The 3D geometry of small-scale relay zones between normal faults in soft sediments

Abstract

Serial cross-sections of faults within soft sediments of Miocene age, on the East coast of Denmark, were collated to provide 3D data sets with which to study the geometry of minor faults (displacements < 10 cm). From the wide variety of geometrical complexities displayed by these faults, many due to mutually cross-cutting relationships between opposed dipping faults, we present relatively simple structures considered to demonstrate stages in the evolution of relay zones between overlapping fault segments. The structures described are: (1) initial embayments in fault tip-lines, (2) established relay zones displaying transfer of displacement between overlapping fault segments, (3) breached relay zones, and (4) fault bound lenses. An individual relay zone may display more than one of these structures along its length and relay zones that are intact on one cross-section may be breached along strike on another. Examples of relay zones that are isolated from the fault tip-line and are effectively holes within a continuous fault are also observed. The observed relay zones breach by propagation of the initial parent fault through the relay zone rather than by the formation of a new breaching fault.