The Main Himalayan Thrust (MHT) is a

décollement Décollement () is a gliding plane between two rock masses, also known as a basal detachment fault. Décollements are a Deformation (geology), deformational structure, resulting in independent styles of deformation in the rocks above and below t ...

under the Himalaya Range. This

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...

fault follows a northwest-southeast 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.

Overview

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 . The MHT also remains locked with the overlying Eurasian plate from its surface expression to the front of the higher Himalayas, nearly 100 kilometres away. 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 The Richter scale (), also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale, is a measure of the strength of earthquakes, developed by Charles Richter in collaboration with Beno Gutenberg, and pr ...

could be in order for regions such as western Nepal. Earthquakes of this magnitude are estimated to have 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 South Tibetan Detachment is one of the major Fault (geology), faults in the Himalaya Mountains. Background Understanding the formation of the Himalayan mountains has been a goal of structural geologists for a long time. Many of the problems an ...

. The MHT is the root detachment of these splays. Currently, the MFT and MHT accounts for almost the entire rate of

convergence Convergence may refer to: Arts and media Literature *''Convergence'' (book series), edited by Ruth Nanda Anshen *Convergence (comics), "Convergence" (comics), two separate story lines published by DC Comics: **A four-part crossover storyline that ...

(15–21 mm/yr). This fault defines where the Indian subcontinent is underthrust beneath the Himalayan orogenic wedge.

Seismic hazard

The MHT is a known hazard and potential source for large earthquakes of magnitude 8.0 or greater. The MHT is also associated with other large 20th-century earthquakes in 1950 ( 8.7) and 1934 ( 8.0). Within the last thousand years, multiple earthquakes have occurred with magnitudes of at least 8.0, as deduced by paleoseismology. ''Michel et al.'' (2021) suggested the maximum magnitude possible on the MHT to be 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 7.8 earthquake failed to rupture towards the surface, with the possibility of future large earthquakes. They said that since the rupture ceased 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.

Associated seismicity

The Main Himalayan Thrust and its splay branches has been the source of numerous earthquakes, including some that are indirectly related. {, class="wikitable" , + !Date !Country !Magnitude !Depth (km) ! MMI !Deaths !Comments !Source , - , 1255-06-07 , Nepal , 8.0+ , - , , , Rupture length uncertain but possibly in the hundreds of kilometers. Killed one-third of Nepal's population. , , - , 1344-09-14 , Nepal , , - , , , , , - , 1408 , Nepal , , - , , , , , - , 1505-06-06 , Nepal, India and China , 8.2–8.8 , - , , , Killed 30% of the Nepalese population. , , - , 1680 , Nepal , <7.5 , - , , , , , - , 1714-05-4 , Bhutan , 7.6–8.6 , - , IX , "Many" , Ruptured the whole Bhutan section of the Main Frontal Thrust. , , - , 1803-09-01 , India , 7.8–7.9 , - , IX , 300 , Damage as far as

New Delhi New Delhi (; ) is the Capital city, capital of India and a part of the Delhi, National Capital Territory of Delhi (NCT). New Delhi is the seat of all three branches of the Government of India, hosting the Rashtrapati Bhavan, New Parliament ...

. , , - , 1833-08-26 , Nepal , 7.5–7.9 , - , IX , 500 , Severely damaged Kathmandu and was felt as far as Calcutta. , , - , 1905-04-04 , India , 7.9 , - , X , 20,000+ , , , - , 1934-01-05 , Nepal and India , 8.1 , 15.0 , XI , 12,000 , Ruptured to the surface via the Main Frontal Thrust. , , - , 1947-07-29 , China , 7.3 , 20.0 , V , , , , - , 1950-08-15 , India, China and Myanmar , 8.6 , 15.0 , XI , 4,800 , Ranks among the largest

Strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

earthquake ever instrumentally recorded. , , - , 1966-06-27 , Nepal and India , 6.1 , 37.0 , , 80 , , , - , 1980-07-29 , Nepal and India , 6.5 , 17.5 , VIII , 200 , , , - , 1988-08-21 , Nepal , 6.9 , 57.4 , VIII , 700-1400 , , , - , 1991-10-20 , India , 6.8 , 10.3 , IX , 2000 , Main Central Thrust. , , - , 1999-03-29 , India , 6.8 , 21.0 , VII , 103 , , , - , 2005-10-08 , Pakistan , 7.6 , 26.0 , XI , 87,400 , , , - , 2009-09-21 , Bhutan , 6.1 , 14.0 , VI , 11 , , , - , 2011-09-18 , India , 6.9 , 50.0 , VII , 111 , Intraplate strike-slip. , , - , 2013-05-01 , Pakistan and India , 5.7 , 15.0 , VII , 1 , Additional 59 injured. , , - , 2015-04-25 , Nepal , 7.8 , 8.2 , VIII , 8,964 , , , - , 2015-05-12 , Nepal , 7.3 , 18.5 , VIII , 218 , Aftershock of the April 2015 earthquake. , , - , 2015-07-24 , Pakistan , 5.1 , 17.0 , V , 3 , , , - , 2019-09-24 , Pakistan , 6.0 , 10.0 , VII , 40 , , {{cite journal , first1=K.M. , last1=Sreejith , first2=M.C.M. , last2=Jasir , first3=R. , last3=Agrawal , first4=A.S. , last4=Rajawat , title=The 2019 September 24, Mw = 6, Mirpur earthquake, NW Himalaya: Geodetic evidence for shallow, near-horizontal décollement rupture of the Main Himalayan Thrust , journal=

Tectonophysics Tectonophysics, a branch of geophysics, is the study of the physical processes that underlie tectonic deformation. This includes measurement or calculation of the stress- and strain fields on Earth’s surface and the rheologies of the crust, ...

, year=2021 , volume=816 , issue=229013 , doi=10.1016/j.tecto.2021.229013 , url=https://www.sciencedirect.com/science/article/abs/pii/S004019512100295X , publisher=

Elsevier Elsevier ( ) is a Dutch academic publishing company specializing in scientific, technical, and medical content. Its products include journals such as ''The Lancet'', ''Cell (journal), Cell'', the ScienceDirect collection of electronic journals, ...

, url-access=subscription

References

Tectonics Himalayas Active faults Structural geology Seismic faults Seismic faults of Asia Thrust faults Seismic faults of Pakistan Geology of the Himalaya Subduction zones Geology of Nepal Geology of Asia Geology of India Geology of Pakistan Geology of China Geology of Bhutan

Overview

Seismic hazard

Associated seismicity

See also

References