Now showing 1 - 4 of 4
  • Publication
    Examples of fault steps controlling event migration in seismic swarms
    (Society of Exploration Geophysicists, 2022) ; ;
    This study provides spatiotemporal constraints on seismicity within fault zones and identifies key links between fault step and event migration. We show that event distributions in seismic swarms can image stepping geometries reminiscent of relay zones commonly observed along fault zones. Earthquake migration can propagate across steps, indicating a transfer of deformation, but can be obstructed by others. Preliminary quantitative results show that whether a step transfers or blocks deformation depends on the separation between the bounding segments relative to the maximum magnitude of the events. These findings support the importance of understanding the role of internal fault geometry on seismicity and show that high accuracy event locations provide a critical understanding of seismicity.
  • Publication
    The role of antithetic faults in transferring displacement across contractional relay zones on normal faults
    Contractional relay zones between pairs of normal faults are sometimes associated with multiple antithetic faults in a geometry similar to that found in Riedel shear zones. Detailed fault displacement profiles of outcrop examples of this geometry demonstrate that the antithetic faults accommodate the transfer of displacement between the synthetic faults that bound the relay zones. The throw on individual antithetic faults, or R′ shears, is typically constant across relay zones while the throw profile on the synthetic faults, or R shears, is stepped; the steps occurring across branchpoints with abutting R’ shears. Transfer of fault displacement occurs by a combination of block rotation and irrotational block translation within the relay zone. As fault throw increases, contractional relay zones are by-passed by the linkage of the synthetic faults, in a manner analogous to the formation of P-shears by the linkage of R shears in classic Riedel shear experiments, but with the original relay zone structure still preserved within the fault zone. With yet further strain bedding may rotate into near-parallelism with the fault surface, with the original geometrical configuration of the relay zone difficult to unravel.
      192Scopus© Citations 5
  • Publication
    Variability in the three-dimensional geometry of segmented normal fault surfaces
    Normal faults are often complex three-dimensional structures comprising multiple sub-parallel segments separated 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.
      51Scopus© Citations 23
  • Publication
    Bed-parallel slip associated with normal fault systems
    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.
      170Scopus© Citations 7