Earthquakes mainly occur along faults because it is at these locations that the tectonic plates of the Earth's crust collide, separate, or slide against each other, causing forces and tensions that eventually release abruptly, leading to earthquakes.
A fault is a fracture in the rocks of the Earth's crust. When the rock blocks on either side of this fault suddenly move, it generates vibrations: this is when an earthquake occurs. Essentially, the Earth is constantly moving, but the rocks are locked along the faults; they resist up to a certain point. When they finally give way, all the accumulated energy is released abruptly, triggering tremors. The longer and deeper the fault, the more violent the tremor is likely to be.
The surface of our planet is divided into large plates, somewhat like a giant puzzle. These tectonic plates constantly move slowly due to the movements of the magma beneath the Earth's crust. Sometimes they drift apart, sometimes they slide laterally, and other times they collide outright. As they move, their edges rub against each other, getting stuck and accumulating varying amounts of pressure and energy. Eventually, it releases suddenly: this rupture causes earthquakes. That’s why regions located near plate boundaries often experience high seismic activity. These delicate lines where the friction is intense are precisely the faults.
Underground, the rocks situated on either side of a fault are constantly pushed against each other, slowly accumulating a huge amount of energy. Most of the time, they remain stuck. But when the pressure becomes too great, it’s like a spring that is suddenly released: the rocks slip all at once, causing a rapid release of all that accumulated energy. This abrupt release generates waves that propagate, shaking the Earth's surface; this is the earthquake. The longer the accumulation time, the greater the accumulated energy, and the more powerful the earthquake can be.
The most violent earthquakes often come from so-called reverse faults, where two rock blocks are compressed and one slips upward. They are common in areas where tectonic plates are converging, making the accumulated energy particularly strong before it breaks. Among the most formidable, you also find thrust faults, a specific type of reverse fault, steeply inclined, capable of moving entire layers of rock over great distances. Strike-slip faults, like the famous San Andreas fault, can also trigger devastating earthquakes, with rapid, brutal, and often unexpected horizontal movements. These rapid lateral movements severely test nearby buildings and infrastructure. In contrast, normal faults, where blocks slide downward, generally cause less powerful earthquakes, although they still remain a source of regular seismic activity.
The famous San Andreas fault in California is responsible for the major earthquake in San Francisco in 1906, which devastated the city. In Japan, the gigantic Tohoku earthquake in 2011 related to the fault located off the coast triggered a catastrophic tsunami and the Fukushima nuclear accident. The North Anatolian fault in Turkey caused the dramatic earthquake in Izmit in 1999, resulting in severe damage. In Haiti, it is the Enriquillo-Plantain Garden fault that caused the terrible earthquake of 2010 in Port-au-Prince, resulting in hundreds of thousands of casualties. These examples clearly demonstrate how known, specific faults can regularly generate major disasters.
Some animals can detect seismic waves just before they are felt by humans, and their unusual behavior can serve as a warning sign of an impending earthquake.
The San Andreas Fault, which runs through California in the United States, is one of the most studied faults in the world and measures over 1,200 kilometers in length. It is responsible for many major earthquakes in this region.
Every year, approximately 500,000 earthquakes are recorded around the globe, but only about 100 to 150 are strong enough to be felt by the population.
The magnitude of an earthquake increases exponentially: a magnitude 6 earthquake releases approximately 32 times more energy than a magnitude 5 earthquake, and nearly 1000 times more than a magnitude 4 earthquake!
During an earthquake, you should immediately seek to protect yourself by getting under a sturdy piece of furniture, such as a table, and covering your head with your arms. Avoid going outside immediately or using the elevator, and stay away from windows to prevent injuries from shattered glass.
Sometimes, certain earthquakes are preceded by small tremors called 'precursors.' However, these signs are not systematic nor always identifiable. There is no scientific certainty regarding the reliability of these signs predicting a major event.
A seismic swarm refers to a series of minor earthquakes that occur in the same region over a short period. This does not necessarily indicate the onset of a major earthquake, but it requires enhanced monitoring of the affected areas as a precaution.
Magnitude measures the total amount of energy released by an earthquake and is determined by measuring instruments such as a seismograph. Intensity describes the effects of the earthquake on people's perception, buildings, and the Earth's surface. Two earthquakes with the same magnitude can have very different intensities depending on where they occur.
No, it is currently impossible to predict exactly when and where a specific earthquake will occur. Researchers are able to identify at-risk areas through seismic studies and the history of faults, but precise forecasting in terms of date, time, or exact magnitude remains beyond our current capabilities.
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