Below-ground CO2 injections caused Texas quakes?

A series of small earthquakes - some larger than magnitude 3 - in Texas may have been triggered by the injection of carbon dioxide into the ground to store the harmful greenhouse gas, a new study suggests.
The study correlates a series of small earthquakes near Snyder, Texas between 2006 and 2011 with the underground injection of large volumes of gas, primarily CO2 - a finding relevant to process of capturing and storing CO2 underground.
Although the study suggests that underground injection of gas triggered the Snyder earthquakes, it also points out that similar rates of injections have not triggered comparable quakes in other fields, bolstering the idea that underground gas injection does not cause significant seismic events in many geologic settings.

No injuries or severe damage were reported from the quakes identified in the study, researchers said.
The study represents the first time underground gas injection has been correlated with earthquakes greater than magnitude 3.
The study by Wei Gan and Cliff Frohlich from The University of Texas at Austin's Institute for Geophysics focused on an area of northwest Texas with three large oil and gas fields - the Cogdell field, the Salt Creek field and the Scurry Area Canyon Reef Operators Committee unit (SACROC) - which have all produced petroleum since the 1950s.

Operators began injecting CO2 in the SACROC field in 1971 to boost petroleum production, a process known as CO2 Enhanced Oil Recovery (CO2 EOR).

Operators began CO2 EOR in the Cogdell field in 2001, with a significant increase starting in 2004.
Because CO2 has been injected at large volumes for many years, the US Department of Energy has funded research in this region to explore the potential impacts of carbon capture and storage (CCS), a proposed technique for reducing greenhouse gas emissions by capturing CO2 and injecting it deep underground for long-term storage.
Using a high-resolution temporary network of seismometers, Gan and Frohlich identified 93 earthquakes in the Cogdell area from March 2009 to December 2010, three of which were greater than magnitude 3.

An even larger earthquake, with magnitude 4.4, occurred in Cogdell in September 2011. Using data on injections and extractions of fluids and gases, they concluded that the earthquakes were correlated with the increase in CO2 EOR in Cogdell.
"What's interesting is we have an example in Cogdell field, but there are other fields nearby that have experienced similar CO2 flooding without triggering earthquakes," said Frohlich.
"So the question is: Why does it happen in one area and not others?" said Frohlich.
In a study last year, Stanford University earthquake researchers Mark Zoback and Steven Gorelick argued "there is a high probability that earthquakes will be triggered by injection of large volumes of CO2" during CCS.