Probabilistic Tsunami Hazard Assessment in The Lesser Sunda Islands, Indonesia

The Lesser Sunda Islands (comprising Bali, West Nusa Tenggara, and East Nusa Tenggara) are situated between three seismic sources: the subduction zone, the fold-thrust back (FTB), and the back-arc thrust fault system in the north. The combined activity of these three sources makes the region highly vulnerable to tsunami hazards. The high population density in coastal areas and the presence of critical infrastructure in this region increase the urgency of conducting a tsunami hazard assessment. This study aims to analyze the tsunami hazard using a Probabilistic Tsunami Hazard Assessment (PTHA) based on a Green’s function approach, derived from simulations of the Shallow Water Equation (SWE). A total of 10,120 tsunami scenarios were developed from 9 fault sources using the stochastic slip distribution based on the Von Karman correlation function. All faults were divided into 108 subfaults to estimate the response of the tsunami wave at 255 observation points. The locations with the highest frequency per year for waves exceeding 1 m include Jembrana and Buleleng, northern and southern Sumbawa, as well as Sikka and west Manggarai. The tsunami hazard maps indicate that for a return period (RP) of 2475 years, more than 57% of the locations experience tsunami waves exceeding 3 m, with maximum heights reaching over 11 m. For the return period of 475 years, the rate is more than 0.4%, and for the return period of 72 years, there’s no location where the tsunami wave height exceeds 3 meters. The faults from the Bali subduction zone, the Sumbawa thrust, the Flores thrust, and the Timor FTB are the dominant contributors to the tsunami hazard in 20 strategic locations.