QCOSTARICA – The 5.7-magnitude tremor, felt at 5:27 pmon Thursday, occurred in a maritime zone with the potential for stronger earthquakes, explained Ivonne Arroyo, coordinator of the Red Sismológica Nacional (RSN) – National Seismological Network
Arroyo indicates that the last similar remezón or low intensity seismic movement occurred on July 21, 2000, and was stronger.
On that occasion, the event had a magnitude of 6.4 and occurred off the coast of Cabo Blanco, Lepanto district, Puntarenas, some 50 km closer to land, than the one on Thursday.
Arroyo stated that fracturing in the Cocos plate* (placa del Coco), with magnitudes greater than 5, is extremely unusual.
“Earthquakes of moderate and larger magnitudes are not common in that area. It originated from the bending of the Cocos plate when it began to sink,” she explained.
Despite its moderate magnitude, a 5.7 on the modified Mercalli scale, this tremor was widely perceived throughout most of the country.
In fact, there were reports in all seven provinces feeling the jolt, in some it was perceived stronger than in others, according to its distance from the epicenter.
However, the aftershocks, so far three with magnitures cloes to 3.5 and one at 2, registered on Thursday and Friday have not been reported as felt.
The first occurred on Thursday at 7:29 pm, another seven minutes later; both occurred in the same marine area, about 100 kilometers south of Malpaís, Cobano district.
At 8:07 am Friday was another, located about 107 kilometers southwest of Cóbano, with a magnitude of 3.5. Minutes before that, there was another of magnitude 2.
The depths have been between 11 and 15 kilometers.
The tremors that the population is regularly used to feeling in Costa Rica have their origin in a local faulting of the Caribbean plate** (placa Caribe) or Panama microplate, or also because the Coco plate gets below others (subduction). But the earthquake This Thursday was different.
“When the Coco plate bends, it fractures and those faults are what generate the seismic movement.
“The radiated waves travel along the ocean, the first ones are the strongest, but because of the distance, the surface waves reached land generate a movement like a hammock,” Arroyo said.
For Esteban Chaves, a seismologist at the Observatorio Vulcanológico y Sismológico de Costa Rica (Ovsicori) – Costa Rica Volcanological and Seismological Observatory – these earthquakes have horizontal displacement and usually generate few aftershocks.
Chaves indicated that they will continue to monitor seismicity in the area, as well as in the rest of the country’s seismic sources.
Will there be stronger quakes in the near future stemming from Thurday’s temblor? Most likely the experts predict.
* The Cocos plate is a young oceanic tectonic plate beneath the Pacific Ocean off the west coast of Central America, named for Cocos Island, which rides upon it, created approximately 23 million years ago when the Farallon Plate broke into two pieces, which also created the Nazca Plate.
** The Caribbean Plate is a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off the north coast of South America. Roughly 3.2 million square kilometers (1.2 million square miles) in area, the Caribbean Plate borders the North American Plate, the South American Plate, the Nazca Plate and the Cocos Plate.