Exposures of Building and Population to Tsunami Hazard in Pangandaran Beach, Indonesia

Pangandaran and Pananjung villages are located in the southern coast of Java Island, prone to tsunami hazard originating from a megathrust earthquake off south of Java Island. Those villages experience a tsunami earthquake on 2006 from an M7.8 earthquake. The National Center for Earthquake Studies released a map of the sources and hazards of Indonesia’s earthquake in 2017 with a potential earthquake of magnitude 8.7-9.2 in the megathrust of Java Island. This research aims to estimate the potential number of buildings and the population affected by tsunami inundation from two scenario; first scenario is based on historical event of a M7.8 intraplate earthquake, and second scenario is based on a plausible M8.7 intraplate earthquake. The first scenario tsunami modeling resulted an inundation of 108.606 ha, while in the second scenario estimate an 867.351 ha of inundation area. Building data is obtained by digitizing aerial photographs taken in November 2021. The calculation of potential affected buildings is carried out by overlaying the tsunami inundation data with the existing building data in the study area. Meanwhile, the population data used is obtained from the local government in 2021. To obtain the number of the affected population, population distribution is first carried out in each class of land cover, overlaid with the tsunami inundation data. The estimated number of buildings and population affected by scenario 1 and 2 in Pangandaran Village is 1,040 buildings along with 2,765 people, and 4,216 buildings with 11,209 people respectively. While in Pananjung Village, it is estimated a total of 149 buildings with 350 people affected, and 4,039 buildings with 9,493 people affected respectively. This indicate that scenario 2 impact is potentially 4 times greater than scenario 1 in Pangandaran village, and 27 times greater in Pananjung village, implying a different strategy of tsunami risk reduction should be taken to save more lives. The results of this study can be used as a basis for policymaking by the government in carrying out a more effective tsunami disaster mitigation efforts in Pangandaran and Pananjung Villages. This study also calls for reevaluation of coastal villages tsunami risk based on each plausible scenario.