Seismic Swarm Near Nabire, Indonesia: February 2004

The seismic swarm designated PS20040205.1 was recorded 39 km east-southeast of Nabire, Indonesia, beginning at 21:05 on 5 February 2004 and concluding at 15:59 on 6 February 2004. Over 18 hours and 54 minutes, eight earthquakes were registered, highlighting a concentrated period of seismic activity in a tectonically complex region.

The sequence initiated with a magnitude 7.0 event at 16 km depth. Subsequent events included magnitudes of 5.9 (37 km depth), 5.0 (10 km), 5.1 (10 km), 5.0 (10 km), 5.0 (14 km), 5.0 (19 km), and a final 5.1 (26 km depth). This pattern reflects rapid stress redistribution following the mainshock, typical of swarm behavior in subduction-influenced settings where multiple fault segments interact.

Nabire lies within western New Guinea, at the boundary between the Australian and Pacific plates. Convergence rates exceed 100 mm per year, producing thrust faults, strike-slip systems, and the New Guinea Trench. The region has a long history of moderate-to-large earthquakes driven by this oblique collision and associated back-arc deformation.

This swarm occurred amid a cluster of strong events in early 2004. A magnitude 7.0 earthquake struck 28 km south of Nabire on the same day as the swarm onset, while a magnitude 7.3 event occurred near the south coast of Papua two days later. Additional magnitude 7.1 shocks followed in November 2004, underscoring the elevated seismic hazard along this segment of the plate boundary.

Such swarms provide insight into fault mechanics, showing how an initial large rupture can trigger distributed aftershocks across varying depths. Monitoring these sequences aids in refining seismic hazard assessments for Papua’s population centers and infrastructure.

References
SeismoSight internal swarm classification PS20040205.1
USGS Earthquake Catalog (events since 2000)