How and why earthquakes occur and what are the most dangerous zones in Ukraine

Earthquakes are among the most deadly natural disasters on Earth. Dangerous tremors occur when huge amounts of energy are released from the Earth's crust in the form of seismic waves.

Ukraine's seismicity is manifested in the western, southwestern, and southern regions, where two main active regions stand out: Carpathian and Crimean-Black Sea. According to geologists, an average of 20 major earthquakes occur on our planet every year, Space.com reports.

What are earthquakes?

According to scientists, earthquakes are short-lived, sudden shaking of the Earth's crust caused by the movement of masses of rock in the Earth's interior. Seismic waves radiate outward from the source of the shock, known as the hypocenter, and can cause irreparable damage to infrastructure when they reach the surface. Indeed, during strong earthquakes, faults, landslides, and tsunamis often occur on the Earth's surface.

According to UNESCO, among all natural disasters, earthquakes rank first in the world in terms of economic damage and death toll.

Earthquakes are rated according to a 12-point scale. From 1 to 5 points - an earthquake is almost inaudible, from 5 to 7 - chandeliers swing on the upper floors of high-rise buildings, from 7 to 9 - cracks appear on the walls of buildings, from 9 to 12 - buildings collapse.

According to the US Geological Survey (USGS), approximately 20,000 earthquakes occur on Earth every year, or about 55 every day. Fortunately, most of them go unnoticed because they are too weak. As for the powerful ones with a magnitude of 7 or higher, there are up to 20 of them a year.

Despite the fact that there is a network of seismic observations around the world, earthquakes are very difficult to predict and impossible to prevent. Therefore, in areas prone to earthquakes, strict building codes have been adopted with seismic resistance in mind to prevent human casualties.

How earthquakes are formed

According to scientists, earthquakes are caused by volcanic eruptions, landslides, and even meteorite impacts, but the most common cause of earthquakes is the movement of tectonic plates.

Scientists explain that between the atmosphere above and the asthenosphere below (the upper layer of the Earth's mantle) lies the outer layer of the Earth - the lithosphere. This layer consists of plates that push against each other at the top of the asthenosphere. Temperatures in the asthenosphere range from 1300 to 1700 degrees Celsius, and the depth is from 100 km to 250 km below the Earth's surface.

The high temperatures cause the asthenosphere layer to have enough elasticity to "flow". This plastic layer can slowly flow down by thermal convection and help move magma and rocks through the Earth, contributing to the movement of tectonic plates.

When two slabs try to drive past each other, friction prevents them from sliding relatively easily, causing tension at the point of contact. Thus, the rock eventually slips, releasing huge amounts of energy in the form of waves that travel through the Earth's interior to the surface and cause the tremors we feel during an earthquake. The point on the Earth's surface that is directly above the center - or hypocenter - of an earthquake is known as the epicenter.

According to the USGS, earthquakes can occur anywhere from the Earth's surface to a depth of about 700 kilometers. They are common along the edges of plate boundaries and, according to the British Geological Survey, more than 80% occur at the edge of the Pacific Ocean, in an area known as the "Ring Of Fire."

However, some earthquakes can occur far from these boundaries, even in the middle of the plate. These are known as intraplate earthquakes. Although little is known about them, some scientists believe that they are the result of existing faults that formed in the Earth's crust in ancient times.

Seismicity in Ukraine

According to the World Data Center, there are two main seismic regions in Ukraine: Carpathian and Crimean-Black Sea.

The seismicity of the Carpathian region is determined by earthquakes with centers in Zakarpattia, the Carpathians, Prykarpattia, and in the adjacent territories of neighboring countries: Poland, Slovakia, Hungary, and Romania. Zakarpattia is the most seismically active region.

A large part of Ukraine is affected by subcortical earthquakes from the Vrancea zone in Romania. Due to their great depths and high magnitudes, earthquakes in the Vrancea zone are felt over a vast area: from Greece in the south to Finland in the north.

The seismicity of the Crimean-Black Sea region is determined by the epicenters of earthquakes located in the Black Sea, near the southern coast of Crimea, which are characterized by the highest magnitudes in Ukraine - up to 6.8.

The Danube Delta region can be considered a separate seismic area. In historical times, earthquakes with a maximum magnitude of about 7 have occurred here, which, together with the Vrancea zone earthquakes, pose a serious danger to the territory of Odesa region.

In the central part of Ukraine, in particular within the Ukrainian Shield, only a few earthquakes with shallow focal depths and low magnitudes have been recorded over the past century.

A national seismic observation network has been created in Ukraine, which includes 18 seismic and 14 complex geophysical stations.

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