At the end of 2017 in Korea there was a fairly powerful earthquake. It arose unexpectedly for seismologists (although the latter are able to predict far from all earthquakes), and gave rise to a number of questions. The magnitude of the phenomenon was 5.4, an earthquake happened on November 15, 2017. According to economists, this disaster has caused the country enormous economic damage - the largest in the history of seismic observations in Korea. And they have been observed for more than a century.
In 1978, an earthquake occurred, comparable in strength to a recent one, the strength of these two catastrophic events is approximately equal. Due to a recent earthquake, the South Korean economy has lost more than $ 52 million. Incidentally, only 82 people were injured, and there were no victims. The region where the earthquake occurred is seismically inactive, so scientists began to find out the causes of the disaster, not understanding why it happened at all.
Two groups of scientists, independently working from each other, had an
assumption that the reason was technogenic, and, as it turned out, the assumption is quite fair. The fact is that this region has a geothermal power station. For its operation, it is necessary to pump water into the wells. As it turned out, precisely because of the water injection, an earthquake occurred.
A group of scholars from a number of Korean universities, led by Kim Kwan-hee, discovered this. He is an employee of Busan National University. Scientists used the testimony of seismographs, which were installed at the station about a week before the earthquake. Another group of scientists, this time not from Korea, but from Germany, Great Britain and Switzerland decided to study seismographic data from the above region. All information is publicly available, so that problems and its study did not arise.
Of course, to understand the causes of an earthquake, you need to know exactly where the power plant is located. It is located in the eastern part of the Eurasian Plate, in the Pohang Basin, rather far from the neighboring geological faults. Part of the station are two wells with a depth of about 4.4 kilometers, which are separated from each other by 600 meters. Fluid was pumped into one of these wells, and heated in the second one. Various observations showed that while drilling wells, the maximum magnitude of earthquakes within a radius of about 10 km did not exceed 2. As for hydraulic tests, some fluctuations in the lithosphere occurred, but their magnitude did not exceed 3.1.
Scientists have found that during the earthquake there was not one push, but several. Before the main one, less severe tremors were observed and after it too. The epicenter of the earthquake was at a depth of about 4.5 kilometers, which is not so much for earthquakes. In some cases, the epicenter occurs at a depth of about 14 km or even lower. Experts compared the time of the appearance of shocks with the introduction of water into the well, after which it immediately became clear that the reason was precisely in the injection of fluid.
According to experts, an earthquake of such force, caused by man-made causes, was still considered possible, but it could occur only if approximately 800 times more fluid was injected into the well than was actually pumped. The model, in principle, is correct, but the problem was that the structure of faults close to the station is very heterogeneous. Clay veins revealed critical pressure, which could cause an earthquake. The introduction of water from the well of the power plant activated the Yansansky Fault, which was already active. A relatively small external factor in the form of fluid injection and caused its full activation.
According to the authors of the study, the data obtained show that the initial data for the model of the occurrence of earthquakes should be revised. We are talking about the information on the basis of which the models of earthquakes that arise under the influence of hydraulic action are created. Scientists say that the developers of stations of this kind need to be more careful when taking into account factors that could cause earthquakes.