Earthquakes could theoretically be predicted two hours before they occur, saving countless lives, but first we must develop GPS sensors that are 100 times more accurate than those in use today.
In recent decades, expert opinion has changed on whether there is any telltale seismic activity before earthquakes, or whether they are inherently chaotic and unpredictable events. Now, Quentin Bletery and Jean Mathieu Nocquet at the University of Côte d’Azur in Nice, France, may have settled the debate.
The pair have used GPS data to identify gradual and accelerating slippage between tectonic plates in the run-up to an earthquake. These slides are too small to show up on seismographs, but could, if detected, indicate when earthquakes are about to start. This approach has been tried before, but Bletery says previous research has only looked at a handful of earthquakes and produced warning signs that are also seen when an earthquake doesn’t follow, or are seen an uncertain amount of time before the earthquake.
The researchers used GPS measurements collected over a five-minute period, making them accurate to within 1 centimeter, taken over the 48 hours preceding 90 separate earthquakes. Using a combined data set of more than 3,000 measurements, they compared the recorded ground motions with the expected direction of motion each site would have. see during an earthquake.
In each case, they found that the greatest movement in the expected direction occurred just before the quake. They also found that the last 23 data points showed a gradually increasing movement in the expected direction, with the last seven being higher than the others over the entire 48-hour period.
Bletery says this is indicative of a gradual, slow, and undetectable slippage between the tectonic plates that begins about two hours before the quakes, something that could lead to a reliable earthquake detector.
But there is a problem. Bletery says that the noise levels of current GPS sensors mean that detection is only possible on the large data set, and not on a single site. That would require GPS sensors capable of detecting movements as small as 0.1 millimeters, she says.
“We can’t detect at the scale of an earthquake, so we can’t make predictions,” says Bletery. “But he tells us that something is going on, and if we make significant progress in the measurement, whether it’s the sensor itself, improving its sensitivity, or just having more of them, we might be able to sense things and make predictions.”
roland burgmann at the University of California, Berkeley, says the work looks promising, but the proposed signals will need to be confirmed by further research. “There have been quite a few retrospective observations of various types of earthquake precursors in the past (resonances, deformations, etc.), however they are not unique in character from similar things that happened at other times,” he says. “As Bletery and Nocquet view this two-hour long trailblazing candidate analyzing dozens of earthquakes, this looks somewhat promising.”
