Numerical Experiments on Tsunami-Tide Interaction over the East Asian Marginal Sea

Abstract:

The East Asian marginal sea (EAMS) including the East China Sea and the Yellow Sea is one of the largest marginal seas in the world bordered with Korea, China, Japan and Taiwan. It is mainly connected to the Pacific Ocean via the Ryukyu Islands, Japan. In the EAMS, the coastal processes and environment are dominated by tide and tidal currents, and topography has a major effect in modifying deep-sea tides. Approximately 7% of the global tide energy dissipates in the EAMS. Tidal ranges exceed 4 m at many coastal ports and tides are of most importance in coastal processes, in influencing anthropogenic activities near the coast, and in the transport of sediments. The general propagation of diurnal tides is from north to south along the East China Sea shelf break and the semi-diurnal tides have a more or less constant phase at the shelf break of the East China Sea, with phases and amplitudes increasing landward. This study investigates the impacts of tides and tidal currents on extreme tsunami propagation in this region throughout numerical experiments with adaptive mesh refinement. Tsunami experiments are conducted based on five scenarios taking the tides and tidal currents at 4 different phases, such as flood, high, ebb, and low tides, into account. The initial tsunami displacement is adopted from one of the seven Ryukyu Trench and Nankai Trough potential earthquake scenarios. Based on the results of numerical experiments, the maximum tsunami heights along the coastlines in the Yellow and East China Seas are mostly reduced after considering the nonlinear tsunami-tide interactions except at some probes whose maximum tsunami heights are increased as tidal ranges get larger near the Gyeonggi Bay, Korea. Likewise, the occurrence times of the maximum tsunami heights show large difference at those probes with increased maximum tsunami heights. Further, the uncertainty in maximum tsunami height, defined as ratio between the difference of maximum tsunami heights with and without tsunami-tide interaction, depict that the calculated maximum tsunami heights in tsunami modelling can include the uncertainty more than 50% in the EAMS. The results recommend simulate tsunamis together with tides in shallow water environments to reduce the uncertainties involved with tsunami modeling and predictions for tsunami hazards preparedness.