Above the mountains: a new model will help predict earthquakes and search for minerals
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- Above the mountains: a new model will help predict earthquakes and search for minerals
For the first time, Russian scientists formulated the "universal law" of rock destruction. Having studied the Primorsky fault of the Baikal rift zone, experts mathematically described the mechanism of formation of cracks and fractures. The model created on the basis of these data can be used to predict areas of possible earthquake occurrence, as well as to increase the efficiency of mining. At the same time, experts note that before practical implementation, it is necessary to additionally verify the stated principle of universality, since many factors affect seismic processes.
The universal principle of rock destruction
Scientists from the Sadovsky Institute of Geospheric Dynamics of the Russian Academy of Sciences and the Institute of Ore Deposit Geology, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences have described for the first time the mathematical principles by which rocks are destroyed. They conducted a study in the area of the Primorsky fault of the Baikal rift zone.
This is a large regional fault that stretches for more than 250 km along the western shore of Lake Baikal. Despite the fact that the rift zone began to form as early as 65-60 million years ago, there is still high seismic activity here.
Cracks and fractures are constantly appearing in the Earth's crust, ranging from microscopic to hundreds and thousands of kilometers long. It is important to take such structures into account when exploring minerals, since it is through them that liquids and gases actively pass: water, oil and fluids, which play a key role in the formation of minerals. For a long time, scientists could not accurately mathematically describe the mechanism of formation of cracks in rocks and their subsequent crushing into smaller fragments. Traditionally, these processes have been explained using the principle of fractality, or self-similarity. According to this model, the development of cracks resembled the branching of a tree, where equally organized smaller branches successively branch off from each branch.
The researchers collected rock samples along a 160-kilometer section of the fault and analyzed them at different scales. At the microscopic level, scientists have studied the structure and nature of cracks in zircon minerals. This mineral is characterized by high hardness and practically does not break down by itself, however, it cracks during seismic deformations of the rock.
In addition, the experts examined thin transparent plates (slices) of rocks, rock outcrops and digital models of the relief of the area existing for this zone, on which cracks tens of kilometers long are discernible. This multi-level approach made it possible to trace the process of destruction and crushing of rocks from the formation of microscopic cracks in crystals to giant faults in the Earth's crust.
The researchers used neural networks to analyze thousands of images and mark out the boundaries and sizes of cracks in the rocks. The algorithm then identified closed areas bounded by these cracks, which the scientists considered as potential fragments into which the rock breaks up. After that, using mathematical statistics methods, the experts checked which theoretical law most accurately describes the size distribution of such fragments.
As a result, scientists have established that the destruction of rocks does not obey the classical principle of fractality. In particular, fragmentation produces significantly fewer small fragments than predicted by existing models. At the same time, the revealed pattern persisted at all scales studied, from microcracks in individual crystals to large fractures in rock massifs.
— Thus, we have shown for the first time that rocks at different scales of consideration — from micrometers to tens of kilometers — are destroyed according to a universal law, different from the previously assumed principle of fractality. Our proposed model will help to more accurately predict the behavior of faults and the occurrence of earthquakes, as well as the hydrological properties of rocks in mining sites," said Gevorg Kocharyan, Doctor of Physico—Mathematical Sciences, Professor, Chief Researcher at the Laboratory of Deformation Processes in the Earth's Crust at the Sadovsky Institute of Geospheric Dynamics of the Russian Academy of Sciences.
The prospect of a method for geological exploration and seismology
The kinetic model of rock fracture in fault zones proposed by the authors better corresponds to the physics of the process, where large blocks contain more defects and are destroyed more easily than small ones. This explains why significantly less dust forms in the fault zone than the classical fractal model suggests, Stanislav Makeev, associate professor of the Department of Deposit Geology and Exploration Methods at the Institute of Mining at Siberian Federal University, told Izvestia.
— From a practical point of view, the latter pattern indicates that a smaller proportion of seismic energy is spent on the formation of new free surfaces during the destruction of rocks than previously thought. And this fact must be taken into account for a more correct assessment of the energy balance in the rupture zones when forecasting earthquake foci. In the exploration of hydrocarbons, the revealed pattern can also be used to predict the filtration properties of rocks," the specialist said.
However, there is not enough evidence base and confirmation of patterns to definitively prove the existence of the new law, said Anatoly Makarov, Professor of the Department of Geology, Prospecting and Exploration of Mineral Deposits at Ural State Mining University, Doctor of Geological and Mineralogical Sciences.
— The universality of the stated principle is questionable, because cracks form as a result of different processes. In addition, scientists have studied the Baikal region, and this is a relatively young structure, so it is very important to take into account the differences in the geological positions of the territories. In the Urals, for example, the situation will be different," the expert emphasized.
According to him, the principle of rock destruction is not crucial for geological exploration. As for earthquakes, it is important to understand that they come in different types: not necessarily tectonic, but, for example, volcanic, avalanche, anthropogenic, and so on. It is not worth reducing all the causes to the process of crack formation, as this significantly limits our forecasting capabilities, the specialist added.
The proposed mathematical model can become the basis for creating artificial intelligence tools used in geology and seismology. The main problem with using AI to study natural patterns is the lack of data, Ilya Kopanichuk, PhD in Chemistry, senior researcher at the AIRI Institute, told Izvestia.
— Unlike the Internet with its already formed information flows, nature is reluctant to reveal its patterns. Field experiments are not always possible, and delivering samples to the laboratory is expensive and does not guarantee reproducibility of the results. Mathematical modeling solves this problem by acting as a synthetic data generator for physicists," the expert added.
The results of the study, supported by a grant from the Russian Science Foundation (RSF), are published in the journal Scientific Reports.
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