Seismic Swarm PS20140412.1 in the Solomon Islands: Geological Context and Event Analysis

The seismic swarm designated PS20140412.1 occurred approximately 84 km south of Kirakira in the Solomon Islands. It began at 20:14 on 12 April 2014 and concluded at 16:51 on 14 April 2014, spanning 44 hours and 36 minutes. During this interval, 26 earthquakes were recorded, with magnitudes ranging from 4.7 to 7.6 and focal depths between 4 km and 50 km.

The sequence featured two prominent mainshocks. The initial event reached magnitude 7.6 at a depth of 22 km, followed hours later by a magnitude 7.4 shock at 39 km depth. Subsequent activity included multiple events above magnitude 5.5 clustered within the first 24 hours, with notable aftershocks such as magnitude 6.6 pairs occurring within minutes of each other on 13 April. The swarm displayed a typical pattern of rapid onset followed by decaying frequency, consistent with stress redistribution along regional fault systems.

The Solomon Islands occupy a tectonically complex segment of the Pacific Ring of Fire, situated at the convergent boundary between the Pacific Plate and the Australian Plate. Subduction along the New Britain-San Cristobal trench drives frequent seismicity, while nearby transform faults and the Solomon Sea microplate contribute to shallow crustal deformation. Depths recorded in the swarm align with both interplate thrusting and intraslab activity within the subducting slab.

Since 2000, four prior swarms have been documented in the same region, occurring in 2002 (two events), 2004 (one event), and 2005 (one event). These episodes underscore recurrent episodic strain release south of Kirakira. In addition, three strong earthquakes exceeding magnitude 7.4 have struck within 65 km of the swarm centroid since 2000, including a magnitude 7.8 event in December 2016 located 69 km west-southwest of Kirakira.

The April 2014 swarm fits within this established pattern of clustered moderate-to-large events along the arc. Depths predominantly below 30 km suggest involvement of the plate interface and upper Wadati-Benioff zone, where fluid migration and slab dehydration can promote swarm-like behavior. No surface rupture or significant tsunami was associated with the sequence, reflecting the predominantly offshore and intermediate-depth character of the activity.

SeismoSight internal classification
USGS earthquake catalog (regional Solomon Islands events)
Global CMT moment tensor solutions for 2014 Solomon Islands sequence