Tuesday, October 23, 2012

Earthquake Caused By Water Extraction?

A killer earthquake in Spain may have been triggered by decades of pumping water out of a nearby natural underground reservoir.
A study in the journal Nature Geoscience (focussing on the May 2011 EQ in the southern Spanish agricultural centre of Lorca) suggests human activities played a role in moving the Earth's crust.
University of Western Ontario scientists reckon the quake was related to a drop in the level of groundwater in a local aquifer, which created pressure at the Earth's surface. They used satellite data to see how the terrain was deformed by the EQ, and found it correlated to changes in the Earth's crust caused by a 250m drop in the natural groundwater level over the last five decades, due to groundwater extraction. The groundwater was tapped by deeper and deeper wells, for irrigation and livestock.
Their findings suggest that human-induced stress on faults, like the one near Lorca, can not only cause an earthquake but also influence how far the fault will slip as a result. While this research doesn't automatically relate to other EQs, it may offer clues about quakes that occur near water in the future. The implications of this research could be far-reaching if ever the effect of human-induced stress on seismic activity is fully understood.
In the meantime, it's worth considering how many Canterbury farms (a traditional wheat-growing region) have converted to dairying, a water-intensive land use...
Canterbury holds 20% of New Zealand's farmland. Statistics NZ says, in 2008, half of NZ’s grain seed and fodder crop land was in Canterbury. Yet between 1994-2009, Canterbury's percentage of the national herd increased from 5% to 15%.
In light of this Spanish study, the possibility that Canterbury's increased water usage may have had a part to play in the two big EQs of 2010 and 2011 should not be dismissed.

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