Earthquakes are relatively easy to explain, but quite difficult to predict. Even with new research based on observing the acceleration of tectonic plate sliding using GPS signals, seismologists cannot precisely predict the magnitude of tremor in a specific region.
Before starting to study the cause of an impending earthquake and trying to predict a catastrophe, it is necessary to consider its origin. The Earth’s surface consists of tectonic plates. They are located in the Earth’s crust and partially in the upper mantle of the planet. The Earth consists of 15 large and about 50 smaller tectonic plates. All of them are in constant motion, approaching and moving away from each other. But these movements are not smooth.
The plates collide, deform and accumulate energy up to a certain threshold value during movement. When the threshold is exceeded, the accumulated energy is released in the form of vibrations, which propagate in the Earth. Destructive earthquakes occur in the most fragile zones of the Earth’s crust – faults, which are the boundary between two tectonic plates.
Are there warning signs before an earthquake? It is known that the energy released in a 7.0 magnitude earthquake is about 900 times greater than the energy of the bomb dropped on Hiroshima. No doubt, a natural phenomenon of such force cannot occur without warning. Therefore, the main problem of modern seismology is not the search for signs of an impending cataclysm, but the ability to detect them.
Main signs of upcoming earthquakes
Seismologists distinguish several signs of earthquakes into separate groups. They are classified by:
- soil movement before an earthquake. Changes in topography, deformation of the ground can indicate an impending earthquake. The latest leveling instruments and GPS tools allow to measure changes in topography with high precision. Unfortunately, such changes cannot be considered an absolute sign of an impending earthquake. Soil movements can also occur for other reasons, such as heavy rainfall and increased groundwater level;
- seismic earthquake signals – shortly before the main event, the slowly deforming crust generates a small series of tremors that precede the main fault. They are accompanied by a rumbling or gurgling sound. These warning acoustic signals, recorded by seismometers, can be concentrated over an area of several kilometers and predict the rupture process;
- changes in the movement of gases and liquids underground. Microcracks, into which liquids penetrate, will form as the Earth’s crust deforms. Such infiltration can lead to disruptions of groundwater circulation and changes in well levels. The gas content of soil water can also vary. Shortly before the earthquake, some observers reported an elevated concentration of radon on the surface, a natural radioactive gas typically found deep underground. However, such a sign can indicate not only an upcoming earthquake, but also other processes occurring in the bowels of the Earth, such as the friction of rocks.
- large number of chaotic thermal, electrical and electromagnetic signals before an earthquake, both on the surface and in the atmosphere. Such signals are observed from satellites and infrared sensors. Thanks to them, animals change their behavior before an earthquake, becoming abnormally active and restless. Such deviations are observed not only before, but also for some time after earthquakes.
It should be noted that the observation of the latter category of changes is carried out not by seismologists, but by physicists. Some signs from this group (deviations in animal behavior before an earthquake) are not considered by seismologists as evidence. Their activity is focused on analyzing historical seismicity, monitoring crustal deformation, measuring changes in gravity and levels of radionuclides. However, as experience shows, earthquake prediction remains an active problem in geophysical research. Both traditional knowledge and innovative methods should be involved for successful prediction.