a reverse fault in which the rocks on the lower surface of a fault plane have moved under the relatively static rocks on the upper surface
Compare overthrust
underthrust in American English
(ˈundərˌθrʌst)
noun
Geology
a thrust fault in which the footwall moved and the hanging wall did not (opposed to overthrust)
Word origin
[1890–95; under- + thrust]This word is first recorded in the period 1890–95. Other words that entered Englishat around the same time include: blanket roll, honky-tonk, masochism, pogey, takedownunder- is a prefixal use of under, as to indicate place or situation below or beneath (underbrush; undertow); lower in grade or dignity (undersheriff; understudy); of lesser degree, extent, or amount (undersized); or insufficiency (underfeed)