A remarkable increase in the rate of M 3 and greater earthquakes is currently in progress in the US midcontinent. The average number of M >= 3 earthquakes/year increased starting in 2001, culminating in a six-fold increase over 20th century levels in 2011. Yes, you did read that correctly….six times!

The US Geological Survey (USGS) will be presenting a paper next month at the annual meeting of the Seismological Society of America in San Diego. The paper will directly link an “unprecedented” increase in frequency and magnitude of earthquakes to drilling for oil and gas. The presentation highlights the M5.8 Central Virginia and the M5.6 Oklahoma Earthquakes of 2011.

This link is not a new one. The USGS already linked about 50 earthquakes in Oklahoma due to fracking. Their investigation found that the earthquakes had a magnitude ranging from 1.0 to 2.8. In January, a single earthquake of the magnitude of 4.0 was strong enough that it was felt in Toronto. The bulk of these occurred within 2.1 miles of Eola Field, a fracking operation in southern Garvin County.

From the report:

Our analysis showed that shortly after hydraulic fracturing began small earthquakes started occurring, and more than 50 were identified, of which 43 were large enough to be located. Most of these earthquakes occurred within a 24 hour period after hydraulic fracturing operations had ceased. There have been previous cases where seismologists have suggested a link between hydraulic fracturing and earthquakes, but data was limited, so drawing a definitive conclusion was not possible for these cases.

In April and May, two small earthquakes near Blackpool, in England also contributed to suspicions of a link between earthquakes and fracking. Finally, the company responsible, Cuadrilla Resources, admitted that its shale fracking operations were indeed responsible.

A depiction of a fracking operation

The latest USGS report states that:

In Oklahoma, the rate of M >= 3 events abruptly increased in 2009 from 1.2/year in the previous half-century to over 25/year. This rate increase is exclusive of the November 2011 M 5.6 earthquake and its aftershocks. A naturally-occurring rate change of this magnitude is unprecedented outside of volcanic settings or in the absence of a main shock, of which there were neither in this region.

Although the report links earthquakes to drilling activities, it is still too early to say whether this is due to the increase in rate of drilling or a specific technique. The connection however appears clear – fracking causes abnormal seismic activity.  The question will now be, what if anything will society do about it?