Abstract - Relay zones accommodate transfer of displacement between pairs of adjacent segments of a fault array
that become linked to form a through-going fault as displacement increases. 3D geometric and kinematic
analysis of two vertically aligned relay zones, that form a complex boundary between two fault segments,
generally support this model of relay zone growth but they also highlight some departures from
this scheme. The two seismically mapped relay zones, although separated vertically by 100 m, were
synchronously active over most of their development history. A causal relationship between them is
proposed with the geometric complexity arising from the formation of the lower relay zone triggering
the formation of the upper. The lower relay zone is now breached but originally formed a hole within the
fault surface up to throws of ca. 50 m. The upper relay zone displays both breached and intact relay zone
geometries at different structural levels demonstrating that relay zone breaching is a protracted rather
than geologically instantaneous process. Geometrically the lower part of this structure resembles a
breached relay zone, but it formed by propagation of a splay fault from a pre-existing bend to enclose an
intervening and steepening ramp, a growth scheme which is the opposite of conventional relay zone
models.
Journal of Structural Geology, 58, 59-68, 2014.