Seismic Swarm PS20131116.1 in the Scotia Sea

The Scotia Sea, situated between the southern tip of South America and the Antarctic Peninsula, represents a tectonically complex region dominated by the Scotia Plate. This oceanic plate is bounded by major transform faults and interacts with the South American and Antarctic plates, resulting in frequent seismic activity. The plate's boundaries include the North Scotia Ridge and South Scotia Ridge, where strike-slip motion predominates, alongside the South Sandwich subduction zone to the east, which contributes to deeper seismicity.

Seismic swarm PS20131116.1 was recorded in this setting, commencing at 03:34 on 16 November 2013 and concluding at 15:53 on 18 November 2013. Over 60 hours and 18 minutes, a total of 24 earthquakes were detected. The sequence began with a magnitude 6.9 event at a depth of 9 km, followed rapidly by a magnitude 5.4 shock at 10 km depth. Subsequent events on 16 November included multiple magnitude 5.0 to 5.5 quakes, all clustered at shallow depths around 10 km.

Activity intensified on 17 November with a prominent magnitude 7.7 earthquake at 09:04, occurring at 10 km depth. This mainshock triggered a series of aftershocks, including magnitudes 5.8, 5.1, 5.3, and additional events ranging from 5.0 to 5.7, with depths varying between 10 km and 18 km. The swarm continued into 18 November, featuring four final events of magnitudes 5.0 to 5.2 at depths of 14 km to 15 km.

This swarm stands out in regional records. Since 1 January 2000, only one prior swarm has occurred in the Scotia Sea, dating to 2003. That year also saw a strong magnitude 7.6 earthquake located 47 km from the center of the 2013 swarm. Such clustering highlights episodic seismic release along the Scotia Plate's transform boundaries, where stress accumulation along strike-slip faults can produce concentrated sequences rather than isolated large events.

Geological context indicates that shallow depths in the swarm reflect activity within the brittle upper crust of the oceanic lithosphere. The Scotia Sea's evolution stems from the fragmentation of the Drake Passage region during the Cenozoic, establishing the current plate configuration and facilitating lateral motion that accommodates relative movement between South America and Antarctica.

References:
USGS Earthquake Catalog
Global CMT Project
SeismoSight internal swarm classification database