Seismic Activity of Swarm PS20001118.1 Near Kokopo, Papua New Guinea

An earthquake swarm designated PS20001118.1 occurred southeast of Kokopo in Papua New Guinea, beginning at 23:54 on 17 November 2000 and concluding at 17:29 on 18 November 2000. Over 17 hours and 34 minutes, the sequence produced 12 earthquakes, all with focal depths of 33 km. The events ranged in magnitude from 5.1 to 6.6, with the largest shock measuring 6.6 at 02:05 on 18 November.

The sequence initiated with a magnitude 5.2 event, followed rapidly by a magnitude 5.5 shock. Subsequent activity included multiple events of magnitude 5.1 to 5.7, interspersed with additional magnitude 5.2 and 5.3 tremors. The final recorded event reached magnitude 5.1. This pattern reflects typical swarm behavior, characterized by numerous earthquakes of similar magnitude without a single dominant mainshock.

Papua New Guinea occupies a tectonically complex region along the Pacific Ring of Fire. The Kokopo area lies near the boundary between the Pacific and Australian plates, where subduction along the New Britain Trench generates frequent seismicity. The swarm's location, 131 km southeast of Kokopo, aligns with this subduction zone, where intermediate-depth events commonly occur due to slab interactions.

Since 1 January 2000, three swarms have been documented in the broader region, with this event marking the first. Stronger earthquakes have also struck nearby. Notable examples include a magnitude 7.8 event 135 km southeast of Kokopo on 16 November 2000, a magnitude 7.6 shock 135 km east of Kokopo on 9 September 2005, and a magnitude 7.5 earthquake 53 km southeast of Kokopo on 29 March 2015. Additional large events comprise a magnitude 7.9 quake 140 km east of Kokopo in December 2016 and a magnitude 7.6 event 48 km northeast of Kokopo in May 2019. These occurrences underscore the persistent seismic hazard in the area.

The 33 km depth of all swarm events suggests they originated within the subducting slab. Such depths are consistent with the regional geology, where the downgoing plate experiences stresses leading to clustered seismicity. Historical records indicate that swarms in this setting often precede or accompany larger tectonic adjustments along the trench.

References

• Swarm parameters and historical statistics provided by SeismoSight internal classification.
• Regional tectonic context drawn from standard geological descriptions of the New Britain subduction zone.