Seismic Swarm PS20150503.1 Near Kokopo, Papua New Guinea

A seismic swarm designated PS20150503.1 occurred in the waters 138 km south-southwest of Kokopo, Papua New Guinea, between 20:21 UTC on 3 May 2015 and 08:09 UTC on 4 May 2015. The sequence lasted 11 hours and 47 minutes and included seven earthquakes with magnitudes ranging from 4.8 to 6.0. Depths were predominantly 35 km, with one event at 24 km. The largest shock reached magnitude 6.0 at 22:32 UTC on 3 May.

This swarm took place in a tectonically active segment of the western Pacific where the Pacific Plate interacts with the Australian Plate through subduction along the New Britain Trench. The region experiences frequent seismic sequences due to ongoing plate convergence, slab dehydration, and crustal faulting. Historical records indicate that swarm activity has recurred regularly since 2000, with 20 documented swarms through 2015. Yearly counts include seven in 2000, one each in 2002 and 2003, two in 2005, three in 2006, two in 2010, and single swarms in 2011, 2013, 2014, and 2015.

Notable large-magnitude earthquakes have also struck near the swarm centroid. A magnitude 7.8 event occurred on 17 November 2000 approximately 10 km from the 2015 swarm center. Another magnitude 7.5 earthquake took place on 5 May 2015 only 10 km away, immediately following the swarm period. A magnitude 7.0 shock was recorded 73 km from the center on 10 October 2018.

Such patterns reflect the persistent strain accumulation and release along the plate boundary. The May 2015 swarm likely represented foreshock activity preceding the subsequent magnitude 7.5 mainshock, illustrating how moderate sequences can precede larger ruptures in this subduction setting. Continued monitoring remains essential for understanding long-term seismic behavior in Papua New Guinea.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
SeismoSight internal swarm classification PS20150503.1