Comment on "Evidence that the 2008 Mw 7.9 Wenchuan Earthquake Could Not Have Been Induced by the Zipingpu Reservoir" by Kai Deng, Shiyong Zhou, Rui Wang, Russell Robinson, Cuiping Zhao, and Wanzheng Cheng

Abstract

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 Δσ n 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): Δ CFF= Δτ - μΔσ n + 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 = ΔP diff+ ΔP u . Diffusive pressure, ΔP diff, represents the time-dependent pressure field generated by the diffusion process and initiates from the bottom of the reservoir. Undrained response pressure, ΔP u , 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 ![Graphic][1] , where … [1]: /embed/inline-graphic-1.gif