A report presented by the National Seismological Network on Monday noted that 4,000 aftershocks have been registered throughout the country after the Nicoya earthquake on Sept. 5.
Two months have passed since the major 7.6-magnitude quake. Since then, seismic activity has occurred mostly in areas of Cartago and San José provinces, including: El Guarco, Desamparados, Tapesco, Zarcero, Athens, Esparza, Puriscal and San Isidro de Perez Zeledón. A temblor also shook Calero Island, in the northeast corner of the country near the Nicaraguan border.
Wilfredo Rojas, a seismology expert at the University of Costa Rica, said that most of the aftershocks were caused by the subduction of the Cocos plate under the Caribbean plate, mainly in the area of the Nicoya Peninsula, the epicenter of the Sep. 5 quake. Other recent temblors are related to local faults in Costa Rica, he added.