Seismic Swarm Analysis: Banda Sea, November 2023

A seismic swarm designated PS20231110.1 occurred in the Banda Sea, beginning at 03:50 on 10 November 2023 and concluding at 06:41 on 11 November 2023. Over 26 hours and 51 minutes, seven earthquakes were recorded. The sequence included events with the following parameters: a magnitude 5.9 quake at 03:50:35 on 10 November at 10 km depth; a magnitude 6.1 event at 20:45:11 on 10 November at 9 km depth; a magnitude 4.3 shock at 21:01:23 on 10 November at 10 km depth; a magnitude 5.0 quake at 21:05:58 on 10 November at 8 km depth; a magnitude 5.3 event at 21:13:35 on 10 November at 10 km depth; a magnitude 5.6 quake at 21:20:12 on 10 November at 10 km depth; and a magnitude 5.7 event at 06:41:51 on 11 November at 10 km depth. This swarm represents the second such episode in the region since 2000, following a single swarm in 2008. The November 2023 activity took place shortly after a magnitude 7.1 earthquake on 8 November 2023, centered 84 km from the swarm location. Earlier strong events in the vicinity include a magnitude 7.1 quake on 10 December 2012 (76 km away) and another magnitude 7.1 event on 2 March 2005 (70 km distant). The Banda Sea lies within the tectonically complex Banda Arc system of eastern Indonesia, where multiple plate boundaries converge. This setting involves the subduction of the Indo-Australian Plate beneath the Eurasian Plate, along with interactions involving the Pacific Plate. The resulting geometry produces frequent intermediate-depth seismicity and shallow crustal events, consistent with the shallow depths observed in the recent swarm. Historical records show the region experiences recurrent large-magnitude earthquakes due to ongoing convergence and slab dynamics. Seismic swarms in subduction-related environments often reflect fluid migration or stress redistribution along fault networks rather than a single mainshock-aftershock sequence. The 2023 swarm, occurring days after the magnitude 7.1 mainshock, illustrates how post-seismic stress changes can trigger clusters of moderate events. Depths clustered near 10 km suggest activity within the upper crust or near the plate interface.

• References
• United States Geological Survey Earthquake Catalog (earthquake.usgs.gov)
• SeismoSight internal swarm classification data (PS20231110.1)