Can human activities cause or exacerbate an earthquake?
According to a study published in the journal Nature Geoscience Sunday, the answer is yes:
Here, we use geodetic data to determine surface deformation associated with the Mw 5.1 earthquake that occurred in Lorca, southeast Spain, on 11 May 2011. We use an elastic dislocation model to show that earthquake nucleation and the area of main fault slip occurred at very shallow depths of 2–4 km, on a rupture plane along the Alhama de Murcia Fault. Slip extended towards the surface, across fault segments with frictional properties that changed from unstable to stable. The area of fault slip correlates well with the pattern of positive Coulomb stress change that we calculate to result from the extraction of groundwater in a nearby basin aquifer. We therefore suggest that the distribution of shallow slip during the Lorca earthquake could be controlled by crustal unloading stresses at the upper frictional transition of the seismogenic layer, induced by groundwater extraction. Our results imply that anthropogenic activities could influence how and when earthquakes occur.
Reuters elaborated on the study's abstract:
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.
The Associated Press reported the day after the quake hit:
Thousands of Spaniards have fled this small agricultural city, fearing major aftershocks might level it after the country's deadliest earthquakes in 55 years killed nine people and caused extensive damage.
Lorca was transformed into a ghost town, with a steady stream of cars carrying many of its 90,000 residents to nearby cities and towns to stay with relatives. Stores, restaurants and schools were closed as the sirens of police vehicles and ambulances filled the air and helicopters hovered overhead.
This video created by Earthquake Video Mex will give you a sense of the damage produced by this relatively small quake: