Seismic Swarm PS20001125.1 Near Kokopo, Papua New Guinea

On 25 November 2000, a seismic swarm designated PS20001125.1 began at 16:09 local time approximately 193 km southeast of Kokopo in Papua New Guinea. The sequence concluded at 05:23 on 26 November after lasting 13 hours and 13 minutes. During this period, seven earthquakes were recorded, all with focal depths of 33 km. Magnitudes ranged from 4.7 to 5.6, with the largest event reaching 5.6 at 16:46 on 25 November.

The individual events occurred at the following times and magnitudes: 16:09 (M5.4), 16:46 (M5.6), 17:41 (M5.0), 18:22 (M5.2), 18:42 (M4.7), followed by two additional shocks on 26 November at 02:14 (M5.2) and 05:23 (M5.2). This tightly clustered activity is characteristic of a swarm, in which multiple events of similar magnitude occur without a single dominant mainshock.

The swarm location lies within the tectonically active Bismarck Sea region of Papua New Guinea. This area forms part of the Pacific Ring of Fire, where the Solomon Sea plate subducts beneath the South Bismarck plate along the New Britain Trench. The resulting compressional regime produces frequent intermediate-depth earthquakes along a well-defined Wadati-Benioff zone. Historical records indicate elevated seismicity throughout the late twentieth century, with the swarm occurring only nine days after a magnitude 7.8 earthquake located 135 km southeast of Kokopo and roughly 96 km from the swarm centroid.

Since 1 January 2000, five seismic swarms have been documented in the broader region, with PS20001125.1 representing the earliest. Such sequences often reflect stress redistribution following larger regional events or fluid migration within the subducting slab. Depths consistently near 33 km align with the upper portion of the subducting slab interface, where brittle failure is common.

The geological setting features complex interactions between multiple microplates, including rapid convergence rates exceeding 10 cm per year. This environment sustains both seismic and volcanic hazards, notably around the Rabaul Caldera northwest of Kokopo. Continued monitoring of swarm activity provides valuable data for understanding stress transfer along the subduction interface.

References
SeismoSight internal swarm classification records
USGS Earthquake Catalog (preliminary locations and magnitudes)
Global CMT Project focal mechanism database