Abstract - Overlap lengths, separations and throw gradients
were measured on 132 relay zones recorded on coal-mine plans. Throws on
the relay-bounding fault traces are usually ² 2m and individual structures
are recorded on only one seam. Throw gradients associated with relay zones
are not always higher than on single faults but asymmetry of throw profiles
is diagnostic of relay zones. Bed geometries around larger faults in opencast
mines are used to assess the displacement accommodated by shear in the
vertical plane normal to the faults and displacement transfer accommodated
by shear in the fault-parallel plane. 3-D structure is defined for two
relay zones, each recorded on 5 seam-plans. These relay zones are effectively
holes through the fault surfaces and overlap occurs between salients or
lobes of the parent fault surfaces. Lobes initially terminated at tip-lines
but, as the faults grew, gradually re-joined the main fault surfaces along
branch-lines. This type of relay zone originates by bifurcation of a single
fault surface at a locally retarded tip-line and is an almost inevitable
result of a tip-line irregularity.
Journal of Structural Geology 17, 1741-1755, 1995.