Two articles dealing with induced (or triggered?) seismicity caught my attention last week. Time came up with a report about “The Seismic Link Between Fracking and Earthquakes“. New studies on that topic had been presented at the SSA annual meeting in Alaska. Basically it’s now possible to link two phenomena: a) The huge increase in shale gas and oil development in Ohio, Oklahoma, and Kansas during the last few years; and b) the huge increase in earthquake activity in Ohio, Oklahoma, and Kansas during the last few years. It’s not the fracking itself that seems to cause seismic events, but it’s rather the disposal of wastewater produced during the hydrocarbon extraction. The contaminated water is pressed back into boreholes. Now it looks like the stress changes caused by the increased pressure may trigger quakes at a greater distance than previously thought, Art McGarr and Justin Rubinstein from the USGS report. In this case, it looks like we have not only triggered seismic events, but really induced them. That’s a great difference and an important one.
Another study concerns the deadly earthquakes in Italy of 20 and 29 May, 2012.
These events might be related to a nearby oilfield. A year before the seismic events, water pressure has been increased in one of the reservoirs in order to extract more hydrocarbons. Now a report released by the International Commission on Hydrocarbon Exploration and Seismicity in the Emilia Region (ICHESE) suggests that the quakes may be related to the oil extraction, with a lot of question marks and a very very careful wording. (This case also doesn’t make the life of seismologists easier in Italy, I guess.) From the Conclusions of the report:
“The Commission believes that it is highly unlikely that the activities of hydrocarbon exploitation at Mirandola and the geothermal activity at Casaglia have produced sufficient stress change to generate an ‘induced’ seismic event. While it cannot constitute proof, the current state of knowledge and all the processed and interpreted information does not allow the ruling out of the possibility that the actions involved in hydrocarbon exploitation in the Mirandola field may have contributed to ‘trigger’ the Emilia seismic activity.”
Download the reports here:
- Report on the hydrocarbon exploration and seismicity in Emilia-Romagna
- Appendices – Report on the Hydrocarbon Exploration and Seismicity in Emilia Region
The Economist states in its article: “A pity […] that the government sat on the ICHESE report for two months after its delivery, and only published it once it had already been leaked.” I have nothing to add.