In which field of scientific study are the terms “horst” and “graben” used?

In geology, "horst" and "graben" refer to regions of the earth's crust that lie between normal faults and are either higher or lower than the area beyond the faults. "Horst" comes from the German word meaning 'heap', while "graben" is borrowed from the German for 'ditch'.

A horst represents a block pushed upward relative to the blocks on either side by the faulting, and a graben is a block generally long compared to its width that has been lowered relative to the blocks on either side due to the faulting.

Horsts and grabens are always formed together. Grabens are usually represented by low-lying areas such as rifts and river valleys whereas horsts represent the ridges between or on either side of these valleys. Examples of grabens are the Jordan–Dead Sea depression and Death Valley. The Vosges Mountains of France and the Palestine Plateau are typical horsts.