Analisis Probabilistik Bencana Tsunami Terhadap Tingkat Kerentanan Bangunan di Kota Painan, Sumatera Barat dengan Metode Logic Tree (Studi Kasus: Gempa Bumi Zona Patahan Nias-Simeulue)

Abstract

Painan city is surrounded by three megathrust zones that are quite dangerous and can generate tsunamis. The three megathrust zones are Nias-Simeulue, Mentawai-Siberut, and Mentawai-Pagai. The purpose of this study is to determine the influence of variations in seismicity level variables and the ratio between large and small earthquakes using the logic tree tool, to assess the potential tsunami hazard using the Probabilistic Tsunami Hazard Assessment (PTHA) method, and to determine the Building Tsunami Vulnerability (BTV) index value as an effort to reduce the impacts caused by tsunamis in Painan city due to the movement of the Nias-Simeulue fault plate. The simulation in this study used the Cornell Multigrid Copled Tsunami (COMCOT) program. From 600 simulation scenarios, calculations of the recurrence period and tsunami height were performed for each building in Painan city. Then, the vulnerability of buildings was determined based on the BTV equation. Based on the processed PTHA data, the maximum height was obtained at a recurrence period of 10,000 years, which is 0.45m, and the resulting hazard curve was not significantly affected by variations in seismicity level variables and the ratio between large and small earthquakes, with a difference in tsunami height of approximately 0.15m for the largest scenario (a = 4.98; b = 0.98) and the smallest scenario (a = 3.98; b = 0.78). Based on the calculated building vulnerability, it was found that 95 (2.45%) buildings in Painan city had a low level of damage, while the remaining 3,781 (97.55%) buildings did not suffer any damage from the tsunami generated by the Nias-Simeulue fault.