Costa Rica

Costa Rica is a geologically young, volcanically active nation that experiences earthquakes almost continuously, occupying a position directly above the convergence of three tectonic plates. The Middle America Trench lies roughly 150 to 200 kilometres off the Pacific coast, where the Cocos Plate subducts beneath the Caribbean Plate at approximately 8 to 9 centimetres per year — one of the fastest [[subduction-zone]] rates in the world. This rapid convergence generates a near-constant background of small and moderate earthquakes, punctuated periodically by larger events that cause significant damage. Onshore, a network of northwest-trending strike-slip faults associated with the Caribbean Plate interior accommodates part of the plate-motion budget, and the Central Volcanic Cordillera runs the length of the country, hosting active volcanoes including Arenal, Rincón de la Vieja, and Poás that generate swarms of volcano-tectonic earthquakes. The Caribbean coast faces a separate seismic regime from the back-arc region, where extension and strike-slip motion along the North Panama Deformed Belt create additional [[fault]] hazard.

Costa Rica's documented seismic history reflects its position at this tectonic confluence. The 22 April 1991 Limón earthquake (magnitude 7.6) struck the Caribbean coast, killing 47 people, destroying 4,000 homes, and permanently uplifting sections of the coastline by up to 1.5 metres, transforming former underwater coral reefs into dry land — a dramatic visible record of [[fault]] displacement. Tsunami waves of up to 1.5 metres struck the coast. The 25 December 1990 Cobano earthquake (magnitude 7.0) severely affected the Nicoya Peninsula. The 5 September 2012 Nicoya earthquake (magnitude 7.6) ruptured a large segment of the [[subduction-zone]] interface directly beneath the peninsula, causing widespread damage and a small [[tsunami]]; remarkably, the [[epicenter]] had been identified as a seismic gap years in advance, making it one of the few accurately forecast large earthquakes in history. The 2009 Cinchona earthquake (magnitude 6.1) triggered devastating [[liquefaction]] and landslides that buried a highway and killed 34 people, illustrating how even moderate events cause severe secondary hazards in Costa Rica's steep, saturated terrain.

The tectonic architecture beneath Costa Rica is among the most studied and complex in Central America. The Cocos Plate itself is not homogeneous: it has two distinct segments with different ages, thicknesses, and surface textures that produce different coupling behaviour at the [[subduction-zone]] interface. The Cocos Ridge — an aseismic volcanic chain on the ocean floor — is currently colliding with and partially subducting beneath the Osa Peninsula, creating localised uplift and anomalously shallow seismicity. Beneath the volcanic arc, fluids released by the dehydrating slab rise into the mantle wedge, triggering partial melting and ultimately feeding the volcanoes at the surface. [[aftershock]] sequences are common and can last months to years after major events. Costa Rica's national seismological network (RSN) maintains dense coverage and contributes real-time data to regional tsunami warning systems operated through NOAA's Pacific Tsunami Warning Center.