Earthquakes are geological events with the potential to destroy entire cities and cause large numbers of deaths. On Wednesday (22), a magnitude 6.1 tremor hit Afghanistan, killing more than 1,000, according to Taliban officials.
Other regions of Central Asia have also racked up deaths from earthquakes over the past three decades. In 2015, 399 people died in the mountainous Hindu Kush region and neighboring Pakistan and India after a 7.5 magnitude earthquake. As early as 1998, an earthquake in the northeast of the Afghan province of Takhar killed at least 2,300 people, with some estimates reaching as many as 4,000 victims.
But, after all, why are tremors so frequent in this part of the planet and how do they happen?
The explanation lies in the movement of tectonic plates, blocks that float on the mantle, one of the layers that is inside the Earth.
“The mantle is the thickest layer. Then comes the eggshell, which is the crust”, explains Adriana Alves, a professor at USP’s Geoscience Institute. “Continental plates are these little husks that are drifting in motion at the mercy of mantle currents.”
Tectonic plates are blocks that float on the mantle, just like boats float on top of the sea, compares the expert. When these “boats” move, they can touch each other and produce earthquakes.
Alves says that three movements can occur: divergent (the plates move in opposite directions), convergent (they bump into each other) and transform (one plate moves laterally in relation to the other). It’s the last two movements that usually cause earthquakes.
In the case of the tremor that hit Afghanistan, the movement was transforming, that is, a lateral movement between the Eurasian Plate and the Indian Plate.
“The entire Himalayan mountain range was formed because of the encounter between these plates”, explains geologist MarÃlia Rocha Zimmermann, who works at the ANP (National Petroleum Agency). “As this movement continues to occur, it generates earthquakes.”
She explains that the situation worsens because both plates are continental. That means they have similar densities, which magnifies the impact of the tremors.
Chile is another region prone to register earthquakes of great magnitude. “The Nazca Plate and the South American Plate are converging, and one plate is going under the other. This movement generates very intense earthquakes”, says Zimmermann.
No wonder the country recorded in 1960 the strongest earthquake ever recorded in the world. The quake reached a magnitude of 9.5, killing 1,424 people and leaving 2 million homeless. The higher the magnitude, the more intense the tremor.
Professor at the Faculty of Geology at Uerj (University of the State of Rio de Janeiro), Claudio Valeriano explains that Brazil is relatively safe from the devastation caused by earthquakes. This is because the country is located in the middle of the South American Plate, that is, it is not at the meeting between one bloc and another.
“Brazil is completely contained in the core of a plate. The strong earthquakes that happen in the country are precisely in Acre, which is the closest possible region to the Andes”, he says, referring to the area where two tectonic plates meet. .
The researcher says, however, that the effects of the tremors in Acre are minimized because they occur in sparsely populated areas. “If a big city like Rio and São Paulo were there in Acre, we would be seeing more serious news about the consequences of earthquakes.”
Despite the destructive power, it is difficult to predict the intensity of a tremor, explains Adriana Alves, a professor at USP. “Predicting precisely what the magnitude will be is impossible.”
