A massive earthquake that injured dozens of people in 2017 was triggered by a process similar to fracking, a new study has found.
The quake, which shook Pohang in South Korea in November 2017, caused NZ$460 million in damages and injured 135 people.
New research conducted by scientists here in New Zealand and in the US has placed the blame squarely on a "high-pressure fluid injection".
"The Pohang geothermal project was intended to demonstrate the feasibility of enhanced geothermal systems in South Korea as the country tries to reduce its dependence on non-renewable energy," said Prof John Townend of Victoria University of Wellington.
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The water triggered a previously unknown fault, resulting in a magnitude 5.5 quake. More than 1000 people were forced into temporary shelter, their homes rendered unliveable. More than 200 schools and nearly a dozen bridges were also damaged by the initial tremor and aftershocks.
"These findings have implications not only for South Korea, but for other parts of the world pursuing similar geothermal projects," said Townend. "They also have broader ramifications for managing risk associated with energy production."
Injecting water into the ground is intended to force open new pathways for heat inside the Earth to find its way to the surface.
"When they began injecting fluids at high pressure, one well produced a network of fractures as planned," wrote Stanford University's Josie Garthwaite. "But water injected in the other well began to activate a previously unknown fault that crossed right through the well.
"Pressure migrating into the fault zone reduced the forces that would normally make it difficult for the fault to move. Small earthquakes lingered for weeks after the operators turned the pumps off or backed off the pressure. And the earthquakes kept getting bigger as time went by."
These ended in the massive 5.5 quake that rocked Pohang that November.
Stanford University geophysicist William Elmsworth said there was "no doubt" the quake was triggered by water injection.
"Usually we don't say that in science, but in this case, the evidence is overwhelming."