A conceptual model for the origin of fault damage zone structures in high-porosity sandstone

Zoe K. Shipton, Patience A. Cowie

Research output: Contribution to journalArticle

167 Citations (Scopus)

Abstract

We present a conceptual model to explain the development of damage zones around faults in high-porosity sandstones. Damage zone deformation has been particularly well constrained for two 4-km-long normal faults formed in the Navajo Sandstone of central Utah, USA. For these faults the width of the damage zone increases with fault throw (for throws ranging from 0 to 30 m) but the maximum deformation density within the damage zone is independent of throw. To explain these data we modify a previously published theoretical model for fault growth in which displacement accumulates by repeated slip events on patches of the fault plane. The modifications are based on field observations of deformation mechanisms within the Navajo Sandstone, the throw profiles of the faults, and inferences concerning likely slip-patch dimensions. Zones of enhanced stress are generated around the tips of each slipping patch, raising the shear stress on adjacent portions of the fault as well as potentially causing off-fault damage. A key ingredient in our model for off-fault damage accumulation is the transition from strain hardening associated with deformation band development, to localised strain softening as a slip-surface develops. This transition occurs at a critical value of deformation density. Once a new slip-surface develops at some distance from the main fault plane and it starts to accumulate throw it can, in turn, generate its own damage zone, thus increasing the overall damage zone width. Our approach can be applied to interpret damage zone development around any fault as long as the host-rock lithology, porosity and deformation mechanisms are taken into consideration.
Original languageEnglish
Pages (from-to)333-345
Number of pages13
JournalJournal of Structural Geology
Volume25
Issue number3
Early online date6 May 2002
DOIs
Publication statusPublished - 31 Mar 2003

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porosity
sandstone
damage
deformation mechanism
fault plane
growth fault
softening
hardening
normal fault
host rock
shear stress
lithology

Keywords

  • fault growth
  • damage zone
  • deformation bands

Cite this

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abstract = "We present a conceptual model to explain the development of damage zones around faults in high-porosity sandstones. Damage zone deformation has been particularly well constrained for two 4-km-long normal faults formed in the Navajo Sandstone of central Utah, USA. For these faults the width of the damage zone increases with fault throw (for throws ranging from 0 to 30 m) but the maximum deformation density within the damage zone is independent of throw. To explain these data we modify a previously published theoretical model for fault growth in which displacement accumulates by repeated slip events on patches of the fault plane. The modifications are based on field observations of deformation mechanisms within the Navajo Sandstone, the throw profiles of the faults, and inferences concerning likely slip-patch dimensions. Zones of enhanced stress are generated around the tips of each slipping patch, raising the shear stress on adjacent portions of the fault as well as potentially causing off-fault damage. A key ingredient in our model for off-fault damage accumulation is the transition from strain hardening associated with deformation band development, to localised strain softening as a slip-surface develops. This transition occurs at a critical value of deformation density. Once a new slip-surface develops at some distance from the main fault plane and it starts to accumulate throw it can, in turn, generate its own damage zone, thus increasing the overall damage zone width. Our approach can be applied to interpret damage zone development around any fault as long as the host-rock lithology, porosity and deformation mechanisms are taken into consideration.",
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A conceptual model for the origin of fault damage zone structures in high-porosity sandstone. / Shipton, Zoe K.; Cowie, Patience A.

In: Journal of Structural Geology, Vol. 25, No. 3, 31.03.2003, p. 333-345.

Research output: Contribution to journalArticle

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