The Pohang earthquake in 2017 was likely triggered by an Enhanced Geothermal System (EGS)
Prof. Jin-Han Ree and his team published the findings of their research in Science Magazine.

▲ Prof. Jin-Han Ree (pictured left) and Dr. Sungshil Kim (right) in the Department of Earth and Environmental Sciences, College of Science, Korea University

A paper about the cause of the 2017 Pohang earthquake, co-authored by Professor Jin-Han Ree and Doctor Sungshil Kim from the Department of Earth and Environmental Sciences at Korea University and four other researchers, was published in Science, a leading academic journal, on April 27, 2018 as a First Release. First Release provides rapid online publication of selected research papers and other articles that have recently been accepted for publication in Science.

This paper presents evidence, based on detailed investigation of geological, geochemical, and geophysical properties of the Pohang Enhanced Geothermal System (EGS) site, that suggests the Pohang earthquake, measuring magnitude 5.4 on the moment magnitude scale—one of the largest instrumentally recorded earthquakes in South Korea—was induced by fluid injection at the EGS site.

Hydraulic fracturing techniques—in which water, sand, and chemicals are injected into the well at high pressure—are commonly used to increase the productivity of shale gas and the efficiency of geothermal power plants, and the high water pressure may cause induced earthquakes. It has been widely accepted among scholars and researchers around the world that the water pressure inducing hydraulic fracturing does not trigger induced earthquakes measuring greater than magnitude 3.5, because EGSs use relatively low water pressures. When applying a popular formula for estimating the maximum possible size of induced earthquakes, triggering the 5.4 magnitude Pohang earthquake should have required more than 800 times more water than was actually used. However, Professor Ree and his colleagues found that hydraulic fracturing can trigger earthquakes of magnitude 5 or higher, and that this widely-accepted formula may be wrong.

Another noteworthy paper was published in the same issue of Science. That study, conducted by Professor Wiemer of the Swiss Seismological Service at ETH-Zurich and colleagues from several European institutions, relied on publicly-available seismic data and satellite measurements showing how the ground shifted during the quake. According to their findings, it is highly likely that the Pohang earthquake was an induced event.

Professor Kwang-Hee Kim at Pusan National University (lead author) and Professor Ree are co-corresponding authors of the paper. The names of YoungHee Kim, Professor at Seoul National University, Sungshil Kim, Doctor at Korea University, Su Young Kang, a researcher at Pusan National University, and Wooseok Seo, a graduate student at Pusan National University, are included on the paper as co-authors. The two co-corresponding authors and Professor YoungHee Kim have been conducting research to identify the source of the Gyeongju Earthquake in 2016—a project that started in 2017 and that was funded by the Nuclear Safety and Security Commission (NSSC).