Seismic Swarm PS20141126.1 in the Molucca Sea Region, Indonesia

The seismic swarm designated PS20141126.1 occurred in the tectonically active Molucca Sea area of eastern Indonesia. It began at 16:29 on 25 November 2014 and concluded at 17:16 on 26 November 2014, centered 133 km ENE of Laikit, Laikit II (Dimembe). Over 24 hours and 46 minutes, eight earthquakes were recorded, with magnitudes ranging from 4.9 to 6.8 and focal depths between 30 and 89 km.

The sequence opened with a magnitude 5.1 event at 37 km depth on 25 November. The following day featured the strongest shock, a magnitude 6.8 earthquake at 39 km depth, followed within minutes by several aftershocks of magnitudes 4.9, 5.1, 5.6, and 5.0 at depths of 30–42 km. Two additional magnitude 5.0 events occurred at 17:16, one at 35 km and the other at 89 km depth. This rapid succession of moderate events within a confined time window and spatial area characterizes swarm behavior, distinct from typical mainshock-aftershock sequences.

The Molucca Sea lies at the junction of the Philippine Sea, Australian, and Sunda plates, where complex collision and subduction processes generate frequent seismicity. The region experiences both shallow crustal earthquakes and intermediate-depth events associated with subducting slabs. Historical records since 2000 show only six prior swarms in the vicinity, occurring in 2001 (three events), 2007 (two events), and 2014 (one event including the present swarm). This low frequency underscores the episodic nature of clustered activity amid the broader background of individual large earthquakes.

Strong events have repeatedly struck near the swarm center. Notable examples include a magnitude 7.1 earthquake 6 km away on 15 November 2014, a magnitude 7.1 event 25 km distant on 14 November 2019, and a magnitude 7.4 shock 76 km away on 1 April 2026. Earlier large earthquakes comprise a magnitude 7.5 event 89 km distant on 21 January 2007 and a magnitude 7.1 earthquake 68 km away on 24 February 2001. These occurrences reflect the persistent strain accumulation along regional fault systems and subduction interfaces.

The 2014 swarm fits within this pattern of intermittent clustering, likely driven by fluid migration or stress transfer along pre-existing structures in the collision zone. Depths predominantly in the 30–42 km range point to activity within the upper portion of the subducting lithosphere, while the deeper 89 km event may relate to slab dynamics. Such swarms provide valuable data for refining seismic hazard models in an area where population centers on nearby islands face elevated risk from both shaking and potential tsunamis.

Continued monitoring of the Molucca Sea remains essential given the documented recurrence of both swarms and great earthquakes. The combination of historical swarm statistics and nearby magnitude 7+ events highlights the region’s capacity for energetic seismic episodes within short time frames.

References

• SeismoSight internal swarm classification records for PS20141126.1
• USGS Earthquake Catalog (historical events since 2000)
• Tectonic summaries from the Geological Survey of Indonesia and peer-reviewed studies on Molucca Sea collision zone dynamics