To confirm this signal was specific to earthquakes, the researchers used the same method on 100,000 random 48-hour periods that did not precede a quake. “This last point is twice as large as the maximum of the first 46 hours,” Bletery says, “so it’s very unlikely that it just happens by chance.” But in the last two hours, they saw an exponential acceleration in the horizontal movement of the sensors. They looked at the amount and direction of displacement for each station and tried to detect any patterns in the signals.įor the first 46 hours of the 48-hour period before each quake, they saw no patterns. Each station automatically recorded its exact location every five minutes, and the researchers analyzed the 48 hours prior to each quake. To find out if faults show any changes in slip behavior before earthquakes, Bletery and his co-author Jean-Mathieu Nocquet, a fellow IRD researcher, combined data from 3,026 GPS stations near the centers of 90 earthquakes of magnitude 7.0 or greater. Still, the movement is significant enough for researchers to detect using GPS sensors. These events are sometimes called “ slow earthquakes” because they can displace the ground by the same amount as an earthquake might-but the slip movement happens so gradually that there are no jolts, shocks or tremors. “To be useful in any sort of predictive thing, you have to figure out how you do it knowing that the main shock is coming.”Īn aseismic slip is ground movement that occurs without producing seismic waves. “Their analysis requires knowing the main shock,” she says. The same problems will likely plague the use of aseismic movement for predictive purposes, Jones says. It’s not clear that a quake is a foreshock until a larger quake happens. As it turns out, after any given earthquake, there’s a 5 percent chance that a larger one will follow. Seismologists once hoped they could use foreshocks to predict big earthquakes, says Jones, who was not involved in the current study. The patterns seen in the aseismic slip are similar in many ways to the patterns seen in foreshocks-smaller quakes that happen before major temblors. Lucy Jones Center for Science and Society. “It doesn’t mean that we know how to predict them, but it means that it’s physically possible.”īut just because there is a pattern of events before an earthquake doesn’t mean the new finding itself will amount to a prediction method, warns Lucy Jones, a seismologist and founder of the Dr. “It’s solid evidence that there is something happening before large earthquakes,” says study co-author Quentin Bletery, an earth science researcher at the French National Research Institute for Sustainable Development (IRD) at the Côte d’Azur University. The new study, published on Thursday in Science, suggests that there are in fact warning signs. Many seismologists have long argued that earthquakes are impossible to predict because Earth’s crust doesn’t give any detectable warning before it snaps. This movement, known as an aseismic slip, may be a potential pathway toward predicting damaging quakes before they happen, the researchers say. Two hours before a large earthquake, the ground seems to move-infinitesimally and without causing any shaking-a new study shows.
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