Seismic Swarm PS20130213.1 Near Lata, Solomon Islands

The seismic swarm designated PS20130213.1 occurred in a tectonically active segment of the southwestern Pacific, centered 135 km west-southwest of Lata in the Santa Cruz Islands. The sequence began at 23:32 on 12 February 2013 and concluded at 15:55 on 13 February 2013, spanning 16 hours and 23 minutes. During this interval, six earthquakes were recorded, with magnitudes ranging from 4.2 to 5.5 and focal depths between 9 km and 19 km.

The events unfolded as follows. The initial shock at 23:32 on 12 February registered magnitude 5.5 at a depth of 9 km. Subsequent activity on 13 February included a magnitude 5.4 event at 10:08 (19 km depth), a magnitude 5.2 shock at 11:08 (10 km depth), a magnitude 4.2 event at 12:41 (10 km depth), another magnitude 5.2 at 12:50 (10 km depth), and a final magnitude 5.0 at 15:55 (10 km depth). Most events clustered at shallow crustal depths around 10 km, consistent with the region’s brittle upper lithosphere.

The Santa Cruz Islands lie within the Pacific Ring of Fire, where convergence between the Indo-Australian and Pacific plates drives subduction along the northern New Hebrides Trench. This setting produces frequent moderate-to-large earthquakes and occasional earthquake swarms, often linked to stress redistribution following major ruptures. The swarm followed the magnitude 8.0 Santa Cruz Islands earthquake of 6 February 2013 by only six days, suggesting a possible connection through afterslip or triggered faulting on adjacent structures.

Historical records since 2000 indicate eight prior swarms in the immediate vicinity, occurring in 2005, 2007, 2008, 2009, 2012, and three instances in 2013. Strong earthquakes have also punctuated the area, including a magnitude 7.1 event on 6 February 2013 located 56 km from the swarm centroid, a magnitude 7.0 shock on 18 July 2015 situated 89 km away, a magnitude 7.0 earthquake on 9 November 2004 at 88 km distance, and the earlier magnitude 8.0 mainshock at 70 km.

These patterns underscore the persistent seismic hazard of the region. Shallow crustal swarms such as PS20130213.1 illustrate how clustered activity can accompany or follow great subduction-zone earthquakes, reflecting complex fault interactions within the overriding plate.

References:
SeismoSight internal swarm catalog (PS20130213.1 parameters).
USGS Earthquake Catalog (historical events 2000–2015).
Global CMT Project (focal mechanisms and depths for regional events).