Seismic Swarm PS20150916.1: Analysis of Activity East-Southeast of Kimbe, Papua New Guinea

On 16 September 2015, a seismic swarm designated PS20150916.1 was recorded approximately 156 km east-southeast of Kimbe, Papua New Guinea. The sequence began at 14:03 local time and concluded at 19:24 the same day, encompassing five earthquakes over a duration of five hours and twenty-one minutes. The events, all relatively shallow, ranged in magnitude from 4.5 to 6.1 and occurred at depths between 6 km and 15 km.

The sequence opened with a magnitude 6.1 earthquake at 14:03:22, followed within minutes by a magnitude 5.0 event at 14:11:08. Subsequent shocks included a magnitude 5.3 at 15:22:24, a magnitude 5.1 at 19:21:13, and a final magnitude 4.5 at 19:24:47. Depths remained consistently shallow, consistent with crustal activity in the region.

This swarm forms part of a longer record of seismic clustering in the area. Since 1 January 2000, seventeen swarms have been documented, with notable concentrations in 2000 (two swarms), 2006 (three), and 2015 (four). Additional swarms occurred in 2003, 2005, 2010, 2011, 2013, and 2014.

The broader tectonic setting explains the frequency of such episodes. Papua New Guinea lies at the complex junction of the Australian, Pacific, and Philippine Sea plates. Convergence along the New Britain Trench drives subduction-related seismicity, producing both shallow crustal events and deeper Wadati-Benioff zone activity. The Kimbe region sits near the eastern margin of this subduction system, where oblique convergence and arc-parallel faulting generate frequent moderate-magnitude earthquakes and occasional swarms.

Several larger events have occurred nearby since 2000. A magnitude 7.0 earthquake struck 119 km east of Kimbe on 10 October 2018, approximately 49 km from the 2015 swarm center. Earlier, a magnitude 7.5 event occurred 131 km south-southwest of Kokopo on 5 May 2015, 77 km from the swarm location. Additional magnitude 7.0 and 7.8 shocks were recorded in 2010 and 2000, respectively, underscoring the persistent seismic hazard.

Swarm activity of this type often reflects fluid migration or stress transfer along local fault networks rather than a single mainshock-aftershock sequence. While individual events rarely exceed magnitude 6.5, the cumulative energy release and proximity to population centers warrant continued monitoring by regional networks.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog
SeismoSight internal swarm classification records