SPANISH CITY EARTHQUAKE

Earth quake caused by ground water

Groundwater removal may have caused the deadly 2011 earthquake in Lorca, scientists studying the fault beneath the Spanish city have said.


Detailed surface maps from satellite studies allowed the scientists to infer which parts of the ground moved where.

Scientists found that those shifts correlate with locations where water has been drained for years, a media report found.

The study highlights how human activity such as drainage or borehole drilling can have far-reaching seismic effects.

Researchers led by Pablo Gonzalez of the University of Western Ontario used satellite radar data to trace the ground movements of the Lorca event back to their source, finding that the earthquake resulted from slippage on a comparatively shallow fault that borders a large water basin south of the city.

That the slippage happened at a depth of just 3 kms explains why the fairly mild magnitude 5.1 quake caused so much damage in the area.

The team went on to study potential reasons for the slippage, finding that the water table in the adjacent Alto Guadalentin basin had dropped by some 250 metres over the last 50 years as water was drained for irrigation in the region.

The study calculations show that this created stresses on the fault that initially triggered the earthquake and defined its eventual magnitude.

However, the area lies on a seismically active region, and the data suggest only that the water drainage sped up and eventually triggered a process that would have eventually happened anyway.

The study was published in Nature Geoscience.