An earthquake is a term used to describe the tremors and vibrations of the Earth’s surface. These tremors are the result of sudden natural displacements and ruptures in the Earth’s crust or mantle. Further, they are transmitted over long distances in the form of elastic vibrations. Earthquakes reflect the internal geological transformations undergone by the planet, caused by tectonic forces associated with temperature changes in the depths of the Earth.
An earthquake happens when two blocks of the earth’s layer are layered on top of each other. The Earth consists of four main layers – these are the inner and outer cores, as well as the mantle and crust, which make up the thin covering of the planet. The surface represented by the mantle and the crust is not static and is a constantly moving space of tectonic plates. Due to the fact that the edges of these plates are quite rough, these boundaries tend to cling to each other during the constant movement of the plates, causing a conflict in movement.
The friction formed between the edges prevents the displacement of earth rocks along the crustal fault, which leads to the accumulation of potential energy. Then the accumulated stress reaches its critical point, which becomes higher than the force of the initial friction. This leads to the release of accumulated energy – a sharp shift of rocks occurs, which causes vibrations of the Earth’s surface. When the energy contained in the process of friction is sloshed out, it spreads in all directions in the form of seismic waves (Scholz 357). Reaching the surface of the Earth, they shake the ground and everything on it, causing cataclysms of different levels of intensity.
The course of an earthquake can be divided into three stages. The primary precursor event is called a foreshock when there are minor but severe vibrations of the Earth’s surface (Scholz 192). Mainshock is the main terrestrial earthquake event, which accounts for the largest burst of energy. How often and for how long, and with what intensity post-cataclysmic fluctuations called aftershocks will occur in this main stage and its intensity?
The focus of an earthquake is the place where the tectonic plate breaks. The strength and duration of the shock that should occur in the future depends on the depth of the location of this gap. Tremors traditionally recorded only by seismographs are not felt by humans and are not dangerous since they are located at a depth of several hundred kilometers. However, in the event of a rupture a hundred kilometers deep, this forceful push can lead to tangible and even destructive consequences. The most dangerous place for an earthquake event is considered to be its epicenter, that is, the point where the greatest power of a seismic event is manifested. The location underground where an earthquake starts is called the hypocenter.
Regardless of what causes an earthquake and in what area it is centered, its duration will be approximately the same – on average, it lasts 20-30 seconds. But cases, when a single shock without repetitions could last up to three minutes are also possible. Signs of an approaching earthquake are the anxiety of animals, which quickly feel the slightest fluctuations in the surface of the Earth and try to get away from the location of the cataclysm. Other signs of an imminent earthquake are the appearance of characteristic elongated ribbon clouds, a change in the water level in wells, and malfunctions in electrical engineering and mobile communications. Often, earthquakes can be caused not only naturally but also by human actions. Events such as explosions of various spectrums of action, strength, and type of energy are unnatural causes of earthquakes. One more cause is the work of reservoirs, whose overcrowding can lead to tectonic shifts or work in mines that can collapse.
Earthquakes can be interpreted by professional monitoring of such natural currents as seismic activity, the water level in the ground, deformations, and movement of the Earth’s crust. However, a short-term fast forecast of seismic activity cannot be realized. Research in this area can only create accurate long-term forecasts with activity once in hundreds or thousands. The problem turns out to be the unpredictable natural parameters behind every upcoming earthquake. In preparation for a seismic event, a huge number of physical and chemical processes take place, where scientists need to clearly identify only those that will be an indicator of an upcoming earthquake. At the same time, for each territory with different geological conditions, these parameters can vary greatly.
The strength of an earthquake is measured by two parameters, the size of the fault and the size of the displacement along the fault. Geologists measure the strength of an earthquake, and its impact, also called magnitude, through a special apparatus called a seismograph. The records made on this instrument are called seismograms, and by their appearance, it is possible to characterize the cataclysm that has occurred. A short and hardly oscillating line would mean a moderate earthquake. A long and strongly fluctuating line means a strong earthquake. If the faults are large, this will be reflected in the length of the line, while the size of the wiggle recorded on the seismogram is determined by the displacement force along the fault. The magnitude of each earthquake is individual and means the energy released during a seismic event. For each earthquake, the magnitude is measured on the Richter scale from zero, where zero means the minimum millimeter fluctuation per kilometer.
The second scale for measuring an earthquake is the Mercalli scale, also known as the intensity scale. It indicates the nature and strength of the impact of the phenomenon on the surface of the Earth, but also on people, animals, and structures in the area of the event. It is based on external rather than internal signs and is calculated on a parameter from 1 to 12, indicating the degree of damage to the environment and landscape. One on this scale – activity is not noticed by people, 12 – complete destruction, violation of the horizon line, the release of individual objects into the air.
For most of human history, people have tended to believe that the origin of earthquakes has to do with divine mythological forces. However, since the 19th century, associations began to appear, looking for a more pragmatic interpretation of this phenomenon. The dynamics of earthquakes are still being studied, and developments in this direction are valuable both for geologists and geodesists, and architectural planners. This seismic activity is considered to be the result of fractured tectonics, manifesting itself sharply and briefly but with dynamic persistence.
Work Cited
Scholz, Christopher H. The Mechanics of Earthquakes and Faulting. Cambridge University Press, 2019.