QCOSTARICA – The potential for an earthquake with a magnitude equal to or greater than 7 could occur in a few years is due to the enormous energy accumulated in a fault located between Drake Bay and Caño Island, below the Osa Peninsula. Experts predict that
Experts indicate that the area has the potential to produce these events with a periodicity of approximately 40 years. The last one occurred 39 years ago, on April 2, 1983, with a magnitude of 7.4.
The 1983 earthquake had its epicenter 15 kilometers northeast of Golfito. It damaged homes, bridges and roads. In the Central Valley, it was perceived with an intensity of 6. The previous cycle of this earthquake occurred on December 5, 1941, with a magnitude of 7.5 and, before that, there was another on December 20, 1904, with a magnitude of 7.7.
An earthquake in the southern zone could activate other local or distant faults, many of them still unidentified. In fact, three months after the earthquake in Golfito, another 5.5-magnitude earthquake occurred, with an epicenter in the Pérez Zeledón Division. It was registered on July 3, 1983, leaving one dead and 500 victims.
What happens in the Osa Peninsula
In the Osa Peninsula, the Cocos plate subducts under the Panama microplate. As part of this process, at a depth of 13 kilometers, one of the plates pushes towards the upper crust at a rate of seven centimeters per year, explains the most recent seismological report from the Observatorio Vulcanológico y Sismológico de Costa Rica (Ovsicori) – Costa Rican Volcanological and Seismological Observatory (Ovsicori), of the Universidad Nacional (UNA).
Throughout the 40 years that the recurrence period takes after each earthquake, those seven centimeters per year are transformed into a thrust close to 2.8 meters.
Ovsicori seismologist, Marino Protti, explained that the speed of collision between plates under the Osa Peninsula is considered worldwide as a rapid displacement.
“As long as there isn’t a sudden displacement, that accumulates; however, slow slides tend to occur that help release part of that convergence. However, there are always two or three meters left, which would slide deep when the earthquake of that seismic cycle occurs,” he explained.
The capacity of a fault to produce weak earthquakes, moderate earthquakes or earthquakes will depend on its ability to block.
Weak faults, poorly blocked or weakly coupled (less than 50%), such as the Central Pacific subduction zone between the Nicoya and Osa peninsulas, produce constant seismicity, but do not produce large earthquakes, because not much slip accumulates in the mistake.
On the contrary, strong faults, well coupled or strongly blocked (more than 60%), such as those under the Nicoya and Osa peninsulas, have the capacity to accumulate slip for decades and release it in large earthquakes.
In Osa, this coupling is estimated at 78%.
In Nicoya there was a recurrence period of 50 years, however, the 2012 earthquake occurred 60 years after the last one, so the time is variable, but the truth is that these periods give an idea of when the telluric movement can be expected.
For the Osa Peninsula, the expected difference between the completion of the period and the earthquake is three years more or three less, which is calculated based on the return period, which is shorter than that of Nicoya. Also, the convergence at Osa is faster and the fault is smaller, Protti said.
This is not the first time that specialists have spoken of the possible occurrence of a major earthquake in the South Pacific.
In 2016, according to publications in La Nación, the Ovsicori estimated that in less than 10 years there would be an earthquake of magnitude greater than 7 degrees near Burica, Golfito canton, the border area with Panama. Since then six years have passed.
Article translated and adapted from La Nacion. Read the original article (in Spanish) here.