A night of unprecedented violence
At approximately 9:30 p.m. on August 1, 1629, the Banda Islands were struck by a megathrust earthquake of enormous power. Dutch East India Company (VOC) records describe violent shaking that continued for about five minutes. Modern analysis of the historical accounts and tsunami modeling estimates the moment magnitude (Mw) between 8.2 and 8.8. The shaking was felt as far as 230 kilometers away on the island of Ambon, but the worst effects were reserved for the epicentral region.
The earthquake originated in the Seram Trough, a segment of the complex Banda Arc subduction system where the Indo-Australian Plate pushes beneath the Banda Sea plate. The rupture occurred along a fault plane estimated to be 500 kilometers long and 97 kilometers wide, at a shallow depth of 10 to 30 kilometers. This immense displacement of the seafloor led to a secondary, and equally destructive, event.
Tsunami and tectonic complexity
About 30 minutes after the shaking stopped, a tsunami slammed into the Banda Islands. Eyewitness accounts and geological models converge on a wave with a run-up height of approximately 15 meters, or 49 feet. The wave arrived from the east, destroying wooden homes and heavily damaging stone fortifications, including the mole at Fort Nassau on Banda Neira.
The earthquake occurred in one of the most geologically convoluted regions on Earth. The Banda Arc is a tectonic plate boundary that features an extreme 180-degree curve. Near the epicenter of the 1629 event lies the Weber Deep, a 7.2-kilometer-deep basin. This is the deepest point in the world's oceans that is not a trench and is technically a forearc basin. Its extreme depth is the result of massive extension of the Earth's crust, accommodated by a huge, low-angle fault system named the Banda Detachment. The 1629 quake was a release of accumulated strain in this dynamic collision zone. Following the mainshock, a period of heightened seismic activity lasted for at least nine years, which scientists interpret as a long sequence of aftershocks.