A probabilistic tsunami hazard assessment for the southern coast of Java, Indonesia: building an inundation database through a two-stage framework

Abstract Probabilistic tsunami hazard assessment (PTHA) at the inundation level over large spatial scales remains computationally challenging, requiring many scenarios, fine-resolution modelling, and high-quality digital elevation models (DEMs). Previous studies have addressed either regional offshore hazards or local-scale inundation, leaving comprehensive regional inundation assessments largely unexplored. We applied a two-stage framework to perform the first inundation-level PTHA covering over 1000 km of the southern coast of Java, Indonesia, for Java megathrust tsunamis. The framework couples coarse-resolution (450 m) offshore propagation modelling using JAGURS (Stage 1) with high-resolution (30 m) onshore inundation using SFINCS (Stage 2). We simulated 4400 earthquake scenarios ( $$M_w$$ 7.0–9.2) using a space- and time-dependent Epidemic Type Aftershock Sequence (ETAS) model with heterogeneous stochastic slip models. Maximum offshore tsunami heights reach 10.3 m, 18.9 m, 23.0 m, and 29.5 m at annual exceedance rates of 1/500, 1/2500, 1/5000, and 1/10000, respectively, with inundation extending several kilometres inland depending on local topography. Sensitivity analyses show that hazard estimates depend strongly on the number of simulated events and that linear shallow water equations in Stage 1 can generate unrealistic large onshore hazards. Open-source DEMs (BATNAS and DeltaDTM) proved suitable for regional PTHA once known dataset limitations are accounted for. The onshore estimates represent a lower bound, and the $$M_w$$ 9.2 scenario a conservative upper bound given structural constraints on the megathrust. This modular framework provides a transferable approach for large-scale inundation-level PTHA in other tsunami prone regions.