Highlights the major discontinuity system of Nepal Himalaya and their engineering significance. [2069 Bhadra] [3]

The Nepal Himalaya was formed by the collision of two continental plates: the Tibetan plate and the Indian Plate. It is believed that Indian plate is going down while Eurasian plate (i.e, Tibetan plate is rising over the Indian plate).This action has generated the following major discontinuities parallel to the Nepal himalaya :

• Main Central Thrust (MCT)
• Main Boundary thrust (MBT)
• Main Frontal Thrust (MFT)

This is the tectonic contact between the Higher Himalayas and Lesser Himalayas. The MCT was active during the early phases of Himalayan orogeny but it is now considered to be less active than main boundary thrust (MBT).

It is a north dipping thrust fault.

This is the active tectonic contact between the Lesser Himalayas and Siwaliks. The MBT has been the source of very large earthquakes in the past. It is seismically most active thrust.

It is a steep north dipping ....

The Nepal Himalaya was formed by the collision of two continental plates: the Tibetan plate and the Indian Plate. It is believed that Indian plate is going down while Eurasian plate (i.e, Tibetan plate is rising over the Indian plate).This action has generated the following major discontinuities parallel to the Nepal himalaya :

• Main Central Thrust (MCT)
• Main Boundary thrust (MBT)
• Main Frontal Thrust (MFT)

Main Central Thrust (MCT):

This is the tectonic contact between the Higher Himalayas and Lesser Himalayas. The MCT was active during the early phases of Himalayan orogeny but it is now considered to be less active than main boundary thrust (MBT).

It is a north dipping thrust fault.

 Main Boundary thrust (MBT):

This is the active tectonic contact between the Lesser Himalayas and Siwaliks. The MBT has been the source of very large earthquakes in the past. It is seismically most active thrust.

It is a steep north dipping fault.

Main Frontal Thrust (MFT) or Himalayan Frontal Thrust (HFT):

This is the tectonic features located at the boundary of Lesser Himalayas and the Terai. This fault is also considered active.

It is a also a north dipping fault.

Engineering Significances of Discontinuities:

• The thrust zones are weak, porous, unstable and incompetent and hence most undesirable geological features that endanger the stability of engineering structures and also creates leakage problems.
• an active thrust occurring close to an engineering sites is vulnerable to earthquake and as such sites should be avoided from construction of any heavy strucyures.
•  Thrust influences the movement of surface water , also causes  the sudden change in the courses of rivers may be due to thrusting.
• These thrust zones are prone to landslides, rockfalls, debris flows, earth flows, mudflows etc.