Just this past November in 2017 Pohang, South Korea was hit with 5.4 magnitude earthquake, taking the title of the second strongest in decades. The earthquake left 1,500 people homeless, 1,536 people were forced to evacuate their homes and 57 people had been injured. So much of Pohang’s infrastructure was damaged as well, taking a toll on their local economy, especially being a port city. Just two days ago an article was posted on ScienceNews claiming that geothermal systems possibly could have triggered the South Korean earthquake. When I read this headline, I was so intrigued and shocked because we all have learned in our geology 101 courses that earthquakes are completely and utterly natural. It also saddened me because now geothermal energy is going to have a negative outlook.
As we briefly learned in class, geothermal electricity is a renewable source of energy and it works by drilling into hot water underground reservoirs and using the heat to power an electrical generator. Using the heat is clean and sustainable, and the heat is constantly being replenished unlike fossil fuels or oil.
There is geothermal power plant located near a fault zone that had been stressed in Pohang. Their system pumps high pressure cold water into the ground, which had make small fractures widen even more to allow the water to be heated by the hot rock beds. Then this hot water is converted into heat to power electricity. Researchers believe these injections of fluids are to blame for the earthquake because they had developed only 4-6 Kilometers below surface points that were only a few kilometers away from the power plant. So, it was concluded by these few studied stated in the article, that the amount of fluid injected into the ground is very closely linked to triggering earthquakes. This happens because injecting the cold water at such high pressures increases subsurface pressure, making fractures more prone to slip. In 2011 there was a 5.7 earthquake in Oklahoma which was caused from injections of 20 million tons of wastewater from oil drilling.
I hope this flaw of geothermal energy does not shy away those in political powers to not accept construction of these plants. If the amount of the injections were smaller, it would not have had this impact on the earthquake. We just have to be careful and learn from our mistakes, and test exactly how much fluid is safe to inject at what pressures for a given area.
This photo shows the correlations of fluid volumes with earthquake magnitudes from the Pohang geothermal plant. Each blue dot shows small earth quakes after each pulse of fluid injections. For example, in January 2016 the plant injected 200-400 cubic meters of fluid into the ground and caused many small earthquakes with magnitude ranging from 0-2.
I am interested to see how this case plays out, because the South Korean government currently has an investigation in place to find whether the November 2017 earthquake is linked to the geothermal plant activity or natural seismic activity. I do believe the company should pay consequences, however, I hope it does not run them out of business because I am sure this plant brought in a lot of jobs to the city of Pohang, and it is such a forward step in our energy production.