Effects of tsunami magnitude and terrestrial topography on sedimentary processes and distribution of tsunami deposits in flume experiments

To identify and interpret tsunami deposits correctly, a better understanding of the effects of both tsunami magnitude and topographic setting are required. In the present study, laboratory experiments were performed to model these effects on sedimentary processes and the distribution of tsunami deposits on coastal lowlands. The experiments directed tsunamis of eight different magnitudes on to three different models of terrestrial topography: one with flat topography, one with a shallow water-filled pool, and one with a deep water-filled pool. The results suggested a relationship between the distribution of tsunami deposits and the hydraulic condition of the tsunami flow onto the terrestrial topography. In particular, the tsunami deposits in the pools were spatially more variable than those on land because of the variation in flow intensity associated with transformation of the flow from supercritical to subcritical with a hydraulic jump. We observed a gap between the landward extent of deposits and the tsunami inundation distance, particularly in the experiments with a pool. The total amount of sediment in tsunami deposits on the terrestrial area was found to depend on the magnitude of the tsunami, but the thickness of the deposits at any one given spot did not always depend on the tsunami magnitude, even in the same topographic. These results show that terrestrial topography has significant effects on the spatial distribution of tsunami deposits that must be taken into consideration when interpreting the history and magnitude of paleotsunami events from tsunami deposits.