Normal Fault Segmentation along the Dip Direction and Impact on Fault Sealing

Fault segmentation along strike is commonly observed in outcrop and subsurface but is less common along dip, particularly using seismic data. We document outcrop and core examples of fault segmentation in the dip direction and compare findings to seismic faults. In all cases, segmented faults formed an echelon array consistently stepping perpendicular to fault strike, towards either the hanging wall or the footwall. Faults step at contacts of competent and incompetent layers (e.g., sandstone and shale). Larger steps correspond with thicker incompetent layers, especially in the case of footwall steps. Continued slip on fault segments produces a coalesced single fault strand.

During fault coalescence, the step deformation can produce two distinct fault rock types depending on step type. In the hanging wall steps, deformation is dominated by shale smearing which involves the rotation of the incompetent layers until they are smeared parallel to the fault. Further slip may case the incompetent layers to thin out and disconnect. In contrast, deformation along footwall steps forces the shale out of the step, and eventually becomes dominated by brecciation of hanging and footwall rocks. The hydraulic properties and sealing capacity of a fault may then depend on the fault step type and associated fault rock material (smearing or brecciation). moreover, higher ratios of competent to incompetent layers force footwall steps to become more laterally distributed, and hence, when coalesced, they will tend to form shallower fault dip angles than hanging wall steps. Examples from seismic data illustrate that along-dig segmentation may be mapped when seismic data is adequate.