THE INDIAN OCEAN TSUNAMI 2004: IDENTIFICATION OF TSUNAMI DEPOSITS OFFSHORE IN THE ANDAMAN SEA BY DIFFERENT PROXIES

It was doubted for a long time that in wave dominated coastal areas the impact of tsunami waves on shoreface deposits can be preserved. Following high resolution mapping with different hydroacoustic methods, positions for grab sampling and coring were identified, where tsunami deposits were supposed to occur. The sampled material was analyzed using a wide range of sedimentological, geochemical, micropalaeontological, chemical, and physical methods. Storm and tsunami event layers could be identified and distinguished. Individual layers, ranging from 12 - 39 cm in thickness, were interpreted as tsunami deposits. Run-up and backwash deposits could be distinguished. Based on foraminiferal transfer functions and textural analyses re-suspension of sediment during run-up seemed to be restricted to about 20 m water depth. On the other hand it could be shown by using PAHs as a chemical proxy that the loaded backwash extends up to 25 km offshore.