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Volume 54 Supplement 11

Special Issue: Slip and Flow Processes in and below the Seismogenic Region

Growth of plastic shear zone and its duration inferred from theoretical consideration and observation of an ancient shear zone in the granitic crust


A new model for growth of plastic shear zone is proposed based on the basis of a theory of fluid dynamics coupled with a rheological constitutive function, and is applied to a natural shear zone. Mylonite, ultramylonite and other ductile fault rocks are well known to deform in a plastic flow regime. The rheological behavior of these kinds of rocks has been well documented as a non-linear viscous body, which is empirically described as , where : strain rate, τ: shear stress, Q: activation energy, R: universal gas constant, T: absolute temperature, and A and n are constants. Strain rate- and temperature-dependent viscosity is obtained by differentiating the equation, and simplified by substituting n = 1. Then, substitution of the equation into a diffusion equation, , derives an equation δ = 4[t/p · A exp(−Q/RT)]1/2, where δ: thickness of active layer of viscous deformation, ν: kinematic viscosity, and ρ: density. The duration of creep deformation along the ancient plastic shear zone (thickness: 0.076 m) is estimated to be around 760 s, in a temperature range from 300 to 500°C. This estimation is rather good agreement with intermittent creep during inter-seismic period, than steady state creep or co-seismic slip.


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Correspondence to Hidemi Tanaka.

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Tanaka, H., Shibazaki, B., Shigematsu, N. et al. Growth of plastic shear zone and its duration inferred from theoretical consideration and observation of an ancient shear zone in the granitic crust. Earth Planet Sp 54, 1207–1210 (2002).

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  • Shear Zone
  • Creep Deformation
  • Steady State Creep
  • Plastic Regime
  • Viscous Deformation