Seismic Swarm Activity Near Kirakira, Solomon Islands: December 2016 Event Analysis

On 20 December 2016, seismic swarm PS20161220.1 was recorded 105 km west-northwest of Kirakira in the Solomon Islands. The sequence began at 04:21 UTC and ended at 23:22 UTC, registering seven earthquakes within 19 hours. This swarm occurred in a region of intense tectonic activity along the convergent boundary between the Pacific and Australian plates.

The events unfolded as follows. The initial shock measured magnitude 6.4 at a depth of 20 km. Subsequent activity included a magnitude 5.2 event at 36 km depth, followed by a magnitude 5.3 quake at 19 km. A magnitude 6.0 shock occurred at 10 km depth, succeeded by a magnitude 4.8 event at 23 km. Later shocks registered magnitude 5.5 at 10 km and magnitude 5.1 at 35 km. Depths remained predominantly shallow, consistent with upper-crustal deformation in this subduction setting.

The Solomon Islands form part of the Pacific Ring of Fire, where the Australian Plate subducts beneath the Pacific Plate at rates exceeding 10 cm per year. This convergence generates frequent moderate-to-large earthquakes and occasional swarms. Shallow focal depths, as observed here, often indicate brittle failure within the overriding plate or along the megathrust interface.

Historical records since 2000 show five swarms in the vicinity, including two in 2002, one each in 2004 and 2014, and the present 2016 sequence. Notable larger events nearby include a magnitude 7.8 earthquake on 8 December 2016 located 69 km west-southwest of Kirakira and a magnitude 7.3 event on 20 January 2003 situated 43 km west of Kirakira. These underscore the persistent seismic hazard.

Swarm sequences such as PS20161220.1 typically reflect fluid migration or stress triggering rather than mainshock-aftershock patterns. The rapid succession of events within a confined area highlights localized strain release along pre-existing faults in this highly active margin.

Data sourced from SeismoSight internal classification for swarm parameters. Regional tectonic framework derived from USGS and peer-reviewed studies on Solomon Islands seismotectonics.