How is the dip direction of a thrust fault indicated on a geologic map?
That other answer is confusing if not just wrong. I use polygons to represent my fault contacts on SUBSURFACE maps, but this cannot be done on a surface geology map, and the direction given is wrong. The tick marks (triangular teeth or rectangular blocks) always point in the direction of the DIP OF THE FAULT PLANE. In a reverse fault this will be pointing towards the hanging wall, or the overriding thrust sheet, OPPOSITE the direction of its movement. If you have a map with bar and ball symbols, these will always be on the downthrown block, whether normal or reverse. A bar and ball symbol is a small solid circle connected to the fault by a short line that is perpendicular to the fault trace. The letters U and D are sometimes put on a fault to show which side is upthrown and downthrown. To see a clear illustration of this go to the last page of this document from the University of Southern California Structural Geology 305 class:
