TSUNAMI HAZARD ASSESSMENT DUE TO POTENTIAL EARTHQUAKE ALONG THE FLORES BACK ARC THRUST IN BULELENG REGENCY

Abstract

Buleleng Regency in North Bali was considered to be widely prone to tsunamis, as it is in close vicinity to the active tectonic zone of the Flores Back-Arc Thrust that can lead to massive earthquakes. Flood area, maximum run-up height, and wave arrival time are the three critical seismic parameters analyzed in this research to assess tsunami risk in the studied region. This study used the COMCOT v1.7 software to perform numerical simulations for a hypothetical Mw 7.5 earthquake, incorporating both all-land and all-water data. The result shows that Gerokgak sub-district, which had the most inundated area, about 8.87 km², and the other sub-districts, such as Buleleng, Banjar, and Sawan, also faced inundation. At moderate water depths (0.5–3 m), the most extensive inundated areas overlap frequently with high-density populated coastal areas, particularly at the river outlets and lowlands. From the arrival time analysis, it is found that the eastern coast has the shortest warning time, e.g., the tsunami arrives at Ponjok Batu Beach 1 min 46 s after the triggering event, while the highest tsunami run-up value occurs at Bukti Beach (Kubu Tambahan), which is 9.86 m. Conversely, areas in the west, such as Gilimanuk, experience a tsunami arrival time exceeding 20 minutes. According to the results, the improvement of tsunami preparedness that includes early warning, evacuation planning, and coastal land use planning is necessary. The results of this study provide critical information for risk reduction strategies in Buleleng and similar coastal places.