Abstract - Normal faults exposed in Kardia lignite mine, Ptolemais Basin, NW Greece formed at the same time as
bed-parallel slip-surfaces, so that while the normal faults grew they were intermittently offset by bedparallel
slip. Following offset by a bed-parallel slip-surface, further fault growth is accommodated by
reactivation on one or both of the offset fault segments. Where one fault is reactivated the site of bedparallel
slip is a bypassed asperity. Where both faults are reactivated, they propagate past each other to
form a volume between overlapping fault segments that displays many of the characteristics of relay
zones, including elevated strains and transfer of displacement between segments. Unlike conventional
relay zones, however, these structures contain either a repeated or a missing section of stratigraphy
which has a thickness equal to the throw of the fault at the time of the bed-parallel slip event, and the
displacement profiles along the relay-bounding fault segments have discrete steps at their intersections
with bed-parallel slip-surfaces. With further increase in displacement, the overlapping fault segments
connect to form a fault-bound lens. Conventional relay zones form during initial fault propagation, but
with coeval bed-parallel slip, relay-like structures can form later in the growth of a fault. Geometrical
restoration of cross-sections through selected faults shows that repeated bed-parallel slip events during
fault growth can lead to complex internal fault zone structure that masks its origin. Bed-parallel slip, in
this case, is attributed to flexural-slip arising from hanging-wall rollover associated with a basinbounding
fault outside the study area.
Journal of Structural Geology, 97, 199-211, 2017.