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Deadly 2011 earthquake linked to groundwater extraction

By Deborah Zabarenko

WASHINGTON (Reuters) - An earthquake that killed nine people in Spain last year may have been triggered by decades of pumping water from a nearby natural underground reservoir, suggesting human activities played a role in moving Earth's crust, scientists reported on Sunday.

The study published in the journal Nature Geoscience centered on the May 11, 2011, quake in the southern Spanish town of Lorca. In addition to the nine deaths, this relatively modest earthquake of magnitude 5.1 damaged numerous buildings in Lorca, an agricultural center.

The study's lead author, Pablo Gonzalez of the University of Western Ontario, said he and his colleagues reckoned that the quake was related to a drop in the level of groundwater in a local aquifer, which can create pressure at the Earth's surface.

To test that theory, they used satellite data to see how the terrain was deformed by the earthquake, and found that it correlated to changes in the Earth's crust caused by a 273-yard (250-metre) drop in the natural groundwater level over the last five decades due to groundwater extraction.

Their findings suggest that human-induced stress on faults like the one near Lorca, known as the Alhama de Murcia Fault, can not only cause an earthquake but also influence how far the fault will slip as a result.

The groundwater was tapped by deeper and deeper wells to irrigate fruits and vegetables and provide water for livestock.

While this research does not automatically relate to other earthquakes, it could offer clues about quakes that occur near water in the future, Gonzalez said by telephone.

"We cannot set up a rule just by studying a single particular case, but the evidence that we have collected in this study could be necessary to expand research in other future events that occur near ... dams, aquifers and melting glaciers, where you have tectonic faults close to these sources," Gonzalez said.

He said this was different from a rash of minor earthquakes seen in Texas over the last two years, some of which occurred near wells where wastewater was injected deep underground.

In an accompanying article, Jean-Philippe Avouac of the California Institute of Technology said the implications could be far-reaching "if ever the effect of human-induced stress perturbations on seismicity is fully understood."

"For now, we should remain cautious ... We know how to start earthquakes, but we are still far from being able to keep them under control," Avouac wrote.

(Reporting By Deborah Zabarenko)

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