It can warn of big earthquakes hours before they happen. Retrospective analysis of 90 strong earthquakes (magnitude equal to or greater than 7) enabled the identification of precursor signals for tremors 2 hours before they occurred. This discovery opens the door to earthquake prediction, one of geology’s great goals yet incomplete.
“The ambition of our study was to answer a fundamental question in seismology: Are earthquakes a chaotic or deterministic phenomenon?” . from work. “Our results strongly support the second option,” continues the expert, whose finding rules out the unpredictability of the chaotic option, and points out that earthquakes do not occur suddenly.
The study provides evidence that two hours before an earthquake starts, the nearby Earth’s surface deforms slowly but quickly. If measured correctly, these movements can be used to predict when and where the tremor will occur. The results of the study open the door to the development of a warning system that minimizes human and economic losses, although “we are still a long way from being able to predict any earthquake,” says Plettieri.
“Meaningful earthquake forecasts must clearly state the expected time, location, and magnitude of the future event.”
The search for precursor signals to earthquakes is something that geologists have been studying, without success, since 1970. Many studies have noted that before some strong earthquakes, there was a slow fault displacement, that is, a slow movement of the ground in the earthquake zone, but no one has yet been able to to establish a causal relationship between these landslides and earthquakes.
“These events are constantly occurring along the faults [fracturas en la corteza terrestre cuyo movimiento causa los temblores] without being followed by earthquakes,” notes the French researcher, “and most importantly, they do not immediately precede them.” In other words, observing said motion does not allow us to know when an earthquake will occur, nor does it even guarantee that it will.
in he paper Published Thursday in the magazine SciencesBletery and his colleague Jean-Mathieu Nocquet improved the search for these movements. French scientists, using GPS measurements, analyzed how the Earth moved at 3,000 points near the foci of 90 earthquakes with a force greater than or equal to 7 moments before their occurrence. In addition, they measured the movements that occur in the direction in which the earthquake will subsequently dislodge the Earth. In other words, they only looked at the points near the core of each earthquake, in the moments before it occurred and in the direction in which they knew the fault would move.
The researchers averaged the signals of 90 earthquakes, and saw how in the two hours leading up to the events the fault displacements that occur have an exponential acceleration. That is, the movement of the earth is faster and faster until the earthquake explodes. It is this acceleration that Bletery asserts that his discovery is, in fact, a precursor to earthquakes, and that “the causal relationship [entre ambos eventos] it is clear”.
However, questions remain. The study didn’t analyze every earthquake specifically, but to get a detectable signal it needed to average over 3,000 observations of 90 events. “If we look at each event one by one, the signal is dominated by noise and we can’t explain the results,” she says. So “we can’t conclude whether this happens before every earthquake, although it would be the most plausible explanation,” admits the French seismologist.
In addition, “it is not clear whether these accelerations of slow displacements are associated exclusively with large earthquakes,” he notes in Comment on the article Also posted this Thursday in Sciences Roland Borgmann, a researcher at the Berkeley Seismological Laboratory in the US, who was not involved in the study. “It will be important to explore the frequency with which similar episodes represent a false start,” he adds, “that is, they are not followed by earthquakes.”
In any case, even if the precursor signal is confirmed, it does not mean that we can actually predict earthquakes before they happen. The study analyzed tremors that occurred in the past, and identified precursor phenomena using data such as the location, magnitude, and direction of the earthquake’s motion, which would be exactly what a prediction of future events would have to predict.
“Meaningful earthquake forecasts must clearly state the expected time, location, and magnitude of a future event,” says Borgmann of Berkeley, something currently available instruments cannot. The aim of the work was not that, Pelletri recalls, but rather “to show that prediction is not physically impossible”.