This Saturday morning (14), a strong 7.2 magnitude earthquake struck southern Haiti, leaving at least 304 dead and more than 1,800 injured.
Shocks like this are nothing new in this small country, one of the poorest in the world and mired in crisis.
On January 12, 2010, an earthquake of similar magnitude devastated Port-au-Prince, the country’s capital, killing more than 200,000 people. Over 300,000 were injured.
And this had already happened in 1887, 1842, 1770 and 1751.
But why are so many earthquakes happening in Haiti?
One of the answers could be found on the afternoon of January 12, 2010, when experts immediately knew that the earthquake would be one of the worst natural disasters in recent history in this country.
In addition to hitting one of the poorest nations in the West – and therefore one of the least prepared to face events of this type, the earthquake occurred in an area where there is a complex web of tectonic plates and geological faults.
Haiti is located in the middle of a vast system of geological faults resulting from the movement of the Caribbean Plate and the enormous North American Plate.
As in other areas where the tectonic plates are contiguous, at the edge of the Caribbean plate, there is significant seismic activity due to these faults.
And it was the sudden slide of one of them, the Enriquillo-Plantain Garden fault, that led to the disaster.
The epicenter of the magnitude 7 earthquake is estimated to have occurred about 15 kilometers from Port-au-Prince. And the hypocenter (a place inside the Earth where rock material begins to break apart, releasing energy in the form of seismic waves) was only five miles from the surface.
What was recorded this Saturday had a magnitude of 7.2 and 10 kilometers from the surface, but had its epicenter in the south of the island.
This proximity to the surface, according to experts, ensured that the shock forces on the ground were more intense and destructive.
NO AMORTIZATION
Buildings located in earthquake-prone areas of developed countries are constructed with damping systems that allow them to “resist” jolts, not only by letting them tip back and forth, but also by rotating them with the motion of the earth. Earth.
But the simple concrete structures of Haitian cities crumble when put under this pressure.
“Proximity to the surface is one of the most serious factors contributing to the severity of an earthquake caused by an earthquake of any magnitude,” David Rothery, planetologist at the Open University, told the BBC. from the United Kingdom.
“Also, the earthquake tends to be larger if it is closer to the source. In this case (the 2010 earthquake), the epicenter was only 15 kilometers from the center of the capital and that’s why it was so destructive. “
Then a series of violent aftershocks – more than ten, all over magnitude five – amplified the devastation.
But despite Haiti being in an area at high risk for earthquakes, the last major earthquake before the 2010 disaster occurred 150 years earlier.
The country’s northern coast is located on the edge of the great tectonic plates of the Caribbean and North America, where large blocks of the earth’s surface move, rubbing against each other in a horizontal motion.
The Caribbean plate is believed to be moving east at a rate of about 2 centimeters each year.
And, as experts point out, before 2010 a landslide was long overdue at the Enriquillo-Plantain Garden fault.
“This has been going on for 250 years,” Roger Busson of the British Geological Survey Service told the BBC of the 2010 earthquake.
“All this time created pressure as the plates slid over each other, and it was really only a matter of time for this release of energy to occur.”
“The question we asked ourselves was whether all of this energy was going to be released in one fell swoop or in a series of little tremors. The answer is, it was all at once.”
In 2010, the surface along the fault was, in parts, separated by up to a meter or more.
The United States Geological Survey (USGS) says the Enriquillo-Plantain Garden fault may have been the source of several major earthquakes throughout history: those of 1860, 1770, 1761, 1751, 1684, 1673 and 1618 .
And also what happened this Saturday.
“As with the 2010 event, the mechanism that produced this earthquake indicates an oblique thrust fault along the Enriquillo-Plantain Garden fault zone,” the USGS reported on its website.