Data from thousands of GPS devices detect a precursor to major earthquakes | Science and Technology

It’s the holy grail for seismologists and geologists: finding reliable evidence about when, where, and of what magnitude an earthquake will strike. So far this century, more than a million people have died as a result of earthquakes, not counting the astronomical cost to infrastructure and the economy, particularly in developing countries. Now, French scientists have discovered a precursor phase that starts hours before a major earthquake. As detailed in the journal Science, they achieved this by analyzing tiny displacements recorded by the Global Positioning System (GPS). These researchers believe that deploying detection networks around major faults can help find that holy grail.

In the 1970s, seismologists were euphoric. Accumulating data on earthquakes, new theoretical models, and laboratory experiments led to the dream of discovering the phenomena and mechanisms that heralded an earthquake. As University of California professor Roland Borgmann says, everything indicates that “earthquakes are often preceded by precursor processes.” But the enthusiasm waned: “As scientists started harder and had better observations of these precursors, they discovered that while they do occur occasionally, they can’t really be distinguished from similar processes that often occur at other times and places.” Julián García Mayordomo, earthquake geologist at the Spanish Institute of Geology and Mining (IGME) also recalls the complexity: “Large earthquakes occur 10 to 15 kilometers (6 to 9 miles) deep in the crust, where we have never been able to dig. In addition, the main fault that produces earthquakes on the order of 6.5 or 7 is a plane that can be tens of kilometers long and 15 kilometers deep. It is a vast area in which many geological processes occur. It is completely impossible to control. There are many variables, which makes this phenomenon highly unpredictable.”

“The big earthquakes happen 15 to 10 kilometers deep in the Earth’s crust, where we’ve never been able to look into.”

Julián García Mayordomo, earthquake geologist at the Spanish Institute of Geology and Mining

But scientists Quentin Plettieri, of France’s Côte d’Azur University, and Jean-Mathieu Noquet, of the Physics Planet Institute in Paris, have found a way to detect the signal of a future earthquake amidst all the noise. Their idea makes use of global navigation satellite systems (GNSS), such as the United States’ Global Positioning System (GPS) or the European Galileo system. The entire planet is littered with geodetic stations that include a number of sensors of interest to geologists. One of them is a GNSS unit that relies on triangulation with GPS or Galileo satellites (and with Russia’s GLONASS or China’s Beidou networks) to determine its location. Installed on the ground, the position of these stations is measured in millimeters and is essential for mapping. But the stations move and are not always in the same place: their location changes throughout the year due to global phenomena, such as continental drift, or local phenomena, such as building a reservoir, drilling for land, or fracking. A major earthquake can also move them from their place and this is recorded by GPS.

What the French scientists did was analyze location data from more than 3,000 geodetic stations where the earth shook with 90 earthquakes of magnitude 7 or greater so far this century (those in Turkey were as high as 7.8 and 7.5). More importantly, they also collected and analyzed GPS data from the 48 hours before each of these major aftershocks. The starting hypothesis was that earthquakes start with a precursor phase characterized by slow displacements, without tremors, at the fault point where the epicenter of the next earthquake will be.

An initial phase is a window of time during which tectonic masses begin to move relative to each other, first slowly and then gradually accelerating.

Jean-Mathieu Noquet of the Institute of Planetary Physics Paris

“Earthquakes are sudden slips along faults that separate two tectonic masses,” says Noquet, co-author of this research. Before the earthquake, the two rock masses were stuck together. “The initial phase is the window of time during which tectonic masses begin to move relative to each other, first slowly and then gradually accelerating to finally reach a fast sliding velocity. The rapid sliding results from seismic waves that cause the damage observed during major earthquakes,” explains the French scientist. Although there is some consensus on the existence of this initial stage, there is no consensus on its main characteristics, such as its duration. For some it only lasts a few seconds, for others it can be seen as a series of small earthquakes over weeks or months. “In fact, our study indicates that the slip gradually accelerates over a few hours, about two hours,” he adds.

To make sure the signal they detected was correct, they repeated their analysis, backed by artificial intelligence, for another 100,000 time windows, but then there was no earthquake. They did not detect a slow but exponential growth signal as observed in the initial phase of a major earthquake.

Wow good news. As the authors themselves admit, they do not find this initial stage in about half of the earthquakes. This does not mean that they do not have one: it may have occurred before the time frame they analyzed. For various reasons, such as the cost of the computational calculations, they did not extend their analysis beyond the hours before each major earthquake. Another reason could be that the earthquake occurred too far from one of these geodetic stations. Nocquet is convinced that “the development of regular, accurate and accurate error monitoring can detect this negative slip into the future for individual events.”

Victor Puente is a researcher in geodesy applied to seismology at the National Geographic Institute. Puente, who appreciates the importance of a study based on information from the last 90 major earthquakes, recalls that the French scientists based their analysis on the database of the Geodesy Laboratory in Nevada (USA). This database contains records from 17,000 stations, instead of 3,000. If all of them were used, the capillary power of the analysis would be much greater. “But this lab delivers data with a two-hour response time,” Puente notes. If there is a detection system that supports them, the alarm will arrive when the earthquake has already occurred. In any case, Puente stresses that if the results achieved by the French researchers are to be confirmed, the response time must be reduced until the data is available in real time. “It will be difficult, but not impossible.”

“The more we know about faults, the better we can figure out the maximum magnitude of earthquakes, and then their intensity at the surface, and then, in a second step, try to predict when they will occur.”

Jesus Galindo is from the Department of Geodynamics at the University of Granada

Another key to the functioning of a system like the one proposed in this paper is the need for in-depth knowledge of all the faults that could be the origin of a major earthquake. Jesús Galindo, from the Department of Geodynamics at the University of Granada, points out that this is a future area of ​​research to pursue. “Like it happened with meteorology, with more stations and better mathematical models, we are now able to predict what the weather will be like, what the temperature, heat waves will be, or when it will rain. Same for faults. What we also need is knowledge of how the Earth moves and other physical parameters, such as deep structure. The more we know about faults, the more we can figure out the maximum magnitude of earthquakes, and then their intensity at the surface, and then in a second step, try to predict when they will happen,” he explains.

“The key is absolutely the data you get near the epicenter,” assures the professor at the Polytechnic University of Madrid, an expert in geodesy applied to earthquake risk. About the research of French scientists, who are at the forefront in this field, he sees it as a great contribution and going in the right direction. “But to be able to say that there will be an earthquake in two hours, we still have a long way to go.”

Barraca, project to identify earthquake risks in southern Spain

The Spanish government research agency has just approved a project to conduct in-depth research on a complex set of open rifts between the southeast Eurasian plate and the North African plate. From northeastern Morocco to beyond Alicante (Spain), passing through the Alboran Sea, the meeting of the two plates puts great pressure on their boundaries, which are cracking to form faults. Obtaining in-depth knowledge of these faults and identifying seismic hazards is one of the main goals of the BARACA project.

Jesus Galindo, a researcher at the University of Granada, is also one of the scientists on BARACA, which includes geodesicists, seismologists, geologists and engineers from several Spanish universities. “There are defects, like San Andreas, many of which are in Japan or on the coast of Chile, very distinct, with a single plane and where the deformation is not distributed,” he explains. It is on these faults that the most catastrophic earthquakes occur. “And then there are areas like here in the Eurasian contact, where there are many small faults, so the deformation is more distributed. The situation we are in is much better because the small faults are being corrected. There is no big one collecting as much energy. It is true that we have a lot of earthquakes, but they are not like those in Japan or Chile or the West Coast of the United States.”

However, there is a relative danger, and every few years an earthquake of similar strength to the one Turkey experienced in February may occur. BARACA is a new attempt to anticipate these as possible.

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