Preliminary study of tsunami simulations on megathrust earthquake scenarios in Pacitan Regency, East Java

Abstract

During the period 1600 to 2007 there have been approximately 109 tsunamis in Indonesia with 90% caused by tectonic earthquakes. Pacitan located in an east java segment subduction area which is very prone to earthquakes and tsunamis. The coastal morphology of Pacitan has great potential for tsunami hazard. This research is focused on conducting numerical modeling of the tsunami generated by the hypothetical megathrust earthquake in the East Java segment with a magnitude of Mw 8.7. The method used is Cornell-Multi Grid Coupled applied shallow water equation with COMCOT 1.7 software. The nested grid system uses 4-layer consisting of 1-layer GEBCO, 2-layer bathymetry, and 1-layer integration of bathymetry and topography to produce tsunami modeling with high resolution. The results showed that the megathrust hypothetical earthquake scenario for the East Java segment caused a vertical displacement at sea level of -4.599 m to 7.019 m. The tsunami propagation northwards towards the Pacitan coast had a maximum amplitude of 33.16 m with a travel time of 23 – 29 minutes and then spreads in all directions. The farthest inundation range occurred in Pacitan Subdistrict as far as 4.189 km to the north of Ranuharjo Beach, while the maximum run-up of 21.82 m occurred in Soge Beach, Ngadirojo Subdistrict. The farthest affected area of inundation occurs on a gently sloping morphology with a slope of 0-8%, the highest run-up is on a moderate to steep sloping morphology with a slope of more than 25%. The results of tsunami simulation can be used for planning tsunami disaster mitigation in Pacitan.