2023-09-04 06:30:42
Thanks to data collected by high-precision GPS stations, IRD researchers have shown that the faults begin to slip, on average, two hours before the onset of major earthquakes. This discovery encourages the development of more precise instruments and denser instrumentation around faults to anticipate major seismic ruptures to come.
Almost a million people. This is the estimate of the number of deaths caused by earthquakes and the tsunamis they generate, over the past thirty years. To limit the human and material cost of these disasters, warning systems exist in some countries, but offer, at best, only a few seconds of anticipation, since they are only triggered once the earthquake has started. Unlike some volcanic eruptions, we cannot therefore predict the imminent occurrence of a major earthquake.
The existence of a phase of fault sliding which precedes major earthquakes has been debated for several decades within the scientific community. Except that the observations made so far have not been conclusive. Some observed landslides do not directly precede earthquakes, or are not identified until most events. And sometimes they are even observed without being followed by an earthquake. In a study published in the revue Scienceresearchers from the IRD (Research Institute for Development) have shown that the faults begin to slip a few hours before the onset of major earthquakes.
To identify these landslides, the IRD scientists used a catalog of GPS data from the Nevada Geodetic Laboratory, an American laboratory specializing in space geodesy. Concretely, they identified 90 earthquakes, whose magnitude is greater than or equal to 7, and selected the GPS data recorded within a radius of 500 km from the epicentres since 2003. In total, they added up the movements measured by 3,026 high-precision GPS time series, projected on all expected directions of the slip, and this, during the 48 hours preceding the start of the earthquake.
Warning signals observed 2 hours before major earthquakes
As a result, no abnormal movement was detected during the 48 to 2 hours preceding the earthquakes. However, in the 2 hours preceding these events, a positive signal was highlighted, supporting the hypothesis of fault sliding in the epicenter area. “Our approach reveals an exponential acceleration of slip in the two hours preceding ruptures, suggesting that large earthquakes begin with a precursor phase of slip, which improvements in measurement accuracy and density might detect and possibly monitor more effectively,” note the authors of this study. This two-hour period before major seismic ruptures is an average. The researchers suggest that this fault-slip acceleration is taking place on a larger time scale, and that the GPS time-series observations might be just the very end of a much longer process of precursor slips.
The identification of this signal in order to anticipate the imminence of a future major earthquake occurring in isolation is still not for tomorrow. It would require considerable technological progress, since it would be necessary to be able to measure signals at least ten times smaller than those currently detected or to develop measurements very close to faults. This detailed study of slips on faults remains the best way to hope, in the long term, to obtain models of a predictive nature. This result encourages the development of more precise instruments and denser instrumentation around faults to anticipate large earthquakes. This is a major challenge for countries in the South, which are highly exposed to seismic risks and tsunamis.
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