A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.

What does overthrust mean?

: to thrust over (as a rock mass)

What is overthrust in geology?

overthrust. / (ˈəʊvəˌθrʌst) / noun. geology a reverse fault in which the rocks on the upper surface of a fault plane have moved over the rocks on the lower surfaceCompare underthrust.