The Main Himalayan Thrust (MHT) is a décollement under the Himalaya Range . This thrust fault follows a NW-SE strike , reminiscent of an arc, and gently dips about 10 degrees towards the north, beneath the region. It is the largest active continental megathrust fault in the world.
15-515: The MHT accommodates crustal shortening of India and Eurasia as a result of the ongoing collision between the Indian and Eurasian plates. The MHT absorbs around 20mm/yr of slip, nearly half of the total convergence rate. This slip can be released from small scale earthquakes and some plastic deformation, but the MHT still accumulates a deficit of moment of 6.6*10^19 Nm/yr. The MHT also remains locked with
30-421: A convergent boundary which occurs with shallow thrust faults that only involves cover rocks (typically sedimentary rocks ), and not deeper basement rocks . The thin-skinned style of deformation is typical of many fold and thrust belts developed in the foreland of a collisional zone or back arc of a continental volcanic arc . This is particularly the case where a good basal decollement exists, usually in
45-773: A return period of over 1000 years in this region. Deformation of the crust is also accommodated along splay structures including the Main Frontal Thrust (MFT), Main Boundary Thrust (MBT), Main Central Thrust (MCT) and possibly the South Tibetan Detachment . The MHT is the root detachment of these splays. At this present moment, the MFT and MHT accounts for almost the entire rate of convergence (15-21 mm/yr). This fault defines where
60-640: A right stepping bend on a sinistral (left-lateral) fault, this will cause local shortening or transpression . Examples include the 'Big Bend' region of the San Andreas Fault , and parts of the Dead Sea Transform . Passive margins are characterised by large prisms of sedimentary material deposited since the original break-up of a continent associated with formation of a new spreading centre . This wedge of material will tend to spread under gravity and, where an effective detachment layer
75-605: A weaker layer like a shale , evaporite , or a zone of high pore fluid pressure. This was first described in Rocky Mountains of the United States , as part of the Sevier Orogeny . In the rock record, this will increase the influence of more surficial rocks, which usually includes sedimentary rocks . Typically, repeated sections of the same rock are seen over and over as thrust faults, coming up from
90-514: A zone of high pore fluid pressure. Thick-skinned deformation refers to shortening that involves basement rocks rather than just the overlying cover. This type of geometry is typically found in the hinterland of a collisional zone. This style may also occur in the foreland where no effective decollement surface is present or where pre-existing extensional rift structures may be inverted . The most significant areas of thrust tectonics are associated with destructive plate boundaries leading to
105-416: Is important as attempts to structurally restore the deformation will give very different results depending on the assumed geometry. Thin-skinned deformation refers to shortening that only involves the sedimentary cover. This style is typical of many fold and thrust belts developed in the foreland of a collisional zone. This is particularly the case where a good basal decollement exists such as salt or
120-531: Is present such as salt , the extensional faulting that forms at the landward side will be balanced at the front of the wedge by a series of toe-thrusts . Examples include the outboard part of the Niger delta (with an overpressured mudstone detachment) and the Angola margin (with a salt detachment ). Thin-skinned deformation Thin-skinned deformation is a style of deformation in plate tectonics at
135-590: The India subcontinent is underthrust beneath the Himalayan orogenic wedge. The 'MHT' is a known hazard and potential source for large earthquakes of magnitude 9.0 or greater. The MHT is also associated with other large 20th century earthquakes in 1950 (M w 8.7) and 1934 (M w 8.4). Within the last thousand years, multiple earthquakes have occurred with magnitudes of at least M w 8.0, as deduced by paleosesmology. Michel et al. (2021) suggested
150-534: The formation of orogenic belts . The two main types are: the collision of two continental tectonic plates (for example the Arabian plate and Eurasian plate , which formed the Zagros fold and thrust belt ) and collisions between a continent and an island arc such as that which formed Taiwan . When a strike-slip fault is offset along strike such that the resulting bend in the fault hinders easy movement, e.g.
165-502: The maximum magnitude possible on the MHT to be M w 8.7 with a recurrence interval of 200 years. In April 2015 , a section of the MHT produced a blind rupture earthquake, killing nearly 9,000 people. Researchers who published their findings in Nature Geoscience revealed that the M w 7.8 earthquake failed to rupture towards the surface, with the possibility of future large earthquakes. They said that since
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#1732766018205180-455: The overlying Eurasian plate from its surface expression to the front of the higher Himalayas, nearly 100km. This locking mechanism combined with the rapid accumulation of deficit of moment are concerning as some professionals estimate that earthquakes up to the size of 8.9 on the Richter scale could be in order for regions such as western Nepal. Earthquakes of this magnitude are estimated to have
195-527: The rupture ceased 11 km (6.8 mi) beneath the Kathmandu region , a shallow section of the MHT, south of Kathmandu, remains unruptured. The shallow section remains locked and could produce an earthquake of comparable size. The research lead, J. R. Elliott, says such an earthquake could be more devastating because of its shallowness. The Main Himalayan Thrust and its splay branches has been
210-445: The source of numerous earthquakes, including some that are indirectly related. Thrust tectonics Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere . It is one of the three main types of tectonic regime, the others being extensional tectonics and strike-slip tectonics . These match
225-632: The three types of plate boundary , convergent (thrust), divergent (extensional) and transform (strike-slip). There are two main types of thrust tectonics, thin-skinned and thick-skinned, depending on whether or not basement rocks are involved in the deformation. The principle geological environments where thrust tectonics is observed are zones of continental collision , restraining bends on strike-slip faults and as part of detached fault systems on some passive margins . In areas of thrust tectonics, two main processes are recognized: thin-skinned deformation and thick-skinned deformation . The distinction
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