Primary Research on Tsunami Depositional Models

摘要

Tsunami depositional process involves two critical processes:rip-up and backwash.As a tsunami arrives at the shore and breaks down,amount of seabed sediments are eroded intensively.Tsunamis can transport these sediment landward as a turbulent flow,including coastal sandstone,pebblestone,silt,clay and lots of shell or fossil fragments[1].As current velocity decrease,its erosive capacity weakens and deposition of coarse sediment increases.Larger bio-clasts may deposit in the coastal plain.Before the water body changes direction,the current stay stagnant when fine-grain silts and clay remain in suspension whereas material coarser than silt can be deposited,and shows normal grading.During the backwash time,the seaward flow take the onshore sediment both in situ and previousy deposited back to sea.If the shallow coastal areas are fiat enough,sediment tends not easy to form gravity flow; if basal topography turns steep,the transportation of sediments by high-density sediment gravity flows happens commonly in valleys and canyons,and deposited fast in the fiat area to form homogenous turbidite.Stacking pattern of sedimentary structures varies in accordance with various sedimentary settings.