Why Is Turkiye So Prone To Earthquakes? What Made The Recent One So Devastating? Here's What An Expert Says
Turkey Earthquake: It is unique not only because of its huge magnitude, but also because the events occurred within the East Anatolian fault system, where major earthquakes had not occurred earlier.
Turkey Earthquake: A devastating earthquake of magnitude 7.8 struck Turkey on Monday, February 6, 2023, at around 4:15 am TRT (Turkey Time). The earthquake hit south central Turkey near the Turkey/Syria border, and just 11 minutes later, was followed by an aftershock of magnitude 6.7. More than 300 aftershocks shook Turkey, the largest of which was a magnitude 7.5 aftershock.
The catastrophic earthquake which struck Turkey is unique not only because of its huge magnitude, but also because the events leading up to it occurred within the East Anatolian fault system, where major earthquakes have not occurred in the past, according to the United States Geological Survey (USGS).
Earlier, most of the major earthquakes in Turkey occurred along the North Anatolian fault system. The surface where two blocks of Earth suddenly collide with each other in the case of an earthquake is called the fault or fault plane.
The science behind earthquakes
Sudden movement along faults within the Earth causes earthquakes due to the release of stored-up 'elastic strain' energy in the form of seismic waves. Elastic strain energy refers to the energy stored in a structure due to its elastic deformation. The elastic strain energy released in the form of seismic waves propagates through the Earth and causes the ground to shake.
According to the British Geological Survey, such movement on the faults or fault lines is generally a response to long-term deformation and the buildup of stress.
The location below the Earth's surface where an earthquake begins is called the hypocentre, while the location directly above it on the surface of the Earth is called the epicentre.
What are tectonic plates?
The Earth consists of four major layers, namely the inner core, outer core, mantle and crust, and the crust and the top of the mantle make up a thin skin on the surface of Earth.
The Earth's outermost layer, also called the lithosphere, is composed of the crust (continental and oceanic), and the upper part of the mantle, and is fragmented into about 15 major slabs called tectonic plates.
Tectonic plates form the lithosphere, and move very slowly relative to each other, typically a few centimetres each year. These movements result in a huge amount of deformation at the edges of tectonic plates, called plate boundaries, and this, in turn, leads to earthquakes.
What causes earthquakes?
Most of the earthquakes around the world occur on faults, which the plate boundaries are made up of. When the plates move against each other, the edges get stuck because they are rough. After the plate has moved far enough, the edges unstick on one of the faults. This is what results in an earthquake.
The Earth shakes when there is an earthquake due to the release of stored-up energy. The energy that would normally cause the blocks to slide past one another is stored up when the edges of faults get stuck together, and the rest of the block is moving. Once the force of the moving blocks overcomes the friction of the jagged edges of the faults, and the block unsticks, the entire stored up energy is released, and radiated outward from the fault in all directions in the form of seismic waves like ripples on a pond.
As the seismic waves move through Earth, they shake it, and when they reach the surface, they shake the ground and everything on it.
What are the different types of faults?
There are three basic types of fault, namely, normal fault, reverse fault and strike-slip fault. A particular plate boundary can have more than one type of fault.
When the block above the fault moves down relative to the block below the fault, it is called a normal fault.
A reverse fault is one in which the block above the fault moves up relative to the block below the fault.
A strike-slip fault is one in which the movement of blocks along a fault is horizontal.
Turkey's devastating earthquake on Monday occurred along long, plate-boundary strike-slip faults.
The rock on one side of the fault suddenly slips with respect to the other, when an earthquake takes place. The fault surface can be horizontal, vertical, or have an arbitrary angle in between.
The angle of the fault with respect to the surface is known as the dip. Faults are classified based on the dip and the direction of slip along the fault.
Strike-slip faults, in which the movement of blocks is horizontal, are classified as either right-lateral or left-lateral.
Why is Turkey so vulnerable to earthquakes?
All the tremors jolting Turkey are taking place within the East Anatolian fault system. In the vicinity of the East Anatolian fault system is a triple junction, which is a tectonically active area. Three tectonic plates, namely the African Plate, Arabian Plate and Eurasian Plate, touch and interact with each other, and also with the Anatolian Plate, which lies in the centre.
The Anatolian Plate is situated in Turkey and forms part of a complex and active system of tectonic activity in the region with its surrounding plates. The Anatolian Plate shares a boundary with the Eurasian Plate, African Plate and Arabian Plate.
The North Anatolian fault system, which is the east-west continental transform fault situated in northern Turkey, separating the Eurasian Plate and the Anatolian Plate, produces persistent earthquake activity along the fault. While most of the destructive earthquakes in Turkey have occurred along the North Anatolian fault system, this time, the quake occurred along the East Anatolian fault system.
The mainshock which occurred in Turkey was 18 kilometres deep.
“Turkey has a very interesting geological setting. Inside Turkey, there is an intersection of three tectonic plates. Movements of tectonic plates cause major earthquakes all around the world. Turkey is located on the centre point of three plates – African Plate, Arabian Plate and Eurasian Plate. Turkey is resting on a plate called the Anatolian Plate. In the case of an earthquake, the Anatolian Plate moves anticlockwise and turns towards the Eurasian Plate, which covers most of Europe. As a result, the Arabian Plate also gets a push. It is similar to three balls surrounding another ball. All these balls are trying to push each other in the form of an anticlockwise movement. Whenever the push goes beyond a certain level, an earthquake occurs,” Professor Subhadeep Banerjee, Geotechnical Engineering Division, Department of Civil Engineering, Indian Institute of Technology (IIT) Madras, told ABP Live via call.
Professor Banerjee explained that Turkey serves as the epicentre for most of the major earthquakes in the Eurasian region, except the Himalayan areas. “Most of the major earthquakes in the Eurasian region, apart from the Himalayan areas, are concentrated in Turkey,” he said.
“There are two major faults along which most of the severe earthquakes occurred in Turkey. These fault lines are located along Turkey’s boundary. One of the fault lines is located on the northern side, and is known as the North Anatolian Fault. It is very long, and extends from the Asian side of Turkey to the European side of the country,” Professor Banerjee added.
The other fault line is small, but it is the one which resulted in the devastating earthquake in Turkey on February 6, 2023. It is known as the East Anatolian Fault. This is like a border between Turkey and Syria.
“Precisely, the tectonic activities in this region of Turkey are very strong because three tectonic plates interact with a common tectonic plate, the Anatolian Plate. When these plates collide with each other, an earthquake occurs,” Professor Banerjee explained.
Professor Banerjee compared the tectonic plates to saucers placed side by side. He said that there will always be friction along the edges of saucers placed side by side.
“Unfortunately, in Turkey, several tectonic plates are interacting with each other. One of the saucers is the Anatolian Plate. Adjacent to the Anatolian Plate, the Arabian Plate, Eurasian Plate and African Plate are located. All the four plates are mutually moving with respect to each other,” he added.
The Anatolian Plate is located at the centre, the African Plate is located to the south of the Anatolian Plate, the Arabian Plate is located to the east, and the Eurasian Plate is located to the north.
“Earthquakes happen along the fault. Fault is nothing but the joint between two plates. It is the interface between two tectonic plates. Together, the faults constitute the Anatolian Fault Region,” Professor Banerjee said.
What results in such a huge earthquake?
Sometimes a large movement, say, a few 100 millimetres, can result in a major earthquake, Professor Banerjee said. At other times, even a small movement between tectonic plates can result in a severe earthquake.
He also said that an earthquake of the level which occurred in Turkey this week requires a significant amount of fault movement.
“The severity of an earthquake does not only depend on the amount of fault movement, but on several other factors,” Professor Banerjee said.
Why was the recent earthquake in Turkey so devastating?
Professor Banerjee explained that some parts of the fault have already been fractured by previous earthquakes. “The part of the fault which has not been fractured has the tendency to cause bigger earthquakes,” he said.
The northern part of Turkey usually had major earthquakes in the past. On August 17, 1999, a catastrophic earthquake struck Turkey.
“The eastern border of Turkey also had some earthquakes, but these were not as major as the ones which occurred in the northern part. Therefore, there was always a probability of a huge earthquake occurring in the eastern border of Turkey. This is because, if there is a fault, it will ultimately fracture, sooner or later. So, there was always a chance of an earthquake of this magnitude occurring along Turkey’s eastern border,” Professor Banerjee explained.
He further said that the magnitude of an earthquake also depends on the ground conditions of a particular region. Ground conditions and the type of landscape can determine the severity of an earthquake.
“Hilly regions and areas with soft soil amplify the damage caused by earthquakes. The ground conditions are suitable for earthquakes to cause serious damage in Turkey. Hence, the ground conditions amplify the effect of earthquakes,” Professor Banerjee said.
He concluded that the earthquake that occurred in Turkey this week was deep, and the ground conditions were suitable for a huge damage.
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