26 December 2004 tsunami deposits left in areas of various tsunami runup in coastal zone of Thailand

Abstract

The tsunami deposits left by the 26 December 2004 tsunami in the coastal zone of Thailand were studied within two months of the event and before any significant postdepositional changes could occur. The sediment structure and texture (grain size), as well as its thickness and spatial distribution, were documented for the tsunami deposits in 12 shore-perpendicular transects from areas of various tsunami runup and wave heights. The tsunami deposits were as thick as 0.4 m and were located as far as 1.5 km inland. They were composed mostly of poorly sorted sand and often consisted of one to four normally graded, massive or laminated layers. The deposits generally became finer in the landward direction; however, landward thinning trend of the deposits is not clear, and the maximum accumulation often is not located close to the shoreline but rather is further inland. In comparable coastal environments with similar available sediment sources the tsunami size (represented as the tsunami runup height) is reflected in the resulting deposits. Larger tsunamis are associated with deposits that are thicker, have a maximum accumulation located farther inland, include a finer sediment fraction (likely from deeper offshore areas) and frequently are composed of normally graded layers.