Fast High-Resolution S-PTHA Along the Western Mediterranean Sea Coastlines. Application to the Bay of Cannes

Probabilistic Tsunami Hazard Assessment (PTHA) is a fundamental framework for producing time-independent forecasts of tsunami hazards at the coast, taking into account local to distant tsunamigenic earthquake sources. If high resolution bathymetry and topography data at the shoreline are available, local tsunami inundation models can be computed to identify the highest risk areas and derive evidence-based evacuation plans to improve community safety. We propose a fast high-resolution Seismic-PTHA approach to estimate the tsunami hazard at a coastal level using the Bay of Cannes as test site. The S-PTHA process is firstly fastened by performing seismic and tsunami hazards separately to allow for quick updates, either from seismic rates by adding new earthquakes, or from tsunami hazard by adding new scenarios of tsunamis. Furthermore, significant tsunamis are selected on the basis of the extrapolation of a tsunami amplitude collected offshore from low-resolution simulations to an a priori amplitude nearshore using Green’s law. This allows a saving in computation time on high-resolution simulations of almost 85%. The S-PTHA performed in the Bay of Cannes exhibits maximum expected tsunami waves that do not exceed 1 m in a 2500-year period, except in some particular places such as the Old Port of Cannes. However, the probability to experience wave heights of 30 cm in this same period exceeds 50% along the main beach of Cannes and these results need to be considered in risk mitigation plans given the high touristic attraction of the area, especially in summer times.

Tsunami Hazard Assessment Along Chinese Coast Using Scaling Relations Developed for Tsunami Prediction

Potential tsunamis in the western Pacific Ocean pose great threats to the Chinese coastal areas. Among all possible tsunami source regions, the Manila subduction zone draws the most attention and there have been many research works on the tsunami hazards in the South China Sea. In this study, we evaluate the tsunami hazard along the Chinese coast by investigating more potential sources, including the subduction zones of Manila, Ryukyu, Nankai, Izu–Bonin and Mariana. Two tsunami scenarios are considered for each subduction zone, a worst scenario of earthquake magnitude 9.0 and a scenario of largest earthquake magnitude known in history in this zone. Earthquake source parameters are calculated using scaling relations that have been shown to be suitable for tsunami generation. Our results show that for the Chinese coast, tsunami hazards from the Manila and Ryukyu subduction zones are severe in the worst scenarios, and tsunami hazards from the Nankai, Izu–Bonin and Mariana subduction zones are mild. Using the largest earthquake magnitude in history, tsunami hazards from all the investigated subduction zones are almost negligible. Through a sensitivity test on earthquake magnitude, we find that earthquakes of magnitude of 8.5 or larger in the Manila and Ryukyu subduction zones cause severe tsunami hazard along the Chinese coast with wave amplitude over 2 m.