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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 6 | Copyright

Special issue: Tsunami impacts on- and offshore in the Andaman Sea region

Nat. Hazards Earth Syst. Sci., 15, 1181-1199, 2015
https://doi.org/10.5194/nhess-15-1181-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Jun 2015

Research article | 12 Jun 2015

Internal structure of event layers preserved on the Andaman Sea continental shelf, Thailand: tsunami vs. storm and flash-flood deposits

D. Sakuna-Schwartz1,*, P. Feldens1, K. Schwarzer1, S. Khokiattiwong2, and K. Stattegger1 D. Sakuna-Schwartz et al.
  • 1Institute of Geosciences, Kiel University, Otto-Hahn-Platz 1, 24118 Kiel, Germany
  • 2Oceanography Unit, Phuket Marine Biological Center, P.O. Box 60, Phuket 83000, Thailand
  • *now at: Oceanography Unit, Phuket Marine Biological Center, P.O. Box 60, Phuket 83000, Thailand

Abstract. Tsunami, storm and flash-flood event layers, which have been deposited over the last century on the shelf offshore Khao Lak (Thailand, Andaman Sea), are identified in sediment cores based on sedimentary structures, grain size compositions, Ti / Ca ratios and 210Pb activity. Individual offshore tsunami deposits are 12 to 30 cm in thickness and originate from the 2004 Indian Ocean Tsunami. They are characterized by (1) the appearance of sand layers enriched in shells and shell debris and (2) the appearance of mud and sand clasts. Storm deposits found in core depths between 5 and 82 cm could be attributed to recent storm events by using 210Pb profiles in conjunction with historical data of typhoons and tropical storms. Massive sand layers enriched in shells and shell debris characterize storm deposits. The last classified type of event layer represents reworked flash-flood deposits, which are characterized by a fining-upward sequence of muddy sediment. The most distinct difference between storm and tsunami deposits is the lack of mud and sand clasts, mud content and terrigenous material within storm deposits. Terrigenous material transported offshore during the tsunami backwash is therefore an important indicator to distinguish between storm and tsunami deposits in offshore environments.

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