Seismic Swarm PS20011007.1: Analysis of Events Near Wewak, Papua New Guinea

An earthquake swarm designated PS20011007.1 was recorded northwest of Wewak, Papua New Guinea, on 7 October 2001. The sequence began at 02:21 UTC and concluded at 08:09 UTC, encompassing five events over 5 hours and 48 minutes. All events occurred at a shallow depth of 10 km, consistent with crustal faulting in the region.

The events unfolded as follows: a magnitude 6.2 earthquake at 02:21:09, followed by a magnitude 5.2 at 02:25:09. Subsequent activity included two magnitude 5.0 events at 04:08:08 and 04:47:26, concluding with a magnitude 4.3 at 08:09:53. This rapid succession of moderate shocks indicates a clustered release of strain along local fault structures rather than a typical mainshock-aftershock sequence.

Papua New Guinea occupies a tectonically complex zone at the convergence of the Pacific and Australian plates. The area northwest of Wewak lies near the New Guinea Trench, where oblique subduction generates frequent shallow seismicity. The region's geology features active thrust faults and strike-slip systems influenced by the collision of the Pacific Plate with the Caroline and Australian plates. Updated plate models confirm ongoing convergence rates of approximately 10–12 cm per year, sustaining elevated seismic hazard.

Historical records document recurrent strong earthquakes in this sector. Notable activity includes the 1998 magnitude 7.0 event near Aitape, which triggered a destructive tsunami. The 2001 swarm occurred in proximity to later significant shaking, notably a magnitude 7.6 earthquake on 8 September 2002 located 68 km east-southeast of Aitape and only 16 km from the swarm centroid. Such spatial clustering underscores the persistent strain accumulation along interconnected fault networks.

Swarm activity of this type often reflects fluid migration or stress triggering in heterogeneous crust. The shallow depths and tight temporal spacing of the 2001 events align with patterns observed in subduction-related forearc settings. No surface rupture was reported, consistent with the moderate magnitudes involved.

Continued monitoring by regional networks remains essential given the proximity of population centers such as Wewak and the demonstrated potential for larger events within the same tectonic corridor.

References

USGS Earthquake Catalog
Global CMT Project
SeismoSight internal swarm classification PS20011007.1