GEOMETRY AND DEVELOPMENT OF RELAY RAMPS IN NORMAL-FAULT SYSTEMS

Relay ramps occur between normal fault segments that overstep in map v iew. The geometry and evolution of exposure-scale relay ramps are desc ribed from the Somerset coast, England, and are compared with larger s cale ramps from elsewhere. Relay ramps can be classified into four gro ups based on the degree of interaction and linkage between the overste pping segments; these groups are interpreted as being evolutionary sta ges. In stage 1, the segments do not interact. Stage 2 involves the re orientation of bedding between two interacting faults to produce a rel ay ramp. In stage 3, connecting fractures start to break the relay ram p. Stage 4 is when the relay ramp is destroyed to produce a single fau lt that has an along-strike bend. These evolutionary stages can develo p through time, but they can also be seen spatially. A branch line bet ween normal faults or an along-strike bend may represent a stage 4 rel ay, with progressively earlier stages occurring updip or downdip. Char acteristic variability in displacement-distance profiles for fault seg ments and linked faults accompanies the interaction and linkage proces ses. Displacement transfer by relay ramps is accompanied by steep disp lacement gradients along fault segments at oversteps. Relay ramps ofte n contribute to a minimum in total fault displacement at a linkage poi nt.