Seismic Swarm Near Kirakira, Solomon Islands: October 2002 Analysis

The Solomon Islands lie along the tectonically active boundary between the Pacific and Australian plates, where subduction processes generate frequent seismic events. This region experiences both deep and shallow earthquakes due to the complex interaction of multiple microplates and the Solomon Sea Plate. The area around Kirakira, on the island of Makira, sits within a zone of elevated seismicity influenced by the San Cristobal Trench to the south.

On 1 October 2002, a seismic swarm designated PS20021001.1 was recorded approximately 79 km west-southwest of Kirakira. The sequence began at 04:32 local time and concluded at 11:58, spanning 7 hours and 26 minutes. During this period, five earthquakes were registered, all at a focal depth of 10 km. The events occurred in the following order: a magnitude 5.6 quake at 04:32:10, followed by a magnitude 5.8 event at 08:46:55. Later activity included a magnitude 5.2 shock at 11:33:38, a magnitude 5.4 event at 11:39:48, and a final magnitude 4.5 quake at 11:58:39. Such swarms typically reflect fluid migration or stress redistribution along fault networks rather than a single mainshock-aftershock sequence.

Since the start of 2000, this swarm represents the sole recorded instance in the immediate vicinity according to internal classifications. A notable nearby event took place on 20 January 2003, when a magnitude 7.3 earthquake struck 126 km west of Kirakira, approximately 70 km from the swarm center. Another significant shock, magnitude 7.8, occurred on 8 December 2016 at 69 km west-southwest of Kirakira, or 24 km from the 2002 swarm location. These larger earthquakes highlight the persistent seismic hazard in the region driven by ongoing plate convergence.

The shallow depth of the 2002 swarm events suggests activation of upper crustal faults, common in the extensional regimes that develop behind the main subduction interface. Historical patterns in the Solomon Islands demonstrate that swarms often precede or accompany periods of heightened tectonic strain release, though each sequence remains unique in its temporal and spatial distribution.

References

• United States Geological Survey Earthquake Catalog
• SeismoSight internal swarm classification database