Machine Learning for Tsunami Waves Forecasting Using Regression Trees

After a seismic event, tsunami early warning systems (TEWSs) try to accurately forecast the maximum height of incident waves at specific target points in front of the coast, so that early warnings can be launched on locations where the impact of tsunami waves can be destructive to deliver aids in these locations in the immediate post- event management. The uncertainty on the forecast can be quantified with ensembles of alternative scenarios. Similarly, in probabilistic tsunami hazard analysis (PTHA) a large number of simulations is required to cover the natural variability of the source process in each location. To improve the accuracy and computational efficiency of tsunami forecasting methods, scientists have recently started to exploit machine learning techniques to process pre-computed simulation data. However, the approaches proposed in literature, mainly based on neural networks, suffer of high training time and limited model explainability. To overtake these issues, this paper describes a machine learning approach based on regression trees to model and forecast tsunami evolutions. The algorithm takes as input a set of simulations forming an ensemble that describes potential benefit regional impact of tsunami source scenarios in a given source area, and it provides predictive models to forecast the tsunami waves for other potential tsunami sources in the same area. The experimental evaluation, performed on the 2003 M6.8 Zemmouri-Boumerdes earthquake and tsunami simulation data, shows that regression trees achieve high forecasting accuracy. Moreover, they provide domain experts with fully-explainable and interpretable models, which are a valuable support for environmental scientists because they describe underlying rules and patterns behind the models and allow for an explicit inspection of their functioning. This can enable a full and trustable exploration of source uncertainty in tsunami early-warning and urgent computing scenarios, with large ensembles of computationally light tsunami simulations.