Seismic Swarm PS20010605.1: Analysis of Earthquake Activity Near Bulolo, Papua New Guinea

A notable seismic swarm occurred on 5 June 2001, approximately 45 km northwest of Bulolo in Papua New Guinea. The sequence began at 09:00 UTC and concluded at 15:13 UTC, encompassing seven earthquakes within a span of just over six hours. All events were recorded at a focal depth of 10 km, indicating shallow crustal activity typical of the region's tectonically active setting.

The swarm initiated with a magnitude 6.4 event at 09:00:05, followed by five moderate aftershocks ranging from magnitude 5.0 to 5.5 between 09:19 and 10:00. Activity concluded with a magnitude 6.0 earthquake at 15:13:58. This pattern reflects clustered seismicity, where an initial larger shock triggers subsequent events along nearby faults without a clear mainshock-aftershock decay typical of isolated quakes.

Papua New Guinea lies at the complex boundary between the Australian, Pacific, and several smaller tectonic plates. The Bulolo area sits within the New Guinea Highlands, influenced by oblique convergence and strike-slip faulting along structures such as the Ramu-Markham Fault Zone. This tectonic regime produces frequent shallow earthquakes, often at depths under 30 km, consistent with the 10 km depths observed in the 2001 swarm. The region's geology features folded sedimentary rocks, metamorphic terrains, and active fault systems resulting from ongoing collision since the Miocene epoch.

Historical records show Papua New Guinea experiences some of the world's highest rates of seismicity. The 2001 swarm occurred amid broader activity in the highlands, where similar clusters have been documented. Post-2000 events underscore persistent risk: a magnitude 7.1 quake struck 32 km northwest of Bulolo on 6 May 2019, just 15 km from the swarm center. Another magnitude 7.1 event occurred 25 km south-southeast of Wau on 14 December 2011, 89 km distant. Most recently, a magnitude 7.6 earthquake took place 70 km east of Kainantu on 10 September 2022, approximately 60 km from the 2001 swarm location. These events highlight the area's capacity for strong, damaging shocks capable of generating landslides in the rugged terrain.

The combination of shallow depths and proximity to population centers like Bulolo and Wau amplifies hazard potential. Mining operations in the Morobe Province, historically centered around gold deposits near these towns, have occasionally intersected zones of elevated seismicity. While the 2001 swarm caused no reported major damage, it exemplifies how moderate-magnitude sequences can precede or accompany larger regional events.

Continued monitoring by regional networks remains essential for understanding stress transfer along local faults. The 2001 data provide valuable insight into swarm dynamics within this convergent margin setting.

References

• U.S. Geological Survey Earthquake Catalog (earthquake.usgs.gov)
• Geoscience Australia National Earthquake Database
• Papua New Guinea Geological Survey reports on highlands tectonics