A major earthquake in Spain that killed nine people was triggered by groundwater extraction, research suggests.
The magnitude 5.1 tremor struck the historic town of Lorca in south-east Spain in May last year. In addition to the lives lost, buildings were reduced to rubble, cars flattened and more than a hundred people injured.
Now scientists say they have evidence that the disaster was man-made - the result of water being sucked out of the ground to feed domestic supplies. Loss of the water caused stress changes in the earth's crust along a major faultline, it is believed.
The disturbance was enough to trigger a rupture in the rock, leading to the earthquake. The findings, published in the journal Nature Geoscience, highlight the extent to which human activity can influence seismic shocks.
Scientists led by Dr Pablo Gonzalez, from the University of Western Ontario in Canada, used satellite data to map the ground deformation caused by the Lorca earthquake.
They then carried out computer simulations of the fault slip. The results showed a pattern that correlated with stress changes due to loss of groundwater. Since the 1960s, natural groundwater levels in the region had reduced by 250 metres.
The researchers wrote: "We conclude that the presented data and modelling results are consistent with a groundwater crustal unloading process, providing a reasonable explanation for the observed fault slip pattern.."
The findings implied that "anthropogenic activities could influence how and when earthquakes occur".
In an accompanying commentary article, Professor Jean-Philippe Avouac, from the California Institute of Technology in Pasadena, US, wrote: "We should remain cautious of human-induced stress perturbations.. We know how to start earthquakes, but we are still far from being able to keep them under control."
Professor Peter Styles, from Keele University, said: "This is a very exciting and stimulating paper. The authors comment on the role which anthropogenic activity can play in stimulating the response of the crust and there will no doubt be speculation as to the implications of this for hydraulic fracturing in the context of shale gas exploration."