Influence of impoundment gravity and pore pressure on reactivation of faults
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ORIGINAL ARTICLE
Influence of impoundment gravity and pore pressure on reactivation of faults Zhu Yujie . Liu Xiaoli
. Wang Enzhi
Received: 10 August 2020 / Accepted: 21 October 2020 Ó Springer Nature Switzerland AG 2020
Abstract For more than seven decades, the impounding of artificial water reservoirs has been known to trigger earthquakes. Accordingly, reservoirinduced seismicity (RIS) has been studied in terms of its identification and mechanisms. In this paper, we report three laboratory experiments to investigate the effects of water impoundment and pore-pressure diffusion on the reactivation of faults in high tectonic stress areas. Results showed that when the horizontal stress is larger than the vertical stress, according to the Mohr–Coulomb criterion, pore-pressure diffusion might be the main factor inducing seismicity instead of the undrained stress compression. The diffusion and oscillation of pore pressure are the controlling factors in triggering the activation of faults and releasing the elastic energy. The Mohr–Coulomb criterion is consistent in describing the critical damage pore pressure of the pre-existing faults; however, it fails to judge whether a fault is in a stable or unstable state after the pore pressure increases. The hydraulic energy from the injection pressure and volume of water is strongly related to the moment magnitude of the induced seismicity owing to pore-pressure diffusion. Moreover, the fault can be transformed from an unstable state into a stable state after continuous seismic events. The enhancement of fault permeability due to Z. Yujie L. Xiaoli (&) W. Enzhi State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China e-mail: [email protected]
the seismic events can promote the fluid flow through fractures and influence the seepage field around the reservoir. Keywords Reservoir-induced seismicity Shear flow experiment Hydro-mechanic coupling mechanism Hydraulic power
1 Article Highlights 1. We investigated the effects of gravity of water impoundment and pore-pressure diffusion on fault reactivation. 2. Pore-pressure diffusion and oscillation might trigger fault activation in high tectonic stress area. 3. The Mohr–Coulomb criterion can predict the critical damage pressure; it fails to predict the stable state.
2 Introduction Reservoir-induced seismicity (RIS) was first studied by Carder (1945) during the investigation of a boulder dam by relating the reservoir loading and earthquake activity. Four damaging earthquakes with magnitudes of over M6 occurred in China, Zambia-Zimbabwe,
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Greece, and India; these were triggered by the impoundment of artificial water reservoir and attracted international attention (Gupta 2002). McGarr and Simpson (1997) distinguished between the terms ‘‘triggered’’ and ‘‘induced’’ seismicity that have been used interchangeably for describing artificially stimulated earthquakes. ‘‘Triggered seismicity’’ in earthquake
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