Seismic Swarm PS20150507.1 Southwest of Panguna, Papua New Guinea

The seismic swarm PS20150507.1 occurred 165 km southwest of Panguna on Bougainville Island in Papua New Guinea. It began at 07:10 on 7 May 2015 and concluded at 03:01 on 8 May 2015, spanning 19 hours and 51 minutes. During this interval, ten earthquakes were recorded, with the sequence dominated by a mainshock of magnitude 7.1 at a depth of 10 km. Subsequent events ranged from magnitude 4.5 to 5.4, most occurring at depths of 10 km except for one deeper shock at 80 km. The sequence unfolded rapidly after the initial event. Within the first hour, five earthquakes above magnitude 5.0 were registered, including magnitudes 5.0, 5.1, 4.5, 5.2 and 5.0. Activity continued through the afternoon with events of 5.4 and 5.1, before two final magnitude 5.0 shocks occurred early on 8 May. This pattern reflects typical swarm behavior in which a strong mainshock triggers numerous aftershocks of moderate size without a clear foreshock phase. Papua New Guinea occupies a tectonically complex zone at the boundary between the Australian and Pacific plates. Bougainville lies along the Solomon Islands arc, where oblique subduction generates frequent moderate-to-large earthquakes. Crustal faults and volcanic systems in the region further contribute to elevated seismicity. Depths around 10 km indicate shallow crustal rupture, consistent with the island arc setting, while the isolated 80 km event suggests limited deeper slab activity. Historical records since 2000 show ten documented swarms in the vicinity. Earlier episodes occurred in 2001 (two swarms), 2007 (three swarms) and 2014 (five swarms). Strong earthquakes have also punctuated the record, including a magnitude 7.5 event 70 km southwest of Panguna on 19 April 2014, located 86 km from the 2015 swarm center, and the magnitude 7.1 mainshock of 7 May 2015 itself, 36 km from the swarm centroid. These events underscore persistent seismic hazard along the arc. The 2015 swarm illustrates the capacity of the region to produce clustered activity capable of generating damaging ground motion. Shallow depths amplified intensities near the epicentral area, while the overall energy release remained concentrated within a brief window. Continued monitoring is essential given the proximity of population centers on Bougainville and the island’s history of both seismic and volcanic unrest.

References

SeismoSight internal swarm classification PS20150507.1
USGS Earthquake Catalog (regional tectonics and plate boundary data)