Central mountains appear to be active earthquake zone

If anyone had doubts that Costa Rica is geologically active, a report this week by the Red Sismológica Nacional will change the mind.

Looking sideways to the north at a cross section of the country. Each green dot represents a previous quake. Graphic: Red Sismológica Nacional/A.M. Costa Rica

The author, Mauricio Mora Fernández, produced the report after the three quakes that took place near Zarcero Friday. The biggest quake, magnitude 5.9, took place at 7:54 p.m. A quake of 3.3 magnitude followed at 10:16 p.m. And that was followed by an 11:15 p.m. quake of 4.1 magnitude.

Mora said that all these quakes took place within the Coco tectonic plate, which is under the bulk of the country.

Because they were so deep, there was no serious damage, and the second and third quakes may not have been sensed by many people, Mora said. The initial quake was estimated to be 84 kilometers beneath the surface. That’s about 52 miles.

Mora noted that a quake Nov. 19, 1948, had a magnitude of 7.0 and that one in 1992 had a magnitude of 6.2. These are infrequent events, he said and due to the great depth usually do not have grave effects.

The Red Nacional is part of the Universidad de Costa Rica and affiliated with the Instituto Costarricense de Electricidad.

The Coco plate reaches 100 kilometers below the surface of the central volcanic mountains, called the Cordillera Volcánica Central. The cross sectional map that the Red Nacional produced shows a green dot for every quake registered between 1985 and 2008.

The deeper the location, the fewer the quakes.

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