Turkey hit by series of powerful earthquakes

What’s in today’s article?

• Why in news?
• What is an earthquake?
• What exactly causes earthquakes?
• How are earthquakes measured?
• News Summary: Turkey hit by series of powerful earthquakes
• What caused this earthquake?
• Why Turkey is a hotbed of Seismic activity?

 

Why in news?

• More than 2,000 people have been killed and thousands injured by a huge earthquake which struck south-eastern Turkey, near the Syrian border.
• The earthquake, which hit near the town of Gaziantep, was closely followed by numerous aftershocks - including one quake which was almost as large as the first.

 

What is an earthquake?

• An earthquake is an intense shaking of the ground caused by movement under the earth’s surface. 
• It happens when two blocks of the earth suddenly slip past one another. 
• This releases stored-up ‘elastic strain’ energy in the form of seismic waves, which spreads through the earth and cause the shaking of the ground.
• The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicentre.

 

What exactly causes earthquakes?

• The earth’s outermost surface, crust, is fragmented into tectonic plates. The edges of the plates are called plate boundaries, which are made up of faults. 
  • World’s major tectonic plates are shown below:

  • 

Image caption: World's Major Tectonic Plates

 

• The tectonic plates constantly move at a slow pace, sliding past one another and bumping into each other. 
• As the edges of the plates are quite rough, they get stuck with one another while the rest of the plate keeps moving. 
• Earthquake occurs when the plate has moved far enough and the edges unstick on one of the faults.

 

How are earthquakes measured?

• They are measured on a scale called the Moment Magnitude Scale (Mw). 
  • This has replaced the Richter scale, now considered outdated and less accurate.
• The number attributed to an earthquake represents a combination of the distance the fault line has moved and the force that moved it.
  • A tremor of 2.5 or less usually cannot be felt, but can be detected by instruments. 
  • Quakes of up to five are felt and cause minor damage. 
  • The Turkish earthquake at 7.8 is classified as major and usually causes serious damage, as it has in this instance.
  • Anything above 8 causes catastrophic damage and can totally destroy communities at its centre.

 

News Summary: Turkey hit by series of powerful earthquakes

• Turkey was hit by three consecutive devastating earthquakes of magnitude 7.8, 7.6 & 6.0 yesterday.

What caused this earthquake?

 

Image Caption: Fault lines around Turkey and Syria

• The region where the earthquake has struck lies along a well-known seismic fault line called the Anatolia tectonic block.
• It is a seismically active zone — though not as active as, say, the Himalayan region.
  • The seismicity in this region is a result of interactions between the African, Eurasian, and Arabian plates.
  • In the present case, it was the Arabian plate moving northwards and grinding against the Anatolian plate.
• Also, the present earthquakes emerged from relatively shallow depths which made them devastating.
  • Shallow earthquakes are generally more devastating because they carry greater energy when they emerge on the surface.

 

Why Turkey is a hotbed of Seismic activity?

• In the eastern Mediterranean region comprising Turkey, Syria and Jordan, tectonics are dominated by complex interactions between the African, Arabian, and Eurasian tectonic plates, and the Anatolian tectonic block.
• Dominant structures here are:
  • Red Sea Rift, the spreading centre between the African and Arabian plates; 
  • Dead Sea Transform, a major strike-slip fault (explained in the diagram below) that also accommodates Africa-Arabia relative motions; 

Image caption: Earthquake cause by strike-slip fault

 

• North Anatolia Fault, a right-lateral strike-slip structure in northern Turkey accommodating much of the translational motion of the Anatolia block westwards with respect to Eurasia and Africa; 
• Cyprian Arc, a convergent boundary between the Africa plate and the Anatolia block.

 

---

Q1) Can earthquakes be predicted?

No. An accurate prediction of an earthquake requires some sort of a precursory signal from within the earth that indicates a big quake is on the way. Moreover, the signal must occur only before large earthquakes so that it doesn’t indicate every small movement within the earth’s surface. Currently, there is no equipment to find such precursors, even if they exist.

 

Q2) What is the Moment Magnitude Scale??

The moment magnitude scale is based on the total moment release of the earthquake. Moment is a product of the distance a fault moved and the force required to move it. It is derived from modeling recordings of the earthquake at multiple stations.

 

---

Source: Turkey hit by series of powerful earthquakes: The science behind it  |  BBC  |  Indian Express