Earthquakes and tsunamis caused by low-angle normal faulting in the Banda Sea, Indonesia

Cummins, Phil R.1,2,3, Pranantyo, Ignatius R.1,4, Pownall, Jon1,5, Griffin, Jonathan D.3,6, Meilano, Irwan7, Zhao, Siyuan1

1Research School of Earth Sciences, Australian National University, Canberra, Australia, 2Global Geophysics Research Group, Institut Teknologi Bandung, Bandung, Indonesia, 3Community Safety Branch, Geoscience Australia, Canberra, Australia, 4Dept. Civil and Environmental Engineering, Brunel University, London, United Kingdom, 5Dept. Geosciences and Geography, University of Helsinki, Helsinki, Finland, 6Dept. Geology, University of Otago, Dunedin, New Zealand, 7Faculty of Earth Science and Technology, Institut Teknologi Bandung, Indonesia

As the world’s largest archipelagic country in Earth’s most active tectonic region, Indonesia faces a substantial earthquake and tsunami threat. Understanding this threat is a challenge because of the complex tectonic environment, the paucity of observed data and the limited historical record. Here we combine information from recent studies of the geology of Indonesia’s Banda Sea with Global Positioning System observations of crustal motion and an analysis of historical large earthquakes and tsunamis there. Analysis of historical accounts of Banda Sea earthquakes from the 19th century and earlier show that past destructive earthquakes were not caused by the supposed megathrust of the Banda outer arc as previously thought, but are more likely due to a vast submarine normal fault system recently discovered along the Banda inner arc. Instead of being generated by coseismic seafloor displacement, analysis of tsunami observations shows that the tsunamis were more likely caused by earthquake-triggered submarine slumping along the fault’s massive scarp, the Weber Deep. This would make the Banda detachment representative not only as a modern analogue for terranes hyper-extended by slab rollback but also for the generation of earthquakes and tsunamis by a submarine extensional fault system. Our findings suggest that low-angle normal faults in the Banda Sea generate large earthquakes, which in turn can generate tsunamis due to earthquake-triggered slumping.


Phil Cummins has a PhD in Geophysics from U. California, Berkeley. He worked at ANU, U. Tokyo ad JAMSTEC, Japan,  before leading earthquake and tsunami research at GA. He now holds  a joint appointment, combining teaching and research at ANU with technical applications of earthquake and tsunami science at GA.

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