Seismic Swarm PS20050223.1 Near Kimbe, Papua New Guinea

A seismic swarm designated PS20050223.1 occurred on 23 February 2005, centered 118 km southeast of Kimbe in Papua New Guinea’s New Britain region. The sequence began at 11:33 local time and concluded at 23:33 the same day, spanning 11 hours and 59 minutes. During this interval, five earthquakes were recorded, with magnitudes ranging from 4.2 to 6.0 and focal depths predominantly at 10 km, except for one event at 40 km.

The sequence initiated with a magnitude 6.0 earthquake at 11:33:52, followed within seconds by a magnitude 5.8 event at 40 km depth. Subsequent shocks included a magnitude 5.6 at 12:12:43, a magnitude 5.1 at 20:03:24, and a final magnitude 4.2 at 23:33:12, all at 10 km depth. Such clustered activity without a single dominant mainshock is characteristic of swarms in subduction-related settings, where fluid migration or stress transfer along the plate interface can trigger multiple moderate events over hours.

The New Britain region forms part of the Pacific Ring of Fire, where the Solomon Sea Plate subducts beneath the South Bismarck Plate along the New Britain Trench. This convergent margin produces frequent shallow to intermediate-depth seismicity and hosts active volcanoes such as Ulawun and Rabaul. Historical records since 2000 document only two prior swarms in the immediate area—one in 2000 and another in 2003—indicating that swarm-type sequences remain relatively infrequent compared with isolated mainshock-aftershock sequences.

Strong earthquakes have also punctuated the regional record. Notable events include a magnitude 7.3 on 18 July 2010 located 41 km from the swarm center, a magnitude 7.0 on 4 August 2010 situated 52 km away, a magnitude 7.0 on 10 October 2018 positioned 71 km distant, and an earlier magnitude 7.0 on 31 October 2001 centered 77 km from the 2005 swarm. These larger ruptures underscore the ongoing accumulation of strain along the subduction interface.

Seismic swarms in this tectonic environment provide valuable indicators of transient stress changes that may precede or accompany volcanic unrest, although no direct link to eruptive activity was associated with the 2005 sequence. Continued monitoring by regional networks remains essential for assessing evolving hazard levels in this densely populated and volcanically active part of Papua New Guinea.

References: USGS Earthquake Catalog (updated through 2024) Global CMT Catalog Papua New Guinea Geological Survey regional tectonic summaries