FRAGILITY FUNCTIONS OF BUILDINGS UNDER ONLY TSUNAMI LOAD IN INDONESIA: A CASE STUDY OF THE 2018 SUNDA STRAIT TSUNAMI

Most of previously developed tsunami fragility functions in many countries used building damage data from local tsunamis. Similar to Indonesia which experienced many tsunamis and some tsunami fragility functions were developed. However, all of them are influenced by earthquake. The 2018 Sunda Strait tsunami was generated by the collapsed of Anak Krakatoa volcano. Therefore, damaged buildings by this tsunami were only caused by tsunami load. This study performed numerical simulation (TUNAMI two-layer model) with nesting grid system using the finest grid size of 20 m to reproduce hydrodynamic parameters of tsunami and verified by measured tsunami trace and actual inundation area. There are several field surveys conducted for this tsunami including preliminary developed tsunami fragility functions using measured maximum flow depth. Simulation results (maximum flow depth, maximum flow velocity and maximum hydrodynamic force) were combined with damaged building data and developed tsunami fragility functions using linear regression analysis for the 2018 Sunda Strait tsunami. It can be seen that more than half of the buildings could withstand 4 m flow depth. In addition, comparison of fragility functions of damaged buildings caused by the 2018 Sunda Strait and the 2004 Indian Ocean tsunami in Banda Aceh shows that damaged buildings in Banda Aceh had higher damage probability (at the same flow depth) than damaged buildings around the Sunda Strait tsunami affected area. This is because it was only short period tsunami for the 2018 tsunami but combination of considerable ground motion (MMI 7.5), long period tsunami as well as debris impact for the 2004 tsunami. This is the first attempt in quantitatively demonstrated such integrated impact on building damage in terms of the fragility functions which will be useful when assessing building damage in the future against different types of tsunamis.