The better-than-6-point quake offshore in the Pacific lasted at least 25 seconds. The quake was felt in nearly all of the country. Recorder displays at the Observatorio Vulcanológico y Sismológico de Costa Rica show that some sensors continued to vibrate for a half hour.
In fact, one hour and 12 minutes after the 6:45 p.m. quake another took place in the same general area. That one was estimated at 4.4 magnitude.
The magnitude of the 6:45 p.m. quake was estimated differently by different agencies. The U.S. Geological Survey said 6.5. The Observatorio Vulcanológico y Sismológico at Universidad de Costa Rica initially said 6.2. At the Laboratorio de Ingeniería Sísmica the estimated was 6.3.
That agency said the 6:45 p.m. quake was 9.3 kilometers south of Sámara and 22.9 kilometers southeast of Nosara in the Pacific. That is about the same area where a 7.6 magnitude quake took place Sept. 5.
The 7:55 p.m. quake epicenter was estimated at 28.6 kilometers south southeast of Nosara and 34.6 kilometers west southwest of Sámara.
There also was a 3.6-magnitude quake at 7:43 p.m. with an epicenter below the mountains east of Samara.
All over the country individuals reacted to the movement although there was little report of damage other than falling objects. Residents still are jumpy from the Sept. 5 quake and predictions by scientists that another big one is likely.
The quakes Tuesday are considered replications of the Sept. 5 event. There have been thousands, but the 6:45 p.m. quake was the strongest yet. The cause is the subduction of the Coco tectonic plate under the lighter Caribbean plate on which Costa Rica rides.