Real-time local shear-wave splitting measurement; application to the vicinity of the Baihetan hydropower plant

Local shear-wave splitting (SWS) measurements can be potentially used to monitor changes in upper crustal anisotropy over time. However, its real-time implementation is not yet available due to the sophisticated measurement procedure. Here, we integrate a fully automated workflow of local SWS measurement into a 4G telemetric nodal seismometer system. This system has operated since October 2021 to monitor seismicity near the Baihetan hydropower plant in southwestern China. We validate the system by retrospective evaluation on the reliability and interpretability of the automated measurements. Most fast-wave polarization directions align with the regional maximum horizontal stress and the nearby fault trends, generally consistent with previous observations. Five stations near the Zemuhe and Xiaojiang faults show a nearly 90 degrees flip in the fast direction during the transition from low to high water storage in the Baihetan plant. Future improvement of this real-time SWS system is to narrow down the analysis with only repeating earthquakes or earthquake clusters, which is anticipated to better facilitate time-lapse seismic monitoring of anisotropic structures and stress changes in the upper crust.