A severe earthquake of 7.8 magnitude hit south-eastern Turkey and Syria leading to a widespread destruction of property and huge loss of lives. The quake was followed by a 7.5 magnitude quake a few hours later, and so far nearly 300 aftershocks have followed significantly smaller than main shocker. Tremors were felt in Lebanon, Cyprus, and Greenland as well which is much far away. The epicentre of the quake was near the Turkish city of Gaziantep. As per the United States Geological Survey (USGS), three earthquakes with a magnitude of over 6 have occurred within 250 km of this location, since 1970. The quake hit Turkey on February 6, 2023.
Against this background, now let us have a look on some important aspects related to earthquakes.
Some of them are as follows:
General Causes with Reference to Turkey
The Earth’s crust consists of about 15 massive segmented separate slabs, called tectonic plates which are constantly in slow motion. However, these plates are prevented by the friction of rubbing up against an adjacent plate. When the friction is overcome by the stress on the edge, energy releases in the form of waves that travel through the Earth’s crust. Consequently, we feel shaking, called earthquake. On the basic of the geological makeup of region, earthquakes can be categorised into (i) tectonic; (ii) volcanic, (iii) collapse; and (iv) induced i.e.; caused by human activity.
Many times, the plates collide, push, and grate against each other. The meeting points of these plates are made up of a series of faults (fractures in the rocks).
One set of rocks rising up relative to the other is called a ‘normal’ fault, and one sliding down relative to the other is known as a ‘reverse’ fault.
As far the quakes in Turkey, they were from a strike slip, which is typical of the earthquakes in the region. In a strike slip earthquake, two tectonic plates move horizontally past each other, whereas in a regular earthquake, the movement of tectonic plates is vertical.
Turkey and Syria lie at the junction of four enormous tectonic plates, namely, the Arabian Plate, the Anatolian Plate, African Plate, and the Eurasian Plate. Turkey lies in complex plate tectonics, soft soil, and has uneven construction of quake-proof buildings which has made the region an extremely seismically active zone. The Arabian Plate has been inching north into Europe. This has been causing the Anatolian Plate to be pushed out west. Most parts of Turkey are on the Anatolian Plate, between the North Anatolian Fault and the East Anatolian Fault. According to geologists, rocks beneath the surface contained points of weakness, movements caused the rocks to deform, and when stress exceeded the strength of the rock, the rock fractured along the fault.
This region has many fault systems which cause many earthquakes. However, only those that result in a release of energy above a certain threshold are captured by seismological instruments. In the Turkey-Syria earthquakes, energy from nearly 300 years of accumulated strain was released. The 7.8 magnitude of the recent earthquake was much bigger than the ones the area has experienced before. The fault system runs along nearly 190 km which led to far-ranging earthquakes.
Another earthquake (7.5 magnitude) occurred further to the north on an adjacent fault system, called the Surgu Fault. The fault rupture was about 18 km below the Earth’s surface, which made the surface movements more intense.
According to the United States Geological Survey (USGS), since 1970, only three earthquakes of over 6 magnitude have happened within 250 km of this location.
The collapse of buildings has the main reason for the huge fatality in this earthquake. Another reason for deadly impact was that it occurred in the early hours, when people were in their houses. Besides, many buildings in the area were constructed of brittle concrete, making them extremely vulnerable to earthquake. Brittle concrete make buildings prone to cracking, spelling, steel corrosion, century old, made up poor quality material. Even those buildings which were constructed after the 1999 disaster do not conform to the safety standards. In Syria, particularly, the impact was made worse by the fact that 12 years of conflict had decimated building standards.
Measurement of Earthquakes
Earthquakes are measured on a scale, called the Richter scale, devised by Charles Francis Richter in 1935. It is a logarithmic scale, where each step-represents a ten-fold increase in magnitude. However, Richter scale is generally effective for regional earthquakes no greater than magnitude 5.
Therefore, scientists have developed a far-more sensitive seismometer, called Moment Magnitude scale (MW), which is more effective for large earthquakes using more variables to calculate the energy released, Seismic moment indicates what occurs during an earthquake, and defines how much force is needed to generate the recorded waves. The number attributed to an earthquake represents a combination of the distance the fault line has moved and the force that moved it.
Usually, tremors of 2.5 or less are not felt; however, could be detected by instruments. Earthquakes up to five are felt and might cause minor damages.
Other Major Earthquakes of the World
In 1960, the largest ever earthquake was registered with a 9.5 magnitude in Chile. It is only broadly true that the magnitude of earthquakes corresponds to death and devastation. The 1960 Earthquake was probably right around the upper limit for what the planet could generate as the chances of a much larger quake are low. Chile has a long history of devastating earthquakes (over 9), and is considered to be a model for earthquake preparedness.
