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Supershear earthquake

Supershear earthquake

What in news about Supershear earthquake ?

  • The study published in Nature Geoscience has declared that the Palu earthquake was a “Supershear” earthquake. Moreover , in 2018, 7.5 magnitude earthquake struck the Palu region of the Indonesia.
  • Besides, The powerful quake triggered a tsunami and left thousands of people killed. Now, five months after the devastation, scientists have found the reasons that made the earthquake dangerous.
  • The 2018 Palu earthquake was a rare seismologic event of very fast character, and this character gave it the power of massive destruction.
  • Till now, fewer than 15 of this kind of superfast and extra-powerful earthquakes have been identified.

How Does an Earthquake Occur?

  • One of the ways an earthquake occurs is by a sudden slip on a fault. In geological terms, a fault is a fracture or discontinuity that exists in a large volume rock. The plate tectonic forces cause large faults to occur within the earth’s crust.
  • Earthquakes generally occur on faults.
  • Moreover, Geological faults can be a few centimeters to thousands of kilometers long. The sudden slip on a fault during an earthquake in turn causes rupture or cracks that can propagate along the fault

About Supershear earthquake

  • In the case of a supershear earthquake, the rupture moves along the fault extremely rapidly resulting in massive intensification of the seismic shear waves.
  • Moreover, The seismic shear waves are the up and down or side to side waves that shake the ground.
  • It occurs in strike-slip fault

About Palu Earthquake scenario :

  • The Palu earthquake occurred on a strike slip fault- a fault in which rock strata are displaced mainly in a horizontal direction, parallel to the line of the fault.
  • The rupture travelled some 150 kilometers within just 35 seconds of its beginning, which is extraordinary.
  • Earthquake ruptures typically spread on a fault at a uniform rate of about 3 kilometers per second, which is below the earthquake’s damaging shear waves.
  • However, These waves originate from the tip of the rupture.
  • The speed limit of the rupture propagation is posed by geological factors. The point of rupture consumes energy and the rupture propagation becomes weaker in velocity.
  • Whereas most of the earthquakes fall under this rule, scientists have found out examples that could violate this.
  • The 1999 earthquakes in Turkey was the first time that these kinds of exceptional quakes were noticed for the first time.
  • The Palu quake also broke that rule. They found that the fault had big kinks rather than a straight runway.
  • The rupture went supershear that travelled more than a kilometer per second faster than a typical earthquake.
  • The supershear character of Palu’s earthquake made the fast moving rupture overtake the slower shear waves moving in front of it and combined these two waves together to a massive wave.

Background :

Terms associated with earthquakes

Focus

  • The place of origin of an earthquake inside the earth.

Epicenter

  • Point on the earth’s surface vertically above the focus.
  • Maximum damage is caused at the epicenter.

Wave Velocity

  • 5 to 8 km per second through the outer part of the crust but travel faster with depth.

Isoseismic Line

  • A line connecting all points on the surface of the earth where the intensity is the same.

 

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