Saint Lucia

Saint Lucia occupies a central position in the Lesser Antilles volcanic arc, between the active volcanic islands of Martinique to the north and Saint Vincent to the south. The island experiences seismicity from the Lesser Antilles [[subduction-zone]] where the Atlantic oceanic lithosphere of the North American Plate descends beneath the Caribbean Plate approximately 150 kilometres to the east. The convergence rate of roughly 2 centimetres per year generates the background seismicity that the island feels. Saint Lucia also has volcanic heritage: the Qualibou caldera in the southwest, with its associated Sulphur Springs hydrothermal field (one of the world's few drive-in volcanoes), represents a potentially active volcanic system whose geothermal activity generates micro-earthquakes. The island's rugged, steep-sided topography — a product of volcanic construction and erosion — makes it susceptible to landslides triggered by strong seismic shaking. Low-lying coastal areas around Castries and Vieux Fort face [[tsunami]] exposure from arc-wide events.

Saint Lucia's historical earthquake record includes significant events from regional sources. The 29 November 2007 Martinique earthquake (magnitude 7.4) was one of the largest instrumented events in the Lesser Antilles in recent decades and was strongly felt in Saint Lucia, causing some minor structural damage and widespread alarm. The great 1843 earthquake (estimated magnitude 8.0) centred near Guadeloupe was felt throughout the arc including Saint Lucia and caused damage to colonial buildings. Hydrothermal earthquake swarms at the Qualibou caldera have been recorded periodically, including episodes in the 1990s. The eastern Caribbean has experienced M5–6 subduction interface events several times per decade in the monitoring era, and Saint Lucia has felt shaking from many of these. There is no record of a locally generated destructive earthquake in Saint Lucia's written history.

The geology of Saint Lucia records approximately 4 million years of volcanic arc activity. The island is built on submarine volcanic foundations and was progressively constructed by eruptions of andesitic to dacitic magma from the subduction system. The Pitons — the iconic twin lava spires on the southwestern coast — are volcanic plugs, the solidified cores of ancient explosive vents. The Qualibou caldera, approximately 8 kilometres in diameter, formed in a major collapse event roughly 32,000 years ago and remains the thermal and volcanic focus of the island's geological activity. The carbonate platform fringing the volcanic core represents younger Quaternary marine deposits. Saint Lucia's earthquake monitoring is conducted by the University of the West Indies Seismic Research Centre and forms part of the regional Eastern Caribbean seismic network operated from Trinidad.