In 1993, a 6.2 magnitude earthquake struck at Latur and Osmanabad, Maharashtra in which approximately 10,000 people died and more than 30,000 were injured. The quake is considered as the deadliest one in the stable continental crust to have ever occurred.
The Bhuj earthquake, that occurred on January 26, 2001 in Gujarat, had a magnitude of 6.9, killing more than 20,000 people. The tremors of the quake were felt in most of the parts of north-western India and in some parts of Pakistan.
In December 2004, a 9.1 magnitude earthquake had struck off the coast of Indonesia, leading to a tsunami, which swept away entire communities around the Indian Ocean.
In 2011, a 9 magnitude earthquake struck off the coast of Japan, and caused widespread damage on land and caused a tsunami. It also caused a major accident at the Fukushima nuclear plant along the coast.
On April 25, 2015 an earthquake of magnitude 7.8 struck near Kathmandu in Nepal, killing more than 9,000 people as well as destroying, several buildings and renowned structures, such as Darbar Square and Dharohar Tower. However, the famous Pashupatinath Temple remained unharmed.
Is India Prone to Such an Earthquake?
The Himalayas was created by the Indian Plate which was colliding into the Eurasian Plate and tilting upwards. So, the reverse faults are the most common type of earthquake in the Himalayan region. Whether it is a strike-slip or a thrust, the waves generated could be very powerful. Therefore, scientists have warned of a massive earthquake in the Garhwal-Kumaon Range.
According to scientists, India is not safe as the Indian Plate is driving into Asia at a rate of approximately 47 mm per year, sustaining the elevation of the Tibetan Plateau. It will deform the Himalaya, Altyn-Tagh, and Tien Shan mountains, and is expected to cause a steady, but unpredictable sequence of earthquakes in Asia and parts of India.
It is because of the constant pressure of the Eurasian Plate on the Indian Plate that strained energy, accumulating under it, has been releasing itself from time to time in the form of earthquakes. However, the release of strained energy or an earthquake cannot be predicted.
Over the past 150 years, four major earthquakes have been recorded in the Himalayan region, including the tremors in Shillong (in 1897), Kangra (in 1905), Bihar-Nepal (in 1934), and Assam (in 1950).
As per the Ministry of Science and Technology and Earth Sciences, a total of 59 per cent of the land mass of India is prone to earthquakes of different intensities considering the recorded history of earthquakes in India.
Seismic Zones in India
In India, the National Centre for Seismology, under the Ministry of Earth Sciences, is responsible for studying earthquake mechanisms and shifts in seismic activities. The seismologists have classified 59 per cent of India’s land mass as prone to earthquakes—Zone V, 11 per cent; Zone IV, 18 per cent; and Zone III, 30 per cent. The Centre has classified the total land mass in the country into four seismic zones (Zone II, Zone III, Zone IV, and Zone V) in accordance with the seismic zone map. Zone five is most fatal; zone four, zone three, and zone two are least fatal.
Zone five constitutes 11 per cent of the country including the entirety of entire north-eastern India, parts of Jammu and Kashmir, Himachal Pradesh, Uttaranchal, Rann of Kutch in Gujarat, parts of North Bihar, and Andaman and Nicobar Islands. About 18 per cent of Indian land falls in zone four including the remaining parts of Jammu and Kashmir and Himachal Pradesh, Union Territory of Delhi, Sikkim, northern parts of Uttar Pradesh, Bihar, and West Bengal, parts of Gujarat, small portions of Maharashtra near the west coast, and Rajasthan. Zone three comprises around 30 per cent and includes Kerala, Goa, Lakshadweep Islands, remaining parts of Uttar Pradesh, Gujarat, and West Bengal, parts of Punjab, Rajasthan, Madhya Pradesh, Bihar, Jharkhand, Chhattisgarh, Maharashtra, Orissa (now Odisha), Andhra Pradesh, Tamil Nadu, and Karnataka. Zone two, the least quake-prone zone, covers the remaining parts of the country.
India’s Preparedness and Earthquake-proof Building Policy
Government authorities have advised to follow certain guidelines while constructing buildings, houses, and other infrastructures. Also, there is a list of Indian standards that deal with earthquake-resistant construction. It sheds light on the design of structures, construction of buildings, improving earthquake resistance of earthen buildings, repair, and seismic strengthening of buildings. Densely populated zone five cities have to adhere to these guidelines in order to evade huge destruction and loss of lives in case of a massive earthquake.
An earthquake resistant building should have four virtues: (i) good structural configuration; (ii) lateral strength; (iii) adequate stiffness; and (iv) good ductility. All these features have been encapsulated in seismic codes, which are unique to a particular region or country. Presently, the Bureau of Indian Standards (BIS) has six codes. The regulations in these codes do not ensure that structures will suffer no damage at all. Rather, they will respond to earthquake shakings of moderate intensity to the extent possible to check total collapse.
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