Seismic Swarm PS20200825.1 Near Kokopo, Papua New Guinea

On 25 August 2020, a seismic swarm designated PS20200825.1 was recorded 149 km south of Kokopo, Papua New Guinea. The sequence began at 19:02 UTC and concluded at 20:02 UTC, encompassing six earthquakes within a 59-minute window. This cluster occurred in a tectonically active segment of the southwestern Pacific, where the interaction between the Pacific Plate and the South Bismarck Plate drives persistent seismicity along the New Britain subduction zone.

The individual events unfolded as follows. At 19:02:58 UTC, a magnitude 6.0 earthquake struck at 23 km depth. Two minutes later, at 19:04:41 UTC, a magnitude 5.5 event occurred at 10 km depth. A magnitude 5.0 shock followed at 19:07:18 UTC, also at 10 km depth. The largest event, magnitude 6.2, registered at 19:08:52 UTC and 22 km depth. Subsequent activity included a magnitude 4.3 earthquake at 19:42:07 UTC and 26 km depth, closing with a magnitude 5.1 event at 20:02:55 UTC and 35 km depth. Depths remained shallow to intermediate, consistent with the regional subduction environment.

Papua New Guinea occupies a complex tectonic junction within the Pacific Ring of Fire. Convergence rates along the New Britain Trench exceed 10 cm per year, producing both megathrust events and upper-plate crustal swarms. The Kokopo area lies near the transition from subduction to strike-slip regimes, where inherited faults facilitate episodic swarm activity driven by fluid migration or aseismic slip transients.

Historical records since 1 January 2000 document 29 comparable swarms in the immediate region. These occurred in the following years and quantities: seven in 2000, one in 2003, two in 2005, three in 2006, two in 2010, one in 2011, one in 2013, one in 2014, five in 2015, three in 2016, and three in 2018. The pattern indicates recurrent swarm behavior superimposed on the background rate of larger earthquakes.

Notable strong events since 2000 further illustrate the seismic potential. A magnitude 7.0 earthquake occurred 119 km east of Kimbe on 10 October 2018, approximately 86 km from the swarm centroid. On 5 May 2015, a magnitude 7.5 event struck 131 km south-southwest of Kokopo, 18 km from the swarm center. The largest recent shock, magnitude 7.8, took place 138 km south-southwest of Kokopo on 17 November 2000, 24 km from the present swarm location.

Such swarms typically reflect localized stress adjustments rather than immediate precursors to great earthquakes. Continued monitoring remains essential given the proximity of population centers and volcanic arcs in East New Britain Province.

References
SeismoSight internal swarm catalog PS20200825.1
USGS Earthquake Catalog (events 2000–2020)
Global CMT catalog for regional moment tensors