Location:

Period:

20 Sep 2002 13:33:41 - 21 Sep 2002 17:20:12 (1 day 3 hours 46 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.6; 102 km SSE of Manokwari, Indonesia; (10 Oct 2002) (40km from the swarm center)

4 swarms found nearby.

2002

PS20021010.1(30.3km)

10 Oct

13 hours

15 earthquakes

2004

PS20040728.1(184.1km)

28 Jul

9 hours

5 earthquakes

2009

PS20090103.1(155.3km)

3 Jan

17 hours

27 earthquakes

PS20090106.1(195.8km)

6 Jan

1 day 14 hours

6 earthquakes

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Seismic Swarm PS20020920.1: Analysis of Events Near Manokwari, Indonesia

Seismic swarm PS20020920.1 occurred 89 km south of Manokwari, Indonesia, beginning at 13:33 on 20 September 2002 and concluding at 17:20 on 21 September 2002. Over 27 hours and 46 minutes, the swarm produced six earthquakes, all at a focal depth of 10 km. The sequence included events of magnitude 6.0 at 13:33:41, 5.2 at 13:45:19, 6.4 at 15:43:35, 5.5 at 21:01:13, 4.1 at 22:39:10 on 20 September, and a final 5.2 at 17:20:12 on 21 September.

This swarm unfolded within a tectonically complex region where the Australian and Pacific plates converge along the New Guinea margin. The interaction generates thrust faulting and strike-slip motion, contributing to elevated seismicity throughout western New Guinea. Manokwari lies near the western extent of this collision zone, where oblique convergence has produced a network of active faults capable of generating both shallow crustal events and deeper subduction-related activity.

Swarm sequences such as PS20020920.1 typically reflect distributed stress release rather than a single mainshock-aftershock pattern. The clustered timing and moderate magnitudes suggest localized adjustments along fault segments, possibly influenced by fluid migration or aseismic slip at shallow depths. All events remained below 10 km, consistent with brittle failure in the upper crust of this rapidly deforming area.

Ten days after the swarm ended, a magnitude 7.6 earthquake struck 102 km south-southeast of Manokwari on 10 October 2002, approximately 40 km from the swarm centroid. This larger event highlights the persistent seismic hazard in the region, where moderate swarms can occur alongside infrequent great earthquakes driven by plate-boundary locking and release.

Historical records document repeated strong shaking in the Manokwari vicinity throughout the twentieth century, underscoring the long-term activity of local fault systems. The 2002 swarm fits within this pattern of episodic moderate seismicity that punctuates intervals of relative quiescence.

SeismoSight internal catalog, swarm PS20020920.1 parameters.
Regional tectonic summaries from peer-reviewed geophysical literature on New Guinea plate boundaries.