Theoretical model of block rotation along circular faults

Abstract The overall structure of rifts is often controlled by normal faults and tilted blocks. In several rifts the crests of the blocks have been strongly eroded while the associated half-graben has undergone large subsidence. The relative movement of the crest of a block can be analysed assuming simple circular geometry of its bounding fault. In such a geometric model, subsidence of the half-graben and relative uplift of the crest are connected and this coupling can be quantified as a function of the fault shape and of the block width. Knowing the geometry of a fault, we can calculate the movements of a rigid block rotating along this fault. Inversely, by knowing the tilting of a block, it should be possible to estimate the geometry of the guiding fault, i.e. its detachment depth, if we assume the fault to be listric. Numerical results show that a large block can undergo an absolute uplift. The direction of the movement depends on the initial width of the block and is quite independent of the tilt angle, except for very low-angle faults.