Costa Rica is one of the most seismically active regions in the world, regularly experiencing earthquakes. Its location within the Pacific Ring of Fire subjects the country to almost constant geological activity. This high level of seismicity is a direct consequence of tectonic plates colliding just off its Pacific coast. The country’s infrastructure and public safety systems are built around the reality of frequent seismic events.
Tectonic Setting of Costa Rica
Costa Rica’s seismic activity results from the collision between two major tectonic plates. The Cocos Plate, an oceanic plate, is actively moving northeastward and diving beneath the Caribbean Plate, which underlies the country. This process, known as subduction, occurs along the Middle American Trench, running parallel to the Pacific coastline.
The convergence rate is rapid, occurring at approximately 8.5 to 9.0 centimeters per year. This movement creates immense stress that builds up along the plate boundary. When this stress overcomes the friction holding the plates together, it releases as a powerful subduction zone, or megathrust, earthquake. The subducting Cocos Plate is geologically heterogeneous, containing features like the Cocos Ridge that influence the depth and magnitude of seismic events.
Major Seismic Zones Within Costa Rica
While the major subduction boundary is off the Pacific coast, seismic activity is distributed across specific zones both offshore and inland. The Nicoya, Osa, and Burica Peninsulas sit directly above the seismogenic zone of the megathrust fault. These areas are prone to the largest and most destructive interplate earthquakes.
Inland, tectonic stress generates a network of shallow, upper-plate faults. The Central Costa Rica Deformed Belt (CCRDB) and the Volcanic Arc Faults (VAF) traverse the Central Valley and the volcanic mountain range. Earthquakes in these crustal fault systems, such as those near San José, tend to be shallower. These shallow-focus events often cause intense shaking and significant damage due to their proximity to population centers.
Frequency and Historical Context
Costa Rica experiences a high frequency of seismic events, although most are too small to be felt. Monitoring institutions record approximately 3,000 earthquakes annually. An average of around 12 tremors are registered daily, primarily by sensitive instruments.
The country experiences a major earthquake of magnitude 7.0 or greater roughly every 7 to 15 years. This pattern highlights the consistent hazard posed by the megathrust boundary. Historically, significant impacts have occurred on both coasts. The 1991 Limón earthquake (M 7.7) struck the Caribbean coast, and the 2012 Nicoya earthquake (M 7.6) ruptured the plate boundary on the Pacific side. The 2009 Cinchona earthquake (M 6.1) near the Central Valley was a damaging example of a shallow, internal quake.
Seismic Monitoring and Public Safety Measures
The country maintains a sophisticated system for tracking and analyzing seismic activity. Two primary institutions, the Volcanological and Seismological Observatory of Costa Rica (OVSICORI) and the National Seismological Network (RSN), continuously monitor data from seismographs and GPS stations. This network allows for rapid analysis and public dissemination of information during and after a significant event.
Institutional preparedness is complemented by strict construction regulations. The national building code, the Código Sísmico de Costa Rica, mandates earthquake-resistant design, including reinforced concrete and steel reinforcement, especially in public and commercial structures. The universally accepted safety protocol is to “Drop, Cover, and Hold On” immediately when shaking begins. Furthermore, anyone near the coast who experiences a prolonged or strong earthquake should immediately evacuate to higher ground without waiting for an official tsunami warning.