Abstract - Branch-lines between normal faults and their sub-parallel splays mapped from 3-D seismic reflection data show a range of forms from straight lines to closed loops. The different geometries are interpreted as representing stages in the failure of relay zones and in the progressive replacement of fault tip-lines with fault branch-lines. The geometries of these normal fault branch-lines are similar to those for thrusts previously inferred from limited 2-D data. The orientation of the axis of a relay and its associated bends relative to a fault slip direction is identified as an important control on the structures developed within the relay. Neutral, restraining and releasing bends can each occur on any fault type (normal, reverse and strike-slip), but data bias is a major factor in determining which bend geometry is most often observed with each fault type.
On normal faults the initial relay zone geometry controls the dominant branch-line orientation and the same control is likely on branch-lines associated with the other modes of faulting. A review of the relay geometries and strains occurring with all three modes of faulting highlights the role of the orientation of the mechanical anisotropy of a bedded sequence relative to the orientations of fault surface and slip directions. This relative orientation determines how the relay strain is accommodated and hence the degree of hard-linkage and development of branch-lines.
Journal of Structural Geology, 21, 1019-1026, 1999.