Seismic Swarm PS20240323.1 Near Ambunti, Papua New Guinea

A seismic swarm designated PS20240323.1 was recorded in Papua New Guinea, beginning at 20:22 on 23 March 2024 and concluding at 03:26 on 24 March 2024. The events occurred 56 km east-northeast of Ambunti in East Sepik Province. Over a period of 7 hours and 4 minutes, six earthquakes were registered, with magnitudes ranging from 4.3 to 6.9 and focal depths primarily between 35 km and 41 km, except for one deeper event at 101 km.

The sequence initiated with a magnitude 6.9 earthquake at 41 km depth. Subsequent events included a magnitude 5.0 quake at 35 km depth, followed by a magnitude 4.3 event also at 35 km. Two closely timed shocks of magnitudes 5.1 and 5.2 occurred at 35 km and 101 km depths, respectively, and the swarm ended with another magnitude 5.2 event at 35 km depth. Such clustered activity reflects the region's dynamic tectonic environment without forming a traditional mainshock-aftershock sequence.

Papua New Guinea lies at the complex boundary between the Australian and Pacific plates, where convergence drives subduction along the New Guinea Trench and associated fault systems. This setting produces both shallow crustal earthquakes and deeper events linked to subducting slabs. The Ambunti area sits within the tectonically active highlands margin, where ongoing collision and strike-slip faulting contribute to elevated seismicity.

Historical records indicate limited swarm occurrences in the vicinity since 2000, with only two prior episodes noted in 2001 and 2002. Notable strong earthquakes nearby include a magnitude 7.0 event 40 km east-southeast of Ambunti on 2 April 2023, located 26 km from the current swarm center, and a magnitude 7.6 earthquake 68 km east-southeast of Aitape on 8 September 2002, positioned 89 km away. These events underscore the persistent seismic hazard in the region.

Insights from the swarm suggest episodic release of strain along local fault networks, consistent with the broader plate-boundary dynamics of Papua New Guinea. Continued monitoring remains essential given the potential for larger events in this high-activity zone.

References

SeismoSight internal classification data for swarm PS20240323.1.
Geological Survey of Papua New Guinea regional tectonic summaries.
USGS Earthquake Catalog historical records since 2000.