--- title: "Major discontinuity systems of Nepal Himalaya" subject: "Engineering Geology II" chapter: 2 key: "semester_4/engineering_geology_ii:nepal-discontinuity-systems" source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/nepal-discontinuity-systems site: BCT Engineering --- # Major discontinuity systems of Nepal Himalaya Engineering Geology II · Chapter 2: Engineering Geology in Himalayas - Asked in: 2081 Chaitra, 2 marks; 2079 Asoj, 1 marks; 2079 Jestha, 2 marks; 2078 Baisakh, 1 marks; 2078 Poush, 2 marks; 2077 Chaitra, 3 marks; 2076 Baisakh, 1 marks; 2073 Magh, 3 marks; 2071 Bhadra, 3 marks; 2070 Magh, 3 marks; 2069 Bhadra, 3 marks; 2069 Poush, 3 marks (asked 12 times) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/nepal-discontinuity-systems - Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-2 ## Question Outline the major discontinuity systems of the Nepal Himalaya and write their engineering significance. ## 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. ## Answer 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is the correct south-to-north order of the major thrusts? A. MCT, MBT, MFT B. MFT, MBT, MCT, STDS C. MBT, MFT, STDS, MCT D. STDS, MCT, MBT, MFT Answer: B. From south to north: MFT (Terai/Siwalik), MBT (Siwalik/Lesser), MCT (Lesser/Higher), STDS (Higher/Tethys). (Key point: Thrust order) 2. Which thrust is the youngest and active, between the Terai and Siwalik? A. MCT B. STDS C. MBT D. MFT Answer: D. The Main Frontal Thrust is the youngest active thrust with fault scarps. (Key point: MFT) 3. Why are thrust zones a problem for tunnels? A. They contain crushed, sheared weak rock causing collapse and squeezing B. They are made of massive strong granite C. They are completely dry D. They are very thin Answer: A. Crushed, sheared rock has low strength; thrust zones also bring large groundwater inflow. (Key point: Thrust zone behaviour) 4. What is a discontinuity? A. A plane of weakness with little or no tensile strength B. A perfectly cemented zone C. A type of soil D. A rock age boundary only Answer: A. Discontinuities such as joints, bedding, faults and thrusts have negligible tensile strength. 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