Why do giant earthquakes hit neighboring countries, but rarely Brazil?
A strong earthquake of magnitude 7.2 hit Venezuela, a neighboring country, causing more than 180 deaths and becoming one of the most intense events ever recorded on the continent. Despite the violence of the tremor to the north, Brazil felt only light aftershocks, with the population of cities such as Manaus and Belém noticing minimal tremors.
This disparity raises the question of Brazil’s apparent immunity to major seismic disasters, a common perception among the population. However, science shows that the reality behind this “calm” is more complex than imagined.
The main reason for Brazil to be spared from intense shocks is its geographic location. The country is located in the center of a tectonic plate, far from the borders where these rocky masses collide and cause the biggest tremors.
Technically, Brazilian territory rests on the central portion of the South American plate, far from areas of greatest geological instability.
Brazil’s unique position on the South American tectonic plate
While Brazil enjoys this relative stability, its neighbors, especially those close to the Andes Mountains, are located in regions of contact between two tectonic plates. It is precisely in these encounters that earthquakes with potential devastating consequences originate.
To understand the difference, it is essential to understand the dynamics of earthquake formation. These phenomena are directly linked to the constitution of the Earth’s crust, the outermost layer of our planet, formed by gigantic rocky plates in constant movement, the so-called tectonic plates.
The incessant dynamics and pressures of the Earth’s plates
The Earth’s surface can be compared to a mosaic, like a “turtle shell” made up of multiple pieces that fit together and interact, as explained by geographer and historian Sergio Ribeiro Santos, professor at Universidade Presbiteriana Mackenzie.
These rock formations move at speeds that can reach up to 10 centimeters annually, a continuous movement, although imperceptible on a human scale.
The South American plate, for example, reaches thicknesses of up to 200 kilometers in certain parts. There are plates that support continents, others that are under oceans, and some that combine both surfaces. Geographer Sergio de Moraes Paulo, master from USP, compares the Earth’s crust to an “eggshell completely fragmented” into large lithospheric plates.
The movement of these plates is driven by the Earth’s mantle, the layer below the crust, which is also in constant agitation, causing the plates to move together, according to Paulo.
The professor highlights that this movement is most evident in the “contact areas”, which are the limits between one plate and another.
Geographer Santos adds that the cause of this movement is the high temperatures present inside the planet.
This constant displacement leads the plates to incessant friction, pushing, scraping and clashing in search of a fit in a limited space. When the accumulated tension reaches a critical point, the rocks fracture and break, similar to a stone that, under extreme pressure, ends up cracking and breaking.
In the context of the vast dimensions of tectonic plates, this rupture is called a geological fault. The energy released by this movement is immense, causing vibrations that propagate throughout the surrounding ground, generating tremors.
The area where two plates collide is known as the convergent boundary, a place of intense seismic activity.
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Seismic stability in the center of the South American plate
“Brazil is positioned in the middle of the tectonic plate, and the highest intensity earthquakes occur predominantly close to its extremes, at the convergent limits. Thus, the country remains far from these regions of instability”, details geographer Anderson Andrade, researcher at the Mackenzie Institute.
Andrade adds that countries neighboring Brazil, especially those close to the Andes Mountains, are much closer to these convergent limits.
What occurs in countries adjacent to Brazil is the interaction between the South American and Nasca plates, which meet on the west coast of South America, bathed by the Pacific Ocean. “At this point, the movement is more intense, generating seismic shocks. Although these tremors can reach Brazil, their intensity is significantly reduced, as we are in the center of the plate”, explains Paulo.
Santos highlights that it was precisely the friction between these two tectonic plates that gave rise to the imposing mountain range of the Andes.
“The Andean countries of South America, to the west, are based on the contact between two large tectonic plates”, summarizes engineer Antonio Eduardo Giansante, professor at Universidade Presbiteriana Mackenzie. “Any movement between them causes tremors and, if it is more intense, results in an earthquake. Often, the contact between these plates stores a large amount of energy, and any variation between them releases this energy and causes a relocation, generating earthquakes of great intensity.”
The history of seismic shocks in the national territory
Data provided by the Institute of Astronomy, Geophysics and Atmospheric Sciences at the University of São Paulo (USP) reveal that Brazil recorded around 100 earthquakes over the last century. The vast majority of these events were of low intensity, going unnoticed by the population.
Earthquakes are measured using the Richter scale, and generally only tremors that exceed 7 degrees on this measurement are capable of causing destruction. The strongest tremor ever recorded in Brazil occurred in 1955, with locations in Mato Grosso reaching 6.6 degrees and in Espírito Santo marking 6.3 degrees on the scale.
In 1980, an earthquake measuring 5.2 on the Richter scale was recorded in Ceará. Three years later, seismographs detected a 5.5-degree earthquake in the state of Amazonas.
In the current century, some significant episodes were also felt in Brazilian territory. In 2007, a 6.1 magnitude earthquake was noticed by residents on the border between Acre and Amazonas. In the same year, Minas Gerais recorded a tremor of 4.9 degrees.
In April 2008, what was perhaps the most recent seismic event in Brazil occurred. At the time, an earthquake measuring 5.2 degrees on the Richter scale was felt in São Paulo, Rio de Janeiro, Paraná and Santa Catarina.
The most recent case of impact tremors was in 2018, when the reflections of an earthquake in Bolivia were noticed in several regions of Brazil.
According to measurements from the USP Seismology Center, the last tremors recorded on Brazilian soil occurred on June 11, when three small earthquakes occurred in the region of Tucuruí, in Pará, with the largest of them reaching 3.5 degrees of magnitude.
The visibility of tremors is directly proportional to their intensity. In other words, small-magnitude earthquakes are extremely common, but rarely gain prominence. “We end up only hearing about the most intense ones, which generate impressive images and cause damage”, observes geographer Paulo.
