Why is it so difficult to predict a big earthquake like the one that hit Turkey?

Every year more than 200,000 earthquakes are officially recorded on our planet, although in fact millions of them occur in the same period.

Many bypass official records because they are too light for us to feel or because they happen in remote areas that are not monitored by the authorities.

Others, like the magnitude 7.8 that hit and left victims in Turkey and Syria this Monday (6), leave thousands dead and a trail of destruction.

Constructing earthquake-proof homes and buildings is, of course, the best strategy to avoid both human and material losses. But would it be possible to remove people in advance from areas that will be affected – as happens during the passage of a hurricane, for example?

The answer is no. That’s because it’s impossible to predict when an earthquake will strike — save for a few minutes.

physical law

The reason is that most earthquakes occur by the sudden release of great tension in the Earth’s crust. This tension builds up gradually due to the movements of tectonic plates, usually along a geological fault, explains the website of the British Geological Survey.

Therefore, it is impossible to predict when earthquakes will occur, “basically by the way this energy is released”, Richard Luckett, a seismologist at the institution, told BBC News Mundo, the BBC’s Spanish-language service.

“We know that tension is being built up in the big faults and we know where they are, but we have no way of knowing when this energy will be released”, he says.

Luckett resorts to the example he normally uses to explain the phenomenon to children. “If you put a brick on a sheet of sand paper and slowly rub it away with something, the brick will move. You can repeat this experiment ten times: although you apply the same force each time, you will see that the brick will suddenly move after different time intervals,” says Luckett.

“In physical terms, it’s completely unpredictable,” he adds.

Knowing whether a tectonic plate where a country is located accumulates pressure “does not help to predict earthquakes, because we do not know when this energy will be released”, he says.

What specialists can know is where a major earthquake is likely to occur, “since they are related to the size of the fault,” Luckett clarifies.

Even so, this does not help predict how strong an earthquake will be, as pressure can be released in a series of small tremors or in a single, large jolt.

In the case of the event that caused damage in Turkey and Syria, it was two strong tremors in a row.

Signals?

But are there other signs we should be on the lookout for? Perhaps a change in weather or animal behavior that can help us predict an earthquake? It is believed that animals can feel the first waves that are generated by the earthquake – and that we do not notice.

“Earthquakes have nothing to do with the state of the weather and there is certainly no connection with climate change”, clarifies the expert. “These are completely different systems,” he adds.

But, according to him, the case of animals is interesting. There are a number of studies on how some animals exhibit different behavior when faced with an imminent earthquake.

It is said, for example, that dogs bark more or that animals generally make more noise.

According to Luckett, “when a strong earthquake happens, it causes different waves that travel through the earth. The first ones are small, they don’t cause damage, and many times we don’t even notice it”, he explains. “But the animals, yes”, he points out.

Still, they don’t help predict an earthquake. “Animals feel these vibrations, but this happens once the earthquake has already happened”, assures the specialist.

“They warn us of danger a little earlier [o tempo depende do intervalo entre as ondas pequenas e as grandes]just like alarms”, he explains. “In this sense, devices are more sensitive than animals”, he adds.

Luckett says he doesn’t believe it will be possible to predict earthquakes. “What we can do is improve our ways of detecting them.”

Other analyzed techniques

Specialists in geophysics have concentrated, among other areas, on the so-called “slow earthquakes”.

They are “slides that occur on a geological fault, in general, and in particular in the subduction zones between two plates that are in contact”, explains Víctor Cruz-Atienza, a researcher at the Institute of Geophysics at the National Autonomous University of Mexico.

In 2021, he and his colleagues published a study on this type of earthquake that occurs in certain seismic regions, such as that of southeastern Mexico, where two plates interact.

Unlike tremors that shake the surface, slow earthquakes release energy little by little over weeks or months, making them imperceptible and non-destructive.

But experts say that studying them is very important to better understand how earthquakes are generated. While a slow tremor doesn’t always anticipate a “normal” one, it is a factor to take into account.

In 2018, other researchers successfully used a fiber optic communications cable in Iceland to assess seismic activity.

The method tested by the team of researchers, led by Philippe Jousset of the German Research Center for Geosciences (GFZ), based in Potsdam, used 15 km of fiber optic cable originally laid in 1994 between two geothermal power plants in Iceland.

A laser pulse sent down a single fiber in the cable was enough to determine if there was any interference. When the ground, and therefore the cable, stretched or compressed, the researchers were able to record it.

They detected local traffic, seismic activity and even pedestrians passing by. They also picked up the signal of a strong earthquake in Indonesia.

The instrument that must be attached to each cable to make monitoring possible is still expensive, but researchers have been working on affordable alternatives.

This text was originally published here.