An earthquake in Spain last year appears to have been triggered by excessive pumping of an aquifer.
The 5.1 magnitude earthquake hit the city of Lorca, Spain on May 11, 2011. Nine people died, more than one hundred were injured, and thousands were left homeless.
The area the quake struck is historically an active seismic zone. Moderate to large seismic events occur in the area fairly often. When a complex, but dormant fault slipped, the damage to nearby buildings was surprisingly large.
Typically, a 5.1 magnitude earthquake will cause minor damage to buildings. The May 11, 2011 earthquake destroyed buildings and homes like a much larger earthquake would have.
Pablo Gonzalez of the University of Western Ontario and fellow researchers found that the earthquake occurred at a shallow depth. With little earth to dampen the shockwave, the earthquake did much more damage than it would have.
Using ground-radar imaging to build maps of the terrain before and after the earthquake, they found evidence of subterranean subsidence over the aquifer. In fifty years, groundwater in the aquifer fell by more than 800 feet. The reduction of pressure in the aquifer allowed the crust to break, shifting the pressures on the fault.
Earlier this year, a University of Texas study found a link between injection wells and earthquake clusters. Earthquakes have also been linked to fracking in Arkansas and Ohio. Previous studies have found mostly minor earthquakes associated with human activity, but the one near Lorca, Spain was significant, highlighting the unpredictability of causing earthquakes.
Cartagena, Spain photo via Shutterstock