Abstract - Stretching of the Earth’s upper crust is commonly accommodated by normal faulting,
fault-related folding and/or fracturing such as veins and joints. However, an increasing number of outcrop-scale
studies highlight that extension is also accompanied by bed-parallel slip (BPS). The identification of BPS surfaces
is, however, challenging due to their localised nature within bedded host rock sequences, the absence of suitable slip
markers, and the scale and resolution of both outcrop and seismic reflection data. Here, we present examples of BPS
identified within extensional fault systems in sedimentary sequences and outline the nature, magnitude, segmentation, and
spatiotemporal distribution of BPS surfaces. These constraints provide a basis for defining the principal structural
controls on BPS development and its geometric and kinematic relationship to normal faulting. We conclude that
BPS is a common feature within multi-layered host rock sequences, irrespective of their lithological and mechanical
properties, and is kinematically associated with a broad range of fault-related deformation, including
bed rotations, flexural-slip folding, and both tectonic and gravity-driven sliding. The presence of BPS within
normal fault systems can increase the complexity of the host rock volumes and fracture arrays with potential
implications on subsurface fluid flow and seismicity.
Normal faults are often complex three-dimensional structures comprising multiple sub-parallel
segments sepa-rated by intact or breached relay zones. Relay zones are classified according to whether they step in
the strike or dip direction and whether the relay zone-bounding fault segments are unconnected in 3D or bifurcate
from a single surface. Complex fault surface geometry is described in terms of the relative numbers of different types
of relay zones to allow comparison of fault geometry between different faults and different geological settings. A
large database of fault surfaces compiled primarily from mapping 3D seismic reflection surveys and classified according
to this scheme, reveals the diversity of 3D fault geometry. Analysis demonstrates that mapped fault geometries depend on
geological controls, primarily the heterogeneity of the faulted sequence and the presence of a pre-existing structure, as
well as on resolution limits and biases in fault mapping from seismic data. Where a significant number of relay zones are
mapped on a single fault, a wide variety of relay zone geometries occurs, demonstrating that individual faults can
comprise segments that are both bifurcating and unconnected in three dimensions.
Earth-Science Reviews, 230, 104044, doi: https://doi.org/10.1016/j.earscirev.2022.104044, 2022.