Seismic Swarm PS20130218.1 Near Lata, Solomon Islands

The seismic swarm designated PS20130218.1 occurred 6 km south-southeast of Lata in the Santa Cruz Islands of the Solomon Islands. It began at 18:27 on 17 February 2013 and concluded at 14:57 on 18 February 2013, spanning 20 hours and 30 minutes. During this interval, five earthquakes were recorded, all at a focal depth of 10 km. The sequence initiated with a magnitude 5.0 event at 18:27:22 on 17 February, followed by a 5.5 event at 19:18:52 and a 5.7 event at 19:23:45. Activity resumed the next day with a magnitude 5.1 quake at 10:50:40 and concluded with a 4.2 event at 14:57:31. All events clustered tightly in time and space, characteristic of swarm behavior rather than a classic mainshock-aftershock sequence. The Solomon Islands lie within the Pacific Ring of Fire at the convergent boundary between the Indo-Australian and Pacific plates. In the Santa Cruz region, the Pacific plate subducts westward beneath the Indo-Australian plate along the northern New Hebrides Trench, producing frequent shallow seismicity. This tectonic regime explains the shallow focal depths observed in the swarm and the region’s history of both isolated large earthquakes and episodic swarms. Since 2000, eleven swarms have been documented near Lata. Earlier swarms occurred in 2000, 2004, 2007, 2008, 2009 and 2012, with five additional swarms recorded in 2013 alone. This elevated rate underscores the area’s persistent seismic restlessness driven by ongoing plate convergence. Several strong earthquakes have struck within 100 km of the swarm center since 2000. The most significant was the magnitude 8.0 Santa Cruz Islands earthquake of 6 February 2013, located 66 km from the swarm epicenter. Two magnitude 7.0 events followed on 6 and 8 February 2013 at distances of 35 km, while a magnitude 7.1 event occurred 35 km southeast on 8 February. Earlier notable shocks include a magnitude 7.2 event 91 km south in September 2007 and a magnitude 7.0 event 76 km west-northwest in July 2015. The February 2013 swarm occurred shortly after the magnitude 8.0 mainshock and its immediate aftershocks, suggesting it may represent continued stress adjustment along the subduction interface. Shallow depths of 10 km for all swarm events align with the typical seismogenic zone in this segment of the trench. References
USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
SeismoSight internal swarm classification PS20130218.1