International Journal of Disaster Risk Reduction 49 (2020) 101654 Available online 20 May 2020 2212-4209/© 2020 Elsevier Ltd. All rights reserved. Tsunami inundation hazard across Japan Jochen Woessner a, * , Rozita Jalali Farahani b a Model Development, Risk Management Solutions Inc, Zurich, 8050, Switzerland b Model Development, Risk Management Solutions Inc, Newark, CA, USA A R T I C L E INFO Keywords: Tsunami hazard Inundation hazard Simulation Japan ABSTRACT Japan faces the world’s highest tsunami hazard and risk due to its tectonic environment, high population density and exposure concentration along its coastlines. It is therefore of paramount interest to quantify and differentiate absolute and relative tsunami hazard and risk on a countrywide scale. We quantify tsunami hazard in terms of inundation depth for the entire Japanese coastline with a probabilistic tsunami hazard assessment utilizing the earthquake source information of the 2017 Japanese seismic hazard model. We simulate a stochastic event set for offshore earthquake sources and generate, for each single source with M W � 7.5, non-uniform fnite-fault slip models. We calculate elastic seafoor and landmass deformations that serve as initial conditions to high- resolution numerical modelling of tsunami wave propagation and coastal inundations by solving the non- linear shallow water equation. Variable land surface roughness based on land cover data is used to simulate accurate hydraulics of coastal inundation. We differentiate tsunami hazard by inundation depth hazard curves and inundation depth return period maps aggregated to city ward polygons as meaningful administrative boundaries. We fnd mega-thrust events on the subduction interfaces constituting the largest hazard. However, events down to M W ¼ 7.5 can contribute to substantial hazard in several regions along the coast. In particular for city wards within the Tokyo bay area, we fnd that earthquakes occurring on the Sagami trough and not the largest mega-thrust events on the Nankai trough, contribute to the highest inundation hazard. Our results also illustrate that tsunami hazard on the western Japanese coast is not negligible. 1. Introduction Tsunamis triggered by earthquakes are perceived as infrequent compared to earthquake ground shaking hazard and therefore treated as tail risk by emergency planners and the insurance industry. Rare mega- thrust subduction earthquakes are the major contributors whereas ground shaking hazard and risk have a more diverse set of contributing earthquake sources down to moderate magnitudes. Despite some pio- neering works in the early 1980s mainly on Japan [1,2], detailed large-scale Probabilistic Tsunami Hazard Assessments (PTHA) have only recently been developed [3–7]. This is primarily due to the scarcity of large tsunamis, the challenges of assessing tsunamogenic earthquake sources, diffculties in differentiating between ground shaking and tsunami impacts as well as the need for detailed inundation modelling. In this study, we perform a PTHA for the entire Japanese coastline for comparative hazard assessment. Evaluating tsunami hazard has improved in recent years through the introduction of probabilistic tsunami hazard assessment [3,4,8]. Many local, regional and global applications have been published aiming to improve the understanding of inundation depths, tsunami wave heights, and fooding areas using different approaches [4]. In particular following the 2004 Andaman-Sumatra and the 2011 Tohoku earth- quakes, many lessons have been learned about requirements for near-feld tsunami assessments in comparison to far-feld assessment and countermeasures for tsunami hazard (e.g. Ref. [9,10]). Geist et al. [11] initially pointed to the importance of rupture complexity for the near-feld tsunami hazard assessment, the uncertainty of incoming tsunami wave heights and inundation depths due to the rupture complexity. This has been further quantifed in detailed studies in several papers mostly following the 2011 Tohoku event [10,12–14]. Japan is prone to tsunami hazard and risk as large portions of the population, commercial and industrial exposure are located close to the coastline. More than 50% of the total population of Asia exposed to tsunami hazard lives in Japan according to Ref. [7]. This specifc exposure distribution increases the ratio of tsunami-to-earthquake haz- ard and risk in comparison to many other countries. For Japan it is * Corresponding author. E-mail address: jochen.woessner@rms.com (J. Woessner). Contents lists available at ScienceDirect International Journal of Disaster Risk Reduction journal homepage: http://www.elsevier.com/locate/ijdrr https://doi.org/10.1016/j.ijdrr.2020.101654 Received 16 October 2019; Received in revised form 26 March 2020; Accepted 7 May 2020