The offshore zone that gave the country a seismic wake up call Monday is well known to geologists. This is about the same spot where a 6.9 magnitude quake took place Aug. 20, 1999, according to the Laboratorio de Ingeniería Sísmica of the Universidad de Costa Rica.
The quake at 4:55 a.m. Monday had a magnitude now estimated at 5.9, said the Laboratorio.
The location is about the same where there was a series of weekend quakes. There was one, a 4.5 magnitude jolt, that took place Saturday at 2:43 p.m. There were three lesser quakes Sunday at 1:39, 2:38 and 2:39 p.m., according to the Laboratorio records.
There also were four quakes there in 2011. The section is about 40 kilometers off the Pacific coast near Dominical. That’s about 25 miles.
Informal reports from expats say there was no serious damage as a result of the Monday quake. Online discussion lists chattered all day over the quake.
Quake magnitudes are expressed exponentially, much like the fictional warp drive on the USS Enterprise spaceship. So a 5.0 quake is 10 times stronger than a 4.0 magnitude quake.
The Red Sismológica Nacional, Costa Rica at the Universidad de Costa Rica noted that a series of smaller earthquakes followed the 4:55 a.m. one. There was one at 6:59 a.m. estimated at 3.8 magnitude, one at 7:07 a.m. estimated at 3.6 and one at 7:36 a.m. estimated at 3.8. There also were many lesser quakes that were not felt by humans.
The Red Sismológica Nacional noted that this is an area of subduction where the Coco tectonic plate is moving under the lighter Caribbean plate.
Although some coastal residents are worried about a tsunami as a result of Pacific earthquakes, the structure of the sea floor would require a quake in the 7 to 8 magnitude range to generate a large wave, said the Laboratorio de Ingeniería Sísmica, based on studies by the U.S. Geological Survey.