Don't Drill Too Deep

I have established that the earth’s crust reacts to a redistribution of stresses along its geological faults. This is precisely how drilling and mining can incur man-made earthquakes. For example, a greater frequency of tremors was detected subsequent to the commencement of oil drilling operations in the North Sea.

Looking forward, we would like to have confidence that geothermal energy development will offer cheap, clean renewable power. This venture has been rocked by reports from scientists and locals that drilling for naturally occurring heat could generate bigger earthquakes. Since its advent in the 1970s, the gradual intensification of geothermal drilling due to improvements in technology have been held responsible for successions of minor earthquakes that were felt thereafter. A particularly insightful example is the now infamous case of Switzerland’s geothermal project in Basel. In 2006, this resulted in a 3.4 magnitude quake after drilling three miles (4.8 kilometres) into the earth’s crust. The aftermath was covered by an article in the New York Times, stating that tremors shook the town and the operation was ceased.

Despite prevailing earthquake fears plus the knowledge of the aforementioned failed project in Basel, American company AltaRock have the intent to drill two miles deep into the San Franciscan ground using a similar method. The site had been chosen in the hope of tapping into the natural geothermal vents (nicknamed The Geysers) which are located approximately 90 miles north of San Francisco, near a town called Anderson Springs. Whilst AltaRock founder Susan Petty has maintained that all large faults will given a wide berth, doubts of the safety and rationality of this project are palpable amongst locals and geologists. A concerning point to make is that within the seismic impact report filed by AltaRock, they dodged the fact that an earthquake had been the cause of the Basal programme’s collapse. Instead, the company allege that the trigger of the quake was not fully understood, in spite of expert seismologists and project officials pleading its guilt. 

Geothermal energy has the potential to be a clean, renewable and reliable resource. However power companies have been limited to harnessing shallow steam beds, geysers and vents to prevent an earthquake risk (even though these projects can still induce very small tremors). Henceforward, tapping the heat from the earth’s core is the challenge faced by engineers. Certain advocates of geothermal energy believe the method adopted in Basel and by AltaRock [shown in the figure below] is the way forward. Obviously, greater earthquakes originate at greater depths so drilling to such  a distance carries a perilous risk. Seismologists insist that currently there is still major gaps in the scientific knowledge that prevent us from predicting with any certainty what will or will not shake the ground.