Www.fault Analysis Group.ucd.Ie Gallery Segmentation

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Fault Zones - Segmentation

Normal faults can be segmented in either cross-section or in map view, or both. Here are schematic illustrations of two end-member models for theformation of segmented fault arrays in plan view; the same basic geometries could apply to their generation in cross-sectional view (Walsh et al.in press). The block diagrams (a, c and d) each show three stages in the growth of a segmented fault array (i - iii). The displacement-distanceplots (b and e) are for the fault traces on the upper surfaces of the block diagrams (bold lines). The bold dashed lines in (c) indicate branch-lines.The coherent fault model is illustrated for segmented fault traces that are (c) hard-linked and formed by fault surface bifurcation and (d) soft-linked and formed by 3-D segmentation. The shaded areas in (b) indicate deficits in displacement between the adjacent fault segments which arenot due to continuous deformation within relay zones (see text). The aggregate displacement profiles (not shown) for the two models differ inthat the points of maximum displacement are preserved where the faults were initially isolated (b - iii) but a simple aggregate profile occurs at allstages of development in the coherent fault model.



Normal faults can be segmented in either cross-section or in map view. Two normal fault traces as seen on cross-sections parallel to the fault slipdirections, in an interbedded chalk.marl sequence at Danes Dyke, Flamborough head, U.K. The offsets of the fault traces are exclusivelyextensional and occur where the massive chalk beds are separated by thin marl units. The fault on the left has an average displacement of 15cmand that on the right has displacements of 1-2cm. The overall dip of both faults is 75 degrees.

Segmented normal fault in an interbedded chalk-marl sequence at Danes Dyke, Flamborough head, U.K. Two fault segments are separated by adilational jog within which the sequence shows a fold that accommodates displacement transfer between segments. The displacement on thearray is ca 10cm.

Segmented normal faults in an interbedded chalk-marl sequence at Danes Dyke, Flamborough head, U.K. Two fault arrays are seen, one with acontractional jog (offset) and the other with dilational jogs.



Segmented strike-slip fault arrays, with intervening relay zones, intersecting steeply dipping beds in the Pyrenees, Spain - the views provided aretherefore equivalent to a map view of normal faults. (a) Array of faults with maximum displacement of ca 25cm from Jaca, showing interveningrelays one of which is strongly fractured and near breaching (Photograph from Graham Potts, University of Liverpool). (b) Small-scale relay zoneon 25cm displacement fault from Collado de Fumanyo, Catalonia (see Walsh et al. 1999).

Normal fault segments associated with a fault zone with ca 10m displacement, from the Carboniferous sandstone and shales of the Morpethopencast site Northumberland, UK. The segments are developed in a sandstone unit contained within an otherwise shale dominated sequence -they are interpreted to be an early localisation array that is subsequently by-passed by a throughgoing hangingwall fault seen on the far workingface.

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Www.fault Analysis Group.ucd.Ie Gallery Segmentation