Table 2. Tsunami deposit identification criteria based on the compilation of recent tsunami deposits studies from Peters and Jaffe (2010) compared to the present case study.
characteristic | recent tsunami deposits (Peters and Jaffe, 2010) | present case |
|---|---|---|
basal contact | most tsunami deposits have sharp contact with the underlying material, in many cases erosional | sharp contact with underlying soil, in some cases erosional |
the deposit geometry | most tsunami deposits forms landward-thinning sand sheets, often patchy near the limit of inundation | sand sheet with sediment patches close to the shoreline and to the inundation limit; thickness usually increases landward and then decreases; however, the trends are variable; for low run up heights, the thickness changes within the sand sheet may follow the landward thinning trend |
deposits thickness | in range of 1–30 cm, the maximum is 150 cm | vary from few mm to more than 40 cm |
number of depositional layers | typically 1–4 layers, often the number of layers decrease landwards | 1–4 layers, no correlation between the number of layers and distance from shoreline |
vertical grading | normal grading is a common feature, although ungraded deposits are also frequent; occasionally, inverse grading is present | normal grading is common, as are ungraded (massive) deposits; in a few cases inverse grading is found |
mud cap | thin layer of mud or finer material often drape the top of deposits | sometimes finer deposits at the top, rare mud cup |
rip-up clasts | many deposits contain clasts of material ripped up from the underlying substrate (mud or soil) | rare mud clasts and soil rip-up clasts |
boulders | common, mainly coral boulders | only in specific sites, coral and granite boulders, as well as blocks of concrete |
sedimentary structures | not common, truncated flame structures, cross bedding, parallel laminations, scour and fill structures | in approximately 15% of sites parallel laminations; moreover, occasional cross bedding, scour and fill structures |
coastal sediment source | tsunami deposits usually have a coastal source reflected in composition, grain size, grain size texture, marine or coastal fossils; some sediments may come from terrestrial environments | common benthic foraminifera, diatoms, shells, grain size similar to beach and nearshore sediments, geochemical salinity indicators; occasional plant fragments, human artefacts |