Seismic Swarm PS20020212.1 Near Rabaul, Papua New Guinea

Seismic swarm PS20020212.1 occurred approximately 73 km west-northwest of Rabaul on the island of New Britain. The sequence began at 09:36 on 11 February 2002 and concluded at 07:49 on 12 February 2002, spanning 22 hours and 12 minutes. During this interval, five earthquakes were recorded.

The individual events unfolded as follows. The first shock registered magnitude 5.5 at 09:36:36 on 11 February at a depth of 33 km. Roughly 34 minutes later, a magnitude 5.4 event occurred at 10:10:27 at 19 km depth. A magnitude 5.0 earthquake followed at 11:13:27, again at 33 km depth. Later that day, at 20:48:42, a magnitude 5.3 shock was recorded at 18 km depth. The final event, magnitude 4.2, took place at 07:49:26 on 12 February at 33 km depth.

This swarm represents one of only two documented swarm sequences in the region since 1 January 2000; the earlier swarm occurred in 2000. The activity took place near the site of the magnitude 8.0 New Ireland earthquake of 16 November 2000, whose epicenter lay 82 km from the swarm centroid.

Rabaul lies within the Bismarck Volcanic Arc, a tectonically complex zone shaped by the interaction of the Pacific, Australian, and several smaller plates. Convergence along the New Britain Trench drives subduction of the Solomon Sea Plate beneath the South Bismarck Plate, generating frequent intermediate-depth seismicity and arc volcanism. The Rabaul caldera itself is a nested volcanic structure whose most recent major eruptive cycle culminated in 1994, when simultaneous activity at Vulcan and Tavurvur vents devastated the town. Ongoing microseismicity and occasional swarms reflect both volcanic unrest and regional tectonic strain accumulation.

Historical records indicate that the broader Papua New Guinea region experiences some of the highest rates of seismicity on Earth. Large megathrust events, such as the 2000 New Ireland earthquake, release strain along the plate interface, while shallower crustal events and swarms often cluster near volcanic centers or fault segments accommodating oblique convergence and slab rollback.

Analysis of swarm PS20020212.1 suggests a short-lived episode of clustered energy release at mid-crustal to upper-mantle depths. The mix of shallow (18–19 km) and deeper (33 km) foci is consistent with stress perturbations near the subducting slab and overlying volcanic plumbing system. No surface rupture or volcanic eruption was associated with the sequence.

References

• SeismoSight internal swarm catalogue (PS20020212.1 parameters)
• United States Geological Survey Earthquake Catalog (regional events since 2000)
• Geological Survey of Papua New Guinea, tectonic summaries of New Britain
• Global Volcanism Program, Smithsonian Institution (Rabaul caldera history)