AUTHOR=Wassmer Patrick C., Gomez Christopher A., Iskandasyah T. Yan W.M. , Lavigne Franck , Sartohadi Junun TITLE=Contribution of anisotropy of magnetic susceptibility (AMS) to reconstruct flooding characteristics of a 4220 BP tsunami from a thick unconsolidated structureless deposit (Banda Aceh, Sumatra) JOURNAL=Frontiers in Earth Science VOLUME=3 YEAR=2015 URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2015.00040 DOI=10.3389/feart.2015.00040 ISSN=2296-6463 ABSTRACT=

One of the main concerns of deciphering tsunami sedimentary records along seashore is to link the emplaced layers with marine high energy events. Based on a combination of morphologic features, sedimentary figures, grain size characteristics, fossils content, microfossils assemblages, geochemical elements, heavy minerals presence; it is, in principle, possible to relate the sedimentary record to a tsunami event. However, experience shows that sometimes, in reason of a lack of any visible sedimentary features, it is hard to decide between a storm and a tsunami origin. To solve this issue, the authors have used the Anisotropy of Magnetic Susceptibility technique (AMS) to characterize the sediment fabric. The validity of the method for reconstructing flow direction has been proved when applied on sediments in the aftermath of a tsunami event, for which the behavior was well-documented like the 2004 Indian Ocean Tsunami (IOT). We present herein an application of this method for a 56 cm thick paleo-deposit dated 4220 BP laying below the soil covered by the 2004 IOT at Lampuuk, SE of Banda Aceh, North Sumatra. We analyzed this homogenous deposit, lacking of any visible structure, using methods of classic sedimentology to confirm the occurrence of a high energy event. We then applied AMS technique that allowed the reconstruction of flow characteristics during sediment deposition. We show that the whole sequence was emplaced by successive uprush phases and that the local topography played a role on the re-orientation of a part of the uprush flow, creating strong reverse current. This particular behavior was reported by eyewitnesses for the 2004 IOT event.