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Pumped Up Man made earthquakes

The Economist has an article on the possible link between enhanced oil recovery techniques and earthquakes - Pumped Up: Man-made earthquakes.

IN MAY 2011 something routine happened at the Cavone oilfield in northern Italy. Padana Energia, its operator, started pumping more high-pressure water into their wells, to squeeze more oil out. This unremarkable event may, though, have had remarkable consequences. A year later, on May 20th and 29th 2012, two nearby earthquakes killed 27 people and injured hundreds more. A report made public on April 15th by the International Commission on Hydrocarbon Exploration and Seismicity in the Emilia Region (ICHESE), a six-strong panel of geoscientists, says the pumping and the earthquakes may be connected.

Most earthquakes are caused by movements in geological faults, places where two bodies of rock are being pushed in different directions but nevertheless remain (mostly) locked together by friction. When the pushing becomes forceful enough to overcome the friction, however, the fault slips, the pent-up energy is released and the earth quakes.

Seismologists have known for decades that pumping water into the ground near a fault can sometimes make it slip. (Such quakes are different from the small tremors generated by the hydraulic fracturing, or “fracking”, used to extract shale gas from impermeable rocks. These are caused by stress created by the slurry used to break the rock open and release the gas, not by the slippage of faults.) But until these two quakes, only one person was believed to have been killed in a tremor triggered by the extraction of hydrocarbons—in Uzbekistan in 1984.