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Dernière mise à jour : le 19/05/2022 à 10:20

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A bizarre sponge-like planet that expands and contracts as water is added and released from it has been detected by scientists using European satellite sensors. It's Earth.

By combining high-resolution InSAR radar images of the Earth taken by European Space Agency satellites, geologists have detected the subtle, inch- by-inch rise and fall as groundwater inflates and deflates the ground. The images are also revealing hidden earthquake faults. "Some faults act as barriers to water and some don't," says Zhong Lu of Raytheon and the U.S. Geological Survey.

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Earthquake faults show up because the underground surface of a fault can block groundwater, swelling the ground to one side of a fault more than the other side. The difference might not be visible from the ground, but it starts to become pretty clear from the satellite imagery.

Lu and colleague Wesley Danskin have published a report on groundwater rising in small areas trapped by faults in the San Bernadino Valley, California. Their paper will appear in the July 1 issue of Geological Research Letters.

The InSAR technique works by superimposing multiple specially prepared radar images of the same area from different times. The resulting image looks like it's under an oily sheen, but the "bulls eye" color patterns that form from the combined images reveal the slight changes in the ground elevation, explained Lu. The movements could also be from slipping of faults, he says, but there has been no seismic evidence of that. InSAR could save geologists untold sums of money in their studies of groundwater supplies, says Lu.

Currently the only way to measure groundwater is to manually check the water levels in wells — if there are any wells. Some remote areas in the Western United States have few or no wells, said Devin Galloway, Western Regional groundwater specialist for the USGS. "It is pretty much cutting edge," said Galloway .

It also allows geologists to see the groundwater swelling entire basins. That's a big advancement over the current method of connecting the dots between wells and making educated guesses about what groundwater is doing throughout a basin.

The method will come in handy for monitoring water in remote areas where little is known about the underground water supplies, Galloway said.

Source : USGS

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