Seismic Swarm PS20141207.1 Near Panguna, Papua New Guinea

Seismic swarm PS20141207.1 occurred approximately 105 km west-southwest of Panguna on Bougainville Island, Papua New Guinea. The sequence began at 01:22 on 7 December 2014 and concluded at 13:15 on 8 December 2014, spanning 35 hours and 53 minutes. During this period, 11 earthquakes were recorded, with magnitudes ranging from 4.3 to 6.6 and focal depths between 10 km and 60 km.

The sequence opened with a magnitude 6.6 event at 23 km depth, followed within minutes by events of magnitude 5.0 and 5.2. Subsequent shocks included four magnitude 5.0–5.6 earthquakes clustered in the early morning hours, two additional magnitude 5.1–5.2 events near midday, and a magnitude 5.4 shock in the evening. The final recorded event reached magnitude 5.0 on 8 December. Most events occurred at shallow depths of 10 km, consistent with upper-crustal faulting in the region.

Papua New Guinea lies at the complex junction of the Australian, Pacific, and several smaller plates. Bougainville Island occupies the northern end of the Solomon Islands arc, where oblique convergence drives active subduction along the New Britain Trench and associated thrust systems. This tectonic setting produces frequent moderate-to-large earthquakes and occasional swarms as stress is released along segmented faults. The 2014 swarm aligns with this pattern of distributed seismicity rather than a single mainshock-aftershock sequence.

Since 2000, eight swarms have been documented in the broader area, occurring in 2000 (one swarm), 2001 (two swarms), 2007 (two swarms), and 2014 (three swarms). The 2014 activity, including PS20141207.1, represents the highest annual swarm count in the record. Four strong earthquakes exceeding magnitude 7.0 have also struck within 81 km of the swarm centroid since 2000: a magnitude 7.9 event in January 2017, a magnitude 7.1 event in May 2015, a magnitude 7.5 event in April 2014, and a magnitude 7.1 event earlier that same month. These larger shocks underscore the region’s capacity for significant seismic energy release.

The 2014 swarm likely reflects localized stress adjustment within a highly fractured forearc setting. Shallow focal depths and rapid succession of events suggest fluid involvement or aseismic slip episodes that can trigger swarm behavior in subduction-related crust. No surface rupture or tsunami was reported, consistent with the moderate magnitudes and depths involved.

Continued monitoring remains essential given the proximity of population centers and mining infrastructure on Bougainville. Seismic sequences such as PS20141207.1 provide valuable data for refining regional hazard models and understanding how swarms relate to the larger tectonic framework of the western Pacific.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
Pacific Earthquake Engineering Research Center reports on Papua New Guinea tectonics