Scenario-based assessment of tsunami hazards in Prigi, Indonesia: understanding the threat from the East Java megathrust

The East Java megathrust is a highly active seismic zone that can generate destructive tsunamis along the southern coast of Indonesia. A seismic gap recently identified in southern East Java suggests considerable potential for future tsunamigenic earthquakes, possibly reaching magnitudes up to Mw 8.7. This study investigates tsunami hazards in the Prigi coastal area of East Java by simulating wave heights, arrival times, and inundation extents using the open-source COMCOT model. Three earthquake magnitude scenarios were analyzed: Mw 7.0, Mw 7.8, and Mw 8.7. The results show that under the worst-case scenario (Mw 8.7), tsunami waves reach the coastline within 35.54 minutes after the earthquake, attaining a maximum height of 20.29 meters and inundating approximately 1,052.3 hectares of land. An important novel finding is the occurrence of the Maximum Delayed (MD) phenomenon, in which the third wave at certain locations exceeded the first wave. This behavior has significant implications for evacuation planning and community risk perception, as early waves may not represent the most significant threat. The study concludes that Prigi is highly vulnerable to tsunami hazards and emphasizes the urgent need for comprehensive mitigation strategies to reduce loss of life and property.