Seismic Swarm PS20160126.1: Analysis of Activity Near Kokopo, Papua New Guinea

A seismic swarm designated PS20160126.1 was recorded southeast of Kokopo, Papua New Guinea, on 26 January 2016. The sequence began at 03:10 and concluded at 22:06, encompassing five earthquakes within an 18-hour 55-minute window. The events occurred at a location 143 km southeast of Kokopo, within a tectonically dynamic segment of the western Pacific.

The swarm comprised the following earthquakes: a magnitude 6.1 event at 26 km depth at 03:10:20; a magnitude 5.0 event at 32 km depth at 15:47:58; a magnitude 5.5 event at 35 km depth at 20:03:47; a magnitude 5.1 event at 22 km depth at 21:34:09; and a magnitude 5.0 event at 27 km depth at 22:06:05. These depths indicate activity within the upper portion of the subducting slab and overlying crust.

The Kokopo region lies along the New Britain subduction zone, where the Solomon Sea Plate descends beneath the South Bismarck Plate. This convergent margin produces frequent seismicity, including intermediate-depth events associated with slab dehydration and brittle failure. Volcanic arcs such as the Bismarck Volcanic Arc further characterize the setting, with magma-related stresses occasionally contributing to clustered earthquake sequences.

Historical records indicate 17 swarms in the area since 1 January 2000. These occurred in 2000 (seven swarms), 2003 (one swarm), 2005 (one swarm), 2013 (one swarm), 2014 (three swarms), and 2015 (four swarms). Such recurrent swarms reflect persistent tectonic loading and fluid migration along the subduction interface.

Multiple strong earthquakes have also struck near the swarm center since 2000. Notable events include the magnitude 7.9 earthquake of 17 December 2016 located 140 km east of Kokopo, the magnitude 7.5 event of 29 March 2015 situated 53 km southeast of Kokopo, the magnitude 7.6 earthquake of 9 September 2005 positioned 135 km east of Kokopo, the magnitude 7.8 event of 16 November 2000 occurring 135 km southeast of Kokopo, and the magnitude 7.0 earthquake of 29 October 2000 located 191 km east-southeast of Kokopo. These larger shocks demonstrate the capacity for megathrust and intraslab ruptures in the immediate vicinity.

The 2016 swarm likely represents a period of accelerated stress release within an already active segment of the subduction zone. Continued monitoring remains essential given the proximity to population centers and volcanic systems around Rabaul Caldera.

References

USGS Earthquake Catalog
SeismoSight internal swarm classification records