Influence of Small Islands against Tsunami Wave Impact along Sumatra Island

Abstract

The big earthquake at Sumatra subduction zone has become yearly event in Indonesia since the Indian Ocean Earthquake on 2004. The last earthquake which has been occurred near Mentawai archipelago on March 2, 2016 caused panic at the several big cities such as Padang and Meulaboh. Seismic gap in Sumatera subduction zone still has energy to cause tsunamigenic earthquake. Then the west coast of Sumatera Island has been at high risk for tsunami disaster. However, some cities, such as Tapaktuan, were not damaged by 2004 tsunami and others after 2004. These cities locate behind small islands. Therefore many residents believe that the islands will protect the cities against tsunami. Disaster management and education in these cities are not enough because of no damage experience. However, the positional relationship between small islands and a rupture area will result in different impact to the coast along Sumatra Island. In this paper, the possibility of tsunami disaster in the cities which were not damaged by the past tsunami is investigated from the viewpoint of influence of small islands against tsunami propagation. The COMCOT model was used for tsunami simulation in this study. Firstly, the numerical simulations of 2004, 2005 and 2012 tsunami were carried out to investigate the tsunami height along the northern part of Sumatra Island. Secondly, the several hypothetical fault conditions are implemented as future tsunami scenarios to investigate the possibility of tsunami damage at Tapaktuan. Small changes of the location of epicenter in future tsunami scenarios will result in different tsunami impact along Sumatra Island due to the influence of small islands. This result indicates that it will be dispensable for the appropriate disaster management and education to grasp the function of small islands along Sumatra Island about future scenarios.