The Makassar Strait Tsunamigenic Region, Indonesia

The Makassar Strait region has had the highest frequency of historical tsunami events for Indonesia. The strait has a seismic activity due to the convergence of four tectonic plates that produces a complex mixture of structures. The main tsunamigenic features in the Makassar Strait are the Palu-Koro and Pasternoster transform fault zones, which form the boundaries of the Makassar trough. Analysis of the seismicity, tectonics and historic tsunami events indicates that the two fault zones have different tsunami generating characteristics. The Palu-Koro fault zone involves shallow thrust earthquakes that generate tsunami that have magnitudes that are consistent with the earthquake magnitudes. The Pasternoster fault zone involves shallower strike-slip earthquakes that produce tsunami magnitudes larger than would normally be expected for the earthquake magnitude. The most likely cause for the increased tsunami energy is considered to be submarine landslides associated with the earthquakes. Earthquakes from both fault zones appear to cause subsidence of the west coast of Sulawesi Island. The available data were used to construct a tsunami hazard map which identifies the highest risk along the west coast of Sulawesi Island. The opposite side of the Makassar Strait has a lower risk because it is further from the historic tsunami source regions along the Sulawesi coast, and because the continental shelf dissipates tsunami wave energy. The greatest tsunami risk for the Makassar Strait is attributed to locally generated tsunami due to the very short travel times.