The TsuSedMod inversion model applied to the deposits of the 2004 Sumatra and 2006 Java tsunami and implications for estimating flow parameters of palaeo-tsunami Michaela Spiske a, ⁎, Robert Weiss b , Heinrich Bahlburg a , Julia Roskosch a , Hendra Amijaya c a Westfälische Wilhelms-Universität, Institut für Geologie und Paläontologie, Corrensstrasse 24, 48149 Münster, Germany b Department of Geology and Geophysics, Texas A&M University, College Station, Texas 77843, USA c Department of Geological Engineering, Gadjah Mada University, Jalan Grafika 2, Yogyakarta 55281, Indonesia abstract article info Article history: Received 29 June 2009 Received in revised form 1 December 2009 Accepted 21 December 2009 Available online 4 January 2010 Keywords: Flow depth Flow speed Inversion Sedimentation Tsunami deposit Palaeo-tsunami Flow depth and speed are crucial but sensitive parameters describing a tsunami's overland flow. Both parameters can be measured in post-tsunami field surveys for recent events, but are difficult to infer for ancient ones. TsuSedMod, an inverse model produced by Jaffe and Gelfenbaum (2007), can be applied to estimate both the minimum flow depth and speed by using the thickness and grain size distribution of a tsunami deposit. For given estimates of flow speeds or flow depths, the application of this code can help to evaluate the magnitude of a tsunami. In this study, we compare flow depths and flow speeds calculated with TsuSedMod to field data obtained in the aftermath of the 2004 Sumatra and 2006 Java tsunami. This study shows that the model gives a reasonable estimation of local tsunami flow depths and speeds for the analyzed tsunami runup sections. These data give information on the tsunami's onshore flow characteristics, such as the number of waves and flow deceleration due to obstacles. Sediment layers from different locations within the runup section can be correlated and assigned to the same wave. The testing of TsuSedMod on recent examples shows it to be a valuable tool for calculating flow depths and speeds of ancient tsunami. Together with the dating of respective tsunami deposits, information on magnitude and frequency of events along a particular coastline can be gained. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Post-tsunami field surveys give researchers the opportunity to directly evaluate the tsunami's impact on ecosystems, landscapes, and coastal infrastructures. On occasions these deposits are preserved for some considerable time. For example, in Lituya Bay evidence of erosion by the 1958 tsunami is still visible (Weiss et al., 2009). In most cases, many of these imprints disappear soon after the event, due to human activity in populated areas and a generally poor preservation potential of flow depth and runup indicators. A variety of different features can serve as traces or imprints of a tsunami. Water marks on buildings and discoloration of vegetation, as well as debris caught in trees are pivotal for estimating minimum flow depths. Furthermore, swash lines comprising tsunami transported debris indicate the minimum inunda- tion distance and runup height. During the 2004 Sumatra tsunami, surveillance cameras and tourists with video cameras recorded sequences of the flooding. These records gave rise to a new perspective on tsunami-inundation dynamics (Fritz et al., 2006). Inverse modelling can be a useful tool to produce quantitative information on historical tsunami (Huntington et al., 2007). Jaffe and Gelfenbaum (2007) developed TsuSedMod to help estimate flow depth and speed. As initial input for the computations, TsuSedMod uses the grain size distributions and the thicknesses of onshore tsunami deposits. TsuSedMod estimates the local tsunami flow speed by making use of a sediment transport model to determine the velocity necessary to suspend the present sediment volume of a certain grain size. Moreover, an iterative procedure is used to match the observed tsunami deposit thickness and grain size distribution. We tested the reliability of TsuSedMod on sediments from the 2004 Sumatra Tsunami in India and Kenya (sections St. James Beach Resort I + II; Ranganathapuram I + II; Ngomeni; Weiss and Bahlburg, 2006; Bahlburg and Weiss, 2007; 65 samples; Fig. 1a, b), and from the 2006 south Java tsunami (sections Bunton; Kelapa; Piepenbreier et al., 2007; 36 samples; Fig. 1c). Grain size data of tsunami sediment samples collected along beach transects and corresponding sediment thicknesses were employed to estimate flow depths. Computed flow depths were then compared to data from our post-tsunami surveys. This study, therefore, evaluates the use of TsuSedMod for various sites with siliciclastic sediments of variable composition and grain size available for tsunami transport. We also studied the influence of the Sedimentary Geology 224 (2010) 29–37 ⁎ Corresponding author. Tel.: +49 251 8333956; fax: +49 251 8333968. E-mail address: spiske@uni-muenster.de (M. Spiske). 0037-0738/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2009.12.005 Contents lists available at ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo