Short Sharp Science

Ohio magnitude 4.0 earthquake linked to fracking

Michael Marshall, environment reporter
(Image: Amy Sancetta/AP/Press Association Images)

Ohio has suspended work at five deep wells used to dispose of waste water from natural gas extraction, following evidence linking the operations to a magnitude 4.0 earthquake on New Year's Eve.

It is the latest case of an earthquake being linked to the pumping of water into underground wells. Two small earthquakes in the UK last year were also blamed on the process.

Although it was relatively small, the quake will only add to the controversy around fracking, a process used to extract natural gas from otherwise inaccessible deposits. Fracking has also been blamed for contamination of drinking water.

Properly known as hydraulic fracture, fracking involves pumping pressurised water into underground rocks to shatter them and release natural gas trapped inside. But as the Christian Science Monitor points out, it was not this dramatic process itself that was to blame for the Ohio quakes. They appear to have been caused by the disposal of the waste water after fracking. This water is pumped into deep wells, and as more water is added, the pressure can gradually rise to levels high enough to cause relatively large earthquakes.

Scientific American explains how the quake was linked to the disposal wells:

Nine small earthquakes had already occurred between March and November 2011 within an eight-kilometer radius of a wastewater injection well run by Northstar Disposal Services. Because quakes are otherwise rare in the Youngstown area... Columbia University's Lamont-Doherty Earth Observatory (LDEO) [placed] mobile seismographs in the vicinity to better determine what was going on... The epicenters of the two holiday quakes were within 100 meters of each other, and within 0.8 kilometer of the injection well... The quakes were caused by slippage along a fault at about the same depth as the injection site, almost three kilometers down.

Reuters adds that the quakes are far from the first case of earthquakes apparently triggered by the disposal of water underground:

A quake of 4.2 magnitude in Ashtabula, Ohio, on January 26, 2001, was believed to be due to deep-well injection... And in 1987 there was an incident with a correlation to high pressure deep well injection.

What's more, NPR notes that gold mining in South Africa in the 1960s was linked to small earthquakes.

According to Arthur McGarr of the United States Geological Survey in Menlo Park, California, the size of the earthquake depends on the volume of water injected. When the volume of water doubles, the maximum possible quake magnitude rises about 0.4.

http://www.newscientist.com/