Location:

Period:

4 Mar 2018 11:44:24 - 4 Mar 2018 20:24:03 (8 hours 39 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.5; 32 km SW of Tari, Papua New Guinea; (25 Feb 2018) (34km from the swarm center)

5 swarms found nearby.

2012

PS20121208.1(178.2km)

8 Dec

14 hours

5 earthquakes

2018

PS20180225.2(28.3km)

25 Feb

2 days 11 hours

40 earthquakes

PS20180225.1(104.7km)

25 Feb

1 hours

8 earthquakes

PS20180302.1(26.8km)

2 Mar

20 hours

6 earthquakes

PS20180306.1(11.7km)

6 Mar

1 day 15 hours

13 earthquakes

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Seismic Swarm PS20180304.1: Analysis of Events Near Tari, Papua New Guinea

On 4 March 2018, a seismic swarm designated PS20180304.1 was recorded 77 km south-southwest of Tari in Papua New Guinea’s Hela Province. The sequence began at 11:44 local time and concluded at 20:24, encompassing five earthquakes within an 8-hour 39-minute window. This cluster occurred in a region characterized by complex tectonic interactions along the boundary between the Australian and Pacific plates.

The events displayed a clear temporal progression in magnitude. The initial shock measured 5.1 at a depth of 10 km. Subsequent activity included a 5.3 event at 9 km depth, followed by a 5.7 quake at 6 km. The largest event reached magnitude 6.0 at 10 km depth, with the sequence terminating in a 4.8 shock also at 10 km. Depths remained consistently shallow, between 6 and 10 km, consistent with crustal faulting in the area.

Papua New Guinea lies within the Pacific Ring of Fire, where convergence of the Australian Plate with the Pacific and several microplates produces frequent seismic activity. The Tari region sits near the New Guinea Highlands, influenced by both strike-slip faulting and thrust mechanisms associated with the ongoing collision. Shallow seismicity here often reflects reactivation of existing faults within the sedimentary basins and basement rocks of the highlands.

Historical records since 2000 indicate four swarms in the immediate vicinity. One occurred in 2012, while three took place in 2018, underscoring episodic clustering. Notably, a magnitude 7.5 earthquake struck 32 km southwest of Tari on 25 February 2018, approximately 34 km from the swarm centroid. This mainshock likely altered local stress conditions, potentially contributing to the subsequent swarm one week later.

Swarm activity of this nature typically reflects fluid migration or aseismic slip along fault networks rather than a single large rupture. The rapid succession of moderate events without a dominant foreshock-mainshock-aftershock pattern aligns with such mechanisms. Given the shallow depths, these earthquakes posed risks of felt shaking and minor structural impacts in nearby communities, though no tsunami threat was associated.

Continued monitoring remains essential in this tectonically active zone. The 2018 swarm, occurring shortly after the February mainshock, highlights the potential for triggered sequences in the New Guinea Highlands and reinforces the importance of regional seismic networks for hazard assessment.

References
United States Geological Survey Earthquake Catalog (earthquake.usgs.gov)
Geological Survey of Papua New Guinea seismic reports
Global Centroid Moment Tensor database (globalcmt.org)