Local amplification of tsunami waves along the west coast of Negros Island and Panay Island

Abstract

Panay Island and Negros Island in the east of the Sulu Sea face hazard of near-field earthquake-generated tsunami. This study aims to assess the tsunami hazard along the west coast of the two islands caused by near-field earthquakes with the largest possible magnitude, and focuses on the high hazard spots which are always attacked by higher tsunami waves. The Negros Trench is considered to be the potential source of seismic tsunami based on the historical tsunami and earthquake data, and special attention is given to the hazard associated with edge waves caused by near-field earthquake and other wave energy convergence mechanisms. A series of tsunami scenarios in this area are numerically simulated based on the widely-used ocean dynamic model FVCOM (an unstructured grid, Finite-Volume Community Ocean Model). The largest historical tsunami in the recent century is simulated and reproduced, and the results are in reasonable agreement with the historical observation. Further, a set of possible scenarios considering earthquakes with largest historical magnitude are simulated, and other seismic parameters are determined through the statistical analysis of the regional historical seismic data and the previous studies. The maximum tsunami wave along the coast in each scenario is analyzed and given. The results show that the near-shore tsunami is greatly affected by the epicenter location and other seismic parameters. The influences of seismic parameters on each coast location are different and complex, due to the winding shoreline and local topography. However, the spatial distribution of tsunami waves along the coast has certain regularity. It is found that there are some spots which always face a higher tsunami hazard. From the analysis of wave propagation, the high hazard along the west coast of Negros Island is ascribed to edge waves formed by the trap of wave energy in shallow water. Moreover, a variety of interesting phenomena associating with other high hazard spots can be found in this area, including wave convergence by bell-shaped mouth, the superposition of incident and reflected waves, and wave refraction around a cape. More attention in coastal protection should be paid on those high hazard spots.