[grah-buh
n] 
| a portion of the earth's crust, bounded on at least two sides by faults, that has dropped downward in relation to adjacent portions. |
gra·ben (grä'bən)  (click for larger image in new window) n. A usually elongated depression between geologic faults. [German Graben, from Middle High German grabe, trench, from Old High German grabo, from graban, to dig; see ghrebh-2 in Indo-European roots.] |