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Speaker: Ignacio Sepulveda, Assistant Professor, Coastal Engineering, San Diego State University

Host: Harm Van Avendonk

Title: Compound and cascading processes shaping tsunami responses: A new era of multidisciplinary research

Abstract: Catastrophic tsunamis in the last few years have evidenced a more complex genesis and coastal response than previously thought. As a consequence, tsunami modeling and hazard prediction tools are under scrutiny. New tsunami research is needed which shall integrate multiple disciplines. Two pressing questions investigated by our group are the influence of compounding processes increasing tsunami hazard and the understanding of non-conventional geophysical processes cascading into tsunamis.

Tides and climate driven sea level rise (SLR) contribute significantly to water level changes in the short and long term, respectively. In terms of magnitude, they could be comparable to tsunamis of interest at certain coasts. New non-stationary probabilistic tsunami hazard assessment (nPTHA) methods are developed to include the mean sea level changes due to a warming climate and the uncertainty of the tidal phase at the moment of tsunami occurrence. A surrogate model is used in the nPTHA method to render the calculation feasible and efficient. The development of formulations based on surrogate models is the key to establishing a method which feasibly can be applied to other regions for comprehensive analysis at a global scale. As an illustration, these methods are applied for assessing tsunamis generated in the Manila Subduction Zone and impacting the coasts of Kao Hsiung and Hong Kong. The results of the illustration case show that tides have a relevant impact on the nPTHA. However, the SLR within an exposure time of 100 years has a stronger impact. It is perhaps counterintuitive for the increase in hazard from SLR to be greater than the increase from tides, when the perception by the general public may be that tides are much bigger than estimates of SLR, because of familiarity. This poses an outreach opportunity for increasing awareness of climate change and tsunami hazards.

Recent catastrophic tsunamis have also evidenced the relevance of non-conventional tsunamigenic sources. The 2022 Hunga Tonga-Hunga Ha’apai Volcano eruption, in particular, triggered a tsunami which was recorded globally. While the highest tsunami crest-to-trough heights, up to 3 meters, were only recorded within the Pacific coastlines, heights up to 1 meter could be also observed in remote locations such as Ghana and Portugal. The high waves and far-reaching character of the tsunami reopened the question about the destructive potential of volcanic tsunami hazards. The signature of the 2022 tsunami around the globe is investigated and new numerical tools to simulate the special forcing mechanisms of volcanic sources are under development. These studies aim to provide tools for volcanic tsunami hazard assessment approaches and to improve the quantification of their uncertainties.