pure and applied geophysics

, Volume 137, Issue 4, pp 409–419 | Cite as

A note on the stress-dilatancy relation for simulated fault gouge

  • Chris Marone
Article

Abstract

Theoretical constraints on the stress-dilation relation for a deforming Coulomb material requirev≤θ ifC=0 andv ≤ sin-1 m m ) always, wherev is the dilation angle, θ is the friction angle,C is cohesion, τ m is the maximum shear stress, and σ m is the mean effective stress. Recent laboratory measurements of friction and dilatancy of simulated fault gouge show that small amplitude shear-load cycling causes compaction and consolidation. Comparison of the data with theory indicates that such load cycling produces: (1) increased coefficient of friction (or friction angle), (2) increased cohesion, and (3) increased dilatancy rate (or dilation angle). Under certain conditions of load cycling without significant plastic shear strain accumulation ( p <0.005) we find thatv exceeds both θ and, in contrast to theory, sin-1 m m ). This result is interpreted in terms of enhanced cohesion and overconsolidation, which lead to residual stresses within the gouge. An analogy is drawn between these special loading conditions and those extant on natural faults. In particular, our results imply that jostling and minor stress variations associated with microearthquakes may produce strengthening of fault gouge and changes in the fault zone's stress-dilatancy relation. Hence, compaction associated with microseismicity may lead to subsequent dilation of fault gouge, even for faults with large displacement rates and large net offsets (e.g., San Andreas). In regions where such dilation persists over sufficient displacements (on the order of the critical slip distance for seismic faulting) it may tend to inhibit unstable slip.

Key words

Fault gouge dilatancy shear localization friction Coulomb failure mechanical healing 

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Copyright information

© Birkhäuser Verlag 1991

Authors and Affiliations

  • Chris Marone
    • 1
  1. 1.Seismographic Station and Department of Geology and GeophysicsUniversity of CaliforniaBerkeleyU.S.A.

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