Main Frontal Thrust
{{Short description|Geological fault in the Himalayas}}
File:Himalayas landsat 7.png.]]
{{Infobox fault|name=Main Frontal Thrust|other_name=Himalayan Frontal Thrust|country=Nepal, India, Pakistan, Bhutan|length=2,400 km|range=Himalayas|type=Thrust|map_image=Himalayan Tectonic Summary.png|displacement=15-21 mm/yr|status=Active|image_caption=Map of the Himalaya region with earthquakes M6+ from 1900-2014. the MFT is at the continuous black line running along}}
The Main Frontal Thrust (MFT), also known as the Himalayan Frontal Thrust (HFT), is a geological fault in the Himalayas that defines the boundary between the Himalayan foothills and Indo-Gangetic Plain.{{Cite web|last1=Paul|first1=R.|last2=Bhakuni|first2=S.S.|title=Structural analysis of main boundary thrust and Himalayan frontal thrust around Dehra Dun, NW Himalaya: Implications of neotectonics|url=http://reports.ias.ac.in/report/18600/structural-analysis-of-main-boundary-thrust-and-himalayan-frontal-thrust-around-dehra-dun-nw-himalaya-implications-of-neotectonics|access-date=21 October 2020|website=Summer Research Fellowship Programme of India's Science Academies}} The fault is well expressed on the surface thus could be seen via satellite imagery. It is the youngest and southernmost thrust structure in the Himalaya deformation front. It is a splay branch of the Main Himalayan Thrust (MHT) as the root décollement.
Background
It runs parallel to other major splays of the MHT; Main Boundary Thrust (MBT) and Main Central Thrust (MCT). The Sunda Megathrust, which extends from the Banda Islands to Myanmar is joined with the MFT.{{Cite journal |last1=Burgess |first1=W.P. |last2=Yin |first2=A. |last3=Dubey |first3=C.S. |last4=Shen |first4=Z–K. |last5=Kelty |first5=T.K. |date=2012 |title=Holocene shortening across the Main Frontal Thrust zone in the eastern Himalaya |url=https://www.researchgate.net/publication/256695341 |journal=Earth and Planetary Science Letters |volume=357–358 |pages=152–167 |doi=10.1016/j.epsl.2012.09.040|bibcode=2012E&PSL.357..152P }} The fault strikes in a NW-SE direction and dips at an angle of 20° to 30° in the north.{{Cite journal |last1=Wesnousky |first1=S.G. |last2=Kumar |first2=S. |last3=Mohindra |first3=R. |last4=Thakur |first4=V.C. |date=1999 |title=Uplift and convergence along the Himalayan Frontal Thrust of India |url=https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999TC900026 |journal=Tectonics |volume=18 |issue=6 |pages=967–976 |doi=10.1029/1999TC900026|bibcode=1999Tecto..18..967W |s2cid=128412302 }}
The Main Boundary Thrust is another major thrust fault in the Himalaya orogenic wedge that was active in the Cenozoic.{{Cite journal |last1=Mugnier |first1=J–L. |last2=Huyghe |first2=P. |last3=Chalaron |first3=E. |last4=Mascle |first4=G. |date=1994 |title=Recent movements along the Main Boundary Thrust of the Himalayas: Normal faulting in an over-critical thrust wedge? |url=https://www.researchgate.net/publication/215614466 |journal=Tectonophysics |volume=238 |issue=1–4 |pages=199–215 |doi=10.1016/0040-1951(94)90056-6|bibcode=1994Tectp.238..199M }} It runs parallel to the MFT with a spacing distance of about 20 km.
Shortening rate
Shortening rate varies across the MFT, these figures provide the speed in various locations.
| class="wikitable"
|+ !Region !Rate (mm/yr) ! |
| Pakistan
|14 ± 4 |minor components within the Himalayas also accounts for shortening |
| Northwestern India
|10-14 | |
| Nepal
|21 ± 1.5 | |
| Bhutan
|15-20 | |
Seismic activity
The MFT accommodates almost the entire rate of subduction of the Indian Plate therefore, it is no surprise that numerous earthquakes have occurred along this fault, and is expected to produce very big earthquakes in the future.{{Cite book|last1=Bilham |first1=R. |editor1-last=Treloar |editor1-first=P.J. |editor2-last=Searle |editor2-first=M.P. |title=Himalayan Tectonics: A Modern Synthesis |chapter=Himalayan earthquakes: a review of historical seismicity and early 21st century slip potential |series=Geological Society, London, Special Publications |year=2019 |volume=483 |pages=423–482 |doi=10.1144/SP483.16|isbn = 9781786204059|s2cid=133821585 }} Many earthquakes associated with the MFT has resulted in visible ground ruptures, as seen in the Bihar earthquake of 1934 and 1505 magnitude 8.2-8.8 earthquake.