Factors controlling onshore distributions of sandy tsunami or storm deposits

Tsunami and storm deposits are useful for estimating inundation area and recurrence intervals of extreme waves in modern, historic and prehistoric ages. However, the distribution of these deposits is very complex and affected by various factors.

Here, we use numerical computations highlighting the factors, which control inundation distance of tsunamis and storm waves, and subsequently govern the distributions of these coastal sand deposits. As a result, the computed extents of inundation limit and sand deposit induced by tsunami were generally larger than the ones from storm waves. However, distribution distance of sandy storm deposit sometimes become long when the deposit was formed in local depression where is located at several kilometers inland from the coastline, so that deposit volume over land is more valid for identification of onshore tsunami deposit. Indeed, the computed volume of storm deposit become significantly small compared to tsunami deposit. The parameters which mostly contribute to inundation distance of tsunami or storm wave and distribution distance of sandy tsunami or storm deposit were land slope. While, the parameters mostly contribute to deposit volume over land of tsunami or storm deposit are respectively land slope and the size of input wave (wave height and wave period). For identifying tsunami deposit based on limited inland extent of storm deposit and limited deposit volume over land, the presented results would be very effective because key parameters that control the distribution of onshore tsunami or storm wave deposits was revealed.

Our numerical computation doesn't consider the two-dimensional effect or detailed shape of topography or bathymetry. Thus, detailed modeling work is necessary to be conducted for quantitative evaluation of the distribution of onshore sandy deposit and inundation area of the both waves in the field site. For properly distinguishing between tsunami and storm deposits, detailed modeling work and use of the many identification criteria are required. Once the tsunami or storm deposits are appropriately identified, size or recurrence interval of extreme waves can be examined, which will be useful for future risk assessment at coastal area in the world.