Spanish farmers' ever-deeper wells blamed for earthquake
Study finds ever-deeper extraction of water probably caused deadly Spanish quake, but others say it would have occurred anyway
Farmers drilling ever deeper wells over decades to water their crops probably contributed to a deadly earthquake in southern Spain last year, a new study suggests. The findings may add to concerns about the effects of new technologies for energy extraction and waste disposal.
Nine people died and nearly 300 were injured when an unusually shallow magnitude-5.1 quake hit the town of Lorca on May 11.
Using satellite images, scientists from Canada, Italy and Spain found the quake ruptured a fault running near a basin that had been weakened by 50 years of groundwater extraction.
During this period, the water table fell 250 metres as farmers bored ever deeper wells to help produce the fruit, vegetables and meat exported from Lorca to the rest of Europe. In other words, the industry that propped up the local economy in southern Spain may have undermined the very ground on which Lorca is built.
The researchers noted that even without the strain caused by water extraction, a quake would probably have occurred at some point. But the extra stress of pumping vast amounts of water from a nearby aquifer may have been enough to trigger a quake at that particular time and place, said lead researcher Pablo Gonzalez of the University of Western Ontario, Canada.
A geologist with Spain's National Natural Science Museum who has worked on the same theory but was not involved in the study, Miguel de las Doblas Lavigne, said the Lorca quake was in the cards.
"This has been going on for years in the Mediterranean areas, all very famous for their agriculture and plastic greenhouses. They are just sucking all the water out of the aquifers, drying them out," he said. "From Lorca to (the regional capital) Murcia you can find a very depleted water level."
It was "no coincidence that all the aftershocks were located on the exact position of maximum depletion", he said.
"The reason is clearly related to the farming, it's like a sponge you drain the water from; the weight of the rocks makes the terrain subside and any small variation near a very active fault like the Alhama de Murcia may be the straw that breaks the camel's back, which is what happened."
Not everyone agreed with the conclusion of the study, which was published online on Sunday in Nature Geoscience.
"There have been earthquakes of similar intensity and similar damage caused in the 17th, 18th and 19th centuries when there was no excess water extraction," said Jose Martinez Diez, a professor in geodynamics at Madrid's Complutense University who has also published a paper on the quake.
The biggest man-made quakes are associated with large dams, whose massive amounts of water put heavy pressure on surrounding rock.
A pioneering geothermal power project in the Swiss city of Basel was abandoned in 2009 after it caused a series of earthquakes. Nobody was injured, but the tremors caused by injecting cold water into hot rocks to produce steam resulted in millions of dollars of damage to buildings.
This year, a report by the National Research Council in the US found hydraulic fracturing to extract natural gas was not a huge source of man-made earthquakes. But the related practice of shooting large amounts of wastewater from "fracking" or other drilling activities into deep underground storage wells has been linked with small quakes.