mega earthquake : Nankai Trough

  Why in news ? Japan  has recently issued its first-ever ‘megaquake advisory’

What is mega earthquake ?

A mega earthquake is typically defined as a seismic event with a magnitude greater than 8. These are extremely rare occurrences, but when they do happen, they can cause catastrophic damage.

Megathrust Earthquakes:
Most mega earthquakes are actually megathrust earthquakes. These occur at subduction zones where one tectonic plate is forced beneath another. When the built-up pressure is released, it can cause immense shaking and displacement of the Earth’s crust.

megathrust earthquake:

Characteristics of Mega Earthquakes
Magnitude: Exceeds 8 on the Richter scale.
Location: Primarily at subduction zones.
Impact: Can cause widespread devastation, including tsunamis, landslides, and liquefaction.
Examples of Mega Earthquakes
Some of the most famous mega earthquakes include:

The 1960 Valdivia earthquake in Chile (magnitude 9.5)
The 1964 Alaska earthquake (magnitude 9.2)
The 2011 Tōhoku earthquake in Japan (magnitude 9.0)

The Nankai Trough is a significant geological feature located off the southern coast of Japan, known for its potential to generate powerful earthquakes and tsunamis. It is a submarine trench formed by the subduction of the Philippine Sea Plate beneath the Eurasian Plate.

Key Features of the Nankai Trough:

1. Location:
   • The Nankai Trough is situated along the Pacific coast of Japan, extending from the southern part of Honshu Island to Shikoku and Kyushu Islands. It is part of the larger Pacific Ring of Fire, known for its high seismic activity.
2. Tectonic Setting:
   • The trough is a result of the convergent boundary where the Philippine Sea Plate is being subducted beneath the Eurasian Plate. This tectonic interaction leads to the accumulation of stress in the Earth’s crust, which can be released in the form of earthquakes.
3. Seismic Activity:
   • The Nankai Trough is known for its history of producing large megathrust earthquakes, typically occurring in cycles of 100 to 150 years. These earthquakes are among the most powerful in the world and are often accompanied by significant tsunamis.
4. Historical Earthquakes:
   • Notable earthquakes associated with the Nankai Trough include the 1944 Tōnankai earthquake and the 1946 Nankaidō earthquake, both of which caused widespread damage and loss of life in Japan.
5. Tsunami Hazard:
   • Earthquakes originating from the Nankai Trough can generate tsunamis that pose a significant threat to coastal regions of Japan and beyond. These tsunamis can travel across the Pacific Ocean, affecting distant shores.
6. Future Risk:
   • There is ongoing concern about the potential for a future large-scale earthquake in the Nankai Trough, sometimes referred to as the “Nankai Trough Megathrust Earthquake.” Japanese government agencies and scientists are actively studying this region to better understand the risks and prepare for future events.
7. Preparedness and Mitigation:
   • Japan has implemented extensive earthquake and tsunami preparedness measures, including early warning systems, disaster drills, and infrastructure designed to withstand seismic events. However, the scale of potential disasters in the Nankai Trough region remains a significant concern.