Seismic Evidence for Fluid‐Driven Pore Pressure Increase and Its Links With Induced Seismicity in the Xinfengjiang Reservoir, South China

Xinfengjiang Water Reservoir (XWR), located in the northeast of Guangdong Province, South China, has hosted a large number of earthquakes since its impoundment. In order to understand potential triggering mechanisms of the reservoir-induced seismicity that could help assess seismic hazard to the Greater Bay Area, the most populated region in China, in this study, we construct a high-resolution shear-wave velocity model in shallow crust at depths from surface to similar to 10 km based on a high-density short-period seismic array recently deployed surrounding the XWR using ambient noise tomography. We image a northwest-southeast (NW-SE)-trending high-velocity belt at depths of 2-6 km and a relatively low-velocity channel (LVC) underlying the high-velocity belt at a depth below 6 km under the XWR. The LVC seems to indicate the existence of a NW-SE-trending channel for water infiltration below 6 km under the XWR. Combined with spatiotemporal variation of focal-depth and frequency of seismicity under the XWR over the past decade, we infer that a NW-SE-trending preexisting fault has reactivated due to pore pressure increase via water infiltration from the dam to a recently most active region, Xichang, northwest of XWR. This scenario could possibly explain the occurrence of increasing seismicity in northwest of XWR since 2012. This study highlights the seismic evidence for pore pressure increase due to water infiltration that triggers seismicity and further offers a reference for other forms of fluid-driven seismicity worldwide.