Why are large earthquakes still difficult to predict? | Sciences

On Monday night (8), an earthquake struck Morocco. Its epicenter was 70 kilometers south of the historic city of Marrakesh, and the earthquake, which reached a magnitude of 6.8 (considered strong), led to the collapse of buildings and, as of the publication of this article, left 1,037 dead and more than 1,200 injured, according to Agence France-Presse. To give you an idea, the earthquake could be felt even in Portugal, Spain and Algeria.

About 19 minutes after this first earthquake, a second earthquake occurred, this time measuring 4.9.

This is not the first time that the North African country has faced this type of disaster: in February 1960, an earthquake near the city of Agadir, in southwestern Morocco, killed between 12,000 and 15,000 people.

The northern region of the country is more vulnerable to earthquakes, because it is located between two tectonic plates: the African plate and the Eurasian plate. The movement of this type of rock masses that make up the Earth’s crust is what can cause earthquakes in different parts of the planet – and also lead to volcanic activities and tsunamis.

Why is it still difficult to predict a major earthquake?

Although geologists can pinpoint the causes of earthquakes after they happen, scientists cannot predict this type of event for several reasons — including the fact that these tremors occur very quickly. Experts say that unpredictability is the nature of these earthquakes. “An earthquake is not like a slow train that eventually picks up speed. It is a sudden, accelerating event,” Ben van der Pluijm, a professor of geology at the University of Michigan, explained in an interview with North America.com. NBC News In February, when Türkiye and Syria were hit by a 7.8-magnitude earthquake.

Moreover, earthquakes give little (or none) signals. Scientists analyze various factors that could serve as a warning, such as changes in underground sounds, possible increases in seismic activity in an area and changes in animal behavior; However, none of these points are consistent evidence that a place will experience an earthquake.

Another challenging factor is that the plate tectonic processes that lead to earthquakes – such as their collision – can take hundreds of years. In other words: these analyzes don’t work well when it comes to earthquake prediction on human time scales.

This was also highlighted by the US Geological Survey (USGS): the agency states in its report location that although scientists have never been able to predict a major earthquake, it is possible to “calculate the probability of a major earthquake occurring in a given area within a given number of years.”

According to North American experts, for earthquake forecasts to be correct, three data must be specified: date and time; location; And its size.

Therefore, scientists warn against false predictions promoted by non-experts through social media. “[Esses alertas] They are not based on scientific evidence, and earthquakes are part of a scientific process. For example, earthquakes have nothing to do with clouds, body aches, or sluggishness.

“These people do not identify the three elements necessary for prediction,” the scientists add. “Their predictions are so general that there will always be an earthquake that fits them; like ‘There will be a magnitude 4 earthquake somewhere in the United States in the next 30 days.'”

USGS too Highlights The probability of an earthquake occurring every day is 100%. Tremors are very common on Earth; But many of them are weak or located far from populated areas. The US agency highlights that “the problem lies in determining the area in which the strong shock will be concentrated and when this will happen.” “Earthquake predictions may one day come true, but only after more is known about them.”

There is no shortage of efforts to predict earthquakes. In July, a study was published in the journal Sciences He argued that GPS data could be used to detect gradual and accelerating slip between tectonic plates up to two hours before an earthquake.

The authors of the paper analyzed GPS data collected over 5 minutes and 48 hours before 90 different earthquakes. They then compared this information to a database containing more than 3,000 measurements of geological movements, noting the direction of ground displacement that each earthquake could cause.

In each of the cases analyzed, the researchers found that the largest movement in the expected direction occurred just before the earthquake. Furthermore, the last 23 data points showed a gradually increasing shift in the expected direction; The last seven were higher than anything else during the entire 48-hour period.

However, given the noise levels of current GPS sensors, earthquake sensing is only possible with a large data set; It is not yet possible to measure it anywhere on Earth. Therefore, to improve calculations, GPS sensors capable of verifying movements of only 0.1 mm will be needed.

“We cannot detect the size of the earthquake; Therefore, we cannot provide forecasts.” NewScientist One of the study’s authors, Quentin Pelletieri, from the University of Côte d’Azur (France). “but [esta pesquisa] It tells us that something is going on, and if we make significant progress in measurement — whether it’s in the sensor itself, improving its sensitivity, or just getting more of it — we might be able to notice things and make predictions. “

Researchers associated with Brazilian institutions and universities are also studying ways to monitor and predict earthquakes. This is the case of the group supported by the São Paulo Research Foundation (FAPESP) that analyzed ionospheric-based methods for detecting earthquakes and tsunamis in near real-time (NRT).

“A small tremor in the atmosphere can be much larger in the ionosphere. For example: the displacement of the Earth’s surface during an earthquake can reach millimeters; researcher Isfahan Alam Khairani, from the National Institute for Space Research (ENPI), said in a statement: “But in the ionosphere the record is 10,000 times higher.” “We know that there has been a lot of work in this field,” he added, in the past three decades, “but our focus is on near-real-time monitoring, which is a challenge that “It’s not resolved yet. The first pulse of tremors lasts about ten minutes. We can actually detect it within six minutes of the earthquake beginning, but we want to reduce that period, perhaps to a couple of minutes or a few seconds.”