Towards the Global Tsunami Model Probabilistic Tsunami Hazard Analysis (GTM-PTHA) tool

The Global Tsunami Model Association (GTM) is presently finalizing a Probabilistic Tsunami Hazard Assessment (PTHA) for earthquake-generated tsunamis at the global scale. Compared to the Davies et al. (2018) global PTHA, the GTM-PTHA incorporates several new features, including stochastic slip models, a spatially higher resolution of calculation points (which also includes relatively small islands), and the consideration of tides and long-term sea level variations. An important aspect is that the GTM-PTHA is interoperable with seismic source models and risk calculation tools from Global Earthquake Model (GEM) (e.g., OpenQuake Engine). The preliminary GTM-PTHA Python framework tool can be used to calculate hazard curves from different subduction interfaces at different points of interest, presently limited to the coasts of the Pacific Ocean. The steps implemented in the workflow integrate long-term seismic information, numerical tsunami simulations of unit sources to build a database of Green’s Functions (GF), a linear combination of the GF, and probabilistic hazard calculations. Specifically, the workflow begins with the definition of a probabilistic earthquake model, based on synthetic earthquake scenarios generated at each subduction interface. The occurrence rates of each scenario depend on the frequency-magnitude distribution specific to each subduction zone. Then, the tsunami waveforms associated with each synthetic rupture are computed through a linear combination of precalculated GF defined for each subduction zone (assuming a linear tsunami propagation). In the final step, probabilistic tsunami hazard curves are generated by combining the annual occurrence rates of the earthquake scenarios with the maximum wave amplitudes computed on a set of predefined points. A dedicated sensitivity analysis is also being performed, whose preliminary results will be illustrated, providing insight into the epistemic uncertainties associated with the new hazard model.

The authors thank the EU ChEESE-2P project (Centre of Excellence for Exascale in Solid Earth, https://cheese2.eu/), which funded part of this project under grant agreement No 101093038. 

Davies, G., Griffin, J., Løvholt, F., Glimsdal, S., Harbitz, C., Thio, H. K., ... & Baptista, M. A. (2018). A global probabilistic tsunami hazard assessment from earthquake sources. Geological Society of London. [doi: 10.1144/SP456.5].