Nicoya Peninsula Moves 11 Milimeters A Year

Q COSTA RICA – The Nicoya Peninsula moves 11 milimeters, the equivalent to more than one centimeter  (.43 inches), going northwest, according to a test made by the Universidad of Costa Rica (UCR) and the Indiana University of Pennsylvania (IPU), a public research university in Indiana County, Pennsylvania, United States.

The Nicoya Peninsula is settled on a tectonic block. The UCR report says thatin the future, in a million years Guanacaste will not have the current position, but will be located further north of where it is now located.”

According to the test, the movement of the tectonic block of the peninsula of Nicoya might be produced by the land lifting provoked by Cocos tectonic plate.

Walter Montero Pohly of the UCR’s Centro de Investigaciones en Ciencias Geológicas (CICG), Jonathan C. Lewis of Indiana University of Pennsylvania, and María Cristina Araya of the National Seismological Network (RSN), UCR and Instituto Costarricense de Electricidad (ICE), are the authors of the study titled The Volcanic Arc Sliver of Guanacaste in northwest Costa Rica, published last May in the Scientific Reports journal.

This research is considered of great relevance by the information that it provides to determine the seismic threats in the country since for the first time it was possible to identify several faults and their characteristics, located near populations like Bijagua, Upala, and Tilarán. Also, there are now known aspects that can shed light on the seismic potential of these faults and the possible consequences for that area.

According to Montero, the study arose from three earthquakes that have occurred around Bijagua de Upala in the last 15 years; The last was on July 3, 2016, and had a magnitude of 5.4. These earthquakes have the peculiarity that they are of intermediate magnitude and very superficial, but have caused local effects.

In addition, two major earthquakes occurred in the last 100 years: the Tilarán earthquake of 13 April 1973, with a magnitude of 6.5, causing several deaths and landslides, and the Guatuso earthquake October 10, 1911, of magnitude 6.5. In addition, in 1853 another earthquake occurred, that affected Cañas of Guanacaste. Although no seismological records of these last two earthquakes exist, the scientists consider that they could be associated with the faults Haciendas-Chiripa.

Montero detailed that the fault system is composed of the faults: Haciendas, which reaches the border with Nicaragua and continues under Lake Nicaragua; Caño Negro, which begins in the north of the country and is about 40 kilometers long; Chiripa and Cote Arenal, located in the environs of Tilarán, and Chiquero, located to the east of the volcano Tenorio.

The researchers updated the information on the Caño Negro fault, one of the most important of the system, in terms of stroke and type of movement.

“The movement of this fault system is predominantly horizontal and dextral (it moves to the right), which tells us that the east and north of Costa Rica (San Carlos and Guatuso plains) are quiet,” Montero said.

To the contrary, the area that is moving is the Volcanic Arc of Guanacaste, which includes places such as the Nicoya Peninsula, Santa Elena Peninsula and the Orosi volcano chain, Rincón de la Vieja, Miravalles and Tenorio, located in The Volcanic Cordillera of Guanacaste.

This tectonic block marks the boundary between the Cocos and Caribbean plates, as the geologist explained: “This tectonic block moves, along with other parts of the Pacific of Central America, at a speed of 11 millimeters per year, between the Coco and Caribbean plates. “

Illustration from Scientific Reports

But, why does that block move?

The hypothesis most accepted by Montero is that it is due to the collision caused by the lifting of the Coco, an oceanic uprising moved by the Coco plate, which is getting under the southern part of Costa Rica. This movement causes compression and the block (the Guanacaste Volcanic Arc) that moves sideways out of the area where the Coco plate rising is pushing Costa Rica.

The tectonic blocks are of smaller size, they are not (tectonic) plates, whose origin has to do with the movements of these, explained the expert.

Another aspect investigated by the geologists and that helped the results obtained is the study of the earthquakes with a greater magnitude that occurred in the area between the years 2006 to 2016, in order to determine what kind of failures were those that caused those tremors.