Published Wednesday, January 6, 2021Plate tectonic faults in Desamparados
city generates several earthquakes
By the A.M. Costa Rica staff
Specialists from the Volcanological and Seismological Observatory detected several earthquakes originated from several plate tectonic faults located right under Desamparados Canton in San José Province.
In just under a week, from Dec. 30 to Jan. 4, according to the specialists of the observatory, Esteban J. Chaves, and Marino Protti, more than 40 tremors have been registered in that area with Richter scale magnitude range that goes from 1 to 3.
The first earthquake was registered on December 30, 2020, at 6:24 a.m., with a Richter magnitude of 1.80. The most recent tremor happened on Monday, January 4, at 7:25 a.m. with a Richter magnitude of 2.5.
This sequence of tremors, which can continue, occurs in a system of the displacement of plate tectonic faults known as strike-slip.
Horizontal displacement predominates in this type of plate tectonic faults, in most cases it can be detected by changes in the soils, similar to how it occurs with the change of direction of a river bed or a fence, the observatory said in its statement.
Plate tectonic faults horizontal movement to the right or left causing areas of crushed rock, which subsequently erodes and creates valleys with a linear direction.
An example of horizontal displacement is the San André's plate tectonic fault in the U.S., which has produced big earthquakes like the one that happened, with a Richter magnitude of 7.9, in San Francisco in 1906.
In the case of the Desamparados Canton located right above the plate tectonic fault, due to the high urban density (houses, low-rise buildings and roads), that fault behavior is not easy to identify.
The difference between these faults that cause a multitude of soft earthquakes, with the faults that can generate one big-scale earthquake and then several aftershocks, is that tremors happen in chains as a domino effect.
According to specialists, these chains of earthquakes can continue for a few hours or up to several years, specialists said.
This is not the first time that an earthquake chain phenomenon has happened in the Desamparados Canton, in 2014 several earthquakes with magnitudes no greater than 3.8 were registered as well.
Specialists continue monitoring the plate tectonic fault in Desamparados to make a better evaluation of the potential and seismic risk in a densely urbanized area.
In Costa Rica, there have been two major earthquakes with the largest Richter magnitude. The first happened in 1991, with an epicenter in the area known as Pandora, in Limón Province with a scale of 7.6. The second happened in 2012, with an epicenter in Nicoya Canton, Guanacaste Province, with the same scale of 7.6.
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