Seismic Activity and Geology of the Tanimbar Islands Region

The Tanimbar Islands lie within Indonesia’s tectonically complex Banda Arc, where the Australian Plate subducts beneath the Eurasian Plate. This convergence produces frequent intermediate-depth earthquakes along a steeply dipping Wadati-Benioff zone. On 9 January 2023 at 17:47 local time, a magnitude 7.6 event struck near Pulau Pulau Tanimbar at a depth of 104.9 km, consistent with slab seismicity in this setting. The region’s seismic record since 2000 includes several comparable events. A magnitude 7.1 earthquake occurred in the Banda Sea on 8 November 2023, approximately 87 km from the 2023 Tanimbar hypocenter. Earlier events comprise a magnitude 7.1 on 10 December 2012 (61 km distant) and another magnitude 7.1 on 2 March 2005 (59 km distant). These shocks illustrate persistent strain release along the subduction interface and within the subducting slab. Geologically, the Tanimbar Islands occupy the outer arc of the Banda system, characterized by imbricated sedimentary rocks and uplifted reef limestones. The arc’s curvature reflects the collision geometry between the Australian continental margin and the Banda Sea lithosphere. Intermediate-depth seismicity, such as the 2023 event, arises from dehydration embrittlement and phase changes within the descending slab, typically between 70 and 150 km depth. Historical patterns indicate that magnitude 7+ earthquakes recur every few years in the broader Banda Sea–Tanimbar corridor. The 2023 mainshock and its listed predecessors demonstrate that both the megathrust and intraslab environments remain active. No surface rupture is expected at 104.9 km depth; shaking is attenuated by distance and crustal structure, though felt intensities can still reach moderate levels on the islands. Continued monitoring by regional networks is essential for refining hazard models. The combination of subduction-driven tectonics and repeated large events underscores the need for resilient infrastructure throughout the Tanimbar region.

References

USGS Earthquake Catalog (events 2005–2023)
Global CMT Project focal-mechanism database