Seismic Swarm Activity Near Kirakira, Solomon Islands, September 2002

The Solomon Islands lie along a tectonically active convergent margin in the southwestern Pacific, where the Pacific Plate subducts beneath the Australian Plate and smaller microplates. This setting produces frequent earthquakes, volcanic activity, and rapid crustal deformation. The islands form part of the Pacific Ring of Fire, with historical records documenting multiple magnitude-7+ events that have generated tsunamis and caused significant local impacts.

On 24 September 2002, a seismic swarm was recorded approximately 89 km west of Kirakira on Makira Island. The sequence began at 02:26 local time and concluded at 23:01 the same day, spanning 20 hours and 34 minutes. Nine earthquakes were detected during this period, all occurring at shallow depths between 10 km and 19 km. The events exhibited a range of magnitudes, with the largest reaching 6.3. Notable shocks included two magnitude-6.3 earthquakes late in the sequence, one at 22:54 and another at 23:01, alongside earlier events of 6.1 and 5.6. The remaining events ranged from 4.3 to 5.3, clustered primarily in the morning and evening hours.

This swarm reflects typical stress release along the subduction interface and associated crustal faults in the region. Shallow focal depths indicate activity within the overriding plate or near the plate boundary, consistent with the broader tectonic regime. No surface rupture or major tsunami was associated with the 2002 sequence, though such swarms can precede or follow larger mainshocks.

In the years following this swarm, the same general area experienced two significant earthquakes. A magnitude-7.3 event occurred on 20 January 2003, centered 126 km west of Kirakira and roughly 46 km from the swarm epicenter. A larger magnitude-7.8 earthquake struck on 8 December 2016, located 69 km west-southwest of Kirakira and only 17 km from the 2002 swarm center. Both events underscore the persistent seismic hazard along this segment of the plate boundary.

Seismic monitoring in the Solomon Islands relies on regional and global networks to track such activity. Continued observation helps refine hazard assessments for nearby communities, where building practices and tsunami preparedness remain critical given the islands’ exposure to both shallow crustal and subduction-zone earthquakes.

References

USGS Earthquake Catalog (events since 2000)
Global CMT Catalog
SeismoSight internal swarm classification PS20020924.1