Seismic Swarm PS20130206.2 Near Lata, Solomon Islands

The Solomon Islands occupy a tectonically complex segment of the Pacific Ring of Fire, where the Pacific Plate subducts beneath the Australian Plate along the New Hebrides Trench. This convergence drives frequent seismicity, including both isolated large events and clustered swarms. The Santa Cruz Islands, located at the northern end of the archipelago, experience elevated activity due to the interaction of multiple microplates and the subduction of the Pacific Plate at rates exceeding 80 mm per year.

On 6 February 2013, seismic swarm PS20130206.2 was recorded 51 km south of Lata. The sequence began at 01:54 UTC and concluded at 23:49 UTC, encompassing 11 earthquakes over 21 hours and 55 minutes. The events exhibited the following parameters:

• 01:54:14 UTC, magnitude 7.0, depth 8 km
• 04:38:08 UTC, magnitude 5.1, depth 16 km
• 05:13:46 UTC, magnitude 5.2, depth 10 km
• 05:16:25 UTC, magnitude 5.3, depth 10 km
• 05:16:26 UTC, magnitude 5.3, depth 10 km
• 05:18:17 UTC, magnitude 4.8, depth 10 km
• 11:53:55 UTC, magnitude 6.0, depth 14 km
• 12:44:29 UTC, magnitude 5.9, depth 10 km
• 17:19:31 UTC, magnitude 5.0, depth 12 km
• 23:39:00 UTC, magnitude 5.0, depth 10 km
• 23:49:35 UTC, magnitude 5.3, depth 10 km

The swarm initiated with a shallow mainshock of magnitude 7.0, followed by a rapid succession of aftershocks clustered at depths of 10–16 km. Magnitudes remained predominantly in the 5.0–6.0 range after the initial event, indicating a typical aftershock decay pattern within a short temporal window.

Regional historical data reveal recurrent swarm activity. Since 1 January 2000, ten swarms have been documented in the area, occurring in 2004 (1), 2006 (1), 2007 (1), 2008 (1), 2009 (2), 2012 (1), and 2013 (3). This pattern underscores the persistent stress accumulation and release along the subduction interface.

The swarm coincided with two notable larger events on the same day: a magnitude 7.1 earthquake 112 km west-southwest of Lata and the magnitude 8.0 Santa Cruz Islands mainshock 98 km from the swarm centroid. Earlier strong events include the magnitude 7.2 earthquake of 2 September 2007, located 97 km south of Lata. These occurrences highlight the capacity of the region to generate both swarm sequences and great earthquakes within short time frames.

Seismic swarms in subduction settings often reflect fluid migration or aseismic slip transients that load adjacent fault patches. The 2013 sequence, with its shallow focal depths and rapid onset, aligns with such mechanisms observed along the New Hebrides margin.

References
United States Geological Survey Earthquake Catalog
Global Centroid Moment Tensor Project
Pacific Tsunami Warning Center archives