TheMain Boundary Thrust (MBT), also known as theMain Boundary Fault, is a discontinuous series of seismicfaults in theHimalayas which form the structural boundary between theOuter Himalayas andLower Himalayan Range. The MBT is itself part of a series of thrusts which helped to accommodate the deformation when theIndian Platecollided with theEurasian Plate in theCenozoic. The MBT fault system began forming in theMiocene. The MBT consists of multiple segments, and is composed from west to east of the Murree and Drang thrust faults, the Krol thrust fault, the Surkhet-Ghorahi thrust fault, the Kathmandu thrust, and the Gondwana/Garu thrust. Despite originating as a thrust fault in the collision ofIndia andEurasia, the MBT system has reactivated as a normal faulting system.

The MBT was formed as a result of thecollision of the Indian continent with Asia. It developed to relieve stresses from thecompression of thecontinental collision. When the MBT initially formed around 10-25 million years ago,^[1] it was a system of thrust faults which accommodated stresses from thecompression of thecontinental collision which led to Himalayan uplift. TheMain Himalayan Thrust is the rootDécollement structure, and results in similar fault system splays such as theMain Himalayan Thrust,Main Central Thrust, and theSouth Tibetan Detachment. These faults accommodated stresses parallel to the MBT and helped the Himalayan mountains grow.^[2] Each of these faults served as the primary reliever of strain in the Himalayan Orogeny until being abandoned in a successive chain of intracontinental thrust faults.^[3] Currently, theMain Frontal Thrust is the main thrust fault in the system.^[4]

The Main Boundary Thrust consists of multiple segments spanning 2,400 km (1,500 mi) in theHimalayas.

The Murree fault is athrust fault which lies inKashmir. To its southeast, the Drang thrust continues as an extension of the Murree thrust inHimachal.^[5]

To the southeast of the Murree and Drang faults, the Krol thrust is the main strand of the MBT and has "caused great shattering, inversionand imbricate thrusting".^[6]

The Surkhet-Ghorahi thrust fault is a northwest trending fault in CentralNepal.^[7] It stretches fromSurkhet toGhorahi in over an extent of 90–120 km (56–75 mi).^[8] At the western bank of theBheri River, the fault slips at a rate of 0.75 mm (0.030 in)/yr.^[9] The fault shows verticalfault scarp of 30 m (98 ft).^[10]

The Kathmandu thrust runs from east of the Surkhet-Ghorahi fault nearKathmandu to west ofThimphu.^[5]

The Gondwana thrust fault system runs from west ofThimphu passing throughBhutan before terminating inWest Kameng. In the east it is termed the Garu thrust, though it is a part of the Gondwana thrust.^[11]

After acting as a thrust fault initially, the Surkhet-Ghorahi may have reactivated as a normal fault—moving the opposite direction of a thrust fault.^[12]

Sources

• Himalayas

• Articles with short description
• Short description matches Wikidata