the inner continental shelf of the Andaman Sea (Thailand) and to identify diagnostic sedimentological and geochemical properties of these deposits. Based on extensive seafloor mapping, three sediment cores were selected for study and were analysed for their sedimentary structures, grain size composition, chemical elemental composition, physical properties and 210Pb activity. Sediment cores retrieved from shallow water (9-15 m) within 7.5 km off the shore revealed distinct event layers, which were interpreted as being tsunami deposits. These 20-25 cm thick deposits were already covered with post-tsunami marine sediments. They were composed of several units, marine sand layers alternating with poorly sorted mud with terrigenous and anthropogenic components, representing different hydrodynamic conditions (probably during run-up and backwash phase). These sedimentological observations were supported by geochemical and physical data and were confirmed using 210Pb dating. A sediment core taken from a depth of 57 m at a distance of 25 km offshore did not reveal clear event deposits. Comparisons with available data from offshore tsunami deposits showed that there is no single set of signatures that could be applied to identify this kind of deposits.
Key words: 2004 Indian Ocean tsunami, offshore tsunami deposits, sedimentology, Khao Lak, Thailand.

Corresponding author E-mail: daroonwan@gpi.uni-kiel.de

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