A low-angle normal fault earthquake and tsunami: The 1852 Banda Sea Earthquake, Eastern Indonesia

In November 1852, the Banda Islands, Eastern Indonesia suffered a devastating earthquake which was followed fifteen minutes later by a tsunami with up to eight meters height. Strong shaking was also felt on Ambon, Saparua, and Haruku Islands. The tsunami was also reported on these three islands. Almost all previous studies suggest that it was due to a giant megathrust earthquake from the Banda Arc. On the other hand, a recent tectonic study and our own research show that a smaller earthquake on the Banda detachment fault system is more likely to have produced the tsunami reported in 1852. The Banda detachment is a low-angle normal fault which has never been considered before as a source of seismic or tsunami hazard in this region. It has a shallow dip angle observed on land consistently along the outer margin of the Weber Deep. The dip gradually decreases to almost flat on the bottom of the basin then reverses sense, forming a bowl-like shape beneath the inner volcanic arc islands. However, recent seismicity shows no evidence for normal earthquakes with low-dip angle mechanism in this area. Thus, the fault could either be creeping or experience infrequent large earthquakes. We apply three techniques to localize the earthquake hypocenter and estimate the magnitude. By using a grid-search, earthquake intensity attenuation function, and tsunami backward-ray tracing methodologies, the source is constrained near the Banda Islands. The only major fault near this constrained area is the Banda detachment. Then we verify this finding by forward tsunami and seismic modelling. Lastly, we conduct seismic and tsunami hazard assessment. We assess the hazard impact for the Banda Sea due to sources from the Banda Arc and the Banda detachment system