Impoundment of the Zipingpu reservoir and triggering of the 2008 M_w 7.9 Wenchuan earthquake, China

Abstract

Impoundment of the Zipingpu reservoir (ZR), China, began in September 2005 and was followed 2.7 years later by the 2008 Mw 7.9 Wenchuan earthquake (WE) rupturing the Longmen Shan Fault (LSF), with its epicenter ~12 km away from the ZR. Based on the poroelastic theory, we employ three‐dimensional finite element models to simulate the evolution of stress and pore pressure due to reservoir impoundment, and its effect on the Coulomb failure stress on the LSF. The results indicate that the reservoir impoundment formed a pore pressure front that slowly propagated through the crust with fluid diffusion. The reservoir loading induced either moderate or no increase of the Coulomb failure stress at the hypocenter prior to the WE. The Coulomb failure stress, however, grew ~9.3–69.1 kPa in the depth range of 1–8 km on the LSF, which may have advanced tectonic loading of the fault system by ~60–450 years. Due to uncertainties of fault geometry and hypocenter location of the WE, it is inconclusive whether impoundment of the ZR directly triggered the WE. However, a small event at the hypocenter could have triggered large rupture elsewhere on fault, where the asperities were weakened by the ZR. The microseismicity around the ZR also showed an expanding pattern from the ZR since its impoundment, likely associated with diffusion of a positive pore pressure pulse. These results suggest a poroelastic triggering effect (even if indirectly) of the WE due to the impoundment of the ZR.

Faults and Non‐Double‐Couple Components for Induced Earthquakes

“…The largest magnitudes of most induced earthquakes are smaller than 2—below the threshold of reliable full moment tensor retrievals based on regional networks largely designed for natural earthquake hazard monitoring. On the other end of the spectrum, the causes of some devastating earthquakes ( M > 7; e.g., the Wenchuan earthquake) are under debate as either natural or partially induced (Ge et al, ; Tao et al, ) and may not represent induced earthquakes with dominating anthropogenic contributions (if any). These debatable cases of seismicity are also excluded from our moment tensor decomposition in section 3.…”

Seismic and Geologic Evidence of Water‐Induced Earthquakes in the Three Gorges Reservoir Region of China

“…One of the largest reservoir-induced earthquakes is the 1967 M 6.3 Koyna Earthquake in India that killed 180 people (Talwani, 1997a). The 2008 M 8.0 Wenchuan Earthquake, a devastating one with a casualty of >80,000 and $150B USD in property damage in western Sichuan of China, may have been induced by the Zipingpu Reservoir ∼20 km from the epicenter (e.g., Ge et al, 2009;Lei, 2011;Peng et al, 2017;Tao et al, 2015), though that conclusion has been disputed (e.g., Chen, 2009;Deng et al, 2010;Gahalaut & Gahalaut, 2010). In many cases, a causal relationship between reservoir impoundment and nearby earthquakes is difficult to establish because our knowledge of crustal structure and stress state, the hydrogeologic framework, and precise locations of earthquakes are rarely all well-known (Ellsworth, 2013).…”

Hydraulic properties of samples retrieved from the Wenchuan earthquake Fault Scientific Drilling Project Hole‐1 (WFSD‐1) and the surface rupture zone: Implications for coseismic slip weakening and fault healing

“…Finally, it has been fiercely debated whether the Wenchuan earthquake was triggered by the impoundment of a nearby large reservoir. This issue has attracted both academic and public attention and has been tested by many studies which sometimes present contrasting results [e.g., Klose , ; Lei et al ., ; Ge et al ., ; Gahalaut and Gahalaut , ; Deng et al ., ; Tao et al ., ]. According to these studies, one of the key factors influencing their results is the depth‐dependent permeability model used.…”