On January 7, 2024, an earthquake killed more than a hundred people in Tibet. The seismologist at Irap (Institute for Research in Astrophysics and Planetology) in Toulouse, Matthieu Sylvander explains to us where earthquakes come from.
The toll continued to rise throughout the day. On January 7, an earthquake killed at least 126 people in Tibet. The earthquake, measuring 7.1, surprised everyone and caused significant damage in the Tingri region.
Where do earthquakes come from?
“The Earth needs to cool down”, explains the seismologist. For that, “the hot material moves from the interior towards the surface and cools on contact with the surface. As it cools, it moves back towards the interior. It’s a kind of conveyor belt.”
A gigantic treadmill. It is this phenomenon, called convection, which moves the plates which form the earth’s crust. These famous tectonic plates move relative to each other as heat is removed: “We’re talking about a few millimeters, a few centimeters per year at most.”
These movements cause stresses, a kind of pressure which, accumulating, exceeds the resistance threshold of the rocks. When they can no longer hold on, they give way: it’s an earthquake.
In the case of this Tuesday’s earthquake in Tibet, “it is the Indian plate – which roughly contains India and Nepal – which moves northwards, and engulfs the Eurasian plate. These two plates, over the millennia, formed the Himalayan chain. And on one of its plateaus is Tibet, in the middle of a friction zone.
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MAXPPP – USGS / HANDOUT
Unpredictable
“It’s absolutely unpredictable,” points out Matthieu Sylvander. We cannot predict when the stresses will be such that the earthquake will occur. Risk areas can be identified: “All we can say is that this region has not failed for a very long time, and therefore there is a greater chance of it breaking.”
Because the plates move so slowly – “this is the speed at which hair and nails grow” – and give in so quickly – “it’s almost instantaneous” – that we will probably never be able to anticipate them: “There really is a big gap between the time scales of stress building and rupture.”
Likewise, the aftershocks are difficult to predict. If we know that for the largest earthquakes, there is probably still energy to be released and therefore that there will be new tremors, we cannot know when they will occur: “The area is very fragile. So, it only takes very few things for it to continue to free itself from all these constraints. All the aftershocks that follow the earthquake are readjustments to finish evacuating all energy.”
Once the aftershocks are complete, the process begins again: stresses build up over years, even tens or hundreds of years, until the breaking point.
A disaster reminiscent of the 2009 earthquake in the region of Kathmandu, the Nepalese capital. The 7.8 magnitude earthquake killed 9,000 people.
