<p>Massive extraction of groundwater helped unleash an earthquake in southeastern Spain last year that killed nine people, injured at least 100 and left thousands homeless, geologists said on Sunday.<br /><br /></p>.<p>The finding adds a powerful piece of evidence to theories that some earthquakes are human-induced, they said.<br /><br />Seismologists were surprised by the May 11, 2011 earthquake which happened two kilometres (1.2 miles) northeast of the city of Lorca.<br /><br />The quake struck in the Eastern Betics Shear Zone, one of Spain's most seismically active regions, where there has been a large number of moderate-to-large temblors over the last 500 years. But the May event was unusual because it was so devastating and yet so mild -- only 5.1 magnitude — in terms of energy release.<br /><br />Researchers led by Pablo Gonzalez of the University of Western Ontario in Canada probed the mystery.<br /><br />Reporting in the journal Nature Geoscience, they found that the quake occurred at a very shallow depth, of just three kilometres (1.8 miles), so the shockwave swiftly reached the surface with little to dampen it on the way.<br /><br />The quake also happened on a complex but dormant fault that ripped open after water had been extensively pumped out of a neighbouring aquifer, causing a domino effect of subterranean stresses, they said.<br /><br />Gonzalez' team first used ground-radar imaging by the European satellite Envisat to build a map of how terrain around Lorca changed before and after the quake.<br /><br />The picture confirmed that the event had occurred on the so-called Alhama de Murcia fault, which slipped between five and 15 centimetres (two and six inches).<br /><br />They then investigated the Alto Guadalentin Basin, an aquifer lying just five kms (three miles) south of the fault, where they found widespread evidence of subterranean subsidence from water extraction.<br /><br />Between 1960 and 2010, the level of groundwater from this aquifer fell by at least 250 metres (812 feet), according to records from local wells.<br /><br />A computer model put together by the team suggests what happens: lowering of the water table caused part of the crust, located next to the Alhama de Murcia fault, to break.<br /><br />This led to an "elastic rebound" of the crust that in turn cranked up horizontal pressure on the fault, bringing it that much closer to rupture.<br /><br />The investigation adds to anecdotal evidence that human activities, ranging from exploration for shale gas, quarrying and even water reservoirs, can cause quakes.<br /></p>
<p>Massive extraction of groundwater helped unleash an earthquake in southeastern Spain last year that killed nine people, injured at least 100 and left thousands homeless, geologists said on Sunday.<br /><br /></p>.<p>The finding adds a powerful piece of evidence to theories that some earthquakes are human-induced, they said.<br /><br />Seismologists were surprised by the May 11, 2011 earthquake which happened two kilometres (1.2 miles) northeast of the city of Lorca.<br /><br />The quake struck in the Eastern Betics Shear Zone, one of Spain's most seismically active regions, where there has been a large number of moderate-to-large temblors over the last 500 years. But the May event was unusual because it was so devastating and yet so mild -- only 5.1 magnitude — in terms of energy release.<br /><br />Researchers led by Pablo Gonzalez of the University of Western Ontario in Canada probed the mystery.<br /><br />Reporting in the journal Nature Geoscience, they found that the quake occurred at a very shallow depth, of just three kilometres (1.8 miles), so the shockwave swiftly reached the surface with little to dampen it on the way.<br /><br />The quake also happened on a complex but dormant fault that ripped open after water had been extensively pumped out of a neighbouring aquifer, causing a domino effect of subterranean stresses, they said.<br /><br />Gonzalez' team first used ground-radar imaging by the European satellite Envisat to build a map of how terrain around Lorca changed before and after the quake.<br /><br />The picture confirmed that the event had occurred on the so-called Alhama de Murcia fault, which slipped between five and 15 centimetres (two and six inches).<br /><br />They then investigated the Alto Guadalentin Basin, an aquifer lying just five kms (three miles) south of the fault, where they found widespread evidence of subterranean subsidence from water extraction.<br /><br />Between 1960 and 2010, the level of groundwater from this aquifer fell by at least 250 metres (812 feet), according to records from local wells.<br /><br />A computer model put together by the team suggests what happens: lowering of the water table caused part of the crust, located next to the Alhama de Murcia fault, to break.<br /><br />This led to an "elastic rebound" of the crust that in turn cranked up horizontal pressure on the fault, bringing it that much closer to rupture.<br /><br />The investigation adds to anecdotal evidence that human activities, ranging from exploration for shale gas, quarrying and even water reservoirs, can cause quakes.<br /></p>