Falkland Islands

The Falkland Islands (Islas Malvinas) sit on the Falkland Plateau — a fragment of continental crust on the South American Plate — in the South Atlantic Ocean approximately 300 kilometres east of the southernmost tip of Argentina. Geologically, the islands are an extension of the South American continental shelf and share the same Precambrian and Paleozoic basement as Patagonia. The territory sits well away from the most active tectonic boundaries, but it is not entirely without seismic context: the Scotia Plate — a small tectonic microplate that fills the gap between the South American and Antarctic plates south of South America — lies approximately 500 kilometres to the south and generates earthquakes along both the North Scotia Ridge (a transform boundary running east of the Falklands) and the South Scotia Ridge. The North Scotia Ridge transform system is the primary seismic source with potential to affect the Falkland Islands, generating moderate-to-large strike-slip earthquakes along this fracture zone. The South Georgia microplate and the convergence at the South Sandwich Trench are additional South Atlantic seismic sources more distant from the Falklands.

The seismic history of the Falkland Islands region includes moderate events from the Scotia arc system. The 12 May 1998 earthquake ([[moment-magnitude]] 7.1) struck near the North Scotia Ridge south of the Falklands and was widely felt on the islands, causing minor damage to older structures in Stanley. The 2013 South Atlantic earthquake ([[moment-magnitude]] 7.0) south of the Falklands produced felt shaking. Historical accounts from the nineteenth century record occasional felt earthquakes in Stanley, likely corresponding to North Scotia Ridge or South American Plate margin events. The South Sandwich subduction zone, approximately 1,500 kilometres to the east and southeast of the Falklands, generates large intraslab and interface earthquakes; a [[moment-magnitude]] 8.1 event struck the South Sandwich Islands in August 2021, generating a small [[tsunami]] recorded at Falklands tide gauges. The Andean subduction zone to the west — particularly the Chilean segment — occasionally transmits [[seismic-wave]]s across the South American Plate to produce weak felt motion in the Falklands.

The geological character of the Falkland Islands reflects their origin as part of the Gondwana supercontinent that rifted and dispersed during the Mesozoic. The islands expose Precambrian metamorphic and granitic basement overlain by a thick sequence of Paleozoic quartzites, siltstones, and diamictites — the Falkland Sound Formation — that dip gently and create the characteristic ridged topography of East and West Falkland. The Falkland Plateau, on which the islands sit, is a continental fragment that rotated approximately 180 degrees during the opening of the South Atlantic, explaining the anomalous orientation of Paleozoic structures relative to equivalent formations in Patagonia. The stable continental basement provides competent bedrock with low susceptibility to [[liquefaction]] or [[seismic-wave]] amplification. [[tsunami]] hazard is relatively low compared to Pacific territories but non-negligible given South Atlantic seismic sources; the 2021 South Sandwich Islands [[tsunami]] demonstrated that South Atlantic events can generate detectable waves at the Falklands.