Just 15 hours after the 7.6-magnitude earthquake that struck the country last September 5, geologists detected mild tremors, originated in Tenorio failures, Cote and Chiripa, located near the Rincon de la Vieja volcano , Miravalles and Tenorio, between Guanacaste and Alajuela.
Shortly after the fault was Angel on the slopes of the Poas volcano that generated shock and almost simultaneous earthquakes were caused by faults; Agua Caliente , Rio Azul, Elia and Ariete, in the cantons of El Guarco, Turrialba and Desamparados.
Until last Thursday, had 16 faults distributed in the provinces of Guanacaste, Alajuela, Cartago and San Jose that were causing tremors, reported the National Seismological Network (RSN), University of Costa Rica (UCR). These earthquakes did not exceed 4 degrees of moment magnitude (Mw). Precisely on Thursday there were several shocks in Zarcero in Alajuela (April 1 degrees) and were allocated to the Congo and Porvenir failures.
Geologist Mario Fernandez Arce, of the RSN, warned that the most destructive and deadly earthquakes in Costa Rica were originated in local faults.
The local faults are fractures in the crust with a movement that can be vertical (one up and one down) or horizontally (moves one to the right and one on the left).
In our country, according to Costa Rica tectonic Atlas published in 2003 that Walter Montero, Guillermo Alvarado and Percy Denyer, there are about 150 fault lines (not all are active).
These fractures are found from the surface to 30 km depth. It is estimated that after that depth subduction earthquakes are due to the collision of tectonic plates.
Experts predict that the tremors from these local faults can extend months or years as with the Cóbano earthquake of March 25, 1990, which triggered earthquakes in Puriscal and Alajuela.
Mario Fernandez said that after the earthquake on September 5 in the area near the epicenter have been hundreds of aftershocks, but generated by the collision of plates. In the area of Nicoya no faults were activated.