Researchers analysed data from November quake and found main shock occurred near fracking site
One of South Korea’s largest earthquakes on record may have been caused by hydraulic fracturing – or fracking – according to a study published on Friday in the journal Science.
A magnitude-5.5 earthquake hit the south-eastern city of Pohang on 15 November, injuring at least 70 people, temporarily displacing hundreds, and causing millions of dollars of damage. In the aftermath, residents and researchers have questioned whether the quake could be connected to a geothermal plant – the country’s first – less than 2km (about 1 mile) away.
A team of researchers from the University of Glasgow, ETH-Zurich in Switzerland and GFZ-Potsdam in Germany analysed data from seismographic stations as well as satellite data to locate where the main shock and 46 aftershocks of the quake occurred.
They found that the main shock occurred within 1.5km of where plant workers had been pumping thousands of cubic metres of water into the ground, creating or opening fractures in the rocks to enable water to pass between boreholes. The last of those injections was about two months before the quake.
They also found that the main shock and aftershocks all occurred at depths of between 3 and 7km, which are shallow compared to previous quakes in that area, but similar to the depths at which the water was being injected.
The researchers have been careful to say only that a connection is plausible. Korean authorities are also conducting their own investigation.
“It would be a very a remarkable coincidence if this earthquake were to be unrelated to the activity at the site, given that it occurred so close to it,” said Robert Westaway, a senior research fellow at Glasgow university’s school of engineering, and one of the paper’s co-authors. “My own personal view is that it is highly likely there is a connection.”
Westaway said further studies were being carried out to explain the two-month delay between the last round of fracking and the quake.
Earthquakes caused by hydraulic fracturing have prompted concerns around the world. Two earthquakes in 2011 led to the UK imposing a fracking moratorium. In Oklahoma, meanwhile, experts have reported a millennium’s worth of quakes in two years because of fracking there.
For decades, the Korean peninsula has seen almost no seismic activity. On 12 September 2016, another magnitude-5 quake struck just south of Pohang in Gyeongju. Since then the country has seen hundreds of smaller earthquakes.
The study’s conclusions could also change how fracking is studied in relation to earthquakes. Previous theories have focused more on the volume of water used, rather than the pressure at which it enters the ground. In the case of the Pohang quake, a relatively small amount of water – about 10,000 cubic metres – was injected.
“No one ever thought that injecting such a small amount of water could lead to such a large earthquake,” Westaway said.