Seismic Swarm S20230209.2: Analysis of Earthquake Activity Near the Northern Coast of Papua, Indonesia

A seismic swarm designated S20230209.2 occurred near the northern coast of Papua, Indonesia, from 11:35 on 8 February 2023 to 19:58 on 11 February 2023. Over approximately 80 hours and 23 minutes, the event sequence recorded 50 earthquakes. The swarm was characterized by shallow focal depths, predominantly between 10 and 15 km, with a few events reaching 19–26 km. Magnitudes ranged from 2.5 to 5.0, with the largest event occurring at 11:35:34 on 8 February.

The temporal distribution showed the highest activity on the first day, including multiple events above magnitude 4.0. Subsequent days exhibited a gradual decline in both frequency and magnitude, consistent with typical swarm decay patterns. Depths remained shallow throughout, suggesting activity within the upper crust.

The northern coast of Papua lies within a complex tectonic setting at the boundary between the Australian and Pacific plates. This region experiences ongoing convergence, including subduction along the New Guinea Trench and strike-slip faulting associated with regional shear zones. Such conditions produce frequent seismicity, with both mainshock-aftershock sequences and swarm-type activity documented historically.

Since 2000, four seismic swarms have been identified in the area according to internal classification records: two in 2007, one in 2016, and the 2023 event. This limited recurrence indicates that swarm activity is infrequent relative to the overall high seismicity rate of the region.

Analysis of the 2023 swarm reveals a clustered pattern of low-to-moderate magnitude events without a single dominant mainshock. The concentration of events at depths of 10–15 km aligns with the expected brittle-ductile transition zone in this tectonically active margin. The absence of deeper events beyond 26 km further supports a shallow crustal source.

Insights from the swarm suggest possible fluid migration or localized stress redistribution along pre-existing faults rather than a large-scale rupture. The rapid onset and subsequent decay over three days are typical of swarm behavior in subduction-related environments, where pore-pressure changes can trigger sequences without significant stress drop from a primary event.

Continued monitoring of this region remains important given its position in a high-strain zone. Future swarms may provide additional data to refine models of crustal deformation and seismic hazard along the northern Papua margin.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
SeismoSight internal swarm classification records