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Abstract:
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Deng et al. (2010) computed the Coulomb stress change induced by the impoundment of the Zipingpu Reservoir and suggested that the reservoir could not have induced the Wenchuan earthquake. They have omitted a crucial term in calculating pore pressure. Thus the calculation of the pore pressure component of the Coulomb stress was flawed, and the conclusions derived from the calculations are unsound. In the following, I elaborate on this omission.
Coulomb stress change includes a shear stress change Δτ and a normal stress change Δσn on the fault plane, as well as a pore pressure change term ΔP (e.g.,Roeloffs, 1988; Cocco and Rice, 2002; Deng et al., 2010):ΔCFF=Δτ-μΔσn+μΔP, where μ is the friction coefficient. The pore pressure change, ΔP, arises from two distinct physical mechanisms, as expressed by equation (2) in Deng et al. (2010): ΔP=ΔPdiff+ΔPu. Diffusive pressure, ΔPdiff, represents the time-dependent pressure field generated by the diffusion process and initiates from the bottom of the reservoir. Undrained response pressure, ΔPu, represents the time-dependent pressure field initiated from an instantaneous undrained pore pressure field in response to a rapid loading and occurs wherever volumetric stress exists. This undrained pressure field is the largest initially and decays through time.
The authors of Deng et al. (2010) considered the undrained response and stated that it can be calculated by  , where …
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