Definition of underthrust in US English:



[with object]Geology
  • 1Force (a crustal plate or other body of rock) beneath another plate or block.

    ‘the Farallon plate was being underthrust beneath the North American plate’
    ‘this sediment may be deformed by the underthrusting’
    • ‘Here the Papua New Guinea continental crust appears to be underthrusting the adjacent marginal basin and obduction of the ophiolite is occurring in an uphill direction.’
    • ‘The tensional stresses in the uplift can be relaxed by, for example, underthrusting in a subduction zone, or contraction in surrounding regions.’
    • ‘Patterns of this type can be readily explained by accretionary tectonism, whereby a packet of sediment accreted at the toe of the prism is underthrust and buried beneath an overburden of older strata.’
    1. 1.1 Be forced underneath (another plate or block)
      ‘plate X is underthrusting plate Y in a northeast direction’


  • An instance of one plate or block being forced underneath another.

    ‘the westward underthrust of the Pacific Ocean plate’
    • ‘We suggest that because the upper portion of underthrust sections lacked any thick, water-saturated clastic deposits this did not favour the formation of melanges.’