Seismic Swarm PS20130305.1: Analysis of Activity Near Kokopo, Papua New Guinea

On 5 March 2013, a seismic swarm designated PS20130305.1 was recorded approximately 100 km south-southeast of Kokopo, Papua New Guinea. The sequence began at 03:58 UTC and concluded at 07:31 UTC, encompassing a duration of 3 hours and 32 minutes during which five earthquakes occurred.

The events unfolded as follows. At 03:58:28 UTC, a magnitude 5.1 earthquake struck at a depth of 10 km. Seconds later, at 03:58:35 UTC, a magnitude 5.0 event was registered at 60 km depth. Activity resumed at 06:06:34 UTC with a magnitude 5.8 earthquake at 22 km depth, followed by a magnitude 5.2 shock at 10 km depth at 06:21:07 UTC. The swarm ended with a magnitude 5.0 event at 10 km depth at 07:31:00 UTC.

This swarm provides insight into localized stress release within a tectonically active setting. The clustering of moderate-magnitude events over a short interval, with varying focal depths, is characteristic of swarm behavior rather than a typical mainshock-aftershock sequence. Such patterns often reflect fluid migration or incremental fault slip along pre-existing structures in subduction-related environments.

The region surrounding Kokopo lies within the Papua New Guinea segment of the Pacific Ring of Fire, where the Solomon Sea Plate subducts beneath the Pacific Plate along the New Britain Trench. This convergent margin produces frequent seismicity, volcanic arcs, and associated hazards. Historical records indicate 13 swarms in the area since 1 January 2000, occurring in the years 2000 (seven swarms), 2002 (one), 2003 (one), 2005 (one), 2006 (two), and 2011 (one). These recurrent episodes underscore the persistent tectonic strain accumulation.

Notable strong earthquakes since 2000 further illustrate the seismic potential. A magnitude 7.5 event occurred 131 km south-southwest of Kokopo on 5 May 2015, approximately 85 km from the swarm center. Another magnitude 7.5 shock took place 53 km southeast of Kokopo on 29 March 2015, about 49 km from the center. In November 2000, two magnitude 7.8 earthquakes struck nearby, one 138 km south-southwest on 17 November (96 km from center) and one 135 km southeast on 16 November (57 km from center).

These data highlight the ongoing seismic hazard in eastern Papua New Guinea, where subduction-driven deformation continues to generate both isolated large events and episodic swarms.

References:
SeismoSight internal swarm classification database (PS20130305.1 parameters and historical swarm statistics).
Regional tectonic summaries from the U.S. Geological Survey Earthquake Hazards Program.