Japan issues its first-ever Megaquake Warning-Nankai Trough Zone

Context: Japan’s meteorological agency issued its first-ever Megaquake advisory.

Nankai Trough Zone

• It is a 900 km long underwater subduction zone where the Eurasian Plate collides with the Philippines sea plate pushing the latter under the former and into the Earth’s mantle.
• It lies in the Pacific Ocean
• Location: It runs from Shizuoka, west of Tokyo, to the southern tip of Kyushu Island.

Basics of Earthquake

• An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth‘s lithosphere that creates seismic waves.
• It may be due to faulting, folding, plate movement, volcanic eruptions and anthropogenic factors like dams and reservoirs.
• The point within Earth where faulting begins is the focus or hypocenter.
• The point directly above the focus on the surface is the
  • The intensity of the earthquake is highest at the epicentre and decreases with distance from the epicentre.
• Richter scale is the scale to measure the magnitude of energy released by an earthquake.
  • The number indicating magnitude ranges between 0 to 9
• Mercalli scale is a seismic scale used to measure the intensity of an earthquake.
  • The number indicating intensity ranges between 1 to 12.

Seismic Waves

• Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth.
• They are the energy that travels through the earth and is recorded on seismographs.
• The two main types of waves are body waves and surface waves.

Body Waves

• Primary waves ( P-waves): These are the fastest seismic waves that can move through gaseous, solid rock and fluids, like water or the liquid layers of the earth. They are Longitudinal Waves.
• Secondary waves ( S-waves):
  • It can only move through solid rock.
  • S-waves arrive at the surface with some time Lag.
  • These are Transverse waves.

Surface Waves

• Love Waves (L-waves)
• Rayleigh waves

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