COMPARATIVE ANALYSIS OF DEPTH AVERAGED, OVERLAND TSUNAMI FLOW VELOCITIES FROM SEDIMENT TRANSPORT MODELS, STRUCTURAL DAMAGE, AND VIDEO RECORDINGS WITH APPLICATIONS TO TSUNAMI PALEODEPOSITS

Knowledge of prior tsunami magnitudes and recurrence intervals is invaluable in estimating local tsunami hazard potentials. However, historic records may be incomplete or may not cover a long enough period for the largest tsunami magnitudes. Sediment deposits left by tsunamis can supplement and extend an incomplete historic record, potentially providing otherwise unavailable information on tsunami intervals and magnitudes if they can be identified in the geologic record. Such tsunami paleodeposits reflect the hydrodynamic conditions (e.g. flow velocity, flow depth, run-up elevation), and thus the magnitude, of the onshore wave incursion. Several recent models have focused on determining overland tsunami flow characteristics from the grading and grain size distribution of the tsunami deposit. For example, the Tsunami Sedimentation Model (TsuSedMod), as developed by Jaffe and Gelfenbuam, (in press) models particle settling as the primary deposition process and is applicable for normally graded deposits. For any given location, the grain size distribution and deposit thickness are used as observational constraints to model the depth averaged, wave height dependent flow velocity of the onshore wave incursion. In this study, we use the TsuSedMod approach to model overland, hydrodynamic tsunami flow conditions from tsunami deposit characteristics. We compare the modeling results to field observations of probable flow depths and velocities determined from structural damage, watermarks, and video recordings from the December 26, 2004 Indian Ocean tsunami in northwest Sumatra and the Andaman coast of Thailand. Preliminary results suggest that for locations where flow depth and velocity data could be well-constrained from field evidence and where the local tsunami sediment deposit is normally graded in a shallow-sloping environment, this approach produces flow velocity/depth results consistent with the observations. This suggests that estimates of flow velocity/depth from tsunami paleodeposit characteristics may be better constrained than previously thought if the paleodeposits can be recognized in the stratigraphic record.