Cayman Islands

The Cayman Islands are a British Overseas Territory located in the western Caribbean, positioned directly above the Cayman Trough — one of the deepest trenches in the Atlantic basin, reaching more than 7,500 metres below sea level — and astride the left-lateral transform [[fault]] system that forms the boundary between the North American Plate to the north and the Caribbean Plate to the south. The Oriente Fault, Swan Islands Fault, and Cayman Trough Fault collectively constitute this boundary, accommodating approximately 2 centimetres per year of left-lateral (sinistral) strike-slip motion between the two plates. Grand Cayman, Cayman Brac, and Little Cayman sit on a shallow submarine platform above this transform system and are among the most seismically exposed territories in the Caribbean. Unlike subduction-dominated islands where deep-slab events occur at great depth, the Cayman transform system generates shallow, brittle crustal earthquakes directly beneath and around the islands at depths of only 10 to 30 kilometres, maximising [[seismic-wave]] delivery to the surface.

The historical earthquake record of the Cayman Islands is defined by its position on the Caribbean-North American transform. On 7 January 2020, a magnitude 7.7 earthquake struck approximately 125 kilometres north-northwest of Grand Cayman in the Oriente Fault zone, the largest Caribbean earthquake in decades and the largest ever recorded in the Cayman region by modern instruments. The event was felt strongly throughout the Caribbean, triggered a [[tsunami]] advisory for the Cayman Islands and Jamaica, and produced small but measurable wave heights at coastal tide gauges. No deaths occurred in the Cayman Islands, though the territory was significantly shaken. Historically, the Cayman Trough fault system produced a destructive earthquake in 1900 (estimated M7.0) and has generated numerous M5–6 events in the instrumental era. The Cayman Islands lack a detailed pre-instrumental earthquake catalogue, but the geological setting implies a history of repeated major fault earthquakes over the Holocene.

The Cayman Islands are built on Miocene to Quaternary carbonate rocks — coral limestone and calcarenite — deposited on the Cayman Ridge, a submerged structural high between the Cayman Trough to the south and the Yucatan Basin to the north. The trough represents the deepest expression of the Caribbean-North American transform, where the crust has been pulled apart along the releasing bend of the sinistral fault system, creating a deep pull-apart basin. [[liquefaction]] in saturated coastal sand and reclaimed land is a significant secondary hazard for Grand Cayman in a major fault earthquake. The territory's [[tsunami]] risk from transform fault earthquakes is real but generally lower than from subduction events of equivalent [[magnitude]], because strike-slip motion generates less vertical seafloor displacement than thrust faulting. However, submarine landslides triggered on the steep slopes of the Cayman Trough are a recognised secondary [[tsunami]] source.