Seismic Swarm PS20150505.1 Near Kokopo, Papua New Guinea

A seismic swarm designated PS20150505.1 occurred in the region 144 km south-southwest of Kokopo, Papua New Guinea. The sequence began at 01:44 on 5 May 2015 and concluded at 07:06 on 6 May 2015, spanning 29 hours and 22 minutes. During this period, 15 earthquakes were recorded, with the largest event registering magnitude 7.5 at a depth of 55 km. Subsequent events ranged from magnitude 4.9 to 5.8, occurring at depths between 9 km and 55 km.

The swarm initiated with the magnitude 7.5 mainshock, followed within minutes by a magnitude 5.8 event at 35 km depth. Additional activity included multiple magnitude 5+ earthquakes clustered in the early morning hours of 5 May, with further notable shocks of magnitude 5.8 and 5.4 occurring later that day and into 6 May. Depths remained predominantly in the shallow to intermediate range, consistent with regional tectonic patterns.

Papua New Guinea lies within the Pacific Ring of Fire, where complex interactions between the Pacific, Australian, and several microplates drive intense seismicity. The area southwest of Kokopo, on the island of New Britain, is influenced by subduction along the New Britain Trench. Here, the Solomon Sea Plate descends beneath the South Bismarck Plate, generating frequent earthquakes and volcanic activity. This tectonic setting produces both shallow crustal events and deeper Wadati-Benioff zone seismicity.

Historical records since 2000 indicate 19 seismic swarms in the broader region. These occurred in 2000 (7 swarms), 2003 (1), 2005 (2), 2006 (3), 2010 (1), 2011 (1), 2013 (1), 2014 (1), and 2015 (2). Three strong earthquakes exceeding magnitude 7.0 have also struck nearby since 2000: the magnitude 7.5 event of 5 May 2015 located 131 km SSW of Kokopo; a magnitude 7.8 quake on 17 November 2000 at 138 km SSW of Kokopo; and another magnitude 7.8 event on 16 November 2000 at 135 km southeast of Kokopo. The 2015 swarm center lay approximately 60 km from the associated magnitude 7.5 epicenter.

Such swarm sequences reflect episodic stress release along subduction-related faults. The 2015 activity, dominated by an initial large shock and subsequent moderate aftershocks, aligns with typical patterns observed in this highly active margin. Ongoing monitoring remains essential given the region's history of clustered seismicity.

References
USGS Earthquake Catalog
Global CMT Catalog
SeismoSight internal swarm classification data