October 22, 2012
Lorca Seismic Event Was Caused By Extraction Of Groundwater
Brett Smith for redOrbit.com - Your Universe Online
The May 2011 earthquake that struck near the Spanish town of Lorca and killed nine people could have been exacerbated by groundwater extraction, according to a new study from a team led by University of Western Ontario researchers.
The 5.1-magnitude quake that occurred along the relatively shallow Alhama de Murcia Fault struck just 1.2 miles northeast of Lorca, caused millions of dollars in damage, and left thousands homeless, according to the group´s report that was published in the journal Nature Geoscience.
By analyzing ground deformations associated with the quake using ground-radar imaging, the researchers were able to trace the origins of the seismic event. Their results showed that the fault had slipped between 2 and 6 inches after the earthquake.
They also focused on the Alto Guadalentin Basin, an aquifer located 3 miles south of the fault, where they discovered evidence of subterranean sinking due to water extraction. The teams also found that the level of groundwater in the basin fell at least 800 feet between 1960 and 2010.
Based on these observations, the researchers created a computer model that showed lowering of the water table caused part of the crust near the fault to break. The kinetic forces of this break resulted in an elastic rebound that increased horizontal pressure on the fault line. This pressure helped to trigger the earthquake and define its magnitude, according to the report.
"Our results imply that anthopogenic [man-made] activities could influence how and when earthquakes occur," said the researchers wrote.
Lead author Pablo Gonzalez of the University of Western Ontario warned against applying the study´s findings on too broad a scale.
"We cannot set up a rule just by studying a single particular case,” he told Reuters. "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."
In an accompanying article that appears in the same edition of Nature, Jean-Philippe Avouac, a geologist at the California Institute of Technology, said the water extraction that was the result of local farmers drilling wells for crop irrigation probably accelerated the earthquake process, but did not directly cause the quake by itself.
"It does not take much to trigger an earthquake - even strong rainfall can do the job,” Avouac wrote. "Numerous examples of seismicity triggered by the impoundment of reservoir lakes, hydrocarbon extraction, quarrying and deep well injections have been documented over the years."
Avouac also warned that human geoengineering efforts should be undertaken with care. In particular, he noted that carbon sequestration, a theoretical method that would pump carbon emissions into underground caverns rather than the atmosphere, may have unintended geologic consequences.
"For now, we should remain cautious of human-induced stress perturbations, in particular those related to carbon dioxide sequestration projects that might affect very large volumes of crust," Avouac said.
"We know how to start earthquakes, but we are still far from being able to keep them under control."
Other geoengineering efforts could be focused on muting or releasing stress along fault lines. If future studies based on the data collected around Lorca could be applied to preventative techniques, those endeavors should be pursued optimistically, but with caution, according to the Cal Tech geologist.
“We might dream of one day being able to tame natural faults with geoengineering,” Avouac suggested.