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Major discontinuity systems of Nepal Himalaya
Short answer
Major discontinuity systems in the Nepal Himalaya are the MFT, MBT, MCT, STDS, and ITSZ. They contain weak sheared rock, cause landslides and earthquakes, act as groundwater conduits, and critically influence slope and tunnel stability.
Outline the major discontinuity systems of the Nepal Himalaya and write their engineering significance.
A discontinuity is a plane of break or weakness in a rock mass that has little or no tensile strength, such as bedding, joint, foliation, fault, thrust or shear zone.
In the Nepal Himalaya, the major discontinuities are large-scale tectonic thrusts that separate the five tectonic zones from south to north.
Major discontinuity systems
| Discontinuity | Position | Description |
|---|---|---|
| Main Frontal Thrust (MFT) | Between Terai and Siwalik | Youngest and active thrust; seismically active, with fault scarps |
| Main Boundary Thrust (MBT) | Between Siwalik and Lesser Himalaya | Zone of crushed, sheared rocks, many landslides |
| Main Central Thrust (MCT) | Between Lesser and Higher Himalaya | Wide zone of high-grade metamorphic rocks and shearing; strong tectonic activity |
| South Tibetan Detachment System (STDS) | Between Higher and Tethys Himalaya | Low-angle normal fault zone |
| Indus-Tsangpo Suture Zone (ITSZ) | North of the Tethys Himalaya, in Tibet | Suture (collision boundary) between the Indian and Eurasian plates |
Other local discontinuities: bedding planes, foliation, joints and faults within each zone.
Engineering significance
- Thrust zones contain crushed, sheared and weak rock with low strength; they cause tunnel collapse and squeezing.
- They are conduits for groundwater, giving large inflows in tunnels and seepage at dams.
- They control landslides and slope failures; many big slides lie along MBT and MCT.
- Active thrusts (MFT, MBT) are sources of earthquakes; structures must be kept away or designed for fault movement.
- Discontinuity orientation relative to a slope or tunnel axis decides wedge and planar failures, overbreak and support requirement.
- Detailed mapping of discontinuities is required in site selection of dams, tunnels and roads.
✓ Answer checked by Claude Opus 5.5 (high effort)
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