Tsunami fragility based characterisation of mosques as alternatives tsunami evacuation buildings: Reconstructing evidence from the 2004 Indian ocean tsunami

Buildings located in coastal areas can also function as protection or shelter during a tsunami wave event. High buildings on the coast such as mosques can be used as vertical evacuation buildings when a tsunami occurs. During the 2004 Indian Ocean Tsunami (IOT), there were many people evacuated and saved at mosques. The community in this region evacuated themselves to some mosques during a tsunami evacuation order on April 11, 2012. However, there is no study has been conducted to prove the fragility of mosques against tsunamis and how the mosques can function as alternative tsunami evacuation buildings. This study is aimed at reconstructing evidence of the impacts of tsunamis on mosques and at assessing the opportunities to use mosques as alternative evacuation buildings. The research was conducted in two modes: (1) a series of numerical modelling were performed to reconstruct tsunami flow depths based on the 2004 Indian Ocean Tsunami (IOT), and (2) impacts of tsunami on mosques were collected based on survivor's eyewitness accounts or photos were taken immediately after the event. The impacts were later used to compose a set of tsunami fragility curves to see the influence of flow depth on the level of mosque damage. Field surveys were at four districts that were severely affected by the 2004 IOT, namely Banda Aceh, Aceh Jaya, West Aceh, and Aceh Besar. Tsunami wave simulations were performed using the Cornell Multigrid Coupled Tsunami Model (COMCOT) to obtain flow depths at mosque locations. Validations of the numerical simulation results were done using secondary flow depth data reported previously. A total of 210 mosque buildings were assessed at the study sites, where 98 % of them were constructed using reinforced concrete with varying building heights ranging from 5 to 11 m (from floor to ceiling). The probability of absolute damage was caused when flow depths exceeded 10 m. The mosque buildings has a lower probability of collapse compared the other building such as house and other building in general. At 3.0 m of flow depth, the mosque would only be totally destroyed by around 12 %. The lower damage probability for mosque buildings can be attributed to mosques being constructed with stronger structures than typical residential buildings